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Yellowstone
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Posts:10
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| 01/15/2008 12:47 AM |
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| An ICF wall built onto an un-insulated footer will loose heat to the ground at this junction. This will be especially true here in Alaska with our very cold ground temps. Has anyone been concerned enough to insulate the footer and If so what technique did you use? |
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Chris Johnson
Registered Users
Posts:341
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| 01/15/2008 2:43 AM |
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Place 2" of EPS insulation over the entire floor (wall to wall) prior to pouring the basement floor. If the budget allows use in floor heating, if the budget does not allow for it at least put the piping in until the budget improves in the future.
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Chris Johnson - Pro ICF
Napa, CA
Come for the wine, Stay for the ICF work |
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Yellowstone
Registered Users
Posts:10
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| 01/15/2008 3:17 AM |
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| It is the practice here in Alaska to insulate under the slab with "Blueboard" XPS foam board. Under the footing is what I am inquiring about. I have never seen any one insulate under the actual footing. I wonder if there is any reason I couldn't do so? |
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Cattail Bill
Registered Users
Posts:246
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| 01/15/2008 8:32 AM |
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This is more of a question than an answer, living here in Minnesota we also get cold not as cold but cold.
We are going down below the frost with our footers and relying on the ground temp for our retention, if you insulate the ground temp wouldn't that reduce the value rather than increase it or at least maintain it?
With that said we do insulate with 2" dow board over the top and out from the wall 2' to help protect from frost perhaps that is not enough but at this point it seems to work. |
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PatrickT
Registered Users
Posts:138
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| 01/15/2008 9:02 AM |
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Yellowstone,
Check out this website. It's foam forms for footers.
LINK
As far as the ground temps, if your footers are deep enough to meet frost depth requirements, you should be down in fairly stable soil temps. So even at 40 deg F, delta T is small (40 deg F vs. 70 deg F). I think I would focus on other thermal bridging where Delta T is greater. With your extream cold temps, I would think some sort of window covering would give you the most bang for the buck, assuming your wall/ceiling/roof insulation is already covered well.
Will you have additional insulation on your ICF like Quad-lock?
Patrick T |
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Yellowstone
Registered Users
Posts:10
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| 01/15/2008 2:31 PM |
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| Yes, the Quad Lock Plus Plus (R-40). I was thinking of using the Quad Lock with their extender ties to form the footing and use some XPS board to insulate between the footer and the ground and on the topside of the footer between the first course of my Quad Lock wall and the outer edge of my footer. I understand energy loss at windows may be greater( I am addressing that), I just want to eliminate as much as possible any thermal bridging. |
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icfcontractor
Registered Users
Posts:237
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| 01/15/2008 6:55 PM |
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Yellowstone,
This is actully very common in commercial construction in areas of inclimate weather or premafrost. Look at this site. LINK The issue you may run into using XPS is that over a few freeze thaw cycles it is known to abosrb alot of water rendering it nearly useless for insulation. I believe EPS has had better results.
ICF Contractor |
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dmaceld
Registered Users
Posts:494
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| 01/15/2008 7:44 PM |
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Be careful you don't get into a region of diminishing returns and spend money and effort you'll never recover. This can particularly occur if your total energy load is so low you can't find a heating system small enough to operate comfortably. The area of footers and the temp difference and the subsequent heat loss may be so low as to not be worth the cost of the insulation. As far as heating systems, I am facing that issue. The smallest heat pump of the type I'm using is 36,000 Btuh. My highest heat load, according to the HVAC program from the Portland Cement Association, is only about 20 to 22,000 Btuh. Even according to Manual J my heat load will be no more than about 20,000 Btuh for 80% of the heating season. So why spend more $$ for ultimate insulation when my equipment cost won't drop and I may be faced with dealing with an oversized heating system! I'd like to have a small gas fireplace for ambiance and heat backup, but I'm afraid even the smallest one will drive us out of the house with it's heat!!!
There really is such a thing as too much of good thing!!
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Building house - what a way to spend retirement! |
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Quantum
Registered Users
Posts:262
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| 01/15/2008 8:11 PM |
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It is important to note that the footer should not rest only on foam or the Beaver Frost Cushion alone. It must be resting on piers of some sort if you're to insulate.
Footers without piers must be resting on solid, undisturbed earth; if you put foam under them the house will settle and crack as it's built, and thereafter! Internal slabs will shift less than walls cracking your grade-beams, cats and dogs will live together, and the world will fall into chaos. EPS, XPS, etc do not have the compressive strength to support the walls of an ICF building. OK, denser EPS for the foundation and grade-beams of stick-built, marginally, but not for ICF walls. If you use foam under the footers for an ICF home and it happens to not crack, the foam will be compressed to near-uselessness anyway. Yes I work in a temperate climate, so if anyone has university studies which contradict me, I would like to see them; not interested in second-hand/third-hand.
ICF stem from the footers on up will thermally isolate the walls for the depth of the frost-line, and by the time you get to the level of living-space, you are about remote enough from the footers to reduce their thermal influence to negligible. If there are any insulation wonks out there besides me (snif), check out my "Insulation 201".
Also FYI, putting any sort of electrical insulator under the footer will ruin your Ufer ground, if they require that yet in AK. They do here in WA now and in many other states.
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dmaceld
Registered Users
Posts:494
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| 01/15/2008 11:10 PM |
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Posted By Quantum on 01/15/2008 8:11 PM
Footers without piers must be resting on solid, undisturbed earth; if you put foam under them the house will settle and crack as it's built, and thereafter!
I wondered about this but here's what seems to be a contridiction. DOW advertises Square Edge Blueboard to have a compressive strength of 25 psi. That translates to 3,600 pounds per square foot. Yet we build the house on 1500 psf soil. If the house doesn't settle sitting on 1500 psf soil why would we expect to see it settle sitting on 3600 psf foam? Is this another case where the real world and engineering math don't seem to coincide, or what?
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Building house - what a way to spend retirement! |
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Yellowstone
Registered Users
Posts:10
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| 01/16/2008 5:08 AM |
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| I assumed it would be ok to build over foam because of the advertised compressive strength, But I am not an engineer. Although they seem to be doing it over in europe. As for getting the heat load too low, that is my goal. Get the heat loss so low I can eliminate a normal heating system (thereby helping to pay for the insulation upgrades - $7,000 to $10,000) and only have a small electric heater maybe only 1500 watts. |
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dmaceld
Registered Users
Posts:494
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| 01/16/2008 10:39 AM |
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Posted By Yellowstone on 01/16/2008 5:08 AM
Get the heat loss so low I can eliminate a normal heating system (thereby helping to pay for the insulation upgrades - $7,000 to $10,000) and only have a small electric heater maybe only 1500 watts. Laudable goal. Don't forget though with a building envelope so well insulated you will also have a very air tight envelope. That will require the use of a ventilator to keep the indoor air healthy and remove excess humidity. Even the best heat recovery ventilator will not return 100% of the heat leaving with the exhaust air, so you will need to supply make up heat for that. On the other hand appliances, light bulbs, computers, TVs, and so on all generate heat, so those may be enough. Basically all I'm wanting to do is caution you that insulation and conserving heat is not a simplistic issue. If you're already aware of all this, then I apologize for bringing it up.
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Building house - what a way to spend retirement! |
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Quantum
Registered Users
Posts:262
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| 01/16/2008 1:06 PM |
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dmaceld, the real world and engineering math had better always coincide, or else someone is mistaken.
Square Edge actually is rated for a dead load of 8.3 psi (1,195 psf) and a live load of 5. Although I hope you are not building on 1,500psf soil without piers, it is true you could enlarge the spread of footers to a size large enough to give a safe margin with Square Edge, but would that be practical? I doubt it. The cost/benefit is just not enough, partly because you are just exposing more surface area.
Yellowstone, that EPS footer foam form is actually rated for stick-built, if you look at the fine print, although stick-built is a rarety over there. But I agree that Europe is the place to look for new technologies, as we seem to be ten years behind and falling further.
For under-slab you always want to use XPS (extruded polystyrene), as expanded has over 2% permeability and over time can get waterlogged. XPS is almost hydro-impermeable. Besides, XPS has a higher thermal resistance value. I am looking casually now for ground-rated XPS with a foil layer, for hydronic; if anyone knows of a brand, please post. True, for a foil layer to be really effective there must be an air-gap, but if the price is similar it would be good customer relations.
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dmaceld
Registered Users
Posts:494
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| 01/16/2008 3:15 PM |
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Posted By Quantum on 01/16/2008 1:06 PM
Although I hope you are not building on 1,500psf soil without piers,
Piers? Or did you mean pilings?
I am. When I started designing my house a year ago I called the BI about this. He said use 1500 psf. When I got the building permit the other day I noticed it said to use 2000 psf. I had my 40 + years experienced civil engineer cousin review my plans a few months ago, specifically the footer design. He said I'm OK. I've got it designed for no more than 1500 psf loading on the soil. 1500 psf is used as the lowest common denominator for soil bearing strength in SW Idaho. No one builds on pilings here except multi-story commercial buildings.
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Building house - what a way to spend retirement! |
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dmaceld
Registered Users
Posts:494
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| 01/16/2008 3:27 PM |
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Posted By Quantum on 01/16/2008 1:06 PM
dmaceld, the real world and engineering math had better always coincide, or else someone is mistaken.
As an engineer I'd like to believe that, but sometimes tain't so.
Somewhere here I posted a thread last spring about radiant heat loss from the underside of a heated floor. If I remember correctly the math, using Stefan-Boltzman equation, says the heat loss would be about 45,000 Btuh. Heat load calculation programs, which I believe are largely based on, and verified by, empirical data says about 6000 Btuh heat loss. The 45,000 number is greater than the entire house heat load according to Manual J. No one ever offered up an explanation as to why the difference. Also, no one that I could find has ever studied the issue of radiant heat loss from a heated floor to the ground below. I found one paper written on the subject. It was based on the math only and pretty much confirmed my calculations.
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Building house - what a way to spend retirement! |
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Quantum
Registered Users
Posts:262
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| 01/16/2008 4:52 PM |
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| Looks like I should have left it up to you then, dmaceld. |
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Yellowstone
Registered Users
Posts:10
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| 01/16/2008 5:31 PM |
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| In Germany, there is the "Passivhous" standard. These homes have no heating systems, but only a small electric resistance strip in the H.R.V. usually 1 KW. Internal loads and maybe some solar gain through southern windows do the rest. These houses mostly achieve this through superinsulation efforts( r-50+ walls and r-70+ ceiling) and attention to detail on airsealing and thermal bridging. This standard has been proven to work there with over 1000 homes being built. Also, it looks like this standard will be adopted as code minimum over the next 8 to 10 years Europe wide. |
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dmaceld
Registered Users
Posts:494
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| 01/16/2008 6:19 PM |
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Posted By Yellowstone on 01/16/2008 5:31 PM
In Germany, there is the "Passivhous" standard. These homes have no heating systems, but only a small electric resistance strip in the H.R.V. usually 1 KW. Internal loads and maybe some solar gain through southern windows do the rest. These houses mostly achieve this through superinsulation efforts( r-50+ walls and r-70+ ceiling) and attention to detail on airsealing and thermal bridging. This standard has been proven to work there with over 1000 homes being built. Also, it looks like this standard will be adopted as code minimum over the next 8 to 10 years Europe wide.
I wonder how the cost of energy has compared to cost of insulation materials in Europe during the past several decades. If the ratio has been, and still is, say something like 2 or 3 times that of the US, then it's understandable why they're ahead of us in energy conservation. For most folks the payback just hasn't been there for the US market where it undoubtedly has been in Europe. I'll have to think about the R 50 walls and R 70 ceiling when I build my next home. I'm too far into the process on this one to go there now.
I found where Quantum got the numbers for live load and dead load for Square Edge. It's based on 5 to 1 and 3 to 1 safety factors for live load and dead load. But DOW has some other versions of Styrofoam that should work for you called Highload 40, Highload 60, and Highload 100. Take a look here http://www.dow.com/styrofoam/na/pro-us/applications/foundations/slabs.htm. The Pink Panther people probably have a similar product.
In relation to my comment about math and real world and foam ratings this is a case of where math, in one sense, doesn't equate with the real world. At least not simple easy to use math. Super duper complex computer models maybe would. In the real world you apply a safety factor to load numbers simply because there are unknown variables in the physical world. So where the math says Square Edge will support 25 psi, the real world says, "Yeah, that's right, but experience says loads often vary drastically from the expected, so throw in a safety factor just to be on the safe side. And for loads that can change, which is the definition of live load, experience has shown that 5 is a reasonable number." Plus, in the case of Stryofoam, a steady load slowly causes the material to compress. So DOW really has two definitions for compressibility, short term and long term. Short term is 2% I think. No idea what the long term compressibility would be as it's probably not linear with load. They've just determined it to be 1/3 the short term compressibility.
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Building house - what a way to spend retirement! |
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Quantum
Registered Users
Posts:262
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| 01/16/2008 7:08 PM |
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Dow Highload foam is still not sanctioned to go under footers, even 100.
Foam under footers is not a good idea.
Ah'm just tellin' ya... |
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Yellowstone
Registered Users
Posts:10
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| 01/16/2008 7:30 PM |
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| So with all this being said, I wonder how does one calculate what the actual heat loss would be through the footer? |
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