Adding to R19 in the ceiling
Fiddler110
| Posted in Energy, Heating & Insulation on
We have purchased some R19 for the 2 x 10 cathedral ceiling but we want to increase the R factor. We have 9 1/2″ of space in the joists/rafters. We need to leave a 1″ air space for ventilation. That leaves about 2″ that I can fill with either more fiberglass (without vapor barrier) or rigid insulation. If I use rigid, on which side of the fiberglass R19 should it be placed? I don’t want to create 2 vapor barriers?
Thanks,
Rick
Rick
Replies
If you are going to use fiberglass you need to take the r-19 back to where you got it and get your money back. There is a R-30 cathedral batt that will fit in that space and still allow the space for the baffle. Cathedral batts are not usually available at Lowes or Hd or the local lumber yards. You need to contact a local insulation company or insulation wholesaler.
FYI - I think what Griffin is referring to is high density (HD) fiberglass batts. More R-value per inch. R-30 should be your minimum. Another option is to nail 2x2 to the rafters to give you more dept ... Then still put HD batts in. R-30 is minimal for a roof in almost any climate. Many codes require R-38 minimum. What is your location? Mild climate may be OK (e.g. coastal climates), but again R-19 is pretty slim.
To answer the question though. Put the batts in, then the insulation (on the warm side) ... just to ensure you have the vapor retarder in the right location.
Yes, that's what I thought. My building inspector said to put the rigid on top of the R19 but I think that's wrong. I'll push the R19 up to 2" beyond the joists lower surface. Then I'll press fit 2" rigid insulation. Then the dry wall. That will leave 1 1/4" between the underside of the roof plywood and the top of the R19 for the ventilation.