Thompson SFP House Detail

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

Views: 481

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. 

Forum Discussions

What causes a temperature plane in a home

Started by Energy Wise Solutions in HVAC. Last reply by Eric Kjelshus 19 hours ago. 9 Replies

Solar panel leasing

Started by Luis Hernandez in General Forum. Last reply by John Nicholas 19 hours ago. 15 Replies

Factory built Net Zero

Started by Steven Lefler in General Forum. Last reply by Steven Lefler May 18. 3 Replies

Latest Activity

Chad Nicholson is now a member of Home Energy Pros
13 hours ago
Eric Kjelshus replied to Energy Wise Solutions's discussion What causes a temperature plane in a home
"Hot air goes up and cool air goes down.   I put in returns high and low.  In summer use…"
19 hours ago
John Nicholas replied to Luis Hernandez's discussion Solar panel leasing
"The variables in buying a solar panel installation: Equipment -  Length of all Guarantees,…"
19 hours ago
Richard Drohan liked Brian Sipp's discussion Minneapolis Duct Blaster System with DG-700 For Sale
yesterday

Photos

Loading…
  • Add Photos
  • View All

© 2017   Created by Lawrence Berkeley National Laboratory.   Powered by

Badges  |  Report an Issue  |  Terms of Service