What is best way to insulate a board-formed concrete wall?
The architect on this project ( residential modern home) designed one the rooms ( the study) of this all standard wood/stucco construction home to be built in 8in board formed concrete. Please correct me if I am wrong but, I believe this gives about an R2 for insulative properties. The rest of the house will have R21 insulation in between the 2×6 studs.
Ideally, the architect wants to see the board formed on both the exterior and interior walls of this room. If that is not possible, the interior could be drywalled.
Is it possible to insert a stiff foam in between the forms while the concrete is being poured? Wouldn’t this affect the structural performance of the wall?
Please help.
How best can we insulate this room?
Thank you,
Barbara
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
What is your climate zone/location?
Zone 3 Pebble Beach, CA
( Dana, you helped mith my other ventilation issue)
thank you
Barbara,
First of all, your architect should be able to answers these questions -- and if your architect can't answer the questions, that's worrisome.
You are absolutely correct that the wall needs to be insulated. You are also correct that if you develop a system to insert a layer of rigid foam between two concrete walls, the structural integrity of the wall would need to be reviewed and approved by an engineer.
The best known wall system that achieves what you are looking for is called the Thermomass system. (See image below.) You can contact Thermomass by calling 800-232-1748.
Thermomass uses smooth concrete forms, not board forms, so I imagine that achieving your goal with the Thermomass system would be challenging. However, if price is no object, Thermomass engineers may be able to come up with a technical solution to your problem.
It's also possible that your architect and an engineer can come up with a site-built solution using board forms and continuous rigid foam in the center of the wall. There are several challenges to this approach, however, and it wouldn't be cheap.
If you don't want sky-high costs, the easiest way to solve your problem would probably be to insulate your walls on the interior (with rigid foam or spray foam), and to cover the insulation with drywall.
.
Martin,
Thank you. I will review Thermomass. I have already posed the question to the engineer on the project.
Best,
Barbara
In zone 3C a code-min high mass wall needs R8 continuous insulation which would take 2" of EPS either on the exterior, or in the middle of the wall, or R13 continuous insulation on the interior.
In the middle of an 8" wall it would run into issues of non-standard rebar placement and could be tough to meet CA seismic requirements. If the exterior walls can be bumped to 8" it could be reinforced and build as two independent 4" walls (on the same footing), which is the minimum thickness for a concrete wall in most areas:
http://publicecodes.cyberregs.com/icod/irc/2012/icod_irc_2012_6_sec011_par004.htm
With the 2" foam on the exteirior you would lose the board-formed appearance on the exterior, but would have any number of finishing options (EIFS/stucco, or any standard siding material), but the total wall thickness would then be a bit over 10".
If it's on the interior of the concrete it would have to be R13 continuous insulation, which could be met with 2" of foil-faced polyiso with 1x furring to provide a 3/4"air gap to the wallboard.