Spray foam for underslab insulation

hr

Gc and owner insisted on this new tech. They are convinced this is an R-20 at 1" thickness. Four times better than the 1" foam in my bid! So they are convinced.

Oh well. It's a basement 9 foot deep, not a huge deal.

They are also spray foaming the exterior over the waterproofing.

I couldn't figure how to get 40 sheets of mesh into this basement that hadn't been backfilled. Found a crane service to dispatch in 20 minutes. Loaded 800 lbs into the basement in about 10 minutes. Would have taken me hours balancing on the foundation wall! $150 well spent.

hot rod

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Constantin

Fools they are...

The only products I know of to reach R20/inch are aerogels and Vacuum-panels, neither of which seems to be applied here.

There are several good reasons that XPS is a lot in foundation work: It's fairly tough, it doesn't absorb water, and its R-value is fairly high (~5/inch). If borates are incorporated into the XPS, it's critter-proof also. As best as I can tell (and I hope I'm wrong), the GC/homeowner combination applied a closed-cell polyurethane to seal the basement floor and insulate the exterior walls.

Closed-cell polyurethane (CCPU) has a high impermability, high R-value (~6.5/inch), and is quick to apply using the above method. However, it is not waterproof! The lack of a vapor barrier inside the basement and the application of CCPU to the exterior foundation walls is pure trouble, IMHO.

As the concrete slab cracks while drying, it'll likely snag the uneven CCPU and crack that too. Where will any extant Radon gases go next? Vapor barriers do more than just retard the flow of moisture....

I don't get why someone who goes through the trouble of applying Rub-R-Wall to the exterior of a foundation cannot be bothered to read their recommendations re: exterior sheathing. Drainboard XPS is recommended for usage with Rub-R-Wall for a reason.

Anyway, congrats on the quick thinking, and I hope that you told those guys in writing that they're crazy for using PU like this (if it is CCPU... perhaps this is a revolutionary product I haven't heard about). I hope that all goes well, even as I fear the worst for this project in the years to come.

hr

You may be right

However borates are a very short term termite treatment.

Several years ago at an RPA REX show we had a panel of foam experts. The rep from DOW Styrofoams Division indicated borates need to be re treated, depending on the site conditions and ground water.

He claimed borates are the best they have currently, that the EPA will allow since banning chloraban, or whatever the previous chemical termicide was called.

I wonder that the ICF will suffer the termite demise. In a "land down under" they require all ICF in ground be wrapped with this stainless steel mesh that looks a lot like regular screen door material. So I'm told. I saw a sample once, at an ICF dealer locally. They also offer it with a vinyl waterproofer for wrapping foundations.

Time will tell.

This job,by the way, does have a vapor barrier below the gravel and a ducted radon gas vent systems with stubs for the addition of fans. Also a lot of french drains inside and out. They also added that dimpled plastic around the footing to allow any water to seep into the inside drainage that runs to 4 sump pump pits.

Sometimes you go to work for the CG you have, not the GC you wish you had.
R. "rubber stamp" Rumsfeld

hot rod

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Weezbo

That application technique has crossed my mind,

luckily my breadth of mine is rather narrow...*~/:)

Constantin

Thanks for the update!

I find the above description of the under-slab layers rather puzzling, to say the least. If I recall correctly, BuildingScience.com had a good piece on how to apply underslab gravel, insulation, etc. in a certain way. I followed their advice...

The first layer above the dirt is 3/4" coarse aggregate. Within this layer, a radon collection system picks up the gases permeating from below. As the aggregate is coarse and 12" thick, the gases have no problem getting to the tube that collects them. The tube exits the floor slab in the utility room.

Above the gravel is a 6-mil vapor-barrier. I would have preferred Tu-Tuff, but it was in short supply, so regular polyethelyne it was. Naturally, the penetrations, seams, and edges were sealed. I think they used the house-wrap tape, it's pretty sticky stuff.

Next came the XPS, 2" throughout. This de-couples the slab almost entirely from the ground below. The XPS was sectioned with a few "breaks" here and there where we wanted the concrete slab to fracture out of sight. The XPS sheets were tied to each other using tape, to ensure they stayed down low as the concrete was applied from above.

Then came the wiremesh matting, the PEX, and the rebar. The floor was reinforced throughout, with the exception of areas where the slab was supposed to break. Re-entrant corners also got rebar at 45° angles to ensure that the slab wouldn't break there either. 4" of concrete, a power-trowler, etc. later and we were in business.

Your question about the longevity of ICF blocks insulated with/made of Polystyrene is a good one. Indeed. making the perimeter of the house as inhospitable as possible in the first place seems like a good strategy. While having a 12" or wider gravel strip around the house may not be the most sightly thing, it does drain well and it does keep the critters out.

Brad_3

Ants?

I've never heard that a strip of gravel would keep out critters, especially ants, any backup to that?

Brad

Constantin

Google is my friend...

I don't have to remember much, except the search terms.

• WI School system integrated pest management program
• URI factsheet on Earwig prevention
• Some pest management at UNL
• No-pest.com on termite prevention
• Etc.

However, I think I got the original recommendation either at Building Science Corporation or some similar resource.