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. 

Videos

  • Add Videos
  • View All

Twitter

Latest Activity

David Holtzclaw replied to Steve Mann's discussion Alnor 6200 LoFlo Capture Hood in the group Energy Auditing Equipment for Sale, Trade or to Purchase
"Hi Steve I'm interested 402-213-3788 dholtzclaw@transductiontechnologies.com thanks david "
6 hours ago
Eric Kjelshus replied to Steve Mann's discussion Alnor 6200 LoFlo Capture Hood in the group Energy Auditing Equipment for Sale, Trade or to Purchase
"call me Monday 816-537-5100 "
7 hours ago
Steve Mann added a discussion to the group Energy Auditing Equipment for Sale, Trade or to Purchase
Thumbnail

Alnor 6200 LoFlo Capture Hood

I've got an Alnor 6200 Balometer (Flowhood) I'd like to get rid of. No longer needed--I have a big…See More
7 hours ago
Paul Raymer posted an event
Thumbnail

MA Crew Chief/BPI Building Analyst Training at Bristol Community College at Commonwealth Landing

September 12, 2016 at 9am to September 16, 2016 at 4:30pm
Bristol Community College has created a hands-on training cabin in their laboratory.  This class…See More
11 hours ago
Daniel Morrison replied to John Nicholas's discussion Slab Edge Insulation - A Side Thread to Melissa's Question
"John, I just collaborated with Steve Baczek on a few videos for ProTradeCraft about slab insulation…"
19 hours ago
Profile IconMichael Sumpter and Bill Gartner joined Home Energy Pros
yesterday
Malcolm Jackson joined allen p tanner's group
Thumbnail

Energy Auditing Equipment for Sale, Trade or to Purchase

Discuss the pros and cons of the equipment you are interested in prior to purchase. Post equipment…See More
yesterday
Amber Vignieri liked tedkidd's discussion What if more efficient homes were actually worth more?
yesterday

© 2016   Created by Lawrence Berkeley National Laboratory.   Powered by

Badges  |  Report an Issue  |  Terms of Service