I have access to some inexpensive double-bubble foil insulation
Tennesseebob
| Posted in Energy Efficiency and Durability on
I’m building a home with cathedral ceilings 8/12 pitch exterior, 6/12 pitch interior. Thinking of using the foil as a radiant barrier at the bottom of the top cord of the truss. This will create a baffle to vent roof . Then using the foil bubble wrap in the interior of the bottom cord of truss then use furring strips to create an air space then drywall. Then fill void in truss webbing with blown cellulose.
Will using vapor barriers in this configuration cause any problems? House to be build in zone 4 Tennessee.
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Replies
Bob,
Foil-faced bubble wrap has a very low R-value, and is almost useless as an insulation. The foil facing is a radiant barrier, and if the foil faces an air space, the foil may add between R-1 and R-2 to the total R-value of the assembly.
The main problem with your plan is that foil-faced bubble wrap is a vapor barrier. You are proposing a roof assembly that has two vapor barriers -- one on the interior side of the insulation, and one on the exterior side of the insulation -- and that is a definite no-no. Such a sandwich can definitely trap moisture that will never dry out.
I strongly suggest that you skip the bubble-wrap.
Thank you for the advise. What about just using it at the ceiling level as this will give me an opportunity to better air seal the cathedral ceiling . Furring out the ceiling will give me an air space that should help radiate heat back into the envelope. Otherwise I will have a hard time air ceiling from above, along with the fact that there's a full width porch across the front that needs to be vented out the ridge.
It's almost always more trouble than it's worth. Maybe as triple-wrapped around a duct it does some good, but is it any easier/better than using some thing else?