ICF on insulated raft.

[gavztheouch]

Thinking about building ICF walls on insulated raft. Has anyone done this? Anything to worry about in terms of failure of the foam under the slab, seems like a lot of weight pushing down. 

 

Possible worries would be, creep of the foam over time, rodent or chemical attack.

 

 

[Bitpipe]

It's not 'foam' it's high grade, rock hard, EPS which is designed to take the point loading of the full structure above it. The SE will spec the grade of EPS once the full structure design is known.

 

We built a 120m2 RC basement (with a TF house on top) built upon a raft of 300mm EPS 200 blocks. They were laid on 150mm compacted type one and 50mm blinded sand. Covered it with a gas membrane and the crew built the RC slab on it as if it was solid ground.

 

We applied 200mm EPS 70 to the exterior of the basement walls so effectively the same structure as ICF minus the internal layer of EPS.

 

I would not worry about rodents, only an issue if you have exposed insulation at ground level and this is easy to avoid with various flashing solutions. What would your external finish be?

 

As for chemical attack, acetone can dissolve EPS but you'd need a lot of it flowing around your entire slab so not sure the circumstances where that could happen.

[BotusBuild]

Building a semi-basement two storey house - 135m2 footprint RC slab. Similar build up as Bitpipe's. All insulted EPS will be either buried or covered with stone once complete. Unless you are building on contaminated ground (you shouldn't be!!!!!!!!) then I would think chemical attack should not concern you.

 

With a raft foundation if anything moves, everything moves with it ? 

[Gone West]

15 hours ago, gavztheouch said:

Anything to worry about in terms of failure of the foam under the slab

We used an Isoquick insulated raft foundation and the insulation is called Peripor which is a type of EPS300. IIRC we were told it had been used in Canada for commercial buildings. The Structural Engineer will ensure it's suitable for your use.

[Conor]

The limit will be the weight of the building above and the rating of the EPS used. We wanted an insulated raft, but our three story icf design was (according to our engineer) too heavy for the compression limit of the EPS. We would have had to use much bigger ring beam to compensate, which wasn't an option due to the limits of the excavation. So we had to go for a normal ground bearing raft.

Edited November 10, 2021 by Conor

[ToughButterCup]

15 hours ago, gavztheouch said:

...

Possible worries would be, creep of the foam over time, rodent or chemical attack.

 

Weight - for us anyway - not an issue.

Chickens are though. They seem to use it as a form of Alka-Seltzer. Now, the EPS is covered with a lead-replacement membrane 

 

 

If it were as problematic an idea as your post suggests, the idea of an EPS insulated raft would have died long ago.

[Adrian Walker]

19 hours ago, gavztheouch said:

Thinking about building ICF walls on insulated raft. Has anyone done this? Anything to worry about in terms of failure of the foam under the slab, seems like a lot of weight pushing down. 

 

Possible worries would be, creep of the foam over time, rodent or chemical attack.

 

 

 

Have you considered using Foamed Glass as an insulation? - https://www.mikewye.co.uk/product/foam-glass-insulation-aggregate/

[riboid]

On 09/11/2021 at 18:40, gavztheouch said:

Thinking about building ICF walls on insulated raft. Has anyone done this? Anything to worry about in terms of failure of the foam under the slab, seems like a lot of weight pushing down. 

 

Possible worries would be, creep of the foam over time, rodent or chemical attack.

 

 

Yes, we did the ICF and on the insulate raft foundation system.  The raft insulation has rebar and concrete poured over it, so compression is ok with that.  All engineered and should be no problem.

[JOE187]

 New Zealand Nudura build  with high compressive strength eps at bottom of  the wall seem a good way to go.

    6mins in shows this detail.