Basement and foam insulation?

[dcg9381]

I'm in Texas, so not a lot of experience with "basement" construction. I'm building a residence - with garages at top and lower levels.

The lower level is a "Texas basement" - meaning we've got a 10' sheet of concrete that is built into a hill, so the lower level is underground on one side, transitioning to exposed level on the other.

The question is this - do we insulate the "earth side" of the lower level concrete with spray foam? I'm hearing arguments both ways. I've checked the temperature of that wall with a laser - when it's in the upper 90s ambient, upper floor wall temps around 95, roof deck temps 97', that concrete wall is 84 degrees.

That's clearly below ambient temperature, but it's above the temperature of our living conditions. I've been told that my measurement is not accurate as it is not "earth temperature" - but it's temperature of concrete immediately exposed to air (which makes sense).

 

[WarDamnEagle]

I had a similar basement in south Alabama. I used a combination of treated 1x4 and 1x2 board attached with tapcons with 3/4" rigid foam insulation in between. I then put drywall over that.

Although I had a single ply membrane on the outside and a very good french drain system below the slab level, I still painted the walls with DryVit paint as a precaution. Never had a water or moisture problem.

Good luck; looks like a nice house.

 

[tjpavlov]

Check out Insofast panels. I used them as interior insulation in my basement. I've never heard of using spray foam as an exterior insulation.

 

[larry4406]

In my area (Northern VA and MD) we call that a walk out basement.

We 2x4 stud the interior of the basement perimeter walls typically at 24" o/c since non-load bearing. These studs are held about 1" away from the perimeter walls. Above the stud wall top plate a piece of ripped 3/4" plywood is often used to seal off the wall cavity for firestopping. After rough trades, this wall is then fire stopped with foam, then batted with R13.

We don't insulate the exterior walls in my area but sounds like things may be different in Texas.

 

[Showkey]

In the north that wall ( all basement walls) would be waterproofed on the outside, 1.5- 2” rigid foam panels applied to the outside, back filled, exposed foam would be coated with cement paint. Inside foam or stud/insulated wall would be optional depending on use.

 

[dcg9381]

Although I had a single ply membrane on the outside and a very good french drain system below the slab level, I still painted the walls with DryVit paint as a precaution. Never had a water or moisture problem.

There is a rubber membrane attached to the exterior concrete and then the whole thing was backfilled. Same deal.. Large french drain at the bottom.

Check out Insofast panels. I used them as interior insulation in my basement. I've never heard of using spray foam as an exterior insulation.

To me, this is interior insulation. I should have mentioned that there is a framed 2x4 wall on the inside of this concrete that IS load bearing (trusses above).

 

[kj_mustang]

See if any local companies do the spray rubber membrane with rigid foam over that on the exterior. I did that for my house walkout basement.

 

[dcg9381]

This type of construction is unusual in Texas and it's too late to do exterior insulation. I have a rubber / looks like tar backed membrane (water/moisture) on the exterior, it's already back filled.
And again, in Texas, cold isn't the problem, it's heat...

I may drill a small 3" hole into the interior concrete today and check temp.

 

[Firebrick43]

Don’t do spray foam, it could potentially turn to a soggy mess, yes even closed cell. As mentioned before use insofast or XPs sheet foam. Isofast handles the framing and insulation in one step

 

[yeldogt]

I'm confused ... What does you contractor want to use.

I do what KJ has above on the outside. Same green spray -- there is a company in my area ..that all they do. The foam on the outside is really just to protect the spray membrane .... it's a tiny R ... but it is a thermal stop.

I spray foam my buildings -- so the inside block walls gets a skim of closed cell foam .. often with block I'm doing PT 2x4's on the flat with a layer of roll foam that you use on a foundation plate behind the PT. The foam seals it all up -- it's not going to be hit with a huge temp delta .. even in a cold climate this works well. With my place in VT years ago the back walk out was north -- we did metal studs thicker foam setting the studs out from the wall so the foam could get behind on the first pass

 

[dcg9381]

I'm confused ... What does you contractor want to use.

The GC is relying on the advice of the insulation contractor who says that I'd be wasting money... Just double checking.

The exterior of this wall (buried) is coated in a waterproofing membrane. I think it is MEL-ROL.

 

[Showkey]

The GC is relying on the advice of the insulation contractor who says that I'd be wasting money... Just double checking.

The exterior of this wall (buried) is coated in a waterproofing membrane. I think it is MEL-ROL.

In Texas ........that insulation contractor is probably correct. Soil temperature 2’ to 4’ down likely is insignificant compared to the building target temperature.

 

[Chuckster in NJ]

The GC is relying on the advice of the insulation contractor who says that I'd be wasting money... Just double checking.

The exterior of this wall (buried) is coated in a waterproofing membrane. I think it is MEL-ROL.

When a contractor who does insulation for a living tells you that you will be waiting money........ Listen to him!

BTW! I would suggest going with the highest R Value that you can fit in the walls and ceiling along with sound proofing batts on the floors and interior walls...... Extra insulation in the attic is also very helpful.

 

[stm317]

I don't know that I'd bother with spray foam, but the cost of 2" XPS panels seems pretty minimal to me relative to the overall cost of the project, and there's no better time to do it.
I'd hate to have to deal with an uncomfortable space for years because I wanted to save a few hundred dollars in the initial build.

 

[yeldogt]

The GC is relying on the advice of the insulation contractor who says that I'd be wasting money... Just double checking.

The exterior of this wall (buried) is coated in a waterproofing membrane. I think it is MEL-ROL.

Got it ... He is most likely correct in TX where is just going to be AC load and the soil is cool. I was reading your post as someone was saying it was wrong to do it. Now it may have an effect on a south side wall over a lone hot spell.

I'm building in the Mid-atlantic and New England -- so the temps are colder. Even so there is much less temp difference in a basement vs the above ground areas.

It's the delta ... In my area a heated full basement 8' in the ground does not really feel cold -- even with no insulation as long as it's not in wet soil. As you feel up the wall it will get colder as the top of the foundation comes out of the ground. The soil may be in the 50's and the room is 70 ..

This totally changes when you heat the slab -- now you are trying to make the slab much hotter and you drive the heat into the ground.

In a hot area -- the ground is your friend

 

[kaymccampbell]

As long as you're insulating inside the foundation, then you're fine.

 

[dcg9381]

Thanks, guys. I know to take contractors seriously that say "you're wasting money" - especially when it is easy for them to do.

This wall is a north facing, so it's not getting southern exposure.

We'll leave it as is.

Heating is rarely an issue. It was 108 yesterday, which is insane...

 

[dcg9381]

BTW, found a recommendation on Greenbuildingadvisor that says basement gets insulation if it is zone 3 or colder.. Definitely doesn't apply to TX.

 

[K'ledgeBldr]

The answer would be relevant to the intended use of the lower level.

If it’s only garage- not heated or cooled, I’d do nothing. If the plan is to finish, heat and cool, have living area + garage, I’d insulate all the walls. XPS on the concrete wall(s), batt for the framed walls. This basically follows IRC requirements.