Insulating detached garage shop

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Forum topic by nickajeglin posted 07-16-2019 01:12 PM 1835 views 0 times favorited 32 replies Add to Favorites Watch
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9 posts in 642 days

07-16-2019 01:12 PM

Hello everyone, I recently bought a house and I’m planning on moving my woodworking shop from my parent’s basement to the detached garage. The only problem is that it’s unbearably hot.

I’m wondering the best way to insulate and heat/cool it enough to work out there. It’s a sloped roof with no soffits.
I did a little research, so I feel pretty confident that the walls aren’t too hard. I would just put 2×4 framing right up on the cinder block, roll out fiberglass between the studs, and nail on drywall, OSB, or plywood.

I’m more confused about how to handle the roof. I see two or 3 possible options:
1) Treat it exactly like the walls: roll out fiberglass, and cover it up. pros: I keep the wood storage in the rafters, high ceilings are nice cons: requires more sq. ft of insulation, I have no idea how to handle ventilation.
2) Build a ceiling, and insulate that from above pros: less insulation needed. cons: I lose the wood storage space and the ceiling is lowered.
3) Build a mini-ceiling about halfway up the roofline so I have a trapezoid shaped ceiling. pros: I keep some storage space, maybe ventilation is easier, it takes slightly less insulation material. cons: ?

With respect to heating and cooling, I don’t need it to be 70F year round, just bearable. Like between 40 and 80. This makes me think that insulating the ceiling is probably enough, and then adding a window unit and space heater would probably do it.

From the small amount of research I’ve done and just general knowledge, I understand that ventilation is super important when it comes to the roof, but I don’t really know the best way to approach this since there aren’t any soffits to place vents in.

Can someone with more experience point me in the right direction? Especially when it comes to how to correctly provide air flow for the roof. I’m leaning towards option 3 right now, as keeping the wood storage is pretty important to me, and it seems like it might make ventilation easier.

I uploaded some pictures here

(This is crossposted from the homerefurbers forum as it doesn’t seem quite as active as this one.)

32 replies so far

View PaulDoug's profile


2524 posts in 2759 days

#1 posted 07-16-2019 02:33 PM

The walls look like they are block, so shouldn’t need a lot of insulation, if any to keep it “bearable” so I would concentrate on the ceiling. Might check on what it would cost to have sprayed on insulation sprayed on it. Or get rolls of insulation and staple it in place, then cover with drywall. Looks like 2×6 or 8 boards up there. I’d make sure it can support the drywall/insulation. I am do expert, so maybe ask some local experts. The roof doesn’t look like it was built to handle a lot of weight, maybe have to beef it up some. Don’t know were you live, do you have to worry about snow weight?

-- “We all die. The goal isn't to live forever; the goal is to create something that will.” - Chuck Palahniuk

View Robert's profile


4522 posts in 2536 days

#2 posted 07-16-2019 02:37 PM

90% of your heat gain is from the roof. In the winter, the walls will work against you.

For now, I wouldn’t insulate the walls. I would install a ceiling (2×6 joints) and R19. Plywood or sheet rock for the ceiling. There are other options such as rigid foil coated sheets. Not sure about applying right next to wood.

That said, my first choice would be spray foam applied directly to the bottom of the roof. Its such a small job you may have trouble getting it done. There are place that will rent a foam machine. Factor the coast against all the carpentry, insulation, soffits and time.

-- Everything is a prototype thats why its one of a kind!!

View Hammerthumb's profile


3088 posts in 3030 days

#3 posted 07-16-2019 03:06 PM

You could re-roof with an insulated roof. Foam on top of existing sheeting, another layer of sheeting on top of foam, then a new roof.

-- Paul, Duvall, WA

View Knockonit's profile


797 posts in 1257 days

#4 posted 07-16-2019 03:12 PM

for the walls, look into foam with furring strips in it for attachment and for ext wall finish, foam is a better insulator than batts on block, and takes less room out of work space. pending where you are might consider a moisture barrier, since i live in the desert, we dont’ worry much about it, but at one time did live in south bend in for a few years and the moisture there was troublesome
Rj in az

-- Living the dream

View Delete's profile


439 posts in 1427 days

#5 posted 07-16-2019 03:12 PM

I couldn’t see your pictures so I probably shouldn’t comment, but here is one idea you may want to adapt to your situation. Foam is nice but some prefer to avoid chemical formulas even if they are solidly approved. For smaller jobs fiber insulation (fiberglass, roxsol, etc.) can be easier and cheaper.

Your option #3 is probably the best of both worlds (high ceiling, low ceiling). Heres a quick sketch of how I do a ceiling like that. Condensation will reduce the efficiency of your insulation, air movement is important. Don’t forget to include a vapor barrier between your insulation and interior wall finish.

Edit: There is an additional benefit to this method. You probably don’t have problems with roof loads such as snow, but if you did or experience volatile weather, the triangulation of the roof rafters will greatly strengthen your roof assembly.

View controlfreak's profile (online now)


1986 posts in 657 days

#6 posted 07-16-2019 03:19 PM

Foam the roofline, it is by far the best way and would leave a higher ceiling for storage. I would not attempt to do foam yourself. The guys that do it usually have pressurised suits to keep the chemicals out of their eyes. They say everything takes on a rainbow tint after it hits your eyes. The walls you may be able to do slats with foam boards but you may want to watch the moisture level to prevent mold.

View clin's profile


1128 posts in 2051 days

#7 posted 07-16-2019 05:13 PM

Moisture issues can be very specific to where you are located. I’d make sure to find out what best practices are in your area. Generally you want to do everything you can to seal the outside. But that is already done, well or not.

The general issue is water vapor passing through the insulation and condensing on cold walls or roof. This for example is why attics are often vented. Any moisture that gets up there has a place to go. There are ways to keep insulation off, but close to a roof and vent it. Usually through soffits (which you don’t have). This is why spray foam can work so well. It seals and ensures no water vapor can reach it.

That said, I’ve also heard that moisture getting in from the outside tends to be the real issue, and the better sealed it is on the inside, just makes it hard for the moisture to dry. This brings me full circle to finding out what is best and common in your area. Often it is a compromise for what is best most of the time. And you’ll need to factor in the details of how the existing structure has been built. What’s best for a stud wall is probably not what is best for a block wall.

Bottom line, get some local expert advice. You don’t want to create a rot or mold problem.

I also think there will be a way to insulate the roof without forming an attic and therefore make use of the overhead space for storage. I think you’re making too much out of the added insulation. Unless the roof is abnormally steep, I doubt the roof area is that much more than the ceiling area.

On that note: Storing lots of wood can be heavy, make sure the roof structure can support that. If not, reinforce as necessary.

-- Clin

View CaptainKlutz's profile


4349 posts in 2550 days

#8 posted 07-16-2019 05:59 PM

Hmm, lot of ways to do this?

Open soffit roof on block walls is old school way to build forging or metal fabrication work shop in ‘mild’ climates?
Current building codes would require some changes to that roof structure. Looking at the roof boards, appears there are replacements, and some with old water damage?

So first:
Suggest you call 3-4 roofing companies and get quotes/designs from them about best way to insulate and deal with that roof. Be sure to ask about any deficiencies in roof that would be upgraded as part of insulation work. This will give a solid direction on methods and costs involved.
Last thing you want to do is insulate the inside, and have leaks to learn you need a new roof. If need a new roof, then option to add reflective foam insulation boards under the sheeting/shingles will be great start to reducing the heat load and might leave you a more open attic area for storage.

+1 Use foam board on walls with furring strips.

+1 Must plan for moisture control.
Be sure to seal the inside of block with water proofing cement paint, and put a moisture barrier under the wall sheeting. Water goes right through block, and then acts sort of like a sponge. Water is always there, till it completely dries out. With painted outside surface slowing moisture transfer, completely dry block walls will never happen.

Best Luck.

-- If it wasn't for bad luck, I wouldn't have no luck at all, - Albert King - Born Under a Bad Sign released 1967

View therealSteveN's profile


7493 posts in 1629 days

#9 posted 07-16-2019 07:19 PM

That said, my first choice would be spray foam applied directly to the bottom of the roof. Its such a small job you may have trouble getting it done. There are place that will rent a foam machine. Factor the coast against all the carpentry, insulation, soffits and time.

- Robert

I agree spray foam is going to be the most economical answer. A person can buy 2 tank mix systems that blow through a $50.00 handset. Not something you are going to go into business with, but for that 40 minute job, more than sufficient. Enough foam to do that is 600 bux, possibly less with the wonders of the innerweb. Add a few bux and you can do the walls. The wonderous thing they are finding about foam it just plain seals out everything, moisture as well as temp. So it’s fine to spray it shut, no worries about moisture causing mold from no air movement, there is none of either. For that reason I would replace the door, spray it closed, and just put in electrical lighting. I agree, not much for mood, but for the lowest cost to get there, it will work.

Also can’t tell from the pic, and didn’t see anything written. What is the floor? Dirt = BAD. Concrete will help cool in the heat, but totally the opposite in the cold, but hard on your legs, and back. But if it’s concrete you can always put foam mats in front of your standing spots. Enough concrete and you can keep the place closed in the Summer, and stay cool enough with a few well placed fans, ceiling are best. In the Winter, you need a heat source, and probably a vented one if you foam it closed.

My concern is all that glass. I’m betting it’s all single pane, leaks like a sieve construction. With that glass in the peak it will be like keeping the main door open all the time, heat, and or cooling are gonna roll right out. Worst of that is it’s a great source of natural light. What a dogfight.

-- Think safe, be safe

View therealSteveN's profile


7493 posts in 1629 days

#10 posted 07-16-2019 07:25 PM

Open soffit roof on block walls is old school way to build

- CaptainKlutz

Except for the windows our first place was almost the same building. I put the shop in the basement. For the first bit every penny was going to something other than a shop. I was at ShopSmith then, so the tools I had went downstairs. Soon enough money wasn’t as tight, and I ended up going out and renting a shop space. kept that place 29 years. Except for paying the rent that is the way to go. :-)

-- Think safe, be safe

View bigJohninvegas's profile


978 posts in 2517 days

#11 posted 07-17-2019 02:22 AM

I agree with captainklutz.
Generally estimates are free. I would call a couple roofing contractors and see what they recommend.
Maybe it’s work you can then handle yourself, or maybe you find out you need a pro.
But if you get it wrong, you will cause all sorts of problems.

-- John

View Jim Finn's profile

Jim Finn

2877 posts in 3977 days

#12 posted 07-17-2019 09:31 AM

The roll up garage door should be insulated using styrofoam sheets. I have done this on two different roll up doors with success.

-- No PHD just a DD214 Lubbock Texas

View Snipes's profile


459 posts in 3300 days

#13 posted 07-17-2019 12:24 PM

Those rafters are not equipped to handle much storage as they are. I would spray foam directly to roof myself. There’s tons of misleading info on hot roofs, roofers will tell you one thing insulators another. It would be the same as sip, and i have had no issues. Also spraying yourself is not worth it imo, cheaper to hire it done.
Regarding walls, put rigid foam against block, and then use either 2×4 or 1×4 flat to save space.

-- if it is to be it is up to me

View dhazelton's profile


2839 posts in 3352 days

#14 posted 07-17-2019 02:25 PM

Everyone is saying spray foam. I agree but just want you to be sure to use CLOSED CELL spray foam. It’s impermeable to moisture and a couple inches of that is an effective air barrier – more than a couple of inches is just a waste of money. You don’t need venting because now your roof deck won’t have warm moist air coming into contact with it in the winter so rot is not an issue. If you go that route you may want to install a couple of ceiling fans to keep the warm or cool air down low where you want it.

View nickajeglin's profile


9 posts in 642 days

#15 posted 07-18-2019 03:23 AM

Thanks for the good advice everyone. I’m in Nebraska. Spray foam seems to be the consensus, but I am worried that it could hide any leaks from above and hold water there. I totally agree that the rafters need reinforcement. There aren’t even any cross beams in the front half, and I can see cracks above the garage door where the roof has been trying to spread the walls.

Considering everything, I like the idea of stripping the roof down to the sheathing and adding a adhered water barrier, and then an insulated roof and new shingles. That would also probably allow me to extend the roofline out past the walls to keep water away from them, and possibly add soffits, internal insulation, and correct ventilation.

That does sound like a project that is too big and expensive for me right now though, so I’m leaning towards something like Carlos drew. That would add some extra support to the rafters, and then I’d also double up the current cross beams for wood storage. When the shingles inetivably need to be replaced, I can add the exterior insulation etc if needed. I will definitely find someone local to come check it out before I start.

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