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Discussion in 'The Garage' started by trailrider383, Dec 28, 2012.
Did you decide on how to insulate your roof?
I think I'm going to use the panels I talked about in my last post.
What's the r factor on the panels?
I was thinking the closed cell spray foam for my 30'x40' but the cheapest I could find was $2900 for 2"
Came across a video of guy installing closed cell panels and using the great stuff spray cans on the edges to seal it.
The r value is in this link: http://www.insulfoam.com/images/stories/docs/6081_RT_IV.pdf
Which thickness were you considering? Looks like about R5 per inch. Any thoughts on installation?
Here's the video http://www.youtube.com/watch?v=i1guAwzyEOQ
I will probably use the 2". My plan is to lay it across the 2x6's and use screws with washers to hold it up. It doesn't weigh much so it won't take much to hold it up there. Then I will use the foil tape to seal the seams.
If the rafter bays are regular and neat, why not just cut the foam panels to fit between the rafters tight to the sheathing? They will stay put w/ pressed in fit or with small cleats, you can add another layer now or in the future, they can be removed easily if required, it looks better/more interesting, and you will save some space/headroom.
My garage is done this way and it works fine.
I don't have a problem with headroom. There is no sheathing, look at my pics on the first page. It's a lot easier to grab a 4x8 piece and stick it to the ceiling than cutting it to fit a zillion different cubby holes. And then I will have the dead air space between the insulation board and the metal roof to add to the r value.
If those are 2x6 on the ceiling then r20 insulation would fit just nice. Looks like 24 inch centers ? And staple a heavy mil poly up there and it would be cheaper then the foam insulation and you would have a way better r value and less sound transmission as well. Covering with drywall would be nice but optional.
I have had the spray foam applied on a few different jobs, for myself and for customers. Cost is pretty much a dollar a board foot. So a buck an inch times your square footage. For your case I think you will be good with the two inch rigid foam. And $20 a sheet is good for 2", here it's going for $32
Do you have building codes where you are? Here in the City Code Enforcement would want the foam covered with a fireproof coating. Either drywall or a special spray on product that costs another dollar a sq ft.
+1. This is how a pro would do it. Most insulative value for the buck. If the itchy bothers you, hire an insulation company to do it, likely still cheaper than all these other shiny products.
What about condensation between the fiberglass and the metal roof? Doesn't there need to be a vapor barrier?
Here are my pics again. I think people are just suggesting things without knowing my situation.
Couple of theories on insulation.
1. Vapor barrier always goes on the warm side of rhe wall. If you live in Idaho the vapor barrier covers the studs and insulation. If you live in California and you have air conditioning then it goes on the outside.
2. It is not the insulation that insulates it us the dead air space in the insulation that insulates.
3. Two theories on wall cavity. A) sealed completly like an envolope. B) on side is vented to take away the humidity / warm or cold air away. It is the warming up during the day and cooling of at night that you get the condensation.
So if those are 6 inch studs then r20 insulation would fill up the wall cavity completly and the vapor barrier would cover it and seal it so there is no air movement.
If those are like 12 inch wood studs then you would want to ventalate with roof vents at the peak and vented soffits.
I just found out that kraft paper faced fiberglass insulation is a vapor barrier. I didn't know that.
This site has some interesting stats about perm ratings of different materials.
Best check with building codes in your area using the paper back insulation. Here in Canada it has not been used in new contruction since the late seventies because of high flame travel. Do you do any welding or grinding or use a torch in your shop ? Or plan on covering up with drywall ?
Yes to all of those. I'm not going to sheetrock the ceiling. I never considered using the paper covered fiberglass anyway. I'm going to stick with the foam board idea.
IIRC, supposed to be a 2" air gap between roof and insulation. There are some extruded foam sheets that act as spacers ready made for 24" of joists as you have.
If it were me, and I have built around 500 homes...., I'd look up insulation contractors in the phone book and have'em come out for an estimate. Get 3 or so, go on professional opinion rather than some wacky anonymous klr riders off adv.
My $.02 is your on the right track with this idea.
If you built your roof construction with a continuous soffit and ridge vent, you would have more than enough ventilation to dry out any condensation that might develop in the air space between the foam board and tin.
One concern in Idaho is roof loading. Pole buildings are usually designed to Barely meet the snow load. Adding ANY weight to the roof will probably take the load above design, unless a ceiling was included in the original design.
We have a 24x30 pole building that was insulated with R11 vinyl-backed fiberglass and it does seem to help even though it is compressed at each purlin.