Insulating 1940s wood garage in Maryland - Rockwool and closed cell foam?

[Rearviewmirror]

Hi all,

Long time reader, first time caller. We recently moved into a house in central Maryland, and the garage is going to be a multiyear project. Longer term goal is to turn it into an indoor gym while retaining parking.





I got a 14,000 BTU window AC for summer, which made it liveable, but my little space heater isn't cutting it in winter. I'm going to have to phase out the project a bit, but I was wondering if I could get some advice on the plan. I've had a couple of contractors come out, and they all recommended some configuration of spray foam and batts.

My main concerns are moisture control and making sure I don't do anything that'll degrade the structure.

My plan is:

Step 1) RockWool in the siding cavities (8ftx14.5"x3" thick)
Step 2) Pay a contractor to either spray foam or putt batts in the ceiling (the structure is about 20ft high and I don't have time/equipment for this step)

I'll do the walls myself with RockWool (either Safe n Sound or Comfortbatt - I have a golf simulator so would love to muffle the noise a bit for my neighbors but know it is lower R value than Comfortbatt).

I know I'll only see some small gains from insulating the walls, and that most bang for the buck will be the ceiling but this approach will save some $$$ and also get it a little warmer faster as I can knock this out over a weekend. I'm a bit torn on batts vs foam for the ceiling, as we get both super humid and also cold weather in Maryland. I'm also a bit concerned about off-gassing given it'll be a workout space.

A few questions:

1) Any concerns on this approach?
2) What do you think in terms of spray foam vs ceiling batts? I'm mainly worried about doing anything that impacts the structural integrity of the wood framing
3) Any rough sense on what total cost should be for the contractor portion? I'm guessing $1,500-$3,000?

Thanks in advance!

 

[Oatmealman]

I would do dense pack cellulose in the walls and if you can afford it spray foam in the ceiling, however before spray foaming, I would make sure the roof decking is good and won't need replacement anytime soon. Dense pack cellulose has a slightly lower r value than rock wool but it greatly inhibits air movement and is more rodent resistant than other options, It is more labor intensive if you are going to DIY it but the sound attenuation it provides is phenomenal. I dense packed my 26x28x8ft shop for about a grand and strived for a 4lbft compaction to maximize insulation and air movement, that being said it did take me about 8-10 hours of hanging/stapling/glueing the insulation netting and then another 4-5 hours of blowing insulation.

Eta: insulate your garage door as well and make sure the seals around the door fit tightly as these are large source of heat loss as well.

 

[Wubicon]

While planning my garage insulation project I looked into the spray foam on the underside of the roof decking. Someone on the forum pointed out that it's possible to get moisture build up between the roof deck and the insulation which will eventually cause the roof decking to rot.

My plan is to put gable or ridge vents in, (I already have soffit vents) and then I'll do an insulated ceiling. That way air can move into and out of the roof/attic area and I can keep the building space itself below that cooler in summer and warm it up faster in winter.

 

[mm08822]

While planning my garage insulation project I looked into the spray foam on the underside of the roof decking. Someone on the forum pointed out that it's possible to get moisture build up between the roof deck and the insulation which will eventually cause the roof decking to rot.

My plan is to put gable or ridge vents in, (I already have soffit vents) and then I'll do an insulated ceiling. That way air can move into and out of the roof/attic area and I can keep the building space itself below that cooler in summer and warm it up faster in winter.

X2 on this^^^^.
Adding the ceiling provides for insulation space as well as some storage. Put a hatchway or folding stairs in to access. Of course, sheathing for flooring.

Add soffit and ridge/gable vents.

 

[gimpyrobb]

Price out spray foam, its crazy.
If you can do the batts and not mind the itch for a weekend project I'd go that way. Also, use the highest r value that you can. It will still dampen the noise even if its not marketed as sound dampening.

 

[Wubicon]

X2 on this^^^^.
Adding the ceiling provides for insulation space as well as some storage. Put a hatchway or folding stairs in to access. Of course, sheathing for flooring.

Add soffit and ridge/gable vents.

Part of my planning was figuring where to store the stuff that I was storing up there. My plan is to only provide access up there for investigating/repairs. No storage. Just makes it easier. However, I'm lucky in that I have 2 other garden sheds that I can store stuff in.

 

[Rearviewmirror]

Thanks to everybody who has replied so far! I think I'm going to go Rockwool for the walls, primarily as it's relatively cheap and will hopefully take the edge off a little bit in winter (I know most heat is lost through the ceiling but that may need to wait until the new year from a project cost perspective).

I want/need to leave the ceilings vaulted to keep space for swinging a golf club and also doing overhead presses.

For the ceiling, I am a bit worried about what @Wubicon has mentioned in terms of moisture build up, and then also potentially creating a hot roof situation which will degrade the asphalt shingles more rapidly.

What do you think about an approach like this with roof baffles and insulation?

It seems like it would preserve the existing natural air flow to the roof.

If I did go that route, one challenge is that the ceiling rafter depth is only 5.5 inches - and so I'm not sure how high an R value I'd be able to go with insulation.

Would fibreglass be appropriate given my climate zone? I'm a bit unsure about the likelihood of mold/creatures given I'm in climate zone 4, and also whether batt facing should face in or out (we get 100ºF+ days and also snow, plus tons of humidity in summer).

 

[Rearviewmirror]

I spent a bit more time looking at the venting situation this morning, and I actually think the current setup is completely unvented - I thought there was a gap between the wall and roofline at the soffit to allow air flow, but it's actually just a crack (probably from the wood contracting and expanding over time).

Given that, is closed cell spray foam in the ceiling probably my best bet?

 

[Leaflessshadetree]

Give it some thought. If you are going to have a ceiling (which will allow for more insulation and reduce the volume of the space) get the framing in for it. I doubt you'll have enough height for a golf simulator. You may want raised rafter ties for other activities.
Then do the HVAC (window unit, mini-split, hanging heater?) wiring and lighting. Insulation and interior walls.
Honestly I don't know how to stretch the work into multi-years. Could be a few weekends.

 

[Skiff Builder]

On a garage with 5.5" rafters, I cut (2) 2" pcs of XPS rigid foam board and placed between rafters, leaving a 1.5" air gap next to the roof decking. Caulk/can foam to seal imperfections. Than placed another 2" XPS over the rafters for an R-30 assembly. Polyisocyanurate board would give you a bit more R value. This is a very light assembly, just measure/cut/place.
You would need ridge and soffit vents cut in -not very hard to do.
There is no fire resistance doing this, though looks like a detached bldg with no resistance now?

EDIT: Just priced out online-looks like $5.00 sq/ft material cost!

 

[bluedog225]

Foam would worry me. Modern mumbo jumbo aside, if it doesn’t breath, it dies. Vented has worked forever.

 

[Rearviewmirror]

Give it some thought. If you are going to have a ceiling (which will allow for more insulation and reduce the volume of the space) get the framing in for it. I doubt you'll have enough height for a golf simulator. You may want raised rafter ties for other activities.
Then do the HVAC (window unit, mini-split, hanging heater?) wiring and lighting. Insulation and interior walls.
Honestly I don't know how to stretch the work into multi-years. Could be a few weekends.

I don't want a ceiling as I want to retain the full height - the current rafter placement and height is perfect for what I want and need for both golf simulator and weight lifting. The project will mainly stretch over a longer period because I'm focused on getting to a more insulated conditioned space first (I already have a window unit and space heater) , and the next step will then be demoing and replacing the badly cracked floor slab.

On a garage with 5.5" rafters, I cut (2) 2" pcs of XPS rigid foam board and placed between rafters, leaving a 1.5" air gap next to the roof decking. Caulk/can foam to seal imperfections. Than placed another 2" XPS over the rafters for an R-30 assembly. Polyisocyanurate board would give you a bit more R value. This is a very light assembly, just measure/cut/place.
You would need ridge and soffit vents cut in -not very hard to do.
There is no fire resistance doing this, though looks like a detached bldg with no resistance now?

EDIT: Just priced out online-looks like $5.00 sq/ft material cost!

Super helpful - am I right in thinking you got to R30 by using three R10 2" XPS boards? The building is detached and also currently has no fire resistance. The plan is to leave it semi-finished so that I don't need to bother with permitting. I only need it to have some modicum of temperature control and half decent lighting. Final looks are unimportant.

 

[mepstein]

Insulating walls with rock wool is a good idea (I really like rock wool for a number of reasons) but will do very little until you do the ceiling. Especially in the winter.

 

[finn]

I used Rockwool for the first time this summer on a sauna building I put up.

I wasn’t particularly impressed, as I found it didn’t have very good structural integrity, ie it crumbled and broke apart easily when handling. If that happened to a piece, throwing it away and starting with a fresh piece was the best option.

It did seal up everything and the resulting noise level is low.

We did spray foam in a kitchen addition about eight or ten years ago, including the ceiling, walls, rim joist and basement walls.

The contractor added plywood or osb baffles to provide an airway from the soffit vent to ridge vent. I recall that he did an inch of closed cell, followed by a couple or more inches of open cell foam, at least on the ceiling, rim joist, and block basement walls. Not sure about the above ground 2x6” stud walls.

He was going to try a hot deck roof on a couple of rental cabins he was constructing for his side business to see how that worked out, but I never followed up on that “experiment “.

 

[Skiff Builder]

I don't want a ceiling as I want to retain the full height - the current rafter placement and height is perfect for what I want and need for both golf simulator and weight lifting. The project will mainly stretch over a longer period because I'm focused on getting to a more insulated conditioned space first (I already have a window unit and space heater) , and the next step will then be demoing and replacing the badly cracked floor slab.

Super helpful - am I right in thinking you got to R30 by using three R10 2" XPS boards? The building is detached and also currently has no fire resistance. The plan is to leave it semi-finished so that I don't need to bother with permitting. I only need it to have some modicum of temperature control and half decent lighting. Final looks are unimportant.

Yes, correct- 2 layers cut between the rafters and the final layer over top of all ( like drywall, on the surface of the rafter)

 

[kj_mustang]

Does the garage have a ridge vent installed? Using baffles is to allow air flow from the eaves up to the ridge vent.

 

[Rearviewmirror]

Does the garage have a ridge vent installed? Using baffles is to allow air flow from the eaves up to the ridge vent.

Not that I can tell - the roof has an uninterrupted ridgeline. I'm guessing they were keeping things pretty simple construction-wise for garages in 1942!

 

[Colin Len]

Your situation is very similar to mine with the exception that you have a more aggressive climate. I did a ton of research over the past few years in planning my remodel and unfortunately I don't think there are any surprise alternatives you haven't stumbled on yet. In order to do it "correctly" you need to either seal or vent the roof. In my research it does not see like hot roofs being dangerous to shingles is really a legit concern. But moisture build up is. Especially if you're going to use it as a workout room where you're going to be sweating and breathing hard.

The devil is in the detail so it's hard to say what's best for you. Personally, properly venting the roof was not a path I wanted to go down. Not only would it reduce the available space for insulation but it would require a lot of work (and cost) to install ridge and soffit vents. Similarly, cut & cobble with the rigid foam sounds like an absolute nightmare and likely still tough or impossible to seal properly. I'd try DIY spray foam before I tried cut & cobble.

I ended up choosing to throw caution to the wind since my climate is pretty mild. I know this is done regularly in my area even though it's not "correct". But, I also don't think I'll be creating much moisture in the space very often and if that becomes a concern perhaps I'll spring for a dehumidifier.



If I were in your situation I'd pay for the spray foam - either fully foamed or a sealing layer followed by batts. Although the cost for this would be fairly high I think it could still be well worth it compared to the work needed to vent everything.

Contrary to what someone else said I found Rockwool quite easy to work with and didn't fall apart at all. I mean, if you're careless, sure but it seemed perfectly durable to me during installation. Provides for a really neat and tidy install too. It's interesting you mention cost because when I priced things out, fiberglass was significantly cheaper. I opted for rockwool as it provides slightly better R value, is better with moisture and provides more sound mitigation. But if I was paying for spray foam on the ceiling I might consider using fiberglass in the walls to save some $.

Good luck!

 

[Rearviewmirror]

Your situation is very similar to mine with the exception that you have a more aggressive climate. I did a ton of research over the past few years in planning my remodel and unfortunately I don't think there are any surprise alternatives you haven't stumbled on yet. In order to do it "correctly" you need to either seal or vent the roof. In my research it does not see like hot roofs being dangerous to shingles is really a legit concern. But moisture build up is. Especially if you're going to use it as a workout room where you're going to be sweating and breathing hard.

The devil is in the detail so it's hard to say what's best for you. Personally, properly venting the roof was not a path I wanted to go down. Not only would it reduce the available space for insulation but it would require a lot of work (and cost) to install ridge and soffit vents. Similarly, cut & cobble with the rigid foam sounds like an absolute nightmare and likely still tough or impossible to seal properly. I'd try DIY spray foam before I tried cut & cobble.

I ended up choosing to throw caution to the wind since my climate is pretty mild. I know this is done regularly in my area even though it's not "correct". But, I also don't think I'll be creating much moisture in the space very often and if that becomes a concern perhaps I'll spring for a dehumidifier.



If I were in your situation I'd pay for the spray foam - either fully foamed or a sealing layer followed by batts. Although the cost for this would be fairly high I think it could still be well worth it compared to the work needed to vent everything.

Contrary to what someone else said I found Rockwool quite easy to work with and didn't fall apart at all. I mean, if you're careless, sure but it seemed perfectly durable to me during installation. Provides for a really neat and tidy install too. It's interesting you mention cost because when I priced things out, fiberglass was significantly cheaper. I opted for rockwool as it provides slightly better R value, is better with moisture and provides more sound mitigation. But if I was paying for spray foam on the ceiling I might consider using fiberglass in the walls to save some $.

Good luck!

Thanks very much Colin. That's really helpful. Your finished product looks great. I agree on Rockwool being pretty durable for me too, I think some sheets got a bit squished in transit, and they were a bit more breakable, but you can kind of just push offcuts in to offset any breakages.

I'm kind of where you are in terms of the amount of labor hours required to add venting or do all foam board pushes this project out of the realm of affordable.

I've contacted three different insulation companies to come out and take a look to get quotes, and I haven't said anything other than "I want to get my garage insulated". Then I'll see if a consensus emerges amongst them on what the most suggested approach is. I am also leaning towards some form of spray foam/sealed roof as it honestly sounds like the best option for a structure of this age/in this state.

If none of the firms suggest closed cell spray foam without being prompted then I might be back to the drawing board, but hoping this is as least a semi-sensible path forward.

It's a good flag on moisture build up for a gym, but honestly it's never likely to be more than 1.5hr sessions at a time, and it's a 17x19ft space with probably 20ft from floor to ceiling at its apex, so I'm not sure if that'll push humidity up much at all in winter, and in summer I would be running the window AC unit anyway, which should act to de-humidify it a bit too. I'll ask the contractors anyway, and see what they think. Similar to you, a dehumidifier would likely be cheaper than venting the whole structure!

 

[Colin Len]

It's a good flag on moisture build up for a gym, but honestly it's never likely to be more than 1.5hr sessions at a time, and it's a 17x19ft space with probably 20ft from floor to ceiling at its apex, so I'm not sure if that'll push humidity up much at all in winter, and in summer I would be running the window AC unit anyway, which should act to de-humidify it a bit too. I'll ask the contractors anyway, and see what they think. Similar to you, a dehumidifier would likely be cheaper than venting the whole structure!

I think you might be surprised how much moisture you could create, especially in such a small space - coincidentally mine is the exact same size. Everyone think's it's a regular 2 car garage but boy oh boy is it tiny once you start trying to park cars and work inside. In reality ours are 20% smaller than a standard 20x20 (which nowadays is on the small side and I'm seeing more and more 20x24 or larger). Sure would be nice! My height is lower though, ~12' to the top of the peak.

Speaking of height... 20' on yours seems crazy and I am wondering if that's correct. Your door has 4 panels and the top of the opening looks closer to your top plate than mine so I think your walls are actually shorter than mine. Your roof pitch is definitely steeper but assuming a similar wall height you'd need a steeper than 12/12 pitch to get you to a 20' height. Based on the photos I bet your height is closer to 14-16" and maybe a ~8/12 roof pitch.

 

[Rearviewmirror]

I think you might be surprised how much moisture you could create, especially in such a small space - coincidentally mine is the exact same size. Everyone think's it's a regular 2 car garage but boy oh boy is it tiny once you start trying to park cars and work inside. In reality ours are 20% smaller than a standard 20x20 (which nowadays is on the small side and I'm seeing more and more 20x24 or larger). Sure would be nice! My height is lower though, ~12' to the top of the peak.

Speaking of height... 20' on yours seems crazy and I am wondering if that's correct. Your door has 4 panels and the top of the opening looks closer to your top plate than mine so I think your walls are actually shorter than mine. Your roof pitch is definitely steeper but assuming a similar wall height you'd need a steeper than 12/12 pitch to get you to a 20' height. Based on the photos I bet your height is closer to 14-16" and maybe a ~8/12 roof pitch.

Yes you're right, it is probably closer to 16' high. The cross beams are around 8.5' high and that's about half the total height.

 

[kj_mustang]

You need at look at the historical humidity levels for your area in the summer also. If the doors and/or windows are open much, it could get higher levels inside, then you will need to condition the air.

 

[Rearviewmirror]

First quote today and interestingly he was suggesting open cell foam to let the roof deck breathe better and also prevent moisture build up. He thought I could get to R20 with 5.5" of open cell.

Next contractor couldn't come out until Jan 14, so will report back once I hear from him.

 

[Colin Len]

First quote today and interestingly he was suggesting open cell foam to let the roof deck breathe better and also prevent moisture build up. He thought I could get to R20 with 5.5" of open cell.

Next contractor couldn't come out until Jan 14, so will report back once I hear from him.

That is precisely opposite of everything I've ever read about spray foam. Everything I've read says to use closed cell and that open cell will create the same moisture issues as just using regular batt insulation. Open cell would work if the roof was vented. But unvented you need the closed cell to provide a non-permeable insulation barrier just under the roof deck. At least that's everything I've ever read.

 

[kj_mustang]

I agree with Colin. A roof is either vented or non vented. Vented roof has many insulation options but you have to maintain the vent path. Unvented roof you have to worry about climate control on the inside depending on your usage and the exterior climate. Open cell foam is not a water vapor barrier and will allow it to pass from the interior to the roof deck.

 

[Rearviewmirror]

I agree with Colin. A roof is either vented or non vented. Vented roof has many insulation options but you have to maintain the vent path. Unvented roof you have to worry about climate control on the inside depending on your usage and the exterior climate. Open cell foam is not a water vapor barrier and will allow it to pass from the interior to the roof deck.

Yeah the current roof is unvented, but it's also an old wooden building, so I'm wondering if some degree of breathability is preferable. I'll report back once I hear from the other companies.

 

[Rearviewmirror]

Alright! Bumping an older thread as I just pulled the trigger and I couldn't be happier. One other really nice upside is that the white foam also makes the whole space seem much brighter and cleaner!

$2,900 all in.