Can You Add Dense-Packed Cellulose + Rigid Foam?
I’m preparing to rehab a three-family home built in 1900 in Greenfield, Massachusetts. I plan to add dense-packed cellulose to the walls to bring me to R-12 and replace the single-paned windows to triple-paned.
Since the asbestos siding has to be removed anyway to install the dense-packed cellulose, I’m wondering if I can also add 2″ polyiso or other rigid foam on the exterior wall sheathing to increase the R-value from R12 to R22. Moisture could dry to the inside, and the foam would keep the outside dry. I could then install new fiber cement siding.
Finally, the house also has forced hot water heat with an oil boiler. I’m also thinking about an air-to-water heat pump to use the existing radiators and stay with hydronic heat, plus provide hot water for the home. I’d like to add cooling, since the house doesn’t have any right now.
How does this sound as a rehab plan for my climate?
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Replies
I did something similar with the envelope of my 1900s house in Central New York and have been happy with the results. I'm assuming you'll have an air space with furring behind the fiber cement.
I like the idea of air-to-water if the sizing calculations and budget support it. You'll need to add hydronic air handlers (ducted or ductless) for cooling; these can be tied into the air-to-water system and can supplement the heat output from the radiators.
Thank you for confirming that the cellulose + rigid foam walls worked well for your home of a similar age and location. Yes, I was planning on an air gap using furring strips behind the fiber cement.
I will have to check into the air handler options on the cooling. I know this technology is newer. I'm more familiar with mini-splits and ducted air source heat pumps but thought the air-to-water might be worth checking into. Appreciate your reply.
Most modern air-to-water heat pumps are not built for the higher temperatures old school radiators require. Check what design temperature the radiators will work at for your heating needs, and compare that to the specs of some of the air-to-water heat pumps you are looking at. At the very least, their efficiency will take a big hit heating the water up to those higher temperature, if they can reach them at all. Do you have gas to the house, and do you plan on keeping it if you do?
Thanks for sharing this insight, Matthew. I did not realize that oil-fired boiler radiators require higher heat. I will definitely check into that!
Yes, natural gas is available to the house but I do not want to use it for both health and environmental reasons, especially since the plan is to create a tighter building envelope. Thank you for your reply.