Do I need to waterproofing the frost wall?

rogerius · Jun 17, 2017

Hello again,
We started building the house couple weeks ago. We fixed the issue with the soft soil under the footing and now we are at the stage of building the frost wall on the walkout basement side of the house. As we are using ICF for all walls, the frost wall will be ICF as well. The question which I've got is: do I have to waterproofing the frost wall? This will be under the basement level anyhow.
I asked the architect and he said that is up to me. For all basement walls, I'm using peel&stick and dimple membrane for waterproofing so not sure if I have to do the same for the frost wall which is 62' long and 4' tall; so cost associated with this...

Thank you for any suggestion.

Rustyiron · Jun 17, 2017

Iirc your water issue was down in the footing excavation, not up at the slab elevation.
Save your money & time, it's all the same dirt below your slab level.

RNeumann · Jun 17, 2017

I'm assuming a frost wall is below the grade of the basement floor? If so the answer is no. If it's above is yes. The basement floor will need a vapor barrier before the slab/floor is poured and since it's a walk out I'd also throw a few inches of rigid insulation down before I poured the floor- that's assuming you are not doing rigid exterior insulation on all the basement walls and the below grade footings (maybe what u r calling the frost wall). Anyhow you get the idea- insulation and waterproofing between the living space on all 5 sides in the basement

dadster4 · Jun 18, 2017

OK I'll ask...what the heck is a frost wall?

rogerius · Jun 18, 2017

dadster4 said:
OK I'll ask...what the heck is a frost wall?

OK. Maybe I had to explain before asking something; apologies for confussion.
Because we are building a house with a walkout basement, the basement will be at the ground level at the back of the house. In order to support the wall in that side of the house a foundation wall is require up to the frost depth, in our case 48". The wall underground which supports the house in that side is the frost wall. Hope I was clear.
Here is a picture for reference.

p.s.: I was looking for a response from people who used ICF in building the house. I know that having bare concrete under the ground is not a aproblem but I don't want the ICF foam to be damage over time and have a thermal bridge from the ground to the basement floor.

mbohuntr · Jun 18, 2017

A walk out basement requires what we call a "Step footing" so that the portion of the footing under the door is under the lower frost line. I think you need a layer of foam under the floor, as well as around the edges to isolate the slab thermally. But We did not have an ICF basement. We had in floor radiant heat and loved it!

Otto Syracuse · Jun 18, 2017

We used ICF in a commercial building, a hotel. All of it was above grade and covered with either exterior sheathing or EFIS. The EFIS was troweled right on to the outside of the ICF, the styrofoam part. This is in Upstate NY, where frost is a 6 month consideration. I would want that styrofoam protected in some way, from the sun or even the lawn mower.
We did have other questions regarding the finish, and the manufacturer was very helpful.

We loved the ICF, we plan to use it again. It should work great in a residential basement too.

Rustyiron · Jun 18, 2017

rogerius said:
OK. I don't want the ICF foam to be damage over time and have a thermal bridge from the ground to the basement floor.

I would think about adding 2" of blue "Dow" insulation to the inside of your ICF's (at your frost wall areas). An additional layer with much higher "r" value than the white ICF foam would address you concerns of thermal bridging. You could add this after you pour the wall and just stick it in place while backfilling the wall.

RNeumann · Jun 18, 2017

rogerius said:
OK. Maybe I had to explain before asking something; apologies for confussion.
Because we are building a house with a walkout basement, the basement will be at the ground level at the back of the house. In order to support the wall in that side of the house a foundation wall is require up to the frost depth, in our case 48". The wall underground which supports the house in that side is the frost wall. Hope I was clear.
Here is a picture for reference.

p.s.: I was looking for a response from people who used ICF in building the house. I know that having bare concrete under the ground is not a aproblem but I don't want the ICF foam to be damage over time and have a thermal bridge from the ground to the basement floor.

To this specific question- ICF (or any rigid foam) is fine below grade. It won't get damaged over time- just during backfill, if any damage at all.

With regards to thermal bridging- with ICF walls and the ICF "frost wall" you have created the thermal break you are after- assuming good construction practices. If you were still worried you could do rigid under the basement slab.

A few peanut gallery comments- most of the thermal bridging issues/losses occur at the top 2' of basement walls (assuming no walk out). The rim joist is the worst offender. Spend some time on that detail.

With the waterproofing on the outside of the ICF your detail at grade/top of waterproofing will be critical. The cap detail will need to ensure no moisture can migrate down from the top of the waterproofing.

Lastly make sure the glue on the peel and stick waterproofing doesn't degrade the ICF over time.

RedNeckRacin · Jun 18, 2017

Just water proof it and be done with it, also, if you are doing in floor heat make sure you put eps foam down or the ground will suck heat out of the basement like you wouldn't believe. They claim you can tape the joints and create a vapor barrier but I put 6mil poly down and put the eps down on top just in case. I used superior walls and they are guranteed water proof for my basement walls and my garage frost walls.