Air sealing priorities for gut renovation and second story addition
The background: We have a 1973 cape cod. The first floor is standard (for the time) 2 x 4 construction with barn board sheathing. Air sealing and insulation where nonexistent. The first floor has been gutted down to the studs.
We ripped off the old roof/second floor and added a full second floor addition with a walk up attic. My framing contractor is finishing up and I’m responsible for air sealing and insulation.
The exterior is being wrapped with Tyvek paper, 2 inches of foil faced polyiso, and new vinyl siding. For now the basement and attic are remaining unfinished.
A few questions:
Should I be worried about gaps between the plywood and barnboard?
While everything is open I need to get this house as tight as possible, where should I focus besides the obvious places (chases, penetrations, plates)?
Anything else I’m missing?
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Replies
The way I see your big problem is you added the Half story on top.
Is the third floor inside the conditioned space now or is the plan to condition the third floor later?
Did I say I hate half stories?
Being as the second floors ceiling is larger than the conditioned space above how does one keep the keep the conditioned air over the ceiling from escaping into the unconditioned attic or do you just give up and move all the insulation to the roof line conditioning the attic. If you condition the attic, you have almost no option but expensive, ungreen and risky spray foam. In fact the spray foam is so expensive the code min R value is has no return on this investment.
Note the sloped ceiling of the third floor are in fact cathedral ceilings do yourself a favor and pick one if the five from this article.
https://www.greenbuildingadvisor.com/article/five-cathedral-ceilings-that-work
Something to read if you do not condition the attic.
https://www.greenbuildingadvisor.com/question/devils-triangle-update
https://www.greenbuildingadvisor.com/article/five-cathedral-ceilings-that-work
https://www.greenbuildingadvisor.com/article/insulating-a-cape-cod-house
Walta
Not interested in conditioning the third floor unless i end up having a boat load of kids 15 years from now. For now we wanted a steep roof pitch, and the extra space was just a bonus. Part of the reason we got rid of the cape style was to avoid the cathedral ceiling.
If I was going to finish it in the future, I would just flash and batt the bays, with 1 inch iso board between the drywall and the rafters to break the thermal barrier. My main focus now is on air sealing the house.
“My main focus now is on air sealing the house”
Sorry but you have to chouse where will your thermal boundary be?
If you make the second floor ceiling the thermal boundary that is great for today but terrible if you finish the “bonus” room later. Because it becomes almost impossible to air seal the bonus room and you have the wrong type of insulation in the wrong location.
If you air seal and insulate the “bonus” room now you must spend more money now for the expensive foam insulation and pay to condition space you are not using.
In my experience half story building are drafty energy pig. It might be possible to build a tight cape but my guess it is only possible with well thought out planning and flawless execution in new construction.
Walta