Thermal breaks in heated slab to ICF wall > GreenBuildingTalk - Green Building Forums on Insulating Concrete Forms (ICF), Structural Insulated Panels (SIP), Radiant Heating, Geothermal Heat Pumps, Solar Power

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Forums > Green Building Forums > General Forum - Residential > Subject: Thermal breaks in heated slab to ICF wall

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PatrickT

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Posts:142

06/24/2008 10:58 AM
As some of you may recall, I had posted the question how the thermally isolate a heated suspended slab from an ICF wall. With Radiant heating, Delt T will be quite large and the ICF wall will act as a heat sink. There are several very different applications through out the home. In some cases simple and straight forward. Others a bit more of a challange. Basic wall floor details; ICF wall, 8" concrete with additional added foam to the outside. The block is 2-5/8" inside and out so we can add either 2" or 4" extra. Home is two levels on a walk out basement, (three levels). All three levels will have 8" ICF Bar joist floor system, 4" slab with Radiant heat. Poured suspended Bar joist deck along south wall at main level. Poured Deck is attached to a wall of arches. Meaning, structurally all loading is the foot of each arch, 12" x12". Poured bar joist/concrete Flat roof. (Cold slab, insulated from below. This is due to a simi green roof/roof top patio.) The interior slab connecting the exterior slab at the deck is a bit more complicated than it first appears. A 2" foam edge isolation strip could be placed down the center of the wall. So edge to edge would be solved. But the slab rest on the wall and the next set of walls rest on the slab. Instead of the heat tranfering via the edge, it just goes above or below through the lowest/higest part of the walls. I could look at the different "conections" from alternate points of view. First would be to consider it OK the heated floors can be conected to the walls. With the 8" of concrete of the ICF wall being inside the 4-1/2" to 6-1/2" foam exterior, it could be considered inside the envelope. This would insure a super solid wal to floor conection. Then the cold roof and the deck would be the only slabs to isolate. There are two materials I have found so far I can try to work with, AAC cut in to a strip and Foamglas, UK site only! The AAC has compression of 800 psi and the foamglas has about 170 psi. The AAC is R-1.1/in and the Foamglas is R-3? The UK Foamglas applies the material as a first cource in masonary walls to stop thermal leaks. Any other load bearing and insulative materials? Or ideas. Patrick T

icfcontractor User is Offline

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06/24/2008 1:51 PM
Patrick, We have had to wrestle with similar issues on most of our building with concrete floors. Most times the descision has been to not worry about an interior thermal break for several reasons. Compromising the strength of the floor connection is number one, energy efficiency is number two, and of coarse cost effectiveness. In some cases we have made the floor in two pours with a thermal break of foam or a product like Insul Tarp between layers. Depending on the strength of your bar joists, this is possibly a good option. On one project with bar joists we poured a 4 inch slab over the pan deck, laid out the Insul Tarp, and poured a 2 inch layer of gypcrete with the radiant tubes. in the topping slab. The topping slab is of course all poured after the next floor walls are erected. Thus thermally isolating your floor from your wall. ICF Contractor.

PatrickT

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Posts:142

06/24/2008 3:25 PM
ICFcontractor, Thanks. I'm with you on the positive wall floor connection. The qty of heat flow is based on Delta T , surface area and length of path. So in my case, the radaint heated floor has an area 4" wide by the perimter wall length. Deta T will be; Floor temp-wall temp. Maybe 85F-65F? The path length is quite long, 12+ feet down to the footer. The heat path length is critical because a gradient forms. Ground temp is 55F and wall Temp could be 65F. That is a small Delta T over a long gradient. The deck and roof are bigest concerns. I will be proposing to the joist manufacture that the deck slab ends at the foam and not cover the wall. The only exposure to the concrete wall would be the joists themselves. And the joist ends could be covered with a thin layer of "foam in a can". In this method, the main homes structure is maintained. The deck is one level. I would like to construct/ poured the roof using the AAC as a top cource on the ICF. Patrick T

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