Options for ceiling insulation in detached hip garage

[Kgray247]

Hello, I'm located in Michigan and use my garage for a golf simulator and occasionally working on my car. My detached garage is about 25' x 25'.

It is 8 inch block with siding and has a hip roof with 3d shingles replaced within the last 10 years. 2 soffits on each side of the garage besides the front, and 1 vent on each soffit side, so 3 total. I have a natural gas 80k btu luxaire heater hanging in the back corner. My attic is wide open which I like for storage. Its rafters are spaced 48 inches apart. About 5 total or so only.

I'm wondering what my best solution could be for insulating the ceiling so all my heat doesn't escape and it isnt so fridgid everytime I walk into it. It seems as if my only option would be to spray foam it which I'm not sure if I like the idea of that as well as the cost. I dont even know if I could throw 1/2 osb down and throw some insulation batting on top of that with how little rafter coverage I have for mounting the board & I'd prefer to mount it on top of the rafters so i didnt lose my height. There are 2 metal I beams in there for helping support as well I believe, maybe prior owners used to use it to pull engines since one is right above where the hood of a car would be.

My roof rafters are 16 oc with 2x6. I wonder if I could put r13 bats (3.5" thick) and still have my room for ventilation and then drill with 1" hole saw where the rafters die off into the hip joists to continue that flow to exit out the vents. I'm of course worried about mold issues with the humidity in the summer. Although I havent experienced any leaks or moisture problems so far in the garage within the last 5 years.

I dont keep it heated and temp controlled at all. I just use the heater when I'm out there for a few hours after work or on the weekends. Also use it mainly in winter time as I golf outside in the summer. Then at the same time, if it is too big of a pain, or not worth the hassle, is it even necessary since I use it so minimal. I don't want to add more rafters and create an attic/ spend 2500 or so on spray foam insulation

Looking for opinions and options of what I could do, I'm a DIY'er so something I could do would be best.

 

[Kgray247]

One other option I was thinking is to 45° some 2x4s and mount them across the top to the roof joists to hang 4x8 sheets of osb to make an attic above the rafters. This would create an attic space up top to make most of the rafters reach the vents on the roof. I could then just put r13 on the rafters up to the "attic" then put r30 up top there. Or run vent chutes and put r21 in the rafters. My 2x6 are truly 5.5 tall. So r13 is 3.5 or r21 is already 5.5 with 1 inch vent chutes, may diffuse the purpose of the thicker insulation, yes?

 

[Kgray247]

Bump. Can anybody offer insight? Thanks

 

[Kgray247]

..not looking good..����

 

[cadunkle]

I did a house with a hip roof starting on top of a 3' or 4' wall at the perimeter like you describe to finish the attic. Rafters were 2x6. I used R13 insulation in the cavities from soffit vents up to the attic area. I used 2x6 for the ceiling joists/collar ties and plywood on top for light storage, R19 insulation, then finished with drywall and made a small access door. The roof already had a powered vent on a thermostat so I retained that.

The way I did it not all jack rafter cavities low in the corners were vented all the way up. There's no great way to insulate a cathedral ceiling on a hip roof. As long as you leave a space from soffit vent to some sort of vent near the top for at least all but the very short rafters in the corners it'll be good enough, in my opinion.

Drywalling and getting a decent finish into the corners really sucked, I would not want to do it again. For a garage though, finish doesn't have to be as nice and I'd be inclined to use OSB instead, make my cuts as tight as possible, caulk any real bad spots, and paint it all white.

Bottom line is you need to make a ceiling, open attic space above, and vent the attic near the peak. The lower the ceiling the better off you'll be as far as both venting and comfort in the space below. R13 on those 2x6 rafters will leave a space, ensure it's clear to soffit vents at the low end.

 

[Kgray247]

I did a house with a hip roof starting on top of a 3' or 4' wall at the perimeter like you describe to finish the attic. Rafters were 2x6. I used R13 insulation in the cavities from soffit vents up to the attic area. I used 2x6 for the ceiling joists/collar ties and plywood on top for light storage, R19 insulation, then finished with drywall and made a small access door. The roof already had a powered vent on a thermostat so I retained that.

The way I did it not all jack rafter cavities low in the corners were vented all the way up. There's no great way to insulate a cathedral ceiling on a hip roof. As long as you leave a space from soffit vent to some sort of vent near the top for at least all but the very short rafters in the corners it'll be good enough, in my opinion.

Drywalling and getting a decent finish into the corners really sucked, I would not want to do it again. For a garage though, finish doesn't have to be as nice and I'd be inclined to use OSB instead, make my cuts as tight as possible, caulk any real bad spots, and paint it all white.

Bottom line is you need to make a ceiling, open attic space above, and vent the attic near the peak. The lower the ceiling the better off you'll be as far as both venting and comfort in the space below. R13 on those 2x6 rafters will leave a space, ensure it's clear to soffit vents at the low end.

Appreciate it, did it seem to make a difference & worth it all? It seems as if that's the only way besides spray foaming it all. At least I could do the makeshift ceiling myself though and a bit cheaper.

 

[banjopete]

If you can swallow the one time cost spray is a great solution. It's not cheap but to make yourself feel better remember it's also an installed hands off cost so comparing it to the cost of DIY batts isn't apples to apples.

It's a superior product and when done right completely seals things off. I've done both and where it counts in poor access places or where significant other work is required to accomodate conventional insulation the cost is much easier to justify.

At least get some quotes. No harm there.

As for closing and insulating a ceiling it's a huge, huge difference for heating. I just insulated a no ceiling garage. At each next stage it just kept getting better as more layers went on. I should have done it much sooner.

Good luck.

Sent from my SM-G960W using The Garage Journal mobile app

 

[Kgray247]

If you can swallow the one time cost spray is a great solution. It's not cheap but to make yourself feel better remember it's also an installed hands off cost so comparing it to the cost of DIY batts isn't apples to apples.

It's a superior product and when done right completely seals things off. I've done both and where it counts in poor access places or where significant other work is required to accomodate conventional insulation the cost is much easier to justify.

At least get some quotes. No harm there.

As for closing and insulating a ceiling it's a huge, huge difference for heating. I just insulated a no ceiling garage. At each next stage it just kept getting better as more layers went on. I should have done it much sooner.

Good luck.

Sent from my SM-G960W using The Garage Journal mobile app

Yes, definitely some good points you've made. If I was planning on living her for plenty more years or insulating the walls, itd be a good investment to just spray it. This is our starter home n have been here 5 years already. But the wife says she never wants to move. Haha I'd like a bigger house once kids come though.

It wouldnt be a bad idea to at least get quotes. Garage is 22.5x 25 on the floor, so itd be a bit more with the pitch of the roof as well. I'm assuming 1400 for 2 inches and 2100 ish for 3 inches of spray. Who knows tho, it may be a lot cheaper and I can receive the better r value that I can only get from some r13

 

[yeldogt]

What's the beam in the middle?

Do some looking around .... I never do vented attics. Unvented have been around for years -- eliminates many issues.

Obviously spray foam get you all the benefits if done correctly .. but, it's the most money.

There are way to use batts and a modern vapor retarder ... or insulate the ceiling if you want.

 

[Kgray247]

What's the beam in the middle?

Do some looking around .... I never do vented attics. Unvented have been around for years -- eliminates many issues.

Obviously spray foam get you all the benefits if done correctly .. but, it's the most money.

There are way to use batts and a modern vapor retarder ... or insulate the ceiling if you want.

Metal I beam above the garage door and above the window and door. My joists are like 46" apart or so though. With doing a ceiling, I'm sure I'd need to add more 22 foot joists to withstand the weight of a ceiling.

I've searched high and low for countless of hours n people say spray foam for hips or a ceiling with an attic. Unfortunately cant do much of either or justify cost of spray unless I was staying in the home for plenty years to come.

How could I do it ventless?

Thanks for the input fellas. Just looking on everybody's opinions/ options/input!

 

[Kgray247]

Possibly more pics of I beam n can see how spaced the joists are

 

[QwikKotaTx]

I think you are confusing rafters and joists, backwards. In my detached I decked the attic for storage and I am going to install some vinyl enclosed insulation underneath of the OSB decking inside the joist cavities. I believe it is Enco Tetrafine. It is white for good light reflectivity.

Sent from my VS987 using Tapatalk

 

[jarhead]

This is what I did in my pole barn,

1x4 pine straps 8-12-14' long etc, spaced 2' OC in the opposite direction of trusses.

I used 1 layer of this stuff and screwed into the pine.

https://www.lowes.com/pd/Common-1-i...ded-Polystyrene-Foam-Board-Insulation/3365576

I have a Dayton 3uG73e heater.

I can can interior get up to 68* on a 10* day.

 

[Kgray247]

Just a little update, with quarantine shutdown going on I had plenty of time on my hands. I ended up making about a 10 ft x 7 ft little attic up top that most of the rafter bays run into. Just hung 3, 2x4s and snuggled up some 3/4 inch insulation board with some r13 batting on top of it. First I ran all the rafters with the r13 batting then capped that all up. Also bought some 1 1/2 board to do the garage door. I'll get the heater going this week and see how well she holds the heat in.

 

[Kgray247]

Few more pictures.