XPS rigid panels under concrete slab
Randy973
| Posted in Energy, Heating & Insulation on
I read in “Energy Smart Homes” magazine,put out by Fine Homebuilding, that I should install XPS rigid panels under my basement slab. Can anyone tell me the proper way to install this product. Thank you
Replies
Best is to use high-density panels available at masonry yards, but the regular blue or pink stuff is ok in a pinch.
I don't know where you're located (hint, fill out your profile) but here in Maine I like to use 2", but 1 1/2" is probably enough.
Install over very smoothly raked crushed stone or sand. Tape the seams with Tyvek tape. Pour concrete.
I use either Dow or Foamular XPS.
I also prefer to set the foam on a good grade and then cover the foam with several inches of sand or 3/4- gravel.
The sand or gravel helps keep the foam from being disturbed and uplifted during a pour.
If you have poured slabs before but never over foam one thing to note is that ALL the water contained in the mix must exit out the top of the slab when foam is installed beneath the slab.
Makes for a difference in setting time.
Thank you. I am in northern NJ. I wasn't sure how to seal between the panels. Does the blueboard have a foil surface? The magazine article says only 1 inch is needed.
No , The Dow (blue) foes not have a foil face. neither does the pink (Foamular) . Both have sites on the web that you can go to for information BTW. You should rip some of the product and place it at the edges of the pour to break the thermal connection at that location if this is for a slab in a dwelling. Might try a search here at this site under "insulated slabs" or something like that and see what comes up as well.
They can't get your Goat if you don't tell them where it is hidden.
The only foam I've ever seen with foil facing is polyisocyanurate and you do NOT want to put that under a slab. That is an open cell foam and once it is wet from ground moisture or wet concrete its capacity to insulate anything is gone. Stick with XPS. Cut the panels so they will be snug, place them flat on smoothly graded surface, and pour away. Doesn't hurt to drape 6 mil poly on top of the foam before the pour but slab guys usually grump about this because it takes a bit longer to cure.
Can anyone enlighten me regarding the boric acid treated rigid foam panels. I did a Google search and several web sites mention that treated panels are available, but no one gave a brand name for the stuff. IIRC, someone mentioned a brand name on a post some time back, possibly Mike Smith. If anyone could provide me with a brand name for such a product, I would appreciate it. I would be interested in knowing whether the boric acid is encapsulated in such a way that it would not leach out when used under a slab and subject to priods of water exposure.
Performguard is one brand name of a treatment for EPS that contains borates to resist termites. They use this EPS in a lot of different products, from ICF's to rigid sheet foam (I think they call it R-Control) Look at this website - http://www.teamindustries.com/performguard.asp
I have heard from various sources that you are not allowed to have bare foam in contact with the ground in termite country unless it has this treatment. I am not sure if it is only the Southern Building Code that mandates this or not. I just know that here in Tallahassee it's not a good idea, so I have been researching this stuff also.
Hope that helps-
Jamie
The only foam I've ever seen with foil facing is polyisocyanurate and you do NOT want to put that under a slab. That is an open cell foam...
Polyisocyanurate is an advanced version of polyurethane, and it is a closed-cell foam with similar insulating properties (approx. R-6/in).
Polyisocyanurate has about the same compressive strength as extruded polystyrene (25 psi), and approximately the same perm rating (1 to 1.5). While it does have a higher water absorption factor (1% by weight compared with 0.1%), in both cases this is insignificant.
Polyisocyanurate is often used for built-up roofing systems, as it is less flammable than XPS. But XPS is less expensive, has almost the same R-value (5/in) and comes in T&G boards which makes it more suitable for sublab applications.Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
What effect on the stated r-value of polyisocanurate does moving that 15 of water thru it? For example , used as a foundation insulation and having the insulation absorb the moisture but not retain it, rather having it move though the insulation.
They can't get your Goat if you don't tell them where it is hidden.
You need to start with well-compacted gravel or sand, then lay a 6 mil poly or TuTuff vapor barrier with taped seams (this is essential), then the foam board with taped seams (1" is OK if it's not a heated slab), then 6" welded wire mesh overlapped and tied together with wire or zip ties.
Slab edge insulation is critical, as this is were most heat loss from a slab occurs. You can bevel the top edge so it doesn't show and can be hidden under baseboard if its finished space.
Do NOT place sand over the foam as this creates a reservoir for any moisture that works its way either up from the ground or down through the slab.
Solar & Super-Insulated Healthy Homes
Edited 1/31/2008 11:07 pm ET by Riversong
I will agree to disagree with your comment about the sand. Moisture barrier is necessary. Mesh can be used as can Rebar for re-enforcing.
They can't get your Goat if you don't tell them where it is hidden.
From the Building Science web site:"A sheet polyethylene vapor barrier should be located over the rigid insulation and in direct contact with the concrete slab. A sand layer should never be installed between the sheet polyethylene vapor barrier and the concrete slab. Sand layers located between the slab and the vapor barrier can become saturated with water, which are then unable to dry downwards through the vapor barrier. In this scenario, drying can only occur upward through the slab is possible which typically results in damaged interior floor finishes (Lstiburek, 2002)."I saw their reasoning explained in an article on the subject of sand layer under the slab, but I can't find it right now. It's out there.Edit: found it: http://www.buildingscienceconsulting.com/resources/foundations/sand_layer_under_slab.htmAdvice I have seen on the slab is to keep the water/cement ratio to about 45% (someone check me on this, pls), since too much excess water won't be able to seep downward during the cure.
Edited 2/1/2008 8:56 am ET by DickRussell
I am aware of that information from Building Science. I just disagree with it.
They can't get your Goat if you don't tell them where it is hidden.
You have a good point. There is an issue with slabs curling as they cure if they can only dry from one side as well.
Even with the sand or gravel between the plastic and concrete there is still only the top surface for the water to escape the concrete. The sand or gravel does however slow that process by providing a reservoir for some of the water to be stored in until it leaves through upward migration. My personal experience leads me to do it the way I do. I have seen too many plastic sheets torn and punctured while a slab is being poured as well as too many sheets of insulation broken and disturbed during a pour. If there is migration of liquid up through a plastic barrier enough that it causes high moisture content in the sand ( I actually prefer 3/4 minus gravel or "rock fines) myself) beneath the slab then there are far bigger problems that need to be addressed. IMO Outside slabs need no barrier at all , and unless there is some sort of real water problem in a dwelling the odds of enough water being dumped on a slab and penetrating to and being stored in the sand/gravel is highly unlikely. Just my opinion. I haven't seen anything but claims to make me change it yet, but if I see some real proof showing me to be wrong I will probably do so.
They can't get your Goat if you don't tell them where it is hidden.
I'm no expert, but just to point out, vapor barriers and insulation do not have to be 100% continuous under a slab to do their job.Both are "percentage effective" type situations. If you have 98% coverage, you're 98% effective. Cracks and punctures are of no real concern.-------------------------------------
-=Northeast Radiant Technology=-
Radiant Design, Consultation, Parts Supply
http://www.NRTradiant.com
I am aware of that . I will ask you ( obviously any one can chime in )a few questions however. Are we discussing the poly being a vapor barrier or a moisture barrier? What volume of water can 1 cu. ft of 3/4 gravel hold or absorb before it reaches saturation point? What volume of water can 1 cu.ft. of concrete hold before reaching saturation point? What % by volume of water content is necessary to support mold growth in both those mediums and at what temperature? These are honest questions on my part. I simply don't know the answers. They are things I wonder about when I read the stuff from building science.
They can't get your Goat if you don't tell them where it is hidden.
I don't either, but are you suggesting that mold growth under a slab would have any consequence above the slab? That's nothing I've been particularly concerned about. I don't plan to hang out under the slab, and I haven't seen mold "climb" its way through concrete, only grow on the surface of wet concrete... something I have never seen on any slab with a vapor barrier under it.But, again, I am not a concrete expert and I don't spend all day tromping around inspecting slabs, either, so maybe I'm just sheltered, but I just haven't seen it.-------------------------------------
-=Northeast Radiant Technology=-
Radiant Design, Consultation, Parts Supply
http://www.NRTradiant.com
No I am not suggesting it. But If I understood the posts from Building Sciences it is one of their concerns.
They can't get your Goat if you don't tell them where it is hidden.
Are we discussing the poly being a vapor barrier or a moisture barrier?
Good question! Poly, even with tears and without taped seams is a pretty effective barrier to vapor migration, but a lousy barrier to water under hydrostatic pressure, as the water will eventually find its way through any openings and pond on top.
What volume of water can 1 cu. ft of 3/4 gravel hold or absorb before it reaches saturation point?
As much as 20 lbs/cf.
What volume of water can 1 cu.ft. of concrete hold before reaching saturation point?
The issue is not so much the reservoir capacity of concrete but its wicking propensity. If a slab is wet underneath, it will dry to the surface.
What % by volume of water content is necessary to support mold growth in both those mediums and at what temperature?
Mold growth isn't likely to occur in the anaerobic environment under the slab or even on the surface, since there is no "food" in concrete to support mold growth.
And it's likely that there will be no noticable moisture at the surface, since it will be evaporating as fast as it can wick up.
The problem is with wood framing, trim, and other finish materials in contact with the concrete, or in a room with consistently high relative humidity. Any woody or carbonaceous material will support mold growth at a surface RH of 19%.Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
So I think we can agree that with slabs exposed to the outside weather
it doesn't matter much either way. The protection layer does reduce the possibility of rips, tears etc IMO and experience and therefore increases the effectiveness of your vapor barrier. How much vapor do you expect to be transferred anyway? What I do not understand is the transference of such a quantity of water vapor though a slab and raising the moisture content of the building to the point of mold growth/high humidity solely because of the layer of sand or gravel unless you have inadequate moisture protection in place to start with. The water vapor will start migrating up and through the slab just as soon as it enters the sand/gravel because as we all know that is the way vapor transmission works. Does concrete act as a vapor retarder to the extent that it actually allows water to pool under the slab before enough is stored to overcome the resistance created by the concrete?If that is the case the slab is going to be awash in water anyway. How many lbs of water does your average building transpire during an hour? I read what is claimed but so far do not believe it based on my experience.
They can't get your Goat if you don't tell them where it is hidden.
So I think we can agree that with slabs exposed to the outside weatherit doesn't matter much either way.
With a slab exposed to the weather, why would you use a moisture barrier at all?
What I do not understand is the transference of such a quantity of water vapor though a slab and raising the moisture content of the building to the point of mold growth/high humidity solely because of the layer of sand or gravel unless you have inadequate moisture protection in place to start with.
You seem to misundestand the purpose of a sub-slab "vapor barrier", and the confusion is in part due to the common term we use for it. We're used to thinking of poly as a "vapor barrier" as that's its most common function in a house. In today's parlance, it's no longer called a "vapor barrier" but a "vapor retarder", as it can only limit the movement of water vapor.
But under a slab, we're not worried so much about water vapor as about liquid water, and the purpose of the poly is as a "capillary break" to stop the flow of water into a highly wicking (high capillarity) material like concrete. It's the same reason we now use foam sill seal instead of the old fiberglass sill seal, which doesn't act as a capillary break.
For a capillary break to function at all, it needs to be in direct contact with the wicking substance (best), or immediately under another capillary break such as rigid foam board (second best).
If the sand/gravel under your slab isn't completely isolated from all sources of groundwater, including through or under the footings or foundation, or through an imperfectly-sealed poly membrane, then hydrostatic pressure can move water anywhere there is an opening - and the poly then becomes a pond liner.
If, however, the hydrostatic pressure is forcing the poly membrane tighter to the underside of the slab, then the ability for water to penetrate is significantly reduced.
Does concrete act as a vapor retarder to the extent that it actually allows water to pool under the slab before enough is stored to overcome the resistance created by the concrete?
Not a "vapor retarder" but a water retarder - water will not flow through concrete but it will wick slowly and steadily by capillary action, and it can rise several feet into a foundation. Since capillary action is much slower than pooling of subsurface water by hydrostatic pressure, then there will always be a pool of water in the fill under the slab, slowly wicking its way to the slab surface and wetting any hygroscopic material in contact with it as well as raising the RH of the space above.Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
""With a slab exposed to the weather, why would you use a moisture barrier at all?"" I only mentioned it because it was mentioned in the Building Science post ""In today's parlance, it's no longer called a "vapor barrier" but a "vapor retarder", as it can only limit the movement of water vapor."" I understood that . ""But under a slab, we're not worried so much about water vapor as about liquid water,..."" As I said, if that is a problem then the problem is the drain curtain and water proofing so why attack something that is not a problem. ""If, however, the hydrostatic pressure is forcing the poly membrane tighter to the underside of the slab, then the ability for water to penetrate is significantly reduced."" That is the first statement that makes sense to me. Now I need to think some on the issue. "" Since capillary action is much slower than pooling of subsurface water by hydrostatic pressure, then THERE WILL ALWAYS be a pool of water in the fill under the slab, slowly wicking its way to the slab surface and wetting any hygroscopic material in contact with it as well as raising the RH of the space above."" Not if you have a properly done drain curtain. So again I come back to the point that the issue is not the sand/gravel but rather inadequate drain curtain and water proofing.
They can't get your Goat if you don't tell them where it is hidden.
So again I come back to the point that the issue is not the sand/gravel but rather inadequate drain curtain and water proofing.
I agree with you up to a point.
But a slab-on-grade or floating slab might not have footing drains, and the footing drain for a basement is sometimes placed on top of the footings or next to them because it's impossible to keep them below the bottom of the slab and still grade them to daylight without undermining the footings.
And how many builders still use asphaltic (black tar) "water-proofing" on their basement walls? At best, it's damp-proofing, but won't stop water under pressure.
When it comes to keeping a basement or slab dry, I prefer the belt and suspenders approach. No sense creating even a potential reservoir under the slab. Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
I wanted to revisit this part of your earlier post : ""If, however, the hydrostatic pressure is forcing the poly membrane tighter to the underside of the slab, then the ability for water to penetrate is significantly reduced."" In the situation mentioned in that post the poly is not acting as a vapor barrier , rather it is acting as a moisture barrier. One cannot have hydrostatic pressure without the liquid being present. So anything done to help keep the moisture barrier from being torn , ripped or punctured is a good thing is it not? Belt and suspenders .
They can't get your Goat if you don't tell them where it is hidden.
So anything done to help keep the moisture barrier from being torn , ripped or punctured is a good thing is it not?
Yes and no. Keeping the membrane intact is a good thing, which is why I use TuTuff instead of poly, place it on sand instead of gravel, and cover it with foam board.
Creating a reservoir above the membrane might not be a problem if everything else is perfect - but perfect is a hard target to hit.
Belts and suspenders, or better safe than sorry, would not rely on perfection.Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
Thank You . Now you know why I disagree with Building Science and I use the sand/gravel.
They can't get your Goat if you don't tell them where it is hidden.
""And how many builders still use asphaltic (black tar) "water-proofing" on their basement walls? At best, it's damp-proofing, but won't stop water under pressure."" Agreed, but with a proper drain curtain there should be no hydrostaic pressure. Good building practice to me dictates that the drains always are placed below the bottom of the sand/gavel layer and always exit at or beneath footing level.
They can't get your Goat if you don't tell them where it is hidden.
but with a proper drain curtain there should be no hydrostaic pressure.
Depends. If site soil (or anthying other than coarse granular fill) is used for backfill, then there could be lots of hydrostatic pressure from surface water against the sidewalls of the foundation before that water can ever get to the footing drain.
A footing drain is really designed to create a drainage path for rising ground water, which is why the holes are placed on the bottom.Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
I'm skeptical of sand as slab fill. It holds too much water. Here I can get 7/8" "drain" rock, which is a crushed product and locks up very nicely under a plate compactor (no one here imports river gravel for drain rock, for better or worse). I use Stego Wrap over the gravel, and no amount of walking on that material will cause perforations even over a crushed gravel base. It does cost a small fortune but in a high stakes situation like wood flooring over a slab it's well worth it. Poly is useless IMO. I have heard of TuTuff but not seen it.
""If site soil (or anthying other than coarse granular fill) is used for backfill, then there could be lots of hydrostatic pressure from surface water against the sidewalls of the foundation before that water can ever get to the footing drain."" True, which is why I said "Proper" drain curtain.
They can't get your Goat if you don't tell them where it is hidden.
"which is why I said "Proper" drain curtain"
If by "drain curtain" you mean a footing drain, then that has no effect on the saturation and hydrostatic pressure of non-permeable fill material above it.
A footing drain removes ground water that rises above the level of the drain, and will relieve surface water IF there is highly permeable fill above it.
The goal, however, is to remove surface water before it gets into the ground around the foundation by gutters and grading. A footing drain is not supposed to evacuate surface water, which will be as much as 500 gallons for each 1" of rainfall on a 1000 sf roof.
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
"" A footing drain is not supposed to evacuate surface water, which will be as much as 500 gallons for each 1" of rainfall on a 1000 sf roof."" Which would explain why I have never connected roof drains and footing drains. (Code doesn't allow it to be done here either.) "Drainage Plane" /"Drainage Curtain " meaning the pourous membrane (or rock ) between the foundation and soils extending from the top of the foundation to the bottom of the footing.
They can't get your Goat if you don't tell them where it is hidden.
" Agreed, but with a proper drain curtain there should be no hydrostaic pressure."But you can have LOTS of water in the soild with out hydrostatic pressure.A proper drain curtain won't keep the soil and thus the gravel tht it can wick into and thus the concrete that it can wick into dry.Even "dry" soil is not dry. It has nots of moisture in it..
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A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
" What I do not understand is the transference of such a quantity of water vapor though a slab and raising the moisture content of the building to the point of mold growth/high humidity solely because of the layer of sand or gravel unless you have inadequate moisture protection in place to start with.The water vapor will start migrating up and through the slab just as soon as it enters the sand/gravel because as we all know that is the way vapor transmission works. Does concrete act as a vapor retarder to the extent that it actually allows water to pool under the slab before enough is stored to overcome the resistance created by the concrete?"The problem is that slabs are oftne covered with materials that slow or stop the evaporation of the moisture into the air.And with the sand base unit it you start out with a large resivor of moisture that is trapped in when the slab is poured.Then 6 months latter a carpet is put over it or a vinyl or engineer wood or laminate.Then that moisture that is still wicking through the sab causes all kinds of problem with the new floor..
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A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
"Are we discussing the poly being a vapor barrier or a moisture barrier?Good question! Poly, even with tears and without taped seams is a pretty effective barrier to vapor migration, but a lousy barrier to water under hydrostatic pressure, as the water will eventually find its way through any openings and pond on top."There is 3rd method of water transmittion. wicking through the gravel and through the concrete.The barrier will work in the simlar percentage of undamaged area as it would vapor..
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A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
OK, so I insulate the ground unde rthe slab and run the pex, hook it to the manifold and pressure test it. Then I laid the insulation around the perimeter and waited for the slab to be poured.
I get to the job site the day the basement slab is being poured to find the perimiter XPS strewn all over the yard. The concrete guys said the carpenter told them to get rid of it because it's in the way and doesn't do anything for the insulation since I insulated the outside of the slab, and it may induce cracking. His 20 years of building tells him this.
This is only my 3rd build as a homeowner, so he has me there. But have I not read that the perimiter is a significant source of heat loss from the slab, because it runs up the vertical wall and out the sill? It's too late to do anything to remedy now because it is already poured. Thoughts?
Sorry I don't have anything constructive to say, but I'd fire your carpenter.
Jon Blakemore RappahannockINC.com Fredericksburg, VA
What do you mean you insulated the outside of the slab? How is that different from perimeter insulation. You're not being clear and you still haven't explained how your slab is coming up to your wall plates.
Explain yourself better or you're not going to get any useful answers.
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
What do you mean you insulated the outside of the slab? How is that different from perimeter insulation. You're not being clear and you still haven't explained how your slab is coming up to your wall plates.
Explain yourself better or you're not going to get any useful answers.
Initial issue: The basement bearing walls have 2 2x4s on the bottom, the bottom one treated and the top one not. I was told the slab would cover the treated board but not the untreated, and I was initially concerned that the fllor under the insulation was too high to have a 3.5-4" slab. They ended up pouring the slab to the top of the untreated bottom plate of the bearng walls, almost to the studs, so full thickness is there. Whether concrete should be poured to the top of the untreated lumber is something I don't know.
I had ripped xps boards and lined them along the inside of the poured walls to isolate the slab from the walls. I wasn'tsure whether to put them on top of the exposed footing ledge (about 1.5" above the height of the insulation on the floor, I hope you can visualize the step down from the wall to a 2" wide ledge of exposed footing, then down another 1.5" to the insulation on the floor) or put them on top of the exposed footing. I chose the latter so the slab could push the foam boards to the wall. In hind sight I could have placed foam the height of the exposed footing and then on top of the footing to isolate the slab from the footings and the walls. When I asked the lead carpenter, he said he's never seen anyone indulate the inside perimeter of a slab, and that I was wasting time and money, especially since I had already insulated the outside of the poured walls with 2" xps before the backfill.
I thought that lateral heat loss through the wall as well as vertical through the wall out the sill area were both concerns that need addressing, particularly when heating the floor.
This is a long post, I apologize. And it is after the fact, so there's not much I can do from here. I like the carpenter and his crew very much, and if he's right he's right and if I'm right too bad at this point. I also understand the carpenter's mindset of the homeowner getting in the way, etc., but you can imagine a guy's surprise when he sees his labor and materials spread across the snow.
I thought I would reach out the group here and get any comments or reactions, anticipating anything from he's right to fire him to no big deal to it happened to me once, etc.
you have to draw up your construction sections and review them with your subs
burying the untreated top shoe would be a no-no
it sounds like you're close to what you want in terms of isolating your RFH slab....
but the devil is in the detailsMike Smith Rhode Island : Design / Build / Repair / Restore
Well, that makes me feel better. When I read the building science section on this issue it sounded to me like I would be losing a ton of heat vertically out the sill area of the poured wall if I didn't isolate the slab from the wall.
If you're saying I got almost what I need for really good heat retention, I'm satisfied. Nothing I could do now if I weren't anyhow!
the exterior walls are the heat sink
interior bearing walls don't have any effect to speak ofMike Smith Rhode Island : Design / Build / Repair / Restore
Around here we are required to isolate the slab from the walls to avoid thermal siphoning. If your subs threw out your perimeter insulation they must not be accustomed to it being there, and they must not understand the need for it. We have an inspection of slab prep during which they specifically note the insulation details, and I could not pour without that thermal break.
You may have installed the insulation in a way that made it difficult for them to pour. What I do is take 2" XPS and rip it on the tablesaw so that there's a 45 degree angle along the 8' edge. I run that 45 pointing upwards with the full thickness against the wall. The result is that the slab tapers to zero where it contacts the wall, and when it shrinks a bit there is no contact. You can see some of it around the perimeter in this photo.
Picture: Are those round piers to be poured integral with the slab? What attaches to the rebar?
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
There are strip footings under the slab fill. The round piers sit on those footings. We use double-wall drainage pipe to form the piers, which are poured along with the slab, embedding the pipe for all eternity. The rebar projecting up thru the piers is bent to horizontal and tied into the slab mat.
I do not like the alternative, which is to form stemwalls under the slab, pour those first, and then pour the slab over them. The slab tends to want to crack along the stemwall lines.
By "strip footings" do you mean shallow elongated pads? Are they steel-reinforced?
If so, why not rely on those to distribute point loads to the soil through the slab without creating round penetrations through the vapor barrier/radon barrier?
This is standard procedure everywhere I've built.
Here's the closest graphic I could find - though I don't allow posts to penetrate slab.
View Image
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
In my photo those pieces of pipe are ~18" long so we save a little concrete by not pouring the footings that high. The footings IIRC are 8" thick, 18" wide, and several feet long each, with (2) #5 bars. Kind of pointless on this job since the whole house is on a basalt ledge, but I did what the plans show and the inspector nodded his head.
Not too many basements around here. This is the land of the shallow, vented crawl space. Typical house is on an inverted-T perimeter foundation with walls ~2' high. LOTS of holddowns and anchor bolts.
I ripped the 2" xps without any angles, and laid it on top of the footing edge. That may have been an error. Your photo (nice one, I might add and thanks) is for a job without a poured wall sitting atop a foting for a full (walkout) basement.
Had I your situation it would be easier--the ripped foam sita at at the edge for a clean pour, no stepping from floor to footing to wall. What's done is done in my case, and it will still be betet than NO insulation, which is what is usually doen in my area (Michigan, adn it's cold). I still can't fathom how reputable builders balk at the idea of insulating slabs in my area--I just don't understand it, it's like I'm speaking in tongues when I mention it.
The only thing that made my job easier than yours was the fact that I could simply align the top edge of the XPS with the top of the wall. In your case you would need to get a laser level, establish a level line around the inside of your walls, and set the XPS to that line. I use the backfill to keep the XPS pressed against the inside of the walls at the right elevation (each of my pieces is 24" wide, but in most places the walls were higher).
If you put the XPS in there in a way that will make the concrete guys' job harder, they will probably take it out. It sounds like you did not give them a way to finish the slab all the way to the walls.
Bottom line, if you are responsible for any piece of work, you need to know exactly what to do and how it will affect the next guy. As a GC I spend a lot of my time making sure we know what we're all doing, and making sure that it will work.
Indeed, I agree with you about the need to do it right if you choose to do it. My involvement was a last resort, not something I planned from the start. I was frustrated that I was unable to find local help -at least with the folks I spoke with- for getting the basement floor insulated. Not the GC, not the concrete contractors, not the HVAC contractors who bid the RIFH, not the insulation contractors. They either looked at me cross-eyed when I inquired about insulating the slab or they suggested bubble-wrap. I figured I would just do it myself as a last resort since I couldn't find someone locally to offer me any plan that sounded reasonable. This forum was one place I looked for information, and I did what I could with what I read here and other places and the time I had to devote to it.At this point I am just happy to have insulated under the slab and around the exterior of the walls.
westmich,
You have a potential problem.
Wood, treated or untreated, which is in contact with curing concrete is damaged on a cellular level by the concrete drawing water from the wood with enough force to damage cell walls. The process is called preferential dessication.
The damage is quite superficial, but just the same, the untreated wood is left more vulnerable to rot than if it not been in contact with curing concrete.
What to do about it? The only thing I can think of is to support the structure above and remove the untreated wood, replacing it with treated. It's easier now than it will be in three or four years.
Ron
Definitely, the slab should not have been poured around untreated lumber and I would not pour a slab around treated lumber as it can still absorb moisture and transmit it to the untreated wood. I hope you have a well-sealed vapor barrier under the slab.
If it were an unheated slab, edge insulation would not matter since you have insulated the foundation wall on the outside. But, since it's a heated slab, it's going to lose a lot of heat to the concrete basement walls. If those walls are insulated on the outside all the way to the sills, then at least you're not going to lose much of that heat to the outside, but it's going to make it harder to keep the slab up to temperature.
Slab edge insulation is much more of an issue for slab-on-grade since the edges are exposed to outside air temps and the bottom is exposed only to ground.
It sounds like you need to communicate better with your carpenter so these kinds of misunderstandings don't happen again.
But he was wrong to prep the slab base as high as he did so that the bearing wall plates were buried, and he was wrong to remove the slab edge insulation on a radiant slab.
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
Re your post to westmich, we are required to use perimeter insulation on an unheated slab also. We could theoretically insulate outside the walls but I have never seen that here. I think westmich is going to be wise to do so.
We could theoretically insulate outside the walls but I have never seen that here.
Really? Everyone there insulates inside the basement walls and loses all that thermal mass? Or are they left uninsulated and thermal envelope ends at the 1st floor deck?
What is your DD climate?
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
including basement walls for their thermal mass is a waste of energy and resources
Mike Smith Rhode Island : Design / Build / Repair / Restore
including basement walls for their thermal mass is a waste of energy and resources
Care to back that statement up?
Recent studies performed by the Oak Ridge National Laboratory have confirmed the effect that massive walls have on home energy consumption. These studies show a “mass effect” for walls that increases the effective R-value of a home’s walls by a factor of 1.2 to 2.1 times.
Thermal Mass - Energy Savings Potential in Residential Buildings
Buildings Technology Center, ORNL
"Comparative analysis of sixteen different material configurations showed that the most effective wall assembly was the wall with thermal mass (concrete) applied in good contact with the interior of the building. Walls where the insulation material was concentrated on the interior side, performed much worse."
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
Edited 2/15/2008 3:52 pm ET by Riversong
bs...
show me how the tests were performed and the cross sections of the structures
Mike Smith Rhode Island : Design / Build / Repair / Restore
Easy to say bs
Show me your documentation. Or even a rational argument. Nothing forthcoming yet but invective.
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
Edited 2/15/2008 5:51 pm ET by Riversong
no... you answer the assignment...
you offered the undocumented claims
show me the sections and the parameters
i want to know what assumptions are going to make a foundation wall acting as a thermal mas, beneficient to the comfort level/ energy consumption
and we aren't talking about PAHS neitherMike Smith Rhode Island : Design / Build / Repair / Restore
First, someone who can only respond with "BS" is not qualified to give out "assignments".
Second, I posted an excerpt from a report from one of the most respected research organizations in the building science field.
Third, you've offer nothing at all to substantiate your claim - no research, no documentation, not even a hint of a rational argument.
The ball's still in your court, buddy.
Either take a swing or leave the game.
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
Quite unlike someone who posts cartoons of people with their head in the sand. Do unto others my friend.
They can't get your Goat if you don't tell them where it is hidden.
this is supposed to mean something ??????
hah, hah, hah... gimme a break
<<<<<<
Recent studies performed by the Oak Ridge National Laboratory have confirmed the effect that massive walls have on home energy consumption. These studies show a “mass effect” for walls that increases the effective R-value of a home’s walls by a factor of 1.2 to 2.1 times.
Thermal Mass - Energy Savings Potential in Residential Buildings
Buildings Technology Center, ORNL
"Comparative analysis of sixteen different material configurations showed that the most effective wall assembly was the wall with thermal mass (concrete) applied in good contact with the interior of the building. Walls where the insulation material was concentrated on the interior side, performed much worse."Mike Smith Rhode Island : Design / Build / Repair / Restore
this is supposed to mean something ??????
hah, hah, hah... gimme a break
I'm trying to give you a break, but all you can do is laugh hysterically.
Offer an argument. Something. Anything.
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
instead of BS like this , you mean....?????
<<<<Comparative analysis of sixteen different material configurations >>>>>
your entire quotation don't amount to one single candle in terms of enlightenment
are we talking about trombe' walls
full foundations?
.. who knows. ??.. apparently you and the authors of the study
what help is that ?
and pulease gimme some more condescension... u do it so well
Mike Smith Rhode Island : Design / Build / Repair / Restore
I'll take that as your acknowledgement that you have no rational argument to make.
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
any way you want ... it's the sound of one hand clapping
do you think speaking in tongues is enlightening the great unwashed ?Mike Smith Rhode Island : Design / Build / Repair / Restore
First you should answer because you like expound on subjects like these.
Second because I'd like to know the answer.
Cheers
MikeWhat Robert "forgets" to mention was that that were saving compared to LIGHT WEIGHT FRAMING houses and for structures EXPOSED TO THE WEATHER.Neither of which have the slightest thing to do with 2 HIGH MASS CONSTRUCTION of different types nor not exposed to the weather.This is the report for Miniapolis.http://www.ornl.gov/sci/roofs+walls/research/detailed_papers/thermal/figures/figure6.pdfAs you can see, for R-20, the high mass with external insulation save about 5% over a conventional framed house. And a high mass construction with internal insulation about 7%.so the difference between the 2 is about 2 percentage points.And that is for walls EXPOSED TO THE WEATHER.The foundation would not experience the daly cyclic weather changes that give even this some improvement..
.
A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
thanks bill.... it sheds a little more light on the subject
Mike Smith Rhode Island : Design / Build / Repair / Restore
robert... here's your statement..
<<<<insulates inside the basement walls and loses all that thermal mass>>>>
and then you switch to a different study that is not talking about basement walls
now which is better .... insulating the outside of a basement wall
or the inside of a basement wall ?
which uses less energy to heat the conditioned space ?
which offers better comfort to the first floor
which offers better comfort to the basement
what assumption(s) does your statement make
is this real world or laboratory ?
c'mon... you can do it.... c'mon.... just defend your statement so i'll know what in the single family home world we're talking about
do your houses have full basements
do you insulate your full basements ... if so.. inside or outside
where do you make your thermal breaks ?
c'mon... you can do... c'mon
or you gonna give me another meaningless study ??????Mike Smith Rhode Island : Design / Build / Repair / Restore
As you can see, for R-20, the high mass with external insulation save about 5% over a conventional framed house. And a high mass construction with internal insulation about 7%.
You read the graph backwards. The more efficient wall has external insulation (internal mass). Internal thermal mass will dampen diurnal and seasonal temperature swings and create a more uniform interior environment, both in terms of temperature and moisture.
The same is true of sub-grade mass, particularly if in semi-conditioned space so it doesn't act as a thermal sink. A high-mass basement will also remain freeze-proof longer during a power outage.
Excess mass is counterproductive for direct or indirect-gain passive solar mass, if the goal is diurnal storage and release. And too much thermal inertia can be problematic for setback thermostats, as it slows the recovery time.
http://www.eere.energy.gov/consumer/your_home/insulation_airsealing/index.cfm/mytopic=11470
Compared to insulating the basement ceiling, insulating basement walls has the following advantages:
Requires less insulation (1,350 square feet of wall insulation for a 36 x 48-foot basement with 8-foot walls, compared with 1,725 ceiling)
More easily achieves continuous thermal and air leakage boundaries because basement ceilings typically include electrical wiring, plumbing, and ductwork.
Requires little, if any, increase in the size of the heating and cooling equipment. The heat loss and air leakage through the basement ceiling is similar to that through the exterior walls of the basement.
These are some other advantages of insulation on exterior basement walls:
Minimizes thermal bridging and reducing heat loss through the foundation
Protects the damp-proof coating from damage during backfilling
Serves as a capillary break to moisture intrusion
Protects the foundation from the effects of the freeze-thaw cycle in extreme climates
Reduces the potential for condensation on surfaces in the basement
Conserves room area, relative to installing insulation on the interior.
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
I did not miss read it, rather I miswrote it. But thanks for the correction.But still, as you can see it is MINIMAL difference between internal and external high mass system for a climate like Miniapolis. Now someplaces, like high desert areas, with a large daily swing, will show a much higher difference. But this will be much closer to VT and RI than any of other places that they tested.I noticed that this time you throw in a link. But it has NOTHING TO DO WITH THE CURRENT DISCUSSION. It talks about basement wall insualtion vs basement ceiling insulation.And you deliberately did not copy that part that had to do with internal basement insulation." And too much thermal inertia can be problematic for setback thermostats, as it slows the recovery time."When you post information out of an article you might want to read it first."The net effect of thermal mass in buildings containing heavyweight components was believed to cause the average indoor temperature and difference across the building envelope to be maintained at a more elevated level. As a result, night temperature setback caused the envelope heat-losses rate to be higher in massive buildings. All of this supported a common belief that night temperature setbacks in massive buildings caused a reduction in the setback energy savings. D. Burch investigated this penalty in setback energy savings and his research confirmed the fact that such a reduction took place. However, the magnitude of this phenomenon was very insignificant. For example, for a typical residence the difference in setback energy savings in the massive house and traditional wood-framed was predicted as only 0.3%.".
.
A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
Edited 2/16/2008 7:50 am by BillHartmann
You quote doesn't have to do with actual basements either.Basement are almost never set back, and as long as they are used regularly, should not be, especially if comfort is a concern. If they are not used regularly, then their heat should be maintained at a low level. I would say the mass inherent in any basement floor is enough to cause issues with setback, adding in walls doesn't appreciably change that scenario.. obviously it increases the mass, but you're already in "plan ahead, silly" territory if you want to do basement setbacks and are concerned about comfort.Basements do not see rapid temperature changes, which would make high mass a liability.In short, "thermal inertia" is a non-issue in basement heating in most cases.I"m not saying that insulation has to go on the outside, but the thermal inertia argument is moot.-------------------------------------
-=Northeast Radiant Technology=-
Radiant Design, Consultation, Parts Supply
http://www.NRTradiant.com
We could theoretically insulate outside the walls but I have never seen that here.
Comparative Analysis of Concrete Insulating Configurations
The thermal advantage of insulation applied to the exterior of a concrete wall is a phenomenon known as thermal inertia, more commonly referred to as thermal mass effect. Thermal mass effect is simply the ability of concrete mass to absorb and store heat. When concrete is used as a wall structure in a building this ability to absorb heat and the placement of the insulation has a profound effect on the building’s performance. When insulation is placed on the exterior of the wall the heat generated in the building conducts through the concrete mass first before meeting the resistance of the insulation on the exterior. If the insulation is sufficient to meet the heating demand on the building the concrete mass will warm to close to room temperature while storing millions of BTU’s of heat energy between the building occupants and the outside elements. This stored heat effectively creates a comfortable living environment by stabilizing indoor temperature fluctuations and reducing condensation. When the cooling of a building is of more concern than heating, the concrete mass can remove unwanted heat from the air reducing the need for air conditioning.
When the insulation applied to a concrete wall is divided equally between the interior surface and the exterior, as in the case with typical insulating concrete forms (ICF), the effectiveness of thermal mass in stabilizing the indoor temperature is not as great... Temperature stability resulting from heat radiating from the mass into the living space or absorption of unwanted heat cannot happen in an ICF structure.
When the insulating layer is placed only on the interior side of a concrete wall the thermal mass element is the least effective compared to the other methods of insulating a concrete structure.
Thermal Mass Walls
Layers of durability and energy efficiency make these walls worth their weight in gold.
Asa Foss, The PATH PartnersOctober 1, 2005Professional Builder
The Partnership for Advancing Technology in Housing (PATH), a program of the U.S. Department of Housing and Urban Development, has found through numerous site demonstrations that thermal mass walls offer significant savings on energy bills, especially throughout the south and in the west.
Oak Ridge National Laboratory's 2001 research on the energy efficiency of 16 different wall configurations (including stick frame, T-Mass, and ICFs) confirms this finding. The study, Thermal Mass — Energy Savings Potential in Residential Buildings, shows that concrete thermal mass walls, "applied in good contact with the interior of the building," are the most efficient wall assembly.
In 2004, students and researchers at the University of Nevada, Las Vegas, approached Pinnacle Homes to help them build a zero net energy, 4500-square-foot home. After examining various aspects of the design, Pinnacle chose thermal mass walls because of their energy efficiency.
Basement Insulation Systems
Nathan Yost, M.D.
Joseph Lstiburek, Ph.D., P.E.
<!----><!----><!---->
Effects of Insulating Basement Walls
From a moisture and thermal perspective, basement walls with insulation on the exterior perform better than basement walls with insulation on the interior. Walls with exterior insulation are “warm” and can dry to the interior. Since the walls are warm there is little risk of condensation of interior moisture. No vapor barrier should be installed on the interior side of externally insulated basement walls.
<!----><!---->
Insulating only on the interior side of basement walls presents problems because of ground water and the alternating direction of the vapor drive discussed above. The fact that ground temperature at various depths frequently is much colder than either exterior or interior air temperatures means that condensation can occur on the interior surface of the foundation wall. The interior basement insulation and the finished wall assembly are subjected to potentially significant moisture loads from vapor driven from both the exterior and the interior at different times of the year.
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
more bs.... more meaningless studies.. how about just answering the questions...<<<<do your houses have full basements do you insulate your full basements ... if so.. inside or outsidewhere do you make your thermal breaks ?>>> upMike Smith Rhode Island : Design / Build / Repair / Restore
Actually his Guru has changed his mind, and now advocates insulation on the inside. I'd post a link but you can trust me ;-)
When you're ready to have a reasonable, rational conversation or debate - I'm always willing.
But I will neither "put up" with your rantings and invective, nor will I "shut up" on your command.
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
define "reasonable"....& "rational"
"put up or shut up" is simply a challenge.... i certainly have no control over wether you ever shut up or not....
and i'd never expect you to.
now... you gonna share or get all huffy ?
c'mon.. u no u wanna
answer the questions...
hah, hah... c'mon.. i double dare ya
Mike Smith Rhode Island : Design / Build / Repair / Restore
I would agree that thermal mass would be a positive feature - if your daily exterior temperature swung above and below the temperature that you have set for your interior temperature. However, I don't understand how thermal mass is supposed to assist energy efficiency when the outside temperature varies between, say, 33 degrees at night and 38 degrees in the daytime while the indoor temperature is held at 70 degrees. In my own case, I am designing my next house to minimize the thermal mass effect and I feel it will give me the best efficiency. My standard procedure for most of my life has been to set back the temperature by a number of degrees during the day when I am at work and to turn off the heat completely at night. I then heat only the bathroom while I get ready for work and only heat most of the rest of the house between when I return from work until I get ready for bed. Thus I want a structure that I can warm rapidly when I come home from work. I see no advantage in having the termal mass to slowly cool down when I am at work or asleep and to slowly heat up when I come home at other then my regular time. Granted, there are some people, such as those with small kids, who prefer to keep the temperture constant, but for me, that would be a waste of energy for most of the day. So, to repeat my primary question: How does thermal mass increase energy efficiency when the outside temperature cycles between cold and colder for several months?
How does thermal mass increase energy efficiency when the outside temperature cycles between cold and colder for several months?
Let's get back to our concrete basement example with 2" XPS exterior insulation. For the sake of simplification, let's assume that the foundation wall is fully in contact with the ground and the ground is covered with snow, so there is a fairly uniform ground temperature outside the basement wall. And let's assume (as is the case here in VT) that the average ground temperature is 45°, and that the basement is heated to 65°.
A 1000 sf basement with 8' high walls of 8" thick concrete (approx. 1000 sf of wall )would have a specific heat of 18 btu/sf. Since the delta-T (65°-45°) is 20°, the total heat capacity of the wall once it's brought up fully to indoor temp is 360,000 btu.
With an inside air film of R-0.68, 8" of concrete at R-1.5, and 2" XPS at R-10, the temperature at the outer edge of the concrete would be 61°. At a delta-T of (61°-45°) 16° through the XPS, the heat loss rate would be 1600 btu/hr. for 1000 sf of surface.
If you set back the thermostat for 8 hours at night, the heat loss from the outer surface of the concrete would be 12,800 btu. Given the high specific heat of the concrete wall, and given that temperature flux moves through concrete at about 1"/hour, the wall should lose 0.7° of average temperature during that 8 hour period.
This is obviously far less of a temperature drop than a low-mass wall would experience and it would require only the same 12,800 btu to bring the entire wall back up to normal temperature (though it would take about 8 hours with a heat drain of 1600 btu/hr).
So the basement space would remain far more comfortable than an equivalent low mass space or a basement that is insulated on the inside, which would also create the potential for condensation behind the insulation (concrete at 47° with R-19 wall).
Additionally, an exposed concrete basement wall will moderate indoor relative humidity swings the same way it moderates temperature swings, maintaining a more uniform indoor environment (assuming, of course, that it's well sealed and not wicking moisture inward).
Please check my numbers and let me know if there are errors. I'm happy to be proved wrong by anyone willing to make a similarly thorough response.
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
-No one sets back basements-Even if they did, where is this energy savings? All you've done is guarantee that setback doesn't work (the goal of which is to drop your temperature as fast as possible, to coast at the lowest possible dT to the cold outside). If relative comfort is the goal, don't set back in the first place. If energy savings is the goal, your mass is hurting you, not helping, if you are trying to save $$ with setback.-Your mass primarily helps above ground. The only arguments for this below ground you summed up in previous post (part of a quote) and you touch on some interesting humidity/condensation arguments here, but none of the math you did says a word about energy efficiency.Did I miss something?-------------------------------------
-=Northeast Radiant Technology=-
Radiant Design, Consultation, Parts Supply
http://www.NRTradiant.com
to get rid of it because it's in the way and doesn't do anything for the insulation since I insulated the outside of the slab, and it may induce cracking. His 20 years of building tells him this.
And just what do the contract documents call for?
His two decades of experience might not trump his signature to execute the work as defined, not as he cares for.
Also, if those contract documents have been submitted to the AHJ, are those two decades of experience going to get the BI to sign off on construction not built to the approved design?
Oh well, pointless to ask, like as not.Occupational hazard of my occupation not being around (sorry Bubba)
I am aware of that information from Building Science.
I just disagree with it.
You're right on the money. Sure it's possible that it will take longer for the slab to dry, but so what, that doesn't mean this should never be done.
I lost interest in the Building Science website because of how strongly they defend some ideas that are half baked or that just don't make sense with high quality building practices. What they have is better than nothing, but they are too full of themselves and try too hard to make things idiot proof and in the process dilute the quality of the information.
Beer was created so carpenters wouldn't rule the world.
I will agree to disagree with your comment about the sand.
The you're also disagreeing with the most respected building scientist in North America, as another poster has already indicated. Here's more specifics from
Sand Layers Should Not Be Placed Between Polyethylene Vapor Barriers and Concrete Floor Slabs
by Joseph Lstiburek, Ph.D., P. Eng.
The following 4 reasons are generally cited for using a sand layer over polyethylene vapor barriers is as follows:
1. The sand layer controls bleed water with high w/c ratio concrete slabs2. The sand layer reduces curl with high w/c ratio concrete slabs when top-side curing is not controlled3. The sand layer reduces plastic shrinkage cracking with high w/c ratio concrete slabs4. The sand layer protects the polyethylene vapor barrier from punctures
The first three reasons are based on sound technical arguments. However, each of the first three are based on the condition that the sand layer be prevented from getting wet during the construction process and beyond and are typically associated with floor slabs that are placed "after the building is enclosed and the roof is watertight." Additionally, the first three are based on the condition that wet curing such as ponding or continuous sprinkling will not occur or that joint sawing using wet methods or power washing will not occur. The first three are also conditional on slab and foundation designs that will not be sensitive to ground water wetting from local water tables and local irrigation.
In the case of exposed slab construction, the first three reasons are rendered moot since the conditions for their use are not met nor can they be met. Accordingly, a sand layer should not be specified.
The fourth reason, "puncture protection", is based on incorrect physics. A sand layer is not necessary to protect polyethylene vapor barriers. Vapor diffusion is a direct function of surface area. Rips, holes, tears and punctures in sheet polyethylene vapor barriers constitute a very small surface area of vapor transmission compared to the total floor slab area. If 95 percent of the surface area of the slab is protected by a vapor barrier, then that vapor barrier is 95 percent effective. This holds true only if air flow or air leakage is not occurring through the vapor barrier. Where concrete is in direct contact with the polyethylene vapor barrier this is the case. Air flow is not occurring. The concrete slab is an "air-barrier" and the polyethylene is the "vapor barrier" and an effective vapor barrier even if the polyethylene has numerous punctures.
In the case of exposed slab construction there is no justification for the use of a sand layer between the polyethylene vapor barrier and the concrete slabs.
The specification of a sand layer over a polyethylene vapor barrier is typically directly responsible for flooring failures, mold and microbial contamination problems.Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
You have that correct . I am disagreeing with him.
They can't get your Goat if you don't tell them where it is hidden.
I agree with Mike Maines , I just did a garage slab and addition with two friends and we put 2 in foam on carefully raked and compacted gravel then rebar wire tied and then poured cement on top and ended up with almost an 8 in thick slab. a little more then planed but thats not a bad thing, thats the way I / we will do it from now on.
Carpentry and remodeling
Vic Vardamis
Bangor Me
Thank you all for your advice. Ive got it now.
Randy
I am in the same situation--currently insulating the floor for a pour. 2 questions:1. When I insulate the edges between slab and poured vertical walls, do I put the insulation up to the "ledge" on the perimeter (is it the exposed footings? I'm not sure) or on top of that ledge? If the former, seems like the slab never gets above that footing, which doesn't seem right.2. It appears that when the concrete contractor tamped the sand/gravel after the rough plumbing was done, they didn't leave room for the 2" of insulation--if they pour 3 1/2 to 4" on top of the insulation it will cover the bottom plates of the stud walls, both the treated and untreated wood. They knew I was insulating the floor with 2"--can I assume that it's a mistake and that I CANNOT actually have it done this way and that a couple inches of sand/gravel have to be shoveled out of there??
1. When I insulate the edges between slab and poured vertical walls, do I put the insulation up to the "ledge" on the perimeter (is it the exposed footings? I'm not sure) or on top of that ledge? If the former, seems like the slab never gets above that footing, which doesn't seem right.
Generally, a basement slab sits on top of the footing, and should be insulated from the footing as well as at the edge where it meets the vertical wall.
2. It appears that when the concrete contractor tamped the sand/gravel after the rough plumbing was done, they didn't leave room for the 2" of insulation--if they pour 3 1/2 to 4" on top of the insulation it will cover the bottom plates of the stud walls, both the treated and untreated wood.
In #1 above, you seem to be describing a basement slab poured inside the concrete foundation walls. What stud walls are you refering to? Is this a walk-out basement with load-bearing exterior walls on one part of the foundation at slab level? If so, then you need 6" of depth below whatever the stud wall is bearing on.
Perhaps you can describe your project better?
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
'Morning Randy973,
Rather than echo much of the info, previously supplied to you from others, I would add a few comments regarding some other thoughts.
I tend to like compacted sand directly under the insulation with a poly layer directly on top of the XPS. I've found a supplier who can get me 10 mil poly, considerably tougher than the regular 6 mil most suppliers can get. I can also get it in very large sizes, 20'X50' on my last floor, which eliminated any seams. The concrete is poured directly on the poly.
I used a 10' steel straight edge and a builder's level to level the sand after damp compacting it well with a heavy plate compactor. My feeling is that the XPS may not initially deflect to conform to a non-flat surface and would tend to bridge across an uneven surface. It would even be possible that the load from the concrete pour would be insufficient to fully deflect the XPS, leaving that final deflection to take place only after the floor was finished and under load. I like Dow-Corning's HI-60, which has a compressive strength of 60 PSF, for the under-slab insulation. (Only because I want to park vehicles on my floor and place machines on the same floor.)
That final deflection is the one I most worry about, if the concrete is cured and without tensile reinforcement, it could crack. (My floor can be subjected to heavy vehicle loads for extended periods, ie. winter storage.)
This is my reason for substantial rebar reinforcement, also. I am unlikely to achieve a perfectly plane surface under the XPS, (it would be a happy accident!) & even if I was so lucky would it stay that way before I got it covered?
I feel I can level sand much better than gravel, and when compacted, it can provide a reasonably supportive base, (at least as good as the native soil beneath it).
I suppose my ultimate would be a well compacted, well drained, gravel sub-base with a Geotextile fabric on top of it to prevent downward migration of fines into the gravel, with a compacted and easily leveled sand layer on the Geotextile, suitably graded & leveled.
A pleasant by-product of a plane surface beneath the XPS is the accuracy of material calculations for your concrete mix order and a consistent floor thickness, which can come in handy if you should want to put in radiant tubing and want a consistent slab thickness for that.
Regards,
STAINLESS
Thank you for your info.
Randy