Replies

1. 
   john_c2 | Oct 20, 2020 10:16am | #1

   The gold standard would be spray foam. It will be the highest R value.

2. 
   lordulrich | Oct 20, 2020 08:27pm | #2

   Check out fhb they have lots of info on insulation. Their podcast alone has hours on the issue. Air sealing is important. A good air barrier is going to be your most effective first step. If I were looking at a retrofit for a shop I'd seriously think of doing zip on the ceiling and tapeing it to get a good air barrier. I probably would not do drywall unless your code official requires it. I have osb on my shop ceiling (and walls), makes it easy to attach things in the future like power or dust collection.

   Assuming you have a vented roof, I found blown cellulose or fiberglass to be the best r for the dollar and effort. It is dirty but not hard or really expensive.

   If I were building from scratch is probably try to insulate at the roof deck instead of the bottom of the truss to allow room for routing things like dust collection, electrical, and some storage without getting into the headroom of the shop. That said my ceiling is pretty low and it is annoying.

3. 
   curmudgeon | Oct 21, 2020 09:56pm | #3

   Don’t know what your roofing material is, but particularly if it asphalt shingles, rolled roofing or simply tarpaper I do know you’re going to want an airspace between the underside of your roof sheathing and the insulation. Even with a vapor barrier. Else you’re gonna be replacing sheathing and maybe the trusses sooner rather than later. Moisture, humidity n eventual rot. Mold. That’s likely where LordU was headed with the vented comment. In other words, IMO don’t blow the cavity above your rigid foam full up to the bottom of the roof sheathing. If it’s not wood sheathing, well... I dunno. Best of luck, Sir!

4. 
   john_c2 | Oct 22, 2020 02:04am | #4

   With closed cell spray foam, you can have it sprayed directly onto the underside of the roof shearing. It also acts as a vapor barrier. And it has a higher R value than op en cell spray foam, which can't be sprayed directly under the roof.

5. 
   joeleonetti | Oct 22, 2020 03:54pm | #5

   For my attached garage, we live in a hot dry climate. I had them blow cellulose into the walls and ceiling. It made a noticeable difference. If I had to guess, the garage was cooler by at least 10 degrees.

6. 
   ysu65 | Oct 22, 2020 04:12pm | #6

   My shop has 2 x 6 sides and roof trusses. All insulated with R-19 fiberglass. Location is upstate NY. Never need AC in the summer, propane mobile home heater for the winter, burn a little over 100 gal in normal winter. -10 F outside, 35-36 F inside, no heat. (Now I know that if we get extended periods of cold, it will freeze inside but so far it has not happened.) I can't vent in the summer because the shop is so cool inside that the warm moist external air condenses on cast iron, not good.

   Good luck, insulate as much as you can afford now. Lower operating costs in the future.

7. 
   DRBWWing | Oct 23, 2020 06:32am | #7

   A lot depends on where you’re located. Spray foam is best, but several x the cost for maybe not much benefit in a shop.

   I don’t see how the rigid foam is going to make that much difference.

   A vapor barrier is probably a good idea, except you won’t know if your roof is leaking :-).

   I would talk to an insulation company ( if you can find one to do a small job). My experience is they can install it for a little more than you can buy it. If Imdont have to mess with insulation that’s a good thing!!

8. 
   Beasley7 | Oct 23, 2020 07:05pm | #8

   Not sure where in PA you are, I am in MD about 2 miles off the PA border. I recently upgraded my shop (2 car attached garage) with heat and insulation. The ceiling was dry walled so I just had insulation sprayed in. I costed out fiberglass and the materials were about $625 and I would have to do the work. I found a guy to spray insulation with better R value for $675. That was a no brainer. I have a small electric heater I run on medium setting and my shop stays a comfy 68 degrees all winter. If you are in south eastern PA, come back in this forum and I can give you his name & number.

9. 
   user-6822566 | Oct 23, 2020 10:45pm | #9

   Here in Wisconsin I have closed cell foam sprayed against the OSB roof boards and cedar siding boards of my shop. It's efficient and the most cost effective although initial cost is greater than alternatives. The greatest heat loss from my shop in the dead of winter is the concrete slab floor. The upside is that ground temperature transmitted up through the concrete cools the interior well into the summer and warms it into December.