10-23-2011 07:42 PM
I would like to insulate the ceiling of my garage. The roof is flat and the beams are irregularly spaced -- anywhere from 20" to 30" apart. What is the best fiberglass insulation to use for this job? In other words, should I just by standard 15"-wide insulation and cut to fit, or is there an easier way?
Thanks for any advice!
10-24-2011 05:10 PM
Hello Patrick and welcome to the How-to-Community.
I’m surprised to hear that your ceiling joists are spaced so far apart?
Anywhere from 20”-30” inches apart wow…what is the span of your roof and size of ceiling joists?
Sorry…let’s get back to YOUR questions?
In my opinion best insulation for this project, considering the irregularity in the beam spacing would be polyurethane spray foam insulation. Now depending on your existing roof construction geographical location and vapor barrier requirements in your area you would either use closed cell or open cell spray foam.
There are several major differences in between these two but the most important ones and ones that are relevant
to your project are “perm” rating and R value.
Closed cell polyurethane is among the most efficient insulating products available nowadays on the market with an R value of 6 per 1” inch. In addition to the efficiency this product, because of its closed cell structure, also provides for a great air and vapor barrier.
Open cell on the other hand it’s not as dense as the closed cell has a lower R value and its vapor permeable.
There is a great post on the community from one of my fellow associates aboveaveragejoe talking a little bit more in detail about differences in between these two, please click HERE to get redirected.
Spray foam is considerably more than fiberglass and if you’re on the low budget for this project and you decide to go withe the fiberglass I would recommend using unfaced insulation spaced for 24” on center. Paper faced insulation would not work considering that is only spaced for 24” or 16” on center.
For the joists that are spaced 24” and less I would recommend using insulation supports (only available for 16” and 24” spacing) and for the ones that are grater than 24” I would recommend using U nails in combination with rebar wire.
Simply you would tack in a U nail approximately every 16” on the inside bottom side of the joist and then pull a rebar wire thru each nail so that wire crosses from left to right creating a support for the insulation.
Hope this helps.
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