ICF and thermal bridging w/brick veneer
Reyesuela
| Posted in Energy, Heating & Insulation on
I’ve run into a snag with the footing for a 4″ masonry veneer in conjunction with ICFs. The footing will cause a MAJOR thermal bridge, rendering the exterior insulation all but useless. Joe Lstiburek, of Building Science, says that he’s tried for 25 years to come up with an affordable and practical way of solving the thermal briding problem with exterior-insulated concrete walls, from highway-rated foam insulation to pouring a separate foundation for the bricks only, and has failed.
Why didn’t these things work? Too expensive? Or were there other, noneconomic problems?
Replies
I'm trying to picture at what point the thermal bridge appears?
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Are you referring to a brick ledge, the kind that is cast into the wall, or doing the veneer from the footers up?
The only thermal bridge would be at the ledge itself, and that will be below grade and partly insulated. I don't see that rendering the exterior insulation useless, just slightly compromised for a small area.
Another option:
There are some very advanced brick systems that hang in tracks - Redland has one. The tracks would screw to the outside of the ICFs, and no thermal bridging would take place.
I'm talking about a ledge built like this:http://www.arxxbuild.com/technical/installation_guide/IG_Sec_3_Exterior.pdfSee page 7.Take a look at this:http://www.buildingscienceseminars.com/handouts/BSD-103_Understanding_Basements.pdfp. 7-8I can't see how this situation would be one whit better in an ICF home., as far as the exterior insulation goes. (Of course, it wouldn't completely suck all heat out of the home because the interior is also insulated, but it would render the exterior pretty worthless.)>There are some very advanced brick systems that hang in tracks - Redland has one. The tracks would screw to the outside of the ICFs, and no thermal bridging would take place.I'll check it out, but I'm actually interesting in a real 4" stone veneer.
Edited 1/25/2007 8:09 pm ET by Reyesuela
Building Sciences certainly does some good work but I have to question Page 4 - Figure 5. On thing that jumps out is that the conclusion for this comes from a study done in 1981 and there has been a heck of a lot of work in this area since so why go back 26 years to get a study that is considered correct. To the best of my knowledge (and I'm not an engineer working at ORNL) heat transfer is based on square footage and isn't like water or electricity that immediately flows to the path of least resistance as this figure suggests. The several energy usage software packages that I've seen determine the total transfer by adding the R-value and Sq ft of each component of the house and then factors in the temperature differential.If Figure 5 is correct then I'd like to know why the building codes require insulation in the walls since almost every house has exterior walls with big holes and a comparatively low R-value window in it.Steve.
The problem wouldn't be the low R-value, per se, but the *active* thermal conductivity of the masonry that is attached to everything in the house. Essentially, it's like having a heat fin on your house. The thermodynamics wouldn't be at all similar even to an open window.I just plain can't see why pouring a second foundation just for the masonry doesn't work, though.
Edited 1/25/2007 8:10 pm ET by Reyesuela
I see your point from the Building Science site, but the area where there is thermal bridging is pretty small in the ICF setup from ARXX. I would think with the gains elsewhere, it is a good compromise (much like having windows is :-) That is a long way from rendering the wall useless. I am in an ICF house now, its 14 degrees outside, and we are comfortable (72) with only a Walmart plugin heater on each floor - no other heat. The things are pretty remarkable.
I would think that a 4" cmu wall outside the ICFs on the same footer would be a good workaround if you wanted to go that way.
Treat every person you meet like you will know them the rest of your life - you just might!
Hey, that would solve everything! Pretty pricy with a basement, though.
Yes, that 8 inches of R-value of .2 per inch/hr masonry flows heat more than 12 times faster than 4 inches of R-value of 5 per inch/hr foam. But I've never seen a heat transfer formula that was different for masonry.The 50-100 sq feet of ledge is going to pass an annoyingly high amount of heat but I don't see how that makes the rest of the insulation wasted.Certainly any alternative method that will increase the R-value of that path will help. I was reading about a company doing something along those lines with a reverse ICF, two panels of concrete with a foam core. Takes care of the thermal bridging, foam protection and insect problem in one shot. Don't remember where I saw it though.Steve.
Air and wood both conduct heat poorly compared to masonry. The heat has to come from somewhere to be able to get out of the house. A window does that relatively badly because it touches gypsum, air, and wood. Masonry does that REALLY well because it touches all the rest of the mayonry in your house!EDIT: I mean that, in an ICF house, the ledge to hold the brick would be part of the entire concrete envelope of the house, meaning that the heat gain of the entire wall system (through both conduction and radiation) could be essentially dumped through the thermal bridge into the exterior.>reverse ICFI found something afte a quick search called a "tiltwall system". Looking more now...
Edited 1/25/2007 8:13 pm ET by Reyesuela
I can't follow what you say here.air does not 'conduct' heat' You lose heat in air thru convection rather than conduction.a masonrysurface does not touch all the other masonry in the house. It only touches the masonry immediately in contact with it. If that masonry is primarily contained within the ICF blanket of insulation, there is no heat loss to that mass. The only point of conductive heat loss is the 4" or less in contact with the base of the brick veneer. Is this a slab house? If so, you can isolate the slab edge from the footer with foam also, if you are that concerned.
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Air does conduct heat--poorly. Its k-value is 0.024. Convection can only circulate air within a closed place. Conduction and radiation are the only two ways for heat to get inside a closed space.My point is that you can't compare the ledge for brick to the effects of a window because conduction is a HUGE problem with concrete, with a k-value of 1-2, while with a window, which is in contact with air and wood, it's negligible. In an ICF house, the brick would be in contact with a ledge that is in total contact with the entire envelope of the house, from the roofline to the basement. (I said "all the masonry" because usually, masonry would only also include the fireplace, and that would be tied into the same system, of course. I'm also considering a poured concrete slab flooring system.)I have a question about fireplaces, too, because it seems to me, with their exposed brick, that they'd be as bad or worse.>Is this a slab house? If so, you can isolate the slab edge from the footer with foam also, if you are that concerned. I will, of course!
Edited 1/25/2007 8:17 pm ET by Reyesuela
The amt of conductive surface you are showing is so small as to be nearly insignificant, and is definitely not destructive to the point of rendering the entire exterior insulative package "worthless"
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What is the PSI load of your brick veneer on the shelf at the top of the foundation wall?
Absolute max - 34 PSIMore typical max - 22 PSI
That small a load would easily be carried by Dow Styrofoam EXPS in the higher compressive strengths.
I read the one link . The author states that they have tried placing "Highway foam" under the brick veneer at the ledge of a full basement and that that approach failed.
I sure would ask how and why?
What constitutes failure in their opinion? 10% heat transfer reduction, 50% reduction ?
It seems to me that using a 2" thick piece of Styofoam xeps under the base of the first course of brick would provide the needed thermal break.
>The author states that they have tried placing "Highway foam" under the brick veneer at the ledge of a full basement and that that approach failed. I sure would ask how and why?I know! I've emailed. We'll see if I get a reply.
Instead of laying the brick right on the brick ledge on your wall, use a 4 wide by 8 inch tall inch cinder block, NOT concrete block, as the first layer. The cinder block has almost 3 times the R of brick, cause its got an air cavity and it is almost half air in itself.. Then foam the cavity of the block, further increasing the R. Then, when laying the block row, mud the front edge only at the web points, ie: the ends and center. Fill that bottom edge gap with foam and put a foam layer on the face of the block. Now you have full support with an R value probably 10 times the original brick situation and going further than that is probably not economically justifiable.I like your approach....now lets see your departure
>Fill that bottom edge gap with foam and put a foam layer on the face of the block.I have aproblem using regular foam because of the PSI of the veneer, but I found this: http://www.foamglasinsulation.com/There is a local dealer who carries it, and I can get it in 1'x1'x1.5" sheets. I'd have to cut wach in thirs and lay them along the top.I also realized that I have a similar problem with the floors because of the design of two balconies. Argh!
The brick veneer acts as a fin, dissipating heat from the wall. But it's a very long fin, made from a very poor conductor. It's "fin effectiveness" is very poor. It also has an air gap, albeit a ventilated one, between it and the exterior layer of ICF insulation, such that only 1/2 of the fin area is fully exposed to the outdoors.
I wouldn't sweat over the heatloss of this connection, nor would I put anything flimsy under the brick in an effort to provide a thermal break. You run the risk of cracking later, all in an effort to deal with a comparatively minor heat loss in the grand scheme of things.
Commercial cellular glass insulation is crumbly, stinky stuff- risky at best as a permanent point of bearing. XPS has too low a compressive strength and I'm sure it has the same tendency to "creep" under protracted loading as all other plastics do.
All you really need to do a fairly good job of disrupting the heatloss from a "fin" is to put in a discontinuity of materials such that there's a significant "contact resistance" between the concrete brickledge and the brick itself. A couple layers of tarpaper would do just fine.
>Commercial cellular glass insulation is crumbly, stinky stuff- risky at best as a permanent point of bearing.Eek! That's not good. I read the specs but, well, sometimes those specs, they ain't so trustworthy. ;-)BTW, I know from my loads that regular foam wouldn't work. And brick ties are just to keep the wall from falling away from the house, not to support it.>All you really need to do a fairly good job of disrupting the heatloss from a "fin" is to put in a discontinuity of materials such that there's a significant "contact resistance" between the concrete brickledge and the brick itself. A couple layers of tarpaper would do just fine.Yeah, I think I am overthinking this. It just freaked me out when I was reading about it! Still haven't gotten a reply from building science--it would help SO much if they published actual studies on the web!!!
Reyesuela,
Problem solved..
Set foam across the top of the brick ledge.. use brick ties to carry the load into the wall.. the foam will settle only a modest amount not enough to cause failure.. If you doubt me go down into your basement, they set foam under the concrete floor didn't they?
Just for information My house has walls of ICF with brick ledge, I did as I said and it's fine for the past 5 years (except I used stone instead of brick)
Edited 1/26/2007 10:30 am ET by frenchy
brick ties carry load?Thanks for the laugh of the week!
You oughta write a book
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Piffan,
If you look at most homes built nowdays around here you'll note foam under the basement floor. It's common practice nowdays.
Then they pour 6 or eight inches of concrete on top of it (more if it's a tuck under garage and they are doing in floor radiant heating).. If the foam compressed too much, you'd soon see a big old crack around the edges and that doesn't happen..
Yes Brick ties can help carry the load! If you do as I did which is put at least two brick ties on each stone, more on larger stones. The reason I went to so much effort is because my stones are in wooden grids (look at the pictures) wood shrinks and swells depending on moisture. I didn't want them to loosen with that shrinking and swelling since some of the beams are 8 inches wide or more (that's a lot of shrinking and swelling) If you come by stones put on the wall 5 years ago are still in perfect shape with absolute,ly no cracks in the mortor joints. None!
Frenchy, I gotta admit, when you first mentioned using brick ties to hold the masonry, I reacted like Piffin. Then, when you describe a method using several ties on every component, I can see how it would actually help, providing the tie was taught and the stone was leaning against the building. Typically though, there is an air space and the stone would have to droop considerably before the tie was taught.
I have seen many brick chunks hanging independently from a frame wall so the idea is not totally without merit.
blue"...if you just do what you think is best testing those limits... it's pretty easy to find exactly where the line is...."
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Blue-eyed-devil,
I can certainly understand why Piffan reacted as he did.. I too have seen enough masons who use a few brick ties to hold the wall and bricks together. If that were all I was talking about then Piffan would be absolutely correct.. I should have made a longer explaination but some of mine get so long winded that they are skimmed rather than read..
However since there is such an easy connection to the fastner strap on ICF's and they are every few inches Assume that people do as I did which is put the stone/brick right against the wall (using a piece of cotton clothes line as your moisture wick) and use at least two ties per brick the slight settling of brick sitting on foam is really insignificent.
Like I said they pour concrete directly over foam and once dry drive and park cars on it.. Can't imagine the loading on say a 3/4 ton pickup parked on top of that foam would be much higher than bricks tied into a wall as I describe..
> Like I said they pour concrete directly over foam and once dry drive and park cars on it.. Can't imagine the loading on say a 3/4 ton pickup parked on top of that foam would be much higher than bricks tied into a wall as I describe..Different foam! Though I'm interested in finding it...
Edited 1/27/2007 9:57 pm ET by Reyesuela
Reyesuela
Normal used Here in Minnesota is the regular Dow Corning stuff.
Then the folks in Minnesota need to learn how to search on Dow Corning's web site because the "normal" stuff like you buy at Home Depot and Lowes is NOT approved for under slab use.Steve.
http://www.owenscorning.com/worldwide/admin/tempupload/pdf.2-74495-157_HighDensBro_E.pdf http://www.dow.com/styrofoam/na/pro-us/products/highload_100.htm
Hey, thanks! I looked, couldn't find...
You have now added the word, "help" to carry the loadI haven't argued the compressive strength of foam here. The right foam can cary most of it, but for my work I would forgo the minor insulation heat loss and go stone to the bricklip with out breaking it with a faom seat.but in your latest rendition, I do think that most times, the ties would help enough over the right foam to proivide the added insurance against failure.But your first rendition was that the ties would do the load carrying and that is clearly against all masonry standards and even the purpose for which the ties exist.I'll go along with helping out tho, if enough are used.
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Piffan,
Like I said I sometimes get so long winded trying to decribe what should be shown peope tend to skim rather than read..
Plus I really should choose my wording more carefully.
Another solution might be a dense plastic or even pressure treated wood..
I Understand the mania about heat loss. I have it bad, I've lowered my heating bill by 2/3 in spite of a bigger house, more windows, and things not properly sealed yet. OH and let's not forget the cost increases..
Yet I want more.. Ill be happy when I can warm my house with a fart in febuary <G>
Not sure why you think lack of cracks in a basement or garage floor is relevant. She is estimating 34 and 22 PSI of load.Test question - How many PSI load on the foam under a 6" slab?Steve.
she?
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Yup. She. 100% chick here. *g*
;)
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(Frenchy may have just guessed--I doubt many guys would write "Eeek!"--but I also gave myself away in another post. Building is a sideline for me, though I'm going to make more at it in 2007 than I will from my main job--writing romance novels. *g* Yup. That's why I studied Mech Eng--to write books and play with houses.)
Edited 1/29/2007 2:20 pm ET by Reyesuela
Memo
Yes, Sue Ella, money can be made in building.LOL, We'll have to invite you to our next novella thread in the Tavern then
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Hehe. I stumbled onto an incredible deal of a house that was about 50% of potential price because of being FREAKING WEIRD. We bought it to live in but then had to move, so renovating it beforehand was a no-brainer. We'll make $4 for every $1 we put in.I'm thinking of buying up some abandoned ghetto houses in my new region and redoing them for rentals--I'd choose neighborhoods on the upswing, and when housing prices got high enough in that area, I'd sell. (The city's been slowly getting better over the past 20 years.) I'd have to learn to do a WHOLE lot on my own first, though, since I really wouldn't want to hire anyone if at all possible. They'd be my weekend projects. :-)I also deperately need to add onto our new house, which is what I'm looking into ICFs, etc., for. Again, huge bargain--but again, because of some distinct deficits. (Built: 1965. Updated: Updated? Who needs UPDATED?) But you can't get several acres that back up to forest preserve so close to Washington, DC, these days for any price--so paying less than the house can quickly be worth was an incredible deal. My new kitchen/breakfast room/workout room, which I plan to build for $50k, will raise the value more than $150k.And, hey, as far as the novella goes--nothing will heave or grow turgid, I promise. I'm not that kind of writer. ;-)
How much weight is put on the slab?