Comments on: Passive Project Foundation and Slab Insulation

By: Teo Muntean

Teo Muntean — Thu, 06 Oct 2011 19:07:07 +0000

Thanks! I am building now a passive house and putting pictures on the website… hope to be a real success!

By: Green Building

Green Building — Wed, 05 Oct 2011 17:17:43 +0000

That’s so cool that you are doing a slab insulation. What a great way to help keep your energy costs low and protect the environment. BTW, I hear that you need the sand to help with the water…

By: Chad Ludeman

Chad Ludeman — Tue, 04 Oct 2011 12:03:16 +0000

Yes. Yes it is.

By: Teo Muntean

Teo Muntean — Tue, 04 Oct 2011 02:21:58 +0000

It is possible to use also EPS300 instead of XPS ? thank you.

By: passivhaus

passivhaus — Tue, 07 Jun 2011 09:04:22 +0000

Passive design is not an attachment or supplement to architectural design, but a design process that is integrated with architectural design. Although it is mostly applied to new buildings, it has also been used for refurbishments.

By: Kris

Kris — Mon, 06 Dec 2010 13:07:40 +0000

Just curious if you have ever considered using Thermomass (T-Mass) for the foundation walls. The key is needing an experienced installer.

By: John O'Brien

John O'Brien — Tue, 05 Oct 2010 19:42:19 +0000

They actually say not to use sand above the poly, as it wreaks havic with the moisture loading below the slab.

By: Greenbuildingindenver

Greenbuildingindenver — Tue, 21 Sep 2010 23:38:40 +0000

Watch out, Building Science Corp. says NEVER use the sand.

By: Richard D

Richard D — Tue, 21 Sep 2010 22:39:37 +0000

I’m on a team that is considering using XPS for foundation insulation. Our project is in north-eastern California and frost is not a problem. Standard practice for a slab on grade here is to have 4″ of crushed rock, topped by 2″ of clean sand, vapor barrier and then the slab. The sand layer is used to run the hot and cold water and then day lighted or “stubbed up.” Sewer is trenched 18″ below the crushed rock. How did you handle the water supply lines? Do you cut chases in the XPS for your lines?

By: Zac

Zac — Thu, 08 Apr 2010 19:45:47 +0000

Regarding the use of foam under structural foundations, check out the topic “geofoam” on wikipedia, or just look at geofoam.com – but it’s completely fine if specified correctly, to give you the short answer.
This pdf gives you an idea of the various compressive strengths of different densities of EPS: http://www.epsmolders.org/PDF_FILES/Geofoam%2520Tech%2520Bulletin%252011-06.pdf

to put these numbers into context, the IBC allows soil pressures of up to 1500PSF (sans soils report) for gravity loads. 1500 PSF = 10.41 PSI, which means you need to use EPS29.

Having said all that, the point is completely moot since all bearing walls in the details above bear completely on concrete footings which in turn bear on the soil, so the foundation here is no different than any other building on a shallow foundation.
Only the slab on grade is bearing on foam, and these loads are relatively light, roughly 0.7 PSI