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jeffski1 05-02-2011 12:02 AM

insulating 2x6 rafters?.how to?...
in the process of adding a new roof to my shop.the shop is 12 x 14,8ft cement block walls...i went with 2x 6 rafters/24" OC/ridge board in place...i was going to use rolled bats(r-19) between the rafters with bird blocks with holes to allow for air movement,will there be room between the insulation and decking to allow air movement?...would this be okay?...also would i need to add other ventilation like a ridge vent ect?...thx ...:)

Gary in WA 05-02-2011 12:38 AM

The R-19 batt is 6-1/4" thick, no it would not leave a 1-1-1/4" air space. Where are you located-- State?
Have you thought about un-vented? 6' span? How many/size of holes?


jeffski1 05-02-2011 01:56 AM

located in Tucson Az.very dry area,hot in the summer,high humidity during the monsoon later in not sure what unvented is?, and i guess i did not do my homework because i thought r-19 batts were smaller in thickness...what do you mean by 6' ft span?...i thought two 1" holes in each birdblock would suffice...thx...:)

Gary in WA 05-03-2011 09:13 PM

Find the Zone;

Find the insulation with the Zone;

Do you have rafters only, no ceiling joists that hold the building/roof from spreading? R-30 is required for your location, need to furr the rafters down to get insulation in with an air space. The 6' is rafter length on each side of ridge. If a low pitch, 2" is suggested for air space above insulation, steeper pitch, 1" minimum. A ridge vent gives 18 NFVA per ft., each side of a gable roof at soffits needs 9 NFVA per ft.;
The circular vents are poor with the screens;
You'd need three 3+" holes, with screen.

Or go to a conditioned roof;


jeffski1 05-06-2011 03:55 AM

thx for the help...the building itself was not built to code per was built 25yrs ago and we could not find anything on it when we purchased the wont be inspected but of course rebuilding to code(roof,electric) would probably help shop is only 12x14...2x6 rafters only,8ft cement brick walls,4/12 run/slope for pitch,will be shingled....i guess i didn't plan my insulation install to well:(...more work to fur out the rafters:(...Friday i will look for a ridge vent,HD/Lowes does not carry,but a building supplier here in town does...i thought about using a rolled out mesh type vent,any thoughts?...:)...

Gary in WA 05-06-2011 06:46 PM

Not for me;

Get the 18 NFVA:

Baffled is best:



jeffski1 05-12-2011 01:53 AM

just getting back...thx for your help...:)...i'm going to try to get to code with the insulation...

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