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post #1 of 11 (permalink) Old 01-15-2011, 11:28 AM Thread Starter
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Default Shop insulation

It's winter. It's cold. My shop is a detached building on a concrete slab. Think of a 1.5 car garage with no overhead garage door. (I put in 6 ft wide french doors instead). Walls are 2x4, and roof structure is 2x4 trusses on 2ft centers with a 4:12 pitch.

I'm looking at insulation. I looked at getting it spray foamed, but at over $2200.... I just don't have it. The non-itchy cotton insulation is about $1700 for materials, delivered. Rodents won't make nests in it, but... definitely pricier than.... fiberglass.

So now I'm back to fiberglass as it may be the only one I can afford, and it's readily available locally. What did YOU use to insulate your shop?

Also, the roof trusses are making my life interesting. I was told by a roofer not to insulate the underside of the roof sheathing between the trusses as that would accellerate the deterioration of the roof. It's also very hard to find 3 or 4 inch thick insulation for that 24 inch spacing of the trusses. Most of the 24inch insulation I find is unfaced and made to lay in an attic space.

So maybe the roofer is right and I should get some light weight sheathing (like 1/4in drywall?) and lay it on top of the bottom web of the trusses and just lay a 10inch unfaced batt on top of that. Leaves the space above that bottom truss web not useable (I can slide 8 or 10 ft pieces of lumber, trim, conduit up there now, but don't have much up there.)

What do you think? Just insulate with fiberglass and stop overthinking it? (I do that a lot) or hold out for the higher tech insulation?

Insulate tight against the roof deck? (how?) or just lay in a ceiling and insulate above that?
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post #2 of 11 (permalink) Old 01-15-2011, 02:37 PM
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the roofer is right you do not just want to start throwing insulation right to the bottom of your truss next to the plywood and sheathing boards... that part of the roof " the deck" needs to have the circulation.. that happens when the air circulates from the soffit to the ridge it keeps your shingles from what they call baking the heat the shingles draw in has to go somewhere ..your best bet is lay insulation on the ceiling part of your truss but remember not to tuck it to tight to the eave or buy the rafter mate vents to stick at the ends to keep your air flowing
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post #3 of 11 (permalink) Old 01-15-2011, 03:41 PM
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Hi Charlie. I stapled vapor barrier up to the rafters, and then fastened 1x2 strapping crosswise from one end to the other. Then I laid batt insulation on top of the vapour barrier. The vapour barrier provided an air seal with the strapping supporting the weight of the insulation. If I was to do it over again, I would spring for drywall as I'm thinking it would have added to the R value of the batt insulation. Laying it in this manner allows you to place boards on top of the rafters and use it for storage if needed.

I also, and I was told this was very important, installed gable vents. You may already have roof vents, I didn't. You must have some type of air circulation in the attic area once you insulate it otherwise you will get moisture buildup and eventually rot.

I'm sure there are others with more experience than I, but this is my story and I'm sticking to it.

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or by imbeciles who really mean it.

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post #4 of 11 (permalink) Old 01-15-2011, 04:55 PM Thread Starter
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I'm thinking I might get 3/8 drywall or even 1/4 ... or Homasote if I can find it locally and run cleats along the bottom truss web so I can set "panels" of drywall or Homasote between the trusses. If I can get 2' x 4' lay in ceiling tiles, those might work as well. Depands on cost (again) I guess.

I have lots of soffit vent and fairly large gable vents, so circulation should be good as long as I don't block the soffit vents.
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post #5 of 11 (permalink) Old 01-15-2011, 07:17 PM
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Charlie,
I would definitely not insulate the rafter part of your roof. If it is -20C (-5F) outside and 20 above (68F) inside, somewhere in between is the dew point for the moisture inside the building. If you close in both sides of your rafters, it will be trapped in between. This will cause rot and reduce the effectiveness of your insulation. If you are in an area that gets snow, the snow will melt at the top of the roof where it is warmer and freeze at the eave where it is still cold. This will create an ice dam that will cause water to back up and probably leak inside your shop.
Put up vapour barrier on the underside of your ceiling, sheath the ceiling and then insulate. Your shop will be warmer in the winter and cooler in the summer. Make sure you have adequate flow thru ventilation as was pointed out. I have used pink fibreglass on a number of buildings and it works well. I put at least a 4" layer between the ceiling joists and (at least)another 6" crossways over the top of that. I have also just used a blown in cellulose. It is similar in cost, fills the gaps around bracing, and is really fast to do with a couple of helpers. Just be careful not to plug off the airflow at the eaves.

Last edited by Cherryville Chuck; 01-15-2011 at 07:21 PM.
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post #6 of 11 (permalink) Old 01-15-2011, 11:30 PM
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Hi Charlie,
I am also in the process of closing in and insulating my shop. Since I live in south Louisiana, the chance of snow is rare. So I went with R13 fiberglass insulation in the walls. I have not decided if I will use R19 or R25 in the ceiling, or use the blown in insulation. Due to the design of the ceiling rafters, I am giving up on the idea of storing stuff above my ceiling line. I am actually considering using the white metal sheets due to weight and ease of installation like Eric (kartracer64) did. I will most likely just lay the insulation batts on top while installing the ceiling sheets.
Whatever you decide to install, it will be an improvement, so that should be some peace of mind.

-George
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post #7 of 11 (permalink) Old 01-16-2011, 05:10 PM Thread Starter
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looks like I'm going to run 2x2 cleats along the bottom truss web leaving about 1/2 inch down from the top of the member. Drop in a piece of 3/8 drywall between the trusses and lay fiberglass insulation on top (parallel with the trusses instead of trying to weave THROUGH them). Maybe use 1x2 for the cleats. Not sure yet. That would leave me some exposed 2x4 (the bottom chord of the truss) for hanging things... light things... nothing too heavy hanging on the trusses.

Just have to price out the insulation and drywall so my wife can tell me when there's money set aside for it. We're trying to pay cash for everything since we're closing in on retiring.
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post #8 of 11 (permalink) Old 01-18-2011, 04:46 PM Thread Starter
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Will 1/2" drywall sag if it spans 2 ft on the ceiling? The only weight on it would be the insulation. I'm trying to stay light weight but stiff enough to not sag.
I don't want to overload the trusses by hanging too much weight on the bottom chord. Is the metal roofing material pretty stiff? I'm guessing it's lighter than the drywall.

Last edited by reikimaster; 01-18-2011 at 05:11 PM.
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post #9 of 11 (permalink) Old 01-20-2011, 12:44 PM
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How about foam insulation? The guy I bought my house from used foam between the blocks and the paneling.
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post #10 of 11 (permalink) Old 01-20-2011, 02:48 PM
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You should just drywall the ceiling and put the insulation in above. Drywall is pretty cheap, and it won't take much to do a ceiling. Much less work and expense than trying to install cleats and then cut drywall to size, etc. You could hang the entire ceiling in less time than it will take you to do all that other stuff.

It will look better, it will reflect the light better, and will do a better job of insulating the working space (less air leaks).

You will have more problems with the little cut sections of drywall than screwing full sheets to the ceiling. You can get 1/2" drywall in 12' sheets making less seams to tape. You just need help getting them up and screwed in place.

Go for R30 in the attic.
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