Cross-section of frost-protected shallow foundation for 12" truss-wall framing system.
Join Home Energy Pros
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.
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.
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?
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.
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.
Welcome toHome Energy Pros
Sign Upor Sign In
Or sign in with:
Started by Jim Tenhundfeld in General Forum. Last reply by Brad Cook 5 hours ago.
Started by CharlieK in General Forum yesterday.
Started by Diane Chojnowski in General Forum yesterday.
Started by Wayne Melancon in HVAC. Last reply by Wayne Melancon on Wednesday.
Started by Mary Sinkler in General Forum. Last reply by Jan E. Graveamker on Tuesday.
Added by Barbara Smith
Added by Tom White
January 23, 2017 to January 24, 2017 – Portland Marriott Downtown Waterfront
January 24, 2017 at 9am to January 25, 2017 at 12pm – Bristol Community College at Commonwealth Landing
January 26, 2017 from 1pm to 2:30pm – Eastern Time
February 8, 2017 to February 10, 2017 – San Diego Convention Center
February 9, 2017 from 1pm to 2:30pm – Eastern Time
Welcome to Home Energy Pros – the unique digital community by and for those who work in the home energy performance arena.
Home Energy Pros was founded by the developers of Home Energy Saver Pro (supported by the U.S. Department of Energy) and brought to you in partnership with Home Energy magazine. Home Energy Pros is sponsored by the Better Buildings Residential Network. Please honor our Guidelines
© 2017 Created by Lawrence Berkeley National Laboratory.
Report an Issue |
Terms of Service
Please check your browser settings or contact your system administrator.