kschweitzer69
New Member
Posts:64
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| 13 Sep 2010 11:19 PM |
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Currently building a home and want to insulate exterior foundation walls with XPS 2" rigid foam insulation. Looking for detail options to protect the foam between grade and brick. Thinking of doing a 45 degree angle cut on foam board to allow water to drain away. Along with having aluminum piece bent to sit on brick and then fold over the foam to keep moisture from getting between foam and concrete. Have looked at various coatings for protecting the exposed foam from the Sun and weedeaters. Looking for a simple yet effective approach. Thoughts or suggestions please. |
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EastMark
New Member
Posts:60
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| 14 Sep 2010 07:10 PM |
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Something to think about....When designing my home and using a energy consultant...he changed my mind on this topic although its a different application of sorts.
I have a walkout. Using the basement for storage and utilities only. Planned 2" foam out on the top 4' above the frostline.
He told me the better way to insulate a foundation is with fire resistant 4x8x whatever foam is desired...on the inside only and taped. He said the outside has little value but do it if I want. The theory is outside your heating system is still heating the mass of the foundation which is a waste of heat. Inside the heat stays...inside.
Made sense to me.
Mark |
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kschweitzer69
New Member
Posts:64
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| 14 Sep 2010 10:04 PM |
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EastMark - On the flip side of that theory if you heat up the concrete it is "thermal mass" that will hold heat and help hold a constant temperature. The warmth within the concrete wall will redistribute stored heat energy for a more comfortable environment. I've had the inside insulation theory pitched to me and honestly feel insulating both sides of the wall is probably the best way to go. I just figure you only have one chance to get the outside of the wall insulated. I also feel there is a benefit to having less condensation/moisture humidity in the basement by insulating outside walls. Everyone has their own theory, but logically this is what makes the most sense to me. I'm placing 2" foam board around the entire house from footer to roofline. Something similar to how ICF is with the foam blocks. |
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Roberth
New Member
Posts:97
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| 15 Sep 2010 10:07 PM |
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Insualtion is better in the middle. Protected and provides a capilary break.
http://www.thermomass.com/ |
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Jelly
Veteran Member
Posts:1017
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| 15 Sep 2010 10:19 PM |
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Posted By kschweitzer69 on 13 Sep 2010 11:19 PM
...Have looked at various coatings for protecting the exposed foam from the Sun and weedeaters. Looking for a simple yet effective approach. Thoughts or suggestions please...
How about a direct applied polymer modified stucco |
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kschweitzer69
New Member
Posts:64
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| 15 Sep 2010 10:29 PM |
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Roberth, I'd agree that thermomass looks like a great product. By the time I happened onto it, it was too late and now my walls are poured, plus it has been my experience pricing out various aspects of this project that any little nitch product not widely adopted in a given area comes with a heafty price tag. Alot of the reason I abandoned ICF. The more I think about it I think I'm just going to leave the 1ft space exposed and see how I think it performs. I believe that most of the insulation advantage is in the area where dirt is backfilled against the house. Once the ground has frozen it will stay that way for a long time and cold damp dirt up agains uninsulated concrete will not warm up during the day like the exposed area would. Just seems too risky to try to cover exposed area. Our climate has cold and hot weather and stucco in general has lots of problems in our area. |
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Roberth
New Member
Posts:97
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| 15 Sep 2010 10:44 PM |
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At this point I think you would be better off insualting the interior with rigid applied direct to the wall. Are you going to spray foam the rim joist. Have you poured the basement slab? |
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Bob I
Veteran Member
Posts:1435
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| 16 Sep 2010 10:59 AM |
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"'I believe that most of the insulation advantage is in the area where dirt is backfilled against the house"
Actually you have this exactly backwards; the most value for foundation insulation is the area above grade where the temps will be the coldest.
As far as covering it, the best solution I've found is to cover the foam with nylon mesh, then a plaster mixture of Thoroseal plaster coating with Acryl 60; both available at masonry supply stores. Done right it is extremely tough and long lasting. If you don't want the bother of plastering it or are in an area with termites, install it inside the basement where you may need to cover it with non flammable paint or drywall. |
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| Bob Irving<br>RH Irving Homebuilders<br>Certified Passive House Consultant |
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kschweitzer69
New Member
Posts:64
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| 17 Sep 2010 12:09 AM |
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Bob - I used to think what you are saying is correct, but the more I think about it. I believe that moisture lain frozen dirt is going to hold a constant cold temperature against an uninsulated foundation. Through the day(s) of winter the sun will warm up the exposed area of concrete while the area below will continue to be cold and frozen during the winter months. I don't disagree however that completly insulating would be best, I just don't like any sort of stucco approach and think I will take my chances exposing that area. Eventually I'll insulate the inside walls and I could always later go back and insulate the 1ft exposed area on the outside if I feel lots of energy is being lost there.
Roberth - I've had several people tell me to just insulate the inside, but I believe there is advantage in insulating the outside. I could be wrong, but again don't think it's going to hurt anything. My rim joist will probably be sprayed with a open cell foam. The basement slab has not been poured yet. I have put alot of effort into insulating the walkout wall down to the frost line in an effort to keep cold from driving through the concrete slab. I've thought about insulating the first two feet underneath floor slab, but not sure there is much advantage since I'm blocking the bulk of the cold at the walkout wall. I know alot of people preach insulating basment floor, but as deep as it is I would not think temperature fluctuates much below the surface. I was just planning for a plastic barrier under basement slab. |
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phillip c snyder
New Member
Posts:2
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| 17 Sep 2010 08:24 AM |
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insulate inside basement with arxx , i sell a arxx insulated 2 inch thick foam panel with wire chase and ribed to screw sheet rock to, glues to wall or tapcons , p.w.t.construction
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Bob I
Veteran Member
Posts:1435
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| 17 Sep 2010 08:42 AM |
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You're probably right that right below the surface the frozen earth will hold constant cold temperatures against the house. And that some ofthe concrete will be warmed by the sun - especially that which is a dark color, which is in direct sunlight (meaning no snow or plantings to shade it). What % of the house foundation will be in direct sun for what % of every 24 hours? Four hours of direct sun on a light grey surface covering 25% of the building diameter will certainly provide a little heat. Or maybe you're thinking of insulating the north, east & west sides?
You're also right about the temperatures under the basement slab: they'll stay at 50 or 55o year round. Since heat transfer always goes to cold, any heat over that temp in your basement slab will disapate into the ground underneath. Doesn't mean you can't heat the basement, just takes more input to balance the losses. |
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| Bob Irving<br>RH Irving Homebuilders<br>Certified Passive House Consultant |
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Roberth
New Member
Posts:97
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| 17 Sep 2010 11:27 AM |
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If you are going to insulate then it needs to be the full wall. Concrete will conduct heat/cold and you would get some benefit from exterior foam but you are missing a critrical area. If the extra exterior foam has not been accounted for during construction will it be asthetically pleasing to have the form on the above grade foundation. I think the problem with exterior foam is protecting it and the potential for termites to move behind the foam.
For those that dont know is that termites will not move on the open wall exposed to light. They will move behind a protection surface or build mud tubes. Mud tubes are easily spoted and tip you off to thier presence,
Sometime the fine details to complete a job make it impractical. Instead of having something that requires perfection to achieve and could be prone to damage I opt for something that is easier to achive and is less prone to compromise. Exterior insulation fall into the hard to achive perfection category. There are coating to protect the exterior insualtion but they can be damaged and what is their life expectancy. Exterior insualtion has the added costs of applying a protective coating. If damaged will the owner promptly repair the coating and will the repair match the existing coatings. You have some insualtion below grade and some above. You have to protect the insulation above grade from UV damage and from physical damage. Below grade is can be subject to insect damage and can be a pathway for termites.
I do agree the combination of exterior insulation and the termal mass is a very good combination. Putting the insulation mid wall can have the same benefit as exterior but it adds several key features. It is protected from the elements and it provides a capilarly break.
Interior insualtion does not provide the benefit of thermal mass but has many benefits. Being inside it will not require a protective coating.
If it comes down to $'s I would spend my money on doing things that get the biggest bang for the buck and that can not be done or will be harder to do after construction. Since I dont know the details about your project I do not know what you are doing for insualtion, air sealing etc. What level of air tighness are you going for and what type of strategies are you employing. What are you using for insualtion. Are you putting insualtion under the slab. I would put these higher on my priority list than exterior foundation insulation, I say that because I could come back later and do interior insualtion with good results assuming that the basement is not being finished at this time.
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kschweitzer69
New Member
Posts:64
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| 18 Sep 2010 10:31 PM |
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Roberth - All good points and well taken. Every situation is unique and I realize that, we are trying for the most bang for the buck approach. Our foundation is poured and due to the design of our home we really only have one wall and a small part of another wall that is affected by the problem I mention. Insulating between ground and floor system, that is. I have already placed the XPS foam on the wall from the footer up 8ft. I have 9ft poured walls and just plan to leave the 1ft above grade exposed with no insulation. This happens to be on a southwest facing wall that gets the most sunlight. I'm unaware of termite severe problems in our area, but I'm sure they exsist given the right circumstances (we are in southern Ohio). I had no plans to protect the XPS foam as I understand it is rated for below grade applications. In fact the pink XPS I have is higher rated to 40psi strength. Perhaps I'm completely in the wrong here, but I thought I would do it this way since you really only have one chance to do it. I still plan insulate from the inside, but that will come later and thought insulating on the outside would help. To elaborate on the rest of the project we are planning to run 2" foil face ISO foam around the rest of the exterior upper level walls down to the top of the concrete wall to cover floor system and walkout basement. This will stop thermal bridging and help create an air tight stealed building envelope. We will stud the exterior walls with 2x4's and have windows and doors framed in at 6" to accomidate our exterior foam. I then plan to spray wet dense pack cellulose into wall cavities. Overall I should achieve R26 in my walls. I will then do spray in cellulose in the attic at R50 rating. I would think the termite tunnelling that you mention could become more of an issue if the foam was ran completely up to framing. Also to add to my detail the house will be fully bricked and this home is being built in a well drained area. |
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