insulating 2x6 rafters?.how to?...

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?

Gary

Gary,
located in Tucson Az.very dry area,hot in the summer,high humidity during the monsoon later in summer...im 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...

Find the Zone; http://publicecodes.citation.com/icod/irc/2009/icod_irc_2009_11_sec001_par001.htm

Find the insulation with the Zone; http://publicecodes.citation.com/icod/irc/2009/icod_irc_2009_11_sec002.htm

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.; http://www.airvent.com/homeowner/products/intakeSoffit-specs.shtml
The circular vents are poor with the screens; http://www.lomanco.com/ProductPAGES/CirkVents.html
You'd need three 3+" holes, with screen.

Or go to a conditioned roof; http://www.buildingscience.com/documents/digests/bsd-149-unvented-roof-assemblies-for-all-climates

http://publicecodes.citation.com/icod/irc/2009/icod_irc_2009_8_sec006_par003.htm

Gary

Gary
thx for the help...the building itself was not built to code per say...it was built 25yrs ago and we could not find anything on it when we purchased the house...it wont be inspected but of course rebuilding to code(roof,electric) would probably help resale...my 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?......
Jeff

Gary,
just getting back...thx for your help......i'm going to try to get to code with the insulation...
Jeff