Dustin P. is building a house with insulated concrete forms (ICFs) in Climate Zone 5 and hopes to hit performance standards that would make it what the Green Building Advisor community would call a “Pretty Good House.”
As he explains in this recent Q&A post, above-ground walls will consist of 2-1/2-in.-thick rigid foam on each side of a 4-in. core of concrete. The assembly, he says, will have a total R-value of about 23. The unvented roof will be insulated with mineral wool batts in the rafter bays (R-32), plus another R-23 of insulation on top of the roof deck.
The roof deck has been covered with a peel-and-stick membrane. The ends of the rafters are flush with exterior walls and end inside a fascia board—Dustin plans on applying rafter tails, eaves, and rakes later.
“In the interim,” he says, “we have had some water intrusion. I think the water is coming off the roof, moving down the ICF, and getting inside at the window bucks and cold-joint between the top of the basement ICF and the above-grade ICF. I hope that getting the overhangs on the roof and the siding up with a rainscreen will take care of that.”
Dustin is looking for suggestions on the house and an adjacent garage, and wonders whether he should add any insulation to the ICF walls. That’s where we start this Q&A Spotlight.
The Pretty Good House (PGH) concept is, in the words of Michael Maines, who helped develop this building approach, both “flexible and open-sourced.” But even then, the house as Dustin describes it doesn’t quite fit.
“A PGH minimizes embodied carbon emissions; building a house entirely of foam and concrete comes with a large carbon footprint,” Maines writes.
Further, the insulation looks a…