Another “How to insulate this old house” question
I am in Louisville, Ky; climate zone 4A. I have a 115 year old 1.5 story house with gambrel roof and have obtained a ton of detail from this site on how to insulate behind and under knee walls, etc. while maintaining a ventilation channel.
I have gutted the old lath and plaster on the second floor (house had been split up into apartments, and everything was in bad shape). On the second floor, one exterior gable wall and the dormer walls have 1×10 horizontal board sheathing with 1/2 gaps, felt paper, and stucco. At the bottom of the stuccoed gable wall is a kickout for a small roof/eve between the first and second floors. The board sheathing follows the framing and transitions from wall to roof sheathing leaving a large hollow cavity at the bottom of the wall. The other gable wall (and all first floor exterior walls) has no sheathing and only thin wood clapboards. The bottom ~third of this wall is also now open to the attic of an addition.
I plan to sheath, add 1″ foam and reside at some point, but it may be a few years before I am able to. To get this 2nd floor back together, I am considering a cut and cobble with 1″ gap for stucco and clapboard to breathe. This would also allow me to close the gaps that I now have at the bottom of each gable wall. I also don’t know if I want to remove the stucco on the 2nd floor in the future. I will, however, definately reside the clapboard wall when I do the first floor.
If I put xps in the stud bay with an air gap, can I come back later and also put sheathing and foam board on the outside? Should I airseal the drywall and just not insulate until I do the siding? I am afraid to have it spray foamed or fill the bay with rockwool or similar now and cause moisture problems in the event it takes me a while to redo the exterior. Any advice is greatly appreciated.
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Replies
Jason,
Your plan to use the cut-and-cobble approach, with an air gap between the rigid foam and the existing sheathing or siding, will work. In your climate zone, this approach will not cause any moisture problems. Including additional insulation on the interior side of the cut-and-cobbled foam is a good idea.
Paying attention to airtightness when you install the drywall is also a good idea, and won't do any harm.
If you later add new plywood or OSB sheathing on the exterior side of your existing sheathing or studs, that change won't add any new moisture problems. Opening up the wall from the exterior will give you the opportunity to add more rigid foam (or some spray polyurethane foam) where the air space used to be, if you want to do that later. You could even add a continuous layer of rigid mineral wool on the exterior side of your new sheathing in a few years if you want to get fancy.