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. 

Featured Forum Discussions

What causes a temperature plane in a home

Started by Energy Wise Solutions in HVAC. Last reply by Peter Krych on Friday. 4 Replies

Velocity Pressure Testing

Started by Horace Douglas Hunt, Jr. in General Forum. Last reply by Horace Douglas Hunt, Jr. Apr 15. 2 Replies

Videos

  • Add Videos
  • View All

Latest Activity

Efficiency First California posted a blog post

Building a Clean Energy Future, Respect for the People Who Will Build It

You don’t need to spend a great of time deal in the policy world before you hear a conversation…See More
9 hours ago
Profile IconDavid G. Tamutus and Sharon Block joined Home Energy Pros
10 hours ago
Gary Reed added a discussion to the group Job Board
Thumbnail

HOME ENERGY ADVISORS WANTED (NEW YORK STATE: Saratoga & Glens Falls Region)

We are currently seeking experienced HOME ENERGY ADVISEOS to join the Jack Hall Plumbing &…See More
yesterday
Profile IconGary Reed and Kurt Shafer joined Diane Chojnowski's group
Thumbnail

Job Board

This group is for posting jobs related to all aspects of the home performance industry including…See More
yesterday
Ron Sarrick liked Energy Wise Solutions's discussion What causes a temperature plane in a home
yesterday
Kurt Shafer added a discussion to the group Job Board
Thumbnail

Installers for Whole House Fans in Various Cities

Invisco Whole House Fan Company in Temecula CA sells the highest performance fans in history. The…See More
yesterday
Kurt Shafer posted a blog post

First Rooftop Whole House Fan for Homes without Attics

Eichler was one of the most famous Mid Century Modern home builders in the 50s and 60s. His homes…See More
yesterday
Travis Lundberg replied to angela stanzione's discussion Used Weatherization and auditing equipment for sale in the group Energy Auditing Equipment for Sale, Trade or to Purchase
"Do you still happen to have a blower door fan, frame and fabric still for sale?  If so please…"
yesterday

Home Energy Pros

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.   Powered by

Badges  |  Report an Issue  |  Terms of Service