Basement insulation question

[toyotadriver]

I'm building a new house in southern MO. We can get temps in the winter down as low as 0*F or even a bit lower sometimes but the temps never stay that low for long. Summer temps are usually in the 90s with occasional 100* days.

This house will be well above average insulation value for this area. I'm building with energy efficiency in mind.

We are getting ready to pour the basement walls. I've been leaning to insulate the basement walls with 2" rigid foam sheets and then frame a 2x4 wall on that. However, I've also thought about insulating the concrete from the outside with rigid foam sheets.

The advantage with insulating the outside is it will keep the concrete above the dew point to prevent condensation. Also, if I put the foam on the outside, I won't lose the 2 inches of square footage that I will lose if I put the insulation on the inside. The disadvantage of insulating the outside is that I won't run the foam sheets up the entire concrete wall (just the part that is covered with the dirt) so there will be some concrete that will transmit the heat out of the house in the winter at the top of the foundation. I plan to leave the concrete exposed where it is out of the ground.

The advantage of insulating from the inside is that I'll have continuous insulation from the floor to the ceiling. The disadvantage is that I'll lose 2 inches of interior space on all the concrete walls.


So....what do you think? Insulate inside the basement with rigid foam or insulate the outside with rigid foam?

Thanks.

 

[TractorJeff]

I believe that if you insulate on the outside, then you do cover the portion that will go above grade. Seems like I read it somewhere?

 

[toyotadriver]

I believe that if you insulate on the outside, then you do cover the portion that will go above grade. Seems like I read it somewhere?

You can but then you have to have a method of covering the foam because the foam will degrade in sunlight and needs protection from damage. I don't want to insulate the exposed portion and then have to find a covering for it.

I am leaning toward insulating from the inside but looking for other opinions and recommendations.

In my last house, we had a crawl space and I covered the concrete walls in the crawl space with 1.5 inch foam sheets. Worked really well and the crawl space stayed warm and dry.

 

[fdtrucks]

You can use a stone or stucco for minimal cost over the foam panels on the exterior. In my basement I did foam inside along with batt between the studs and is nice and warm. My parents recently built and did rigid foam on the exterior and half the basement is finished. Where finished, they have batt between the studs on the interior. In the unfinished area, its exposed concrete walls, and only 1 vent for heat/ac. Its a large area probably 20x15, and is just as comfortable as the finished area. Having the exterior thermal break makes a difference.

 

[zmaxmotorsports]

Do they still make the styrofoam concrete forms?

 

[finn]

2" foam boards outside and spray foam inside after you stud the walls.

 

[Showkey]

Foam on the outside above grade is often covered with a special brush on coating that looks like stucco cement. Sold at the big box stores in buckets.

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[DC73]

I am leaning toward insulating from the inside but looking for other opinions and recommendations.

Visit the Q&A forum at GreenBuildingAdvisor. They'll be able to give you climate specific details on how best to proceed.

DC

 

[p_mori7]

Inside.

Apply waterproofing to the outside.

Rigid foam boards OK, but sprayfoam better.

Frame your downstairs walls at least 1" away from the concrete.

 

[justinjoyal]

3in foam/vapor barrier insulation (inside) here in Quebec. Love it!

Waterproofing on the outside.

Best way to go IMO.

This:

Walls end up looking like this (you can also build 2x3 or 2x4 walls instead of using 1x3 directly) :

Don't forget to insulate the floor, it makes a huge difference.

 

[toyotadriver]

Walls are up and the insulation will be going on the inside.

Thanks everyone for your input!

 

[66coronet500]

http://www.insofast.com/

 

[overkill 19]

I'm going to use this stuff in my basement.
This between the studs.
http://m.homedepot.ca/product/ProductDetails.aspx?productid=900116&lang=EN
This against the wall

http://m.homedepot.ca/Product/productdetails.aspx?ProductId=995375&lang=EN

 

[toyotadriver]

I'm going to use this stuff in my basement.
This between the studs.
http://m.homedepot.ca/product/ProductDetails.aspx?productid=900116&lang=EN
This against the wall

http://m.homedepot.ca/Product/productdetails.aspx?ProductId=995375&lang=EN

I would be a little nervous about that. It says it's vapor permeable. I think I would want something nearly vapor impermeable to go against the concrete walls.

 

[overkill 19]

I believe It's designed to breath but not absorb moisture. You still need a vapour barrier on inside between drywall and studs. I thought about spray foam insulation between the studs on the concrete wall but I did not want to trap moisture giving mold a place to grow. I like the being able to breath part the best.
If you YouTube it tons of people using it in the basement.

 

[overkill 19]

I also used dricor for the subfloor. But my house is 95 years old. You do have to carful of too much insulation in basement if you have a long straight outside wall. Depending on your temps and frost levels in your area.
Lots of new houses around here now use a 4" thick insulation on outside wall. But it acts as a cushion too so the frost won't pressure crack the wall. Old school was never a problem due to enough heat loss threw basement to keep frost away. Lots of the first basements with ICF system around here cracked bad from frost pushing walls in