R-Max insulation boards

[Holbs]

Thanks to this forum, late fall i started insulating my 2car 24'x24' attached garage. I started out with R-19 24" paper-faced batts to go between my 2"x4"trusses with duroplex (?) plastic venting for the soffits ( I know.. R-19 doesn't fit as it needs 3.5"). I'm 75% complete done ( Xmas duties and funds can run interference). A little over a month ago, I also scored on a Reznor v3 series 60,000BTU residential garage rated heater for $75, new and never used (i bought at a estate auction). I plan on hanging it myself with unistrut and all-thread, electrical, thermostat; just have to have gas man tap into the main gas line 10' away and run a feed into it and then test.
I've learned alot reading the forums here regarding insulation types (except for my booboo of using R-19 instead of R-13 for trusses).

Today, while at work (i am a field technician for phone systems) I was at one of the " RMAX" insulation plants. To my awe, lots of 4'x8' foam boards Then I asked more. It seems the slightly damaged (mostly, cosmetics) are sold at a huge discount, only in person at the facility. 1" 4'x8' board for $5.12 as compared to box stores of $23+. The 4.5" is $21.60.

I may have to revisit the past forums posts about the pro's / con's for insulation boards. If it seems all thumbs up to use this stuff for my trusses, and possibly in my walls (i was going to go for blown-in insulation).... what to do with my R-19 paper faced batts?

-eric

 

[Holbs]

Never mind.
Insulating the garage roof is a science I do not fully comprehend because I am no professional nor am I qualified to have all the fire code, do's/dont's involved.

I originally removed the finished drywall ceiling to have space above my head.
The science is just.... too much. I have soffits every 4 feet (i think i need a soffit vent EVERY 24" to ventilate EVERY truss bay), no ridge vent (would the 1 passive vent 2' from my peak be enough? i doubt it), only a sheet of OSB separating house from attached garage (a nono in firecode), 2x4" trusses (R-13 max, not including durovents). I think re-installing with new gypsum fire-rated drywall under the trusses is the best economical fire code way to go. I'll figure out how to insulate after that (maybe re-use the R-19 onto of the drywall with blown-in ontop of that to get upto the r-30 range).

 

[rebelranger]

Here is a great link on insulation. http://www.buildingscience.com/docu...ing-hygrothermal-modeling-basement-insulation

Using drywall make sure it's 5/8s and there is fireblocking (google it). Foam board is great insulation, its just like spray foam only in a rigid state. Glue it and then use sealant (hvac tape, can foam) to air seal the corners.