Creating a Thermal Break Between Porch and Wall
I am close to starting a build on a large ICF house. There are a lot of porches and balconies on the house and my builder is planning to use insuldeck to form the porches out of concrete. These porches will attach to the concrete of the ICF wall and be supported by columns at the other end of the porch. Before anyone asks, we have specific reasons for not wanting to build the porches out of wood.
My concern is that there will be free thermal transfer between the porches and the concrete wall, thereby negating the thermal benefits of the concrete layer of the icf and leaving me with only 2 1/2 inches of polystyrene insulation. I’m also concerned about the possibility of condensation on the concrete wall, resulting in mold growth within the wall. It seems crazy to go to the added effort and expense of building with ICF and then completely sabotaging the energy efficiency of this type of construction by ignoring thermal transfer from the porches.
I have searched for a product that can provide a thermal break between the wall and the porch concrete and still be structurally sound. But the few products I have found for this application are either designed for tying into an interior concrete floor (ours is wood trusses) or are designed for a much thicker slab for the porch (over 6” vs. ours which is 4” sloping to 2”). Making the porch slab thicker creates a lot of engineering issues.
Does anyone have any suggestions for how to create a thermal break in this scenario, while retaining structural integrity? Thanks for any advice you can give me.
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Anyone know of a product available in the US to create a thermal break in this situation? Shoek isokorb won’t work as it requires a concrete floor to concrete floor connection. Halfen offers a product that can tie into an ICF wall, but it requires a thicker deck slab and thicker wall than I’m willing or able to do.
In the event I can’t create a thermal break between the wall and porch, I am considering insulating the top of the porch with a rigid insulation board like a PIR panel. Since the bottom of the porches will be formed with insul-deck, they will already be insulated. I’m hoping that by insulating the top surface as well, I can limit thermal transfer between the wall and porch.
Does this sound like a viable backup plan? Does anyone have any suggestions for a rigid insulation board for exterior use between a concrete slab and a tile floor (with U.S. availability)?
Whenever I end up with a choice of solutions of the complexity y0u are suggesting might be necessary, I go back and see what design choices have lead to requiring these highly technical fixes, and review whether fundamental changes aren't a better way forward than trying to use solutions you don't often see on houses - because they really shouldn't be necessary.
I’m afraid I won’t be re-visiting my design choices to a great degree. I have already applied for the building permit and don’t wish to delay the project any longer. Ultimately, I want an ICF house. However, I don’t want interior floors for the 2nd and 3rd story to be concrete, as I find it very hard and uncomfortable not to mention more expensive than wood trusses. But I do want the exterior balconies to be concrete, because they are much more solid, permanent, resistant to insects, and low maintenance. So I am left with figuring out how to make all of this work in the most energy efficient way possible.
Just a couple of ideas you can bounce off your engineer.
You could look at using an ICF brick ledge form to support the porch slab. If you set the slab onto a composite 2x4, it should create a decent thermal break. You would still have to tie the slab back to the house but that could be done with some stainless hardware to minimize heat loss.
You can also look at Simpson ICF ledger system for CFS:
Hang a CFS beam as a ledger on the outside to support the porch slab or use a steel composite form. Don't know if this would work in a covered porch situation as they are meant for interior use.
Thank you. These are some good ideas. I have considered the ICF brick ledge form idea with my contractor. Will continue to investigate that.
Not sure why you should feel compelled to tie into the main foundation wall with one side of any porch or entry pad. The balconies are another case. I have built my last half dozen or so decks free of connection to the houses by setting my piers a few feet from the main foundation just like I needed to set all the other piers for the deck.
If you have faith in the outboard piers being designated now, there should be no reason to fear any movement in the piers next to your main wall. Even less concern if you create extended footing bumps to carry those piers. Setting the porches on independent piers will allow you to drop the odd choice of making a porch slab over Insul-deck. This should be considerably less costly if it becomes a slab on ground situation. If the deck/porch is above grade then I would suggest steel pan to replace the Insul-deck and simplify the final finishing. You will (I think) end up with a thinner porch deck profile. The required support during a pour should be similar for either.
I admit to being puzzled by balconies on an ICF structure and suggest that you scan the other companies websites to see if there might be a suggestion so far overlooked. Otherwise, why not do the balcony as a pretty normal cantilever of the interior floor structure through the ICF wall? The functional hit on your thermal barrier will be no worse than the door and windows that presumably open out onto the balcony.
Thank you for your response. I believe I misled you with my use of the term porches, when balcony may be more correct. This house has multiple levels of porches/balconies, both covered and uncovered. I am referring specifically to the ones on the 2nd and 3rd levels, not the ground floor level. They are supported on the far end by columns, but must be attached to the ICF wall at the near end.
We are using insul-deck to form the balconies because my contractor is very proficient with it and believes his labor costs will be lower using that over standard forming and bracing for a concrete pour. It also makes it easier for him to finish out the ceiling of the porch below the way we have designed.
I can’t do the balcony as a cantilever because I have wood truss floors on the interior but want a concrete balcony. So I am just trying to figure out a way to minimize thermal transfer from the balconies to the ICF walls in a structurally sound manner.