Air sealing open web trusses between floors
We have a second story built into attic trusses. Part is above living space and part is above the garage. It is a vented attic. Our plumbing and HVAC are run through open web trussing on the bottom of the attic trusses. (The entire space between the first and second floor is open web trussing.) We are using rigid foam to air seal the sides of the open web trussing below the second floor conditioned space. The space will also be between drywall below and the decking of the second floor above. (Conditioning the entire attic wasn’t able to be done due to budget and truss design.)
My question is, does this open webbing space need some sort of ventilation? Or will it be okay since it is connected to the conditioned space above?
The picture I’ve attached is looking from the first floor up into the open web trussing between floors.
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Replies
For the section of the floor above the living space, you don't need to do anything with it. It is fine to cover with drywall. Since it is part of the living space, there is need to have conditioning there.
The section of the garage, needs a good air barrier bellow the trusses and needs to be well insulated. Check out some of the details here:
https://www.finehomebuilding.com/2012/03/08/how-to-insulate-a-cold-floor