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Baroness of TisaWee Farm
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Discussion Starter · #1 ·
I have 10" rafters on my cathedral ceiling. If I put in R30 insulation I'll still have an inch or so "exposed" at the top. Will that work as ventilation space, or do I need to run those duravent things on the whole roof?? I've put them on the first 4' from the eaves, but they are expensive!! The only reason I used them in the first 4' is so that I have something to block up against when I put the foam/insulation up to the eaves.

Does any of this make sense? :)
 

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I have 10" rafters on my cathedral ceiling. If I put in R30 insulation I'll still have an inch or so "exposed" at the top. Will that work as ventilation space, or do I need to run those duravent things on the whole roof?? I've put them on the first 4' from the eaves, but they are expensive!! The only reason I used them in the first 4' is so that I have something to block up against when I put the foam/insulation up to the eaves.

Does any of this make sense? :)
In theory, the inch gap should be sufficient, but if a batt becomes compressed during installation and later expands (or you bump it up while putting on ceiling material), you end up blocking the air flow for the entire length of the roof.

I don't know what product you are using, but I used these 3 foot things that ran about $0.20 each. They were white styrofoam, similar to an egg carton and very light. You don't need anything fancy, just something to keep it off the roof covering.
 

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Baroness of TisaWee Farm
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Discussion Starter · #3 ·
I'd love to find those 20cent things! Mine were on sale at just over a buck a piece. I think I bought 200 of them so far! I joked about stapling egg cartons up there, but my son scoffed at me. :)
 

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I have rough cut full 2"x 6" rafters and used the regular r19 designed for the 5 1/2 inch space if using storebought 2x6's with no vent thingys and have no problems at all, the one inch space for the roof lathing along with that extra 1/2 inch seems to provide plenty of vent space.
 

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It really depends on the type of roof you are putting on.
If you are using asphalt shingles you want to be sure to have enough ventelation or the heat will kill the life span of the shingle. They make a small wire called lightning rods used to hold insulation up into floor systems that bends and wedges itself between the joists. You may use them spaced out to hold insulation down off the decking. I'm not sure but i think they would be less costly than the duravents at $1.00 per.
 

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Baroness of TisaWee Farm
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Discussion Starter · #6 ·
The roof is already on. It is tar paper and 25 year asphalt "architectural" shingles on top of 5/8" OSB. So I can't change anything there. I'll check on those "lightning rods", though, and see what they'd do. Maybe just string a few lines of wire along the cavity to keep it from going too far into the cavity?

I was watching the trash man come and pick up the HUGE bags of shredded paper that we have weekly. Can I use that stuff for insulation?? Probably a fire hazard, huh? I've used it for chicken bedding and all over my gardens, but that's different.
 

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The roof is already on. It is tar paper and 25 year asphalt "architectural" shingles on top of 5/8" OSB. So I can't change anything there. I'll check on those "lightning rods", though, and see what they'd do. Maybe just string a few lines of wire along the cavity to keep it from going too far into the cavity?

I was watching the trash man come and pick up the HUGE bags of shredded paper that we have weekly. Can I use that stuff for insulation?? Probably a fire hazard, huh? I've used it for chicken bedding and all over my gardens, but that's different.
Use proper insulation, penny wise and pound foolish, as the saying goes. Fibreglass batts are easiest, blown cellulose is good too. Shredded paper is not only a fire hazard but is more likely to host rodents and insects.
 

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It really depends on the type of roof you are putting on.
If you are using asphalt shingles you want to be sure to have enough ventelation or the heat will kill the life span of the shingle. They make a small wire called lightning rods used to hold insulation up into floor systems that bends and wedges itself between the joists. You may use them spaced out to hold insulation down off the decking. I'm not sure but i think they would be less costly than the duravents at $1.00 per.
Actually, the reason for ventilation is to remove excess heat AND moisture from the rafter bay. Most shingle manufacturers now warranty unvented applications for two reasons. Structural insulated panel roofs are very difficult to vent and typically get covered with shingles, so they lose market share by not allowing their product to be used on SIPS panels. Second, their research indicated that is really no huge difference in shingle temp. or lifespan, if the roof isn't vented. As for the lightning rod idea, I wouldn't waste my time. Doubtful it would work at all, and impossible to verify that it did.
 

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I have rough cut full 2"x 6" rafters and used the regular r19 designed for the 5 1/2 inch space if using storebought 2x6's with no vent thingys and have no problems at all, the one inch space for the roof lathing along with that extra 1/2 inch seems to provide plenty of vent space.
How is this working? Venting to the outside?

I sorta dealing with the same quandary.
Cabin is 2 X 6 rough cut rafters, rough cut roof boards, felt paper, and asphalt shingles.

As these are the sleeping lofts, I can use all the head room as I can get.
Didn't want to just put the insulation diredtly against the roof boards, for all the above stated reasons.

Was thinking about 3-1/2" bating, hanging down from the boards about 1", tack up the insulation then cover with carsiding, tacked to 1"X1" strips inside the rafters.
This would give ne still about 2" of of remaining head room.
Was thinking about roof cap vent, those egg crate "thingie's, buttom vent hole in the eve boards.
Yeah, I know sounds like a lot of screwing around, for not much insulation value.
 

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How is this working? Venting to the outside?

I sorta dealing with the same quandary.
Cabin is 2 X 6 rough cut rafters, rough cut roof boards, felt paper, and asphalt shingles.

As these are the sleeping lofts, I can use all the head room as I can get.
Didn't want to just put the insulation diredtly against the roof boards, for all the above stated reasons.

Was thinking about 3-1/2" bating, hanging down from the boards about 1", tack up the insulation then cover with carsiding, tacked to 1"X1" strips inside the rafters.
This would give ne still about 2" of of remaining head room.
Was thinking about roof cap vent, those egg crate "thingie's, buttom vent hole in the eve boards.
Yeah, I know sounds like a lot of screwing around, for not much insulation value.
I would take one of two paths, depending on the budget. My first choice would be to have it spray foamed with urethane. this is called a hot roof in these parts. The entire cavity is filled, sealing everything tight, and eliminating the need for ventilation. My second choice would be r-15 high density batts made for 2x4 walls, no need for foam vent trays. Then a layer of foil faced 1" polyisocyanurate foam insulation. Hang this foam like drywall, tape all the seams with foil tape and screw 1x2 furring strips through it, into each rafter. You now have a nice base to attach your T&G ceiling boards to. I did this to a small house that I didn't have room to properly insulate, it worked great.
 

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How is this working? Venting to the outside?

I sorta dealing with the same quandary.
Cabin is 2 X 6 rough cut rafters, rough cut roof boards, felt paper, and asphalt shingles.

As these are the sleeping lofts, I can use all the head room as I can get.
Didn't want to just put the insulation diredtly against the roof boards, for all the above stated reasons.

Was thinking about 3-1/2" bating, hanging down from the boards about 1", tack up the insulation then cover with carsiding, tacked to 1"X1" strips inside the rafters.
This would give ne still about 2" of of remaining head room.
Was thinking about roof cap vent, those egg crate "thingie's, buttom vent hole in the eve boards.
Yeah, I know sounds like a lot of screwing around, for not much insulation value.
Well, the big difference for me was using metal roofing as apposed to shingles, at my age I have no desire to ever get back up on that roof. The metal roof is much cheaper in my case too. Shingles wont last nearly as long as the metal will. The other advantage is the ventilation thing. with the lath strips on top of the rafters there is about an inch of vent space throughout the whole thing, even with the full thickness of insulation. on the inside I just nailed my oak boards directly to the rafters, put some little strips over the end seams for trim and stained and polyed the whole mess. It looks good, breathes well and gives no trouble at all. You can see photos on Yvonnes youtube page. Just go to youtube, do a search for evola15 and check out the various stuff she has labeled as cabin building or progress or whatever she comes up with to label the videos.
 

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10-4, will give it a try.
 

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Guess you will need to give me a little more info. Search of "evola15" came up with a goofy group of stuff.
Thanks anyway.
 

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Are you using a vapor barrier? Moisture will negate any benefit of insulation. there are formulas for square inches of ventilation opening for the size of the area to be ventilated. Beside temp loss moisture problem will eventually rot boards or ruin drywall. Moisture on metal roof will condensate and drip or deteriorate purlins and screws will pull out. Although many metal roofs are put on wood strips no metal manufacturer I spoke to recommends it except for barns and sheds.
 

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Are you using a vapor barrier? Moisture will negate any benefit of insulation. there are formulas for square inches of ventilation opening for the size of the area to be ventilated. Beside temp loss moisture problem will eventually rot boards or ruin drywall. Moisture on metal roof will condensate and drip or deteriorate purlins and screws will pull out. Although many metal roofs are put on wood strips no metal manufacturer I spoke to recommends it except for barns and sheds.
I use the pink stuff with the paper vapor barrior to the interior. Keep it tightly stretched twixt the rafter and make sure you have a good tite fit at any joints to keep the moisture from the interior from escaping to the metal. I have been doing this type insulating with metal roofs for 30 years and never had any problems when done correctly. I sold a cabin to one feller a few years back, he put up his own insulation, but left about a four inch gap at the lower end of a couple rafters, just above the top plate of the wall. he immediately developed a condensation issue between those rafters. thought he had a leaking roof but it happened even when not raining! Putting a couple peices of insulation with vapor barrier in those gaps stopped the problem. :)
 

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Y.H. Thanks for the link, doesn't it seem that this process goes on for ever?
Back when, we bought the property, put a couple of old travel trailers on it, shed etc.
Used it for deer, turkey, duck hunting, 4 wheeling, camping, canoeing, and general partying.
Now it seems like all we do is work on it.
 
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