Garage ceiling insulation question.

[GarageGuyNY]

Hello,

I'm trying to figure the best way to go about insulating the ceiling of my garage.

I have a 20'x20' detached unfinished garage that I'd like to insulate and heat. The roof is a pyramid hip style that is about 13' at its peak and is not vented. The studs and rafters are 2'x4' and are 24" OC. The walls are going to be insulted with fiberglass insulation and most likely be covered in plywood or Sheetrock, and I plan on heating the garage with a 26,000BTU 220 electric forced hot air heater.

I've considered spray foam, but around here they want $3.25 a square foot for 2" (R12) which is pricy for me. And on top of that is very flammable and would either require a special fire retardant coating applied if left uncovered, or sheetrock. Probably end up costing me $2,000 just to insulate and close up the ceiling.

My second option was installing 2" thick rigid foam panels that would also give me an r12. I can do that for around $600 and don't think I'd need to Sheetrock.

My third and final option would be fiberglass bats which would give me an r13. I can do the ceiling for about $300+ sheetrock which is nice. My question is, will I have issues with mold using fiberglass insulation since the ceiling is not vented at all?

Here are some pics of my garage. Thanks

 

[Radix2]

Rigid foam is just as flammable as the spray foam, so same issue if you want it firesafe.

Personally I think the only options are spray foam and drywall with no venting or add venting and go with batts and drywall.

 

[GYPSY400]

Batt insulation with good vapor barrier tape job and add in attic venting.. does the outside walls have eve's?

Sent from my SM-G903W using Tapatalk

 

[Jlbc212]

Go with your third option and cut some vents into the roof (a relatively easy job to do).

 

[GarageGuyNY]

So it seems like the general consensus would be to have adequate venting if using fiberglass batts. How would I vent in this scenario? Since it's a pyramid shaped roof I can't install a ridge vent. I do have eaves.

 

[Pen & Wrench]

Are you building an "attic"? or would the fiberglass batts be put right up against the roof sheeting? If you build an attic structure, you could do soffit and roof vents, but I'd probably opt for 2 gable end vents on each end for a total of 4, not sure how you would vent it if there is no air space between the ceiling insulation and the roof.

 

[GarageGuyNY]

There's not going to be an attic. As pricey as it is, looks like spray foam and Sheetrock are my best bet.

 

[Colin Len]

Glad I ran across this thread. I'd been thinking about spray insulation for my garage (similar to your situation but standard gable roof instead of pyramid) but assumed it would be OK to just leave it exposed (although it wouldn't look awesome). I have some added bracing up there because the roof was sagging and needed to be shored up so doing drywall around all of that I think will be a pain.

I'm not sure how I feel about setting up venting and I really liked the concept that the foam seals and insulates at the same time. I suppose I'll have to just come back to this in a couple years when I'm ready to renovate my garage and make my decision then.

Are you planning to spray the ceiling and then use batts for the walls to save money? That's what I was thinking.

 

[GarageGuyNY]

Glad I ran across this thread. I'd been thinking about spray insulation for my garage (similar to your situation but standard gable roof instead of pyramid) but assumed it would be OK to just leave it exposed (although it wouldn't look awesome). I have some added bracing up there because the roof was sagging and needed to be shored up so doing drywall around all of that I think will be a pain.

I'm not sure how I feel about setting up venting and I really liked the concept that the foam seals and insulates at the same time. I suppose I'll have to just come back to this in a couple years when I'm ready to renovate my garage and make my decision then.

Are you planning to spray the ceiling and then use batts for the walls to save money? That's what I was thinking.

Yes, after considering my options, I will be spray foaming and sheetrocking the ceiling and use batts and either Sheetrock or plywood on the walls. I too like the idea that it completely seals everything. I calculated 440sf of ceiling @ $3.25 a sf for 2" of foam (r12) it's going to cost me around $1,430, plus another $200 in Sheetrock. It's considerably more than I was looking to spend but it's gotta be done right. I don't want the headache of having to deal with moisture issues down the road.

 

[BearsFan315]

Just did mine, put in R15 in the rafters over vents, so it could breath. one concern was the deterioration of the shingles and under layment if the deck is not vented. did not want to void my warranty on my NEW roof & shingles.

Garage Roof/ Rafter Insulation...

Vents were about $100 to do 20x30, insulation was another $450 then about 2 days of work.

 

[GarageGuyNY]

I have the Spray Foam Guys coming to give me an estimate tomorrow. He said that they do both closed and open cell spray foam and suggested that I really don't need closed cell for my ceiling. I see allot of contridicting info on the net on closed vs open cell foam for ceilings. What are your thoughts?

 

[bczygan]

You need way more than R12. Try R38

 

[Colin Len]

I have the Spray Foam Guys coming to give me an estimate tomorrow. He said that they do both closed and open cell spray foam and suggested that I really don't need closed cell for my ceiling. I see allot of contridicting info on the net on closed vs open cell foam for ceilings. What are your thoughts?

All of the reading I've done has said that closed is the way to go. I'm not sure if there's a price difference or not but the closed cell will seal everything up whereas the open will be permeable. Closed will better help seal air, and in turn, moisture. I'm not sure if there are any benefits to open cell (maybe price?) but seems to me that closed is the way to go.

 

[GarageGuyNY]

You need way more than R12. Try R38

I have 2x4 joists.

 

[GarageGuyNY]

All of the reading I've done has said that closed is the way to go. I'm not sure if there's a price difference or not but the closed cell will seal everything up whereas the open will be permeable. Closed will better help seal air, and in turn, moisture. I'm not sure if there are any benefits to open cell (maybe price?) but seems to me that closed is the way to go.

Open cell is 50 cents an inch (R4 per inch thick)

Closed cell is $1.50 an inch (R6 per inch thick)

I was thinking I could maybe do 1" closed cell (which I'm thinking should give me my vapor barrier), and fill the remaining 2.5"s of the joists with open cell. That in theory should give me an R16 for the same price that I would have paid for just 2" of closed cell at only an R12.

Hmmmmm...

 

[forAK]

What about adding an attic? You could square off the ceiling a little lower then blow in some cellulose and have a ton more insulation. Looks like the center peak is at about 14 or 15'. Bring it down and flatten it off on the inside unless you're putting in a 2 post.

 

[Colin Len]

Open cell is 50 cents an inch (R4 per inch thick)

Closed cell is $1.50 an inch (R6 per inch thick)

I was thinking I could maybe do 1" closed cell (which I'm thinking should give me my vapor barrier), and fill the remaining 2.5"s of the joists with open cell. That in theory should give me an R16 for the same price that I would have paid for just 2" of closed cell at only an R12.

Hmmmmm...

Wow, that's a big difference! Bad assumption on my part. I like that idea though - lay down an air tight layer then cover up with a cheaper thermal barrier. I'm interested to see what the insulation company would have to say about that.

 

[DC73]

. . . I was thinking I could maybe do 1" closed cell (which I'm thinking should give me my vapor barrier), and fill the remaining 2.5"s of the joists with open cell.

Go to GreenBuildingAdvisor.com and pose your questions in their Q&A forum. They have some building science gurus who frequent the forum and can set you on the right path. It's more complicated than others make out and the details can be highly climate specific. The guys at GBA can calculate for you the minimum amount of closed cell foam you need to avoid condensation issues. Once you get that minimum, you can fill the rest of the cavity with open cell, fiberglass, mineral wool, etc.

Research "flash and batt", "unvented attics", and "cathedral ceilings" on GBA and on BuildingScience.com and you'll get plenty of good info to help you.

DC

 

[bczygan]

I have 2x4 joists.

You have 2x4 rafters.

Fill them full with closed cell and add a layer of rigid foam 2". then drywall, if the spans will allow it.

What do you have tying the walls together? And is it a ridge board? If so, I've seen them fail when the walls bow out from too few ceiling joists. One across the street from me is sway backed, bowed out walls, and about to collapse.

What is the roof deck? And how many layers of shingles, and what type?

More photos? The one I see shows a structure just as I describe, that is woefully inadequate to support drywall, and may even have difficulty with any additional reworking.

What you need, is ceiling joists spaced appropriately, and fastened to the top plates with metal fasteners, so as to hold the side walls together. It looks like you have a metal cable trying to hold the walls from bowing out. This won't do.
Bill

 

[Jlbc212]

After examining the posted picture I suggest you install a suspended ceiling with fiberglass batts laid over the suspended ceiling. You can also install the lights in the suspended ceiling. Place some roof louvers on two or more sections of the roof or add a cupola to the peak. Quick, cheap and allows for plenty of insulation.

 

[GarageGuyNY]

What about adding an attic? You could square off the ceiling a little lower then blow in some cellulose and have a ton more insulation. Looks like the center peak is at about 14 or 15'. Bring it down and flatten it off on the inside unless you're putting in a 2 post.

I was thinking about that originally, but the roof is completely unvented so might not work out well.

 

[GarageGuyNY]

Wow, that's a big difference! Bad assumption on my part. I like that idea though - lay down an air tight layer then cover up with a cheaper thermal barrier. I'm interested to see what the insulation company would have to say about that.

The rep came over this afternoon to give me an estimate. He suggested 3" of closed cell for the ceiling, which would give around an R18. He measure 430sf for the ceiling @ $450bf for 3" of closed cell, which came out to $1,935.

He also suggested that I really didn't need to cover up ceiling with sheetrock, if I didn't want to. I'm not too sure about that. I've read that that stuff needs to be covered up.

 

[GarageGuyNY]

Go to GreenBuildingAdvisor.com and pose your questions in their Q&A forum. They have some building science gurus who frequent the forum and can set you on the right path. It's more complicated than others make out and the details can be highly climate specific. The guys at GBA can calculate for you the minimum amount of closed cell foam you need to avoid condensation issues. Once you get that minimum, you can fill the rest of the cavity with open cell, fiberglass, mineral wool, etc.

Research "flash and batt", "unvented attics", and "cathedral ceilings" on GBA and on BuildingScience.com and you'll get plenty of good info to help you.

DC

Great suggestion. I'll do that. Thanks

 

[GarageGuyNY]

You have 2x4 rafters.

Fill them full with closed cell and add a layer of rigid foam 2". then drywall, if the spans will allow it.

What do you have tying the walls together? And is it a ridge board? If so, I've seen them fail when the walls bow out from too few ceiling joists. One across the street from me is sway backed, bowed out walls, and about to collapse.

What is the roof deck? And how many layers of shingles, and what type?

More photos? The one I see shows a structure just as I describe, that is woefully inadequate to support drywall, and may even have difficulty with any additional reworking.

What you need, is ceiling joists spaced appropriately, and fastened to the top plates with metal fasteners, so as to hold the side walls together. It looks like you have a metal cable trying to hold the walls from bowing out. This won't do.
Bill

To be honest I really didn't put too much thought into the structure in regard to how it will handle the added weight of sheetrock and insulation. I'll take some pictures later and post tonight.

To answer some of your questions, here's what I do know:

Joists are 24" OC

Roof deck consists of 1"x 8" tongue and groove planks.

There appears to be one layer of asphalt shingles with tar paper unerneath.

There are metal bars with turn buckles that cross each other that appear to be there to keep all four walls from bowing out.

 

[rayra]

So it seems like the general consensus would be to have adequate venting if using fiberglass batts. How would I vent in this scenario? Since it's a pyramid shaped roof I can't install a ridge vent. I do have eaves.

cupola.

 

[rayra]

I have 2x4 joists.

Sister the joists to double their depth and structural support, shoot the ceiling with spray foam, have it ground level with the joists. Then add layer(s) of rigid foam insulation before capping with 1/4" drywall for a cosmetic surface.
Put a thick insulation cap under that roof. You're in NY.

 

[rayra]

After examining the posted picture I suggest you install a suspended ceiling with fiberglass batts laid over the suspended ceiling. You can also install the lights in the suspended ceiling. Place some roof louvers on two or more sections of the roof or add a cupola to the peak. Quick, cheap and allows for plenty of insulation.

AND if new spanning ceiling joists are added, no load on that flimsy roof.

 

[rayra]

scratch all that. Seriously consider adding some horizontal 2x6 joists at about the level of your fluorescent fixtures, converting that open roof layout into an A-truss design. That will retain some ceiling height while also allowing a big increase in ceiling / roof insulation.

That will help forestall the walls bowing out and stiffen up your roof for both internal and external loads. The sight of those cable stays and the thought of a heavy snow load makes me cringe at what would happen if one of those cables snapped while there was a heavy snow load.

 

[GarageGuyNY]

Sister the joists to double their depth and structural support, shoot the ceiling with spray foam, have it ground level with the joists. Then add layer(s) of rigid foam insulation before capping with 1/4" drywall for a cosmetic surface.
Put a thick insulation cap under that roof. You're in NY.

If I'm understanding you correctly, you're suggesting doubling the depth of rafters by sistering the joists, then fill that flush with spray foam, then add layers of rigid foam on top of that?

Seems to me like the cost would outway the benefit. We're talking about $4,000 in spray foam alone + lumber + rigid foam insulation panels.

I know that for a home and conserving energy we need to get the R value way up in the ceilings, but my objective is to be able to heat my garage with a 7500 watt 220 electric heater and keep it at comfortable temperature when I'm in there working once and a while.

I've used propane heaters in the garage as it sits right now in the dead of winter and am able to work in a t-shirt. The issue is that I have to keep that sucker running full blast to keep up with the heat loss.

I'm no expert (and I sincerely appreciate all your advice) but I have to think that R19 closed cell foam in the ceiling and R13 batt insulation on the walls would be a rather drastic improvement, don't you think?

 

[GarageGuyNY]

scratch all that. Seriously consider adding some horizontal 2x6 joists at about the level of your fluorescent fixtures, converting that open roof layout into an A-truss design. That will retain some ceiling height while also allowing a big increase in ceiling / roof insulation.

That will help forestall the walls bowing out and stiffen up your roof for both internal and external loads. The sight of those cable stays and the thought of a heavy snow load makes me cringe at what would happen if one of those cables snapped while there was a heavy snow load.

This was actually my first thought. but don't I need adequate venting of the "attic" roof for this?

 

[forAK]

cupola.

Here's your venting. Along with punching in some holes along the eave.

 

[Radix2]

I don't know where you guys get that this roof is weak...or at least weak in the way claimed here.

Properly constructed, a hip roof like this has no force to bow the walls out ( I don't know why they have those turnbuckles either). In this design all of the thrust is directed into the corners by the hip rafters and shows up as a tension along the length of the side walls. The rafters running from the hip rafters to the walls cannot push the walls out unless the hip rafters fail in compression or come off the corners.

If wires are used at all for this they should be across the corners or made into a hoop around the walls. What is installed there makes no sense.

This roof is not like a normal gabled roof that needs ties between the walls to counteract the fact that the normal ridge construction is too weak to prevent it from bowing, which directly results in the walls being forced out. Here there is no ridge and so the forces act on the corners which is a stable geometry.

I make no comment on the sizing of rafters on this particular example, but on the geometric strength of the design.

 

[Jlbc212]

I installed overhead doors in many garages exactly like yours. Many had tin ceilings nailed to 1x3 wood laths which were nailed to a couple of widely spaced 2x4 joists spanning the width of the garage. I still believe your cheapest, easiest and best insulation alternative, as i suggested before, is to put in a suspended ceiling, with fiberglass batts laid over the suspended ceiling panels. Fiberglass insulation weighs very little. You could easily put a double layer of R38 or greater (overkill). Add a couple of roof louvers in the roof and your done.

 

[GarageGuyNY]

I installed overhead doors in many garages exactly like yours. Many had tin ceilings nailed to 1x3 wood laths which were nailed to a couple of widely spaced 2x4 joists spanning the width of the garage. I still believe your cheapest, easiest and best insulation alternative, as i suggested before, is to put in a suspended ceiling, with fiberglass batts laid over the suspended ceiling panels. Fiberglass insulation weighs very little. You could easily put a double layer of R38 or greater (overkill). Add a couple of roof louvers in the roof and your done.

I think I'm kind of liking the idea of the drop ceiling

It's light

Probably cheaper when all said and done as compared to spray foam and Sheetrock

Easy to insulate with batts

Have access to the attic via panel removal if ever I have any issues with the roof

And the lights I have came out of a drop ceiling so they should work and look nice too!

 

[GarageGuyNY]

I've been doing some more thinking. I'm coming around to the idea of a ceiling/attic setup but not sure if a drop ceiling is the best option.

The drop ceiling will limit me in terms of having the flexibility to hang things from the ceiling such as cord reals and an overhead garage door.

If I frame out a ceiling as others have mentioned before that should allow me to hang and attach things from it. I was thinking that instead of drywall, I can use white corigated metal paneling like what's used in steal buildings. That way I don't have to tape/compound and paint, and if ever there is an issue with the roof, I can just unscrew a panel.

As far as the structure is concerned, would it be ok to attach the new horizontal joists that would span from one side of the garage to the other, to the old rafters? In theory I would thing that adding these joists would add even more strength to the roof, right?

 

[BADSIX]

good idea dropped ceiling. your going to stretch a 2x4 or 2x6 20 feet then hang sheet rock or steel that's going to be heavy ,your going to need some engineering.
Jay D.

 

[493 scamp]

Is that Big block going in the Dart? My Scamp has a stroked 440 (493)
I am looking to insulate my pole barn as well. Probably not going to happen before winter hits due to costs. Hope you do better.

 

[GarageGuyNY]

Is that Big block going in the Dart? My Scamp has a stroked 440 (493)
I am looking to insulate my pole barn as well. Probably not going to happen before winter hits due to costs. Hope you do better.

Yes, it's a 383 big block pulled out of a 68' Charger. Also have an 8-3/4 Suregrip with 3.23 gears and a 727 ready for rebuild.

So busy working on the house and doing yard work during the warmer months, that the only time I have to give my hobbies any attention is during the colder months. It's just tough to work comfortably in a cold garage.

 

[GarageGuyNY]

good idea dropped ceiling. your going to stretch a 2x4 or 2x6 20 feet then hang sheet rock or steel that's going to be heavy ,your going to need some engineering.
Jay D.

I'm probably going to use 2"x6" 16' joists and attach them to the rafters. That'll give me more ceiling height. The new joists have to support themselves, the batt insulation, the corigated steel sheets which are pretty light, and the lights. I think that should be strong enough, right? Not going to storing anything up there or walking around on it. I'm no engineer maybe there's some calculator out there that can help me figure out how much load a span can carry,

 

[GarageGuyNY]

I'm probably going to use 2"x6" 16' joists and attach them to the rafters. That'll give me more ceiling height. The new joists have to support themselves, the batt insulation, the corigated steel sheets which are pretty light, and the lights. I think that should be strong enough, right? Not going to storing anything up there or walking around on it. I'm no engineer maybe there's some calculator out there that can help me figure out how much load a span can carry,

Correction: going with 2x8's instead...