amccarty,

We are building with a flat concrete roof. I have asked this question here of 'slab isolation' and have not received much of any replies. I called my ICF block guys and Hambro. Again, not much could be stated. Finally I called the engineering dept in Hambro Canada div. They said this question comes up very seldom. I offered my solution of placing a 1/4" fiber glass sheet the width of the concrete core on the top prior to placing the steel joists. In addition, use 90 deg fiberglass Rebar to tie the wall to the slab. Since Hambro can be placed on wood framed walls, I see no reason the joists cound'nt sit on fiber glass sheet. certainly has a higher compression than wood.

Since we are using Radient heating, some heat will flow in to the wall system. But in our case, we will have 4 5/8" of foam on the outside and 2 5/8" on the inside. Heat loss into the walls still can/could be considered 'in side the thermal envelope'.

I'm just not sure what kind of heat loss I would face if I did nothing

Patrick T.

Most of the ICF floor systems such as the one pictured do offer a thermal break as they are foam.  No concrete is exposed on the inside of the thermal envelope.  Additionally, you can add more EPS or use a urethane foam on the underside....or on the top of the roof.

To seal the roof from water penetration, there are a myriad of options....a membrane, either liquid applied or sheet, metal, tile..

You can use an overlay, admixtures in the concrete and coatings, etc...to make the roof look like a composition, the finished look just depends on what you want, making the roof water tight is not tough.

Concrete as a roof structure as the one pictured is a viable alternative to wood frame, seems few people are willing to pay the premium for it.

Also, if design will allow, use the roof as a deck and make the roof flat...or with minimal pitch...a traffic overlay like grailcoat will offer sealing and a nice appealing deck surface.

Ian,

I guess the thermal envelope should be defined. If the roof slab is poured in contact with the ICF wall concrete, you typically have only 2.5" of foam seperating you from exposure in the walls. The idea idea of Lite deck/Panel deck is foam on the underside. The exposed concrete roof deck will pull or receive the heat from the ICF wall in winter and push heat to the ICF wall in summer.

Patrick T.

ICFcontractor,

Now thats a big roof at 9000 sq-ft! I thought my 3400 sq-ft flat roof was big. What add mix you using? I've looked in to Zypex a bit and it's ava local.

Is the Logix system a foam form system needing shoring like Panel/Lite deck?

Patrick T.

Patrick, I agree, but considering the wood option, the ICF option offers more benefit, even though it may not be perfect.  I would also submit that the entire roof is storing heat or cold energy, but the transmittance of that energy through the EPS has to be lower than that of a generic roof structure.  Again, one could add more insulation such as the spray applied to either side.

Ian

Here is the model.