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I’m new to the forum but I have been a lurker for awhile. My ? is this. What type of rigid insulation should I use under the slab of my basement? Will the weight compress it? Ruin the R value? I plan on using the basement as a teen living space. jeffysail |
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Comparison of Under-Floor Insulation Systems
http://www.healthyheating.com/blog/index.php?cat=20
RBean
http://www.healthyheating.com
http://www.healthyheating.com/blog
Short answer, yes!
use the 2 inch thick pink (blue) stuffset on top of a 6 mil vapor barrier and then use radiant in floor heat, your kids will love you..
Welcome to Breaktime.
If you're planning on using the basement as living space, then you need to insulate below the slab. The most common underslab in use around here (IL) is extruded polystyrene (XPS).
Sometimes called "blueboard", but also comes in pinkboard form (different companies, blue is Dow, pink is Owens Corning).
I think standard blueboard has a compression strength of around 25psi, which if my math is correct, would be around 3600lbs/sqft. Commercial applications can use XPS with compression strengths up to 100psi. Average R is around 5/inch.
DO NOT use the white stuff! It is EPS (expanded polystyrene). Basically the same stuff that styrofoam cups are made out of. You don't use EPS below grade unless it is a specially manufactured hybrid for below grade use. Regular EPS will break down when used below grade.
jt8
When women love us, they forgive us everything, even our crimes; when they do not love us, they give us credit for nothing, not even our virtues. -- Honorý de Balzac
Edited 1/25/2005 2:22 pm ET by JohnT8
I am building a new house this spring and will be using 6 mil poly for a vapor barrier and 2 Lb Corbond Spray Foam (about $1.25/sq ft) to insulate the slab with 2" chairs and an 18" grid of #3 rebar. There are multiple problems with foam board such as making the stone bed level so the board sets flat and unless you are on site watching them pour, the concrete guys will destroy it. The foam does and incredible job and makes a flat, 1 piece surface. I will also be insulating the exterior of my foundation, from top to footing, creating an insulated, waterproof barrier. At $1.25/sq its the cheapest, fastest way to do it
are you planning on putting the 6 mil poly on top of the foam or under it ?
when you describe the system as waterproof, are you intending on installing any waterproofing materials on the outside of your foundation walls ?
insulate the slab with 2" chairs and an 18" grid of #3 rebar
are the chairs and rebar going in the concrete or in the foam ?
carpenter in transition
Hi Tim, I am using a company I had a very good experience with (Standardinsulating.net). I had used wet blown cellulose on my last house but they stopped using/selling it because of seasonal use here in the NorthEast. As part of the basement Rec room finish we had studded the walls and put PT sleepers on the floor, they sprayed with 2 LB foam, absolutely amazing how it turned out. So when I called Chuck the owner of Standard we got into a discussion of options on my next house. #1 The poly is put down over the stone but you really dont need it, you can spray the foam directly on the stone bed, the poly just makes it a little more even. #2 The "chairs" are 2" tripods that sit on top of the foam and hold the rebar in the middle of the 4" pour. i will not use mesh wire in a finish pour because it ALWAYS sinks to the bottom and is useless, I don't want my floors to crack like they did in the last house. #3 This is the best part!! I had looked into the warm-n-dry system where they rubberize the exterior for waterproofing and then install 2" compressed fiberglass panels for protecting the rubber, and insulating the foundation. But it was about $2.45 a square foot and had heard some negatives about it because water and fine silt can saturate the fiberglass and ruin its R value. After talking with Chuck I am now going to spray the entire foundation from top of wall down and out to footing, creating a drainage plane to footing drains. The foam is super dense, waterproof and will give a little bit if the foundation cracks. the hard part is the foam is about 1-1/2" thick so you need to set your sill out over it, install termite flashing and the chicken wire with cement parjing to make it look like foundation wall.
If you live in a cold climate where winter means ground frost never put in slab heating in a basement floor. Simple physics heat travel to cold. The in slab radiant heat will heat the ground under the slab more than the room above, your heating bills will be high. As I mentioned it depends where you live and the ground temperature. You can insulate the heck out of it but it is not that efficient.
But...
1. The basement floor could be below the frost line
2. and besides, the insulation should provide a thermal barrier to conductive losses
I sure wouldn't want to try it without under-slab insulation, but properly insulated, it should work just fine.jt8
There is no revenge so complete as forgiveness. -- Josh Billings
Have someone do a heat lose calculation for you just to be sure. A technician/engineer should be able to calculate the energy costs for the system you are thinking of installing.
One of the largest radiant heating markets in the world is Alberta, Canada.
Radiant slabs on grades and radiant basements are done a dime a dozen.
Temp ranges -10 to -60 deg F
Heat loss to the grade below isn't radiant its conductive.
Conduction is based on soil conductivity and the differece in temperature between the grade and the heated slab.
The higher the soil conductivity which is based on moisture content and soil type and the greater the temperature difference the higher the slab insulation R value.
Since most floor coverings are under R-2.5 a 2" high density rigid insulation is more than adequate 4:1 ratio.
So the business about cold climates and radiant is no more of an issue than refrigerated buildings or hockey rinks in the deep south (Florida) that heat the soil below the slabs to prevent frost penatration in the middle of summer.
Its all about controlling heat transfer.
RBean
http://www.healthyheating.com
http://www.healthyheating.com/blog
Edited 1/25/2005 4:26 pm ET by RB
You get that information from where?You recommend against doing what is probably the best way of heatingh a house in a cold climate that I know of. I live in one and am enjoying warm feet as I speakThe whole reason for placing the XPS foam under the slab is to prevent the problems you feel are of concern. With adequate insulation, the heat provided goes to living space instead of to ground.but even without insulation, the colder the air is, the less disadvantage there will be in he3ating the slab. Ambient soil temps in most of the northern US ranges around 55°F. That is a whole lot better than -10°F air temps
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
Piffen, as I have mentioned in previous postings the diversity of construction situations never ceases to amaze me. 55 degree Fahrenheit ground temperature is perfect for an in slab heating system.
I will give you an example of Yukon soil temperatures, my water line is buried 12' it runs about 30' from the city's main to my house it has a heat trace wrapped around it which is wired into a transformer which is turned on in October and turned off when the frost leaves the ground in May/June. The water line and heat trace is also wrapped in 2" styrofoam.
I built a house last winter and sold it in the spring, because the ground directly under the house had froze before framing started that ground eventually was sitting under a well insulated crawl space. The frost never came out of it until well into summer. That crawl space was an ice shed you could hardly work down there.I won't even bother to start in on perma frost which never thaws and is frozen year around.A litre of heating fuel here is .70, propane even more expensive there is no natural gas. The average heating bill would be somewhere in the $300.00 to $400.00 range. a friend of mine has a large house his bill was $800.00 last month. Some houses with very expensive in slab heating have been disastrous for the home owner, $1200.00 per month heating bills. The joke is the homeowner is heating the ground. What works in one area does not work in others.Alberta, has some of the cheapest energy costs in Canada this and the climate there makes in ground heating systems affordable.
It is probably best to keep that diversity in mind when using words like "never"It seems that what you meant was only when nearing the permafrost temps so the temperature gradient is more extreme than where much of the rest of the us recieves some frost in the ground.I can just picture a slab on grade with radiant heat and no insulation on permafrost. Just for fun, how fast do you suppose it would sink in to the depth of the windowsills.
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
jeffy....
EPS got a bad rap for a lot of years.. i wouldn't use it.. but the studies i've seen say it works great under slabs
so... i stopped using Dow ( Stryo-SM). blue...
i stopped using Amoco ( green )
i stopped using Foam-u-laR ( pink )
now.. all i use is EPS with a density of 2.0 lb/cf (for under slabs ) ... and i buy the kind treated with Borax ( tradename R-Control ).. so termites and vermin will not eat thru it
don't use 1" under your slab .. it's so thin it gets destroyed by the workers..
use only 2"... it's strong enough to take some abuse
but, hey, whadda i no ?
but
now.. all i use is EPS with a density of 2.0 lb/cf (for under slabs ) ... and i buy the kind treated with Borax ( tradename R-Control ).. so termites and vermin will not eat thru it
Dang Mike, you're just a source for all kinds of good stuff. First solartubes and now R-control.
I thought R-Control was "special" EPS? Special formula or bond or some such that made it superior to regular EPS.
http://www.r-control.com/
They have a EPS geofoam that is used for fill projects (such as highway overpasses).
http://www.r-control.com/products/geo/projects.asp
Can you imagine using some of these as slab underlayment? View Image
Gawd, what kinda R value would they have?! I suppose if you can build a highway overpass on them, you could build a house.
jt8
There is no revenge so complete as forgiveness. -- Josh Billings
yes, R-Control is some kind of trademark franchise... they must license formulas and such to their member companies..
the one we deal with is Branch River Foam.... what an operationMike Smith Rhode Island : Design / Build / Repair / Restore