Thompson SFP House Detail

Cross-section of frost-protected shallow foundation for 12" truss-wall framing system.

Comment

You need to be a member of Home Energy Pros to add comments!

Join Home Energy Pros

Comment by Robert Riversong on September 6, 2012 at 10:52am

I forgot to include the BSC link: http://www.buildingscience.com/documents/insights/bsi-003-concrete-...

The other consideration is the very high global warming potential of XPS, for which a new analysis by Alex Wilson and friends shows becomes worse over its lifetime at more than about R-15-20.

http://www2.buildinggreen.com/blogs/insulation-keep-us-warm-not-war...

http://www2.buildinggreen.com/content/global-warming-potential-insu...

Comment by Robert Riversong on September 6, 2012 at 10:47am

David,

This represents a balance between minimizing heat loss from a radiant slab into the ground and allowing sufficient downward heat loss to maintain the foundation as frost-proof (as well as moderately earth-coupling the house to the ground in the event of prolonged periods without supplemental heat, such as power outages or winter vacations).

Most proponents of superinsulated building would put more than R-10 under the slab, particularly a heated slab, with Passive House folks sometimes using as much as R-40. So I consider 2" XPS a minimum for this application, which includes FPSF, radiant and solar thermal mass slab.

Comment by David Williams on September 6, 2012 at 9:48am

Extruded (of course).  I also like the way that you achieve the R15 edge requirement.  I have modeled energy loss comparing 2" XPS with 1" XPS in well drained + soils climate zone 6. and have reservations about the added cost of 2" under the slab.  Knowing that you only get 1 shot at getting this right, I wonder what you thoughts are and where you would draw the line between 1" & 2".

Can you offer a link to the Building Science Corp reference?

Comment by Robert Riversong on September 6, 2012 at 9:18am

David,

Yes, that should have been noted in the section. I use a Tu-Tuf 4 mil laminated vapor barrier that is designed for sub-slab applications and is highly tear-resistant. All seams are taped, as well as all seams of the XPS (not EPS) insulation board.

It is a bad idea to put any "reservoir" layer of sand between the vapor barrier and the slab - Building Science Corp addresses this - as it is likely to create moisture problems. The slab finisher loves it because he can power trowel the slab and get home to his Budweiser sooner, but a vapor barrier does not cause slab cracking or curling.

Comment by David Williams on September 6, 2012 at 8:56am

Do you have a moisture barrier below the slabs' EPS?  I have found that a 1" layer of sand, placed over the EPS helped to protect both the insulation and vapor barrier.  This may have also provided some amount of moisture control during the curing phase.  I have had concrete contractors exclaim that slabs poured over EPS are very prone to cracking because of the way the the moisture escapes form the curing slab.

I have not had these cracking issues, on the radiant heated slabs that I have done over the past 30 years, but I have seen them in slabs that did not have proper edge insulation. 

Home Energy Pros

Home Energy Pros was founded by the developers of Home Energy Saver Pro (sponsored by the U.S. Department of Energy,) and brought to you in partnership with Home Energy magazine.

Latest Activity

David Eakin replied to Kaushal Bharath Raju's discussion Affordability & Deep Energy Upgrade/Passive House Retrofit in Berkeley, California.
"I mis-spoke - I was referring to the Midori House in Santa Cruz. Have an in-depth discussion with…"
4 hours ago
Profile IconScot Davidson, j jarvella and Michael joined Home Energy Pros
10 hours ago
Kaushal Bharath Raju replied to Kaushal Bharath Raju's discussion Affordability & Deep Energy Upgrade/Passive House Retrofit in Berkeley, California.
"Hi David & Bud, $400/sqf > $300 sqf. The latter is the minimum cost of new construction in…"
11 hours ago
David Eakin replied to Kaushal Bharath Raju's discussion Affordability & Deep Energy Upgrade/Passive House Retrofit in Berkeley, California.
"Kaushal, There was a deep energy retrofit upgrade project (to Passive House standards) in San Jose…"
13 hours ago
Kim Tanner updated an event

Beyond Residential Testing at The Energy Conservatory

May 14, 2014 to May 16, 2014
The Energy Conservatory (TEC) is hosting a Beyond Residential Testing event. In addition we are…See More
15 hours ago
Casey Gesell posted a video

Super Attic - Attic Insulation System

http://www.drenergysaver.com | 1-888-225-6260 The new Super Attic: Advanced Conversion System -- converts your attic from a vented attic into an unvented at...
16 hours ago

Casey Gesell just added their location.
(via Member Map)

17 hours ago
H.O. Electric posted a video

H.O. Services, Generator, Electrical, Plumbing, Heating, Cooling, Belmont, Lexington, Arlington, MA

H.O. Services is your residential Electric-Plumbing-Heating-Cooling Specialist. We are an electrical contracting company providing homeowners the best Electr...
18 hours ago
Jim Gunshinan's blog post was featured
18 hours ago
Luis Hernandez posted a discussion

Air Source Heat pump or mini-split efficiency

Greetings everyone!    I have a technical questions I hope I could get some feedback! I understood…See More
20 hours ago
Jim Gunshinan posted blog posts
yesterday
H.O. Electric posted a photo

about us-team

H.O. Services is your residential Electric-Plumbing-Heating-Cooling Specialist. We are an…
yesterday

© 2014   Created by Lawrence Berkeley National Laboratory.

Badges  |  Report an Issue  |  Terms of Service