Brenton is building a new house in southern Maine (Climate Zone 6) that he currently plans to insulate with a combination of open- and closed-cell spray foam plus a continuous layer of exterior insulation in the form of R-6 Zip R-sheathing.
He’s willing to take suggestions on that approach, as he explains in this Q&A post, but a more pressing concern is how to heat and cool the house.
“I have been planning on installing a hydronic radiant system throughout the whole house with a wall hung Viessmann Vitodens 100 propane boiler,” Brenton writes. “My wife would like ac for the humid summer months here in Maine so I’ve been considering adding a 5 zone Fujitsu air sourced heat pump.”
“My question is this,” he continues, “would I be better off going solely with heat pumps for my heat and ac and scratch the radiant and put that money into solar? Or should I install the radiant and have the heat pumps for ac and auxiliary heat?”
That’s where we begin this Q&A Spotlight.
First, review your insulation plan
Before discussing heating and cooling, GBA Editor Brian Pontolilo suggests Brenton take a second look at his plans for spray-foam insulation, particularly in the roof where Brenton is planning to use 11 inches of open-cell foam.
“Because you weren’t specific about the roof and venting, I want to point out that when using open cell spray foam in the roof, the assembly should be vented,” Pontolilo says. “Closed-cell spray foam is the only reliable option for beneath the roof deck in an unvented assembly.”
A second option for an unvented roof would be to install rigid foam over the roof deck, which would allow Brenton to use a number of insulation types below the sheathing.