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jjmay77
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# Posted: 28 Apr 2023 02:43pm
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I have a 16x24 Gambrel style cabin. The upstairs is unfinished but has been insulated for the last few year with faces fiberglass R30. I will be adding drywall or tongue and groove pine. Before closing it up I want to be sure I am insulating properly and my situation is a bit atypical. I have metal roof with the bubble insulation under it attached right to the purlins (no plywood. Does anyone see an issues putting drywall over my current faced fiberglass? I am concerned a bit about airflow and double vapor barrier. I heat with a wood stove and electric heat only a few times each year otherwise the sturcture is generally not heated. Any thoughts would be appreciated. Thanks
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AJC
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# Posted: 2 May 2023 07:09am
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What you are describing sounds like a hot roof system, without venting. Normally this is accomplished with closed cell spray foam. The issue with fiberglass is air sealing. Any air infiltration will allow condensation under the metal roof and no way for it to escape. I looked into this as we are looking to insulate between our roof rafters and do not have any way to vent at the soffit - practically no overhang. The idea would be for soffit venting at eaves , ridgevent at roof and baffle space for airflow between fiberglass and roofing. Using spray foam eliminates this, although expensive. My only option is sprayfoam, unless I do a lot of work to the eaves to allow soffit venting.
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Brettny
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# Posted: 2 May 2023 08:45am
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I just dont think your going to get enough air flow around a gambrel corner to really make a difference in a gambrel roof.
What you could do is pull back some of your fiberglass and look for condensation or mold. R30 is 10in thick. You have 2x12 roof rafters?
Cathedral ceilings can move quite a bit and between that and if you dont have a proper depth foundation your drywall on the ceiling especially can crack easy.
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Cedar Fever
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# Posted: 2 May 2023 08:55am
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I have the same setup. I have been wanting to tear the entire roof off and start over. Sounds like a lot of work and I don’t want to fall off the damn thing. I will likely spray foam it sometime.
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Brettny
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# Posted: 2 May 2023 08:24pm
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Why do you want to tear it off and start over?
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Cedar Fever
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# Posted: 3 May 2023 09:41am
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I want to add plywood sheathing. And some rafters for soffit vents, a ridge vent, and a better roof overhang. And add insulation on the outside. But my area is super windy so I am not sure that is a good idea.
But currently the metal roof directly on wood rafters is sturdy and working fine so spraying foam and moving on is easier.
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gcrank1
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# Posted: 3 May 2023 10:47am
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Spray foam is kind of expensive.
But it is effective, and far easier (it looks like, I have t done it) than tearing off a roof (which I have done multi times) and rebuilding it (also expensive) in your preferred way.
And with a tear off/re-do your structure is exposed and MUST be done asap. I hate being backed into a corner like that....
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travellerw
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# Posted: 3 May 2023 10:53am
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If you search in this forum you will find a few examples recently of insulated Gambrel roofs (including mine). Another user is W1llie.
Mine was done buy using foam board to create a 1" air channel from the soffit to the ridge vent. After that 2x6 batt insulation was installed and finally drywall.
I worried that the combo of 2x6 and foam board (about R25) would not be enough. However, we have stayed at -40c and the wood stove would cook you out. We also used the mini-split AC last year at +32C. No problems at all cooling the space to +20C
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Brettny
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# Posted: 3 May 2023 12:13pm
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Quoting: travellerw worried that the combo of 2x6 and foam board (about R25) would not be enough. However, we have stayed at -40c and the wood stove would cook you out. We also used the mini-split AC last year at +32C. No problems at all cooling the space to +20C
Warmth isnt the metric for measuring for enough insulation in this situation. Mold growing above the insulation is. But since you used foam board as the top layer that my really save you there.
I'm still deciding if we are going to do foam board between the perlins and rafters. I'm useing 2x10 roof rafters so with 2in foam board and R30 insulation I should be close to code.
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gcrank1
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# Posted: 3 May 2023 08:36pm
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Fwiw, on ours Im not trying to make 'code', just want to fill in the available rafter space with insulation that makes sense.
We have rafters topped with rough cut boards then metal roofing. I think the po/builder put some heavy duty truckers tarp over the rafters before the boards, not sure, then stuck Kraft faced f-glass up inside and made the cath 'ceiling' with more rough cuts boards. It sure is rustic! And a lovely place for the rotten little devil red squirrels to nest.....
So, with the tips here Im thinking about pulling the ceiling (arg) and f-glass (arrggg), finding/fixing the squirrel access hole(s), venting the 'soffit' & peak and making that 1" gap to the roof with rigid styro. After that I can decide what to fill the rest of the rafter height with before a new ceiling.
To me it makes sense to have that air flow to the peak beneath the roof rather than insul tight up to it.
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jjmay77
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# Posted: 4 May 2023 10:18am
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I took a closer look at mine when I was out there recently. The 2x4 purlins go perpendicular to the Rafters and the insulation is R19 not 30. The rafters are 2x6. So there is actually a gap of a couple inches between the metal roof and the fiberglass. This may leave some airflows similar to baffles. Also there is a layer of foamy plastic under the metal roof. I am now rethinking everything after seeing how the mice like the fiberglass. One year I was lax on the traps and poison and now the insulation is pretty nasty. Thinking fiberglass is less than ideal.
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Brettny
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# Posted: 4 May 2023 12:38pm
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Mice also like rockwool and can chew through foam. I'm planing on building in a way to keep the rodent highways to a minimum along with sealing up every single gap and crack durring the construction process with hardware cloth.
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gcrank1
Member
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# Posted: 4 May 2023 01:16pm
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Ime rodents will always build new 'highways' 
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travellerw
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# Posted: 5 May 2023 11:42am
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Quoting: Brettny Warmth isnt the metric for measuring for enough insulation in this situation. Mold growing above the insulation is. But since you used foam board as the top layer that my really save you there.
There is a 1" air channel from the soffit to the ridge vent. It works too as you can hold a piece of vinyl tape at the soffit and see it being sucked up on a hot day.
Another thing that was suggested by a local building fella was to not seal that foam board to the rafter. Lots of people like to seal that air channel off using expanding foam. He suggested that would be a mistake and the small irregularities from cutting the foam to fit between the rafters would provide a path out for moisture. No matter how hard I tried to seal my vapor barrier, he said that moisture will find its way in the cavity with the batt (below the foam and above the drywall). Having a path for it to get out is important.
Anyway, it has worked out for me so far.
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jjmay77
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# Posted: 5 May 2023 01:54pm
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I am tempted to put up some pine tongue and groove and leave a void between the metal roof and the T&G. Seems like rodents will get into most anything other than the spray foam. I have a wood stove and the area I am finishing is upstairs. I am wondering if I can simply blast a ton of heat in a small cabin so insulation is less of a concern. In the winter the wood heat is dry.
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Brettny
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# Posted: 5 May 2023 08:27pm
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Quoting: travellerw There is a 1" air channel from the soffit to the ridge vent. It works too as you can hold a piece of vinyl tape at the soffit and see it being sucked up on a hot day
That may be enough. I'm not sure. I have a failed ridge vent in my shingled house. I had to retrofit a gabel vent and fan. Il never do another ridge vent again if I cant easily retro fit another option.
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Brettny
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# Posted: 5 May 2023 08:28pm
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Quoting: jjmay77 I am tempted to put up some pine tongue and groove and leave a void between the metal roof and the T&G. Seems like rodents will get into most anything other than the spray foam. I have a wood stove and the area I am finishing is upstairs. I am wondering if I can simply blast a ton of heat in a small cabin so insulation is less of a concern. In the winter the wood heat is dry.
So no insulation? Maybe I dont follow.
More heat dosnt mean less insulation or less mold.
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gcrank1
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# Posted: 5 May 2023 09:04pm
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After some vermin get into that void and start nesting, peeing (and that running out the ceiling) and scurrying about, especially in the night, you will wish you had not given them a space to play in.
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travellerw
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# Posted: 6 May 2023 12:50am
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Quoting: Brettny That may be enough. I'm not sure. I have a failed ridge vent in my shingled house. I had to retrofit a gabel vent and fan. Il never do another ridge vent again if I cant easily retro fit another option.
How does a ridge vent fail? Maybe its different with a shingled roof. In my tin roof its like a 6" wide channel (3" each side of the peak). Its then capped with a filter to keep out bugs and snow!
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Brettny
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# Posted: 6 May 2023 06:49am
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Quoting: travellerw How does a ridge vent fail? Maybe its different with a shingled roof. In my tin roof its like a 6" wide channel (3" each side of the peak). Its then capped with a filter to keep out bugs and snow!
Dosnt allow enough air up under the roof. I have the plastic baffles and nothing blocking them along with vented sofit. Just didnt work as good for me. I had moisture build up due to poor insulation and not knowing things back then. This is why I always tell people to air seal and insulate properly. Thankfully I have a window in my attic and leave that cracked along with put in a gabel fan.
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jjmay77
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# Posted: 7 May 2023 12:03pm
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Good point about the vermin in the void. Is there really any way around this? Seems like fiberglass in the roof its inevitable mice will find it
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travellerw
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# Posted: 7 May 2023 06:30pm
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Quoting: Brettny I had moisture build up due to poor insulation and not knowing things back then. This is why I always tell people to air seal and insulate properly. Thankfully I have a window in my attic and leave that cracked along with put in a gabel fan.
%100 insulation and sealing are crucial in northern climes. I went crazy and even taped the staples in the plastic. Black accoustical sealant around all wire penetrations and at bottom plate.
However, even with all that moisture seems to find a way in. Gotta also think of a way out as well..
Sucks it didn't work for you. Interesting though, I wonder why!
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jjmay77
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# Posted: 8 May 2023 10:55am
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Seems like sealing a metal roof without plywood from vermin would be nearly impossible. I could add plywood between the joists by screwing the plywood to the purlins. Getting airflow however would be interesting
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spencerin
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# Posted: 17 May 2023 11:50pm
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jjmay77, that's commonly how the Amish build roofs. Was yours Amish-built?
Anyway, I don't see why you wouldn't be able to put drywall over your current faced fiberglass. Any condensation on the underside of the metal roof panels would drip onto the bubble insulation and not into the fiberglass. Also, if you're heating with a wood stove, it'll dry out the air on the inside, so any warm air hitting the underside of the cold metal roof wouldn't hold as much moisture. Finally, you're heating the space only a few times a year, not much to worry about there.....
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gcrank1
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# Posted: 18 May 2023 08:06am
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Mice, and red pine squirrels Will dig their way through plywood and more. Wood only slows 'em down for a while.
Moisture is the same, lol.
Iirc, warm air hold moisture better than cooler air, so if there is condensation you know there is air leaking through.
Our poorly built sawmill board cabin has enough air leaks everywhere that condensation isnt a problem nor is air exchange.....
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Aklogcabin
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# Posted: 18 May 2023 10:03am
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I don't have a problem with mice. It's not as if mice get into every cabin built.
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Nobadays
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# Posted: 18 May 2023 11:46am
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Quoting: Aklogcabin I don't have a problem with mice. It's not as if mice get into every cabin built.
Same. Our cabin is well built and tightly sealed, they don't get inside. Underneath, well different story! We have spray foamed under the floors and the skirting (post and beam, metal skirting. ) we try to keep Tomcat blocks under there all the time. The crawlspace is totally unaccessible to pets so no worries there.
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gcrank1
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# Posted: 18 May 2023 01:47pm
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The cabin I built in '83-'84 was done tight too, with lots of consideration to keeping the critters out. Took 'em a while but they couldnt resist finding their way into a snug place to live.
I hope you have better luck.
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jjmay77
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# Posted: 18 May 2023 02:30pm
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Yes my cabin was Amish built. Unfortunately no closure strips on the metal roof and no plywood. I removed the 7 year old faced insulation and plan to start new. I will close up what I can and keep plenty of traps and poison out. I also cut back all vegetation around the cabin and plan to lay some stone to deter them from crossing in the open. Spencerin I agree with heating only a handful of times per year and the bubble insulation I think I am good on condensation. Plus the purlins leave a couple inches for air flow.
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spencerin
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# Posted: 18 May 2023 09:33pm
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What's the cabin siding made out of, and well as the eaves? Wood?
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