# Insulating "rafters" in shed with no attic?



## cc-rider (Jul 29, 2003)

I'm not sure how to do it! I have a small storage building and I'm converting the 2nd story to living quarters.....oK, camping quarters. The rafters are 2X6's and the plywood roof is attached to that. 

I want to put insulation in the rafter space, and then put pine-plank siding on for the wall/ceiling covering. Other than the gable ends, there are no vertical walls.... the other two walls slope (it's a gambrel-style barn).

I'm confused!! Do I need "breathing room" under the roof?  If I put 6" insulation in, there won't be. Or do you only need ventilation and breathing room if you have an attic? 

Should I put a vapor barrier on the inside, too? So the "sandwich" would be shingles, plywood, rafters w/insulation, vapor barrier, wall covering? 

Thanks, again, for your invaluable help! My SO is getting tired of me saying, "well, on Homesteaders, they say....", but when we get stumped, he tells me to ask! 

Chris


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## SolarGary (Sep 8, 2005)

Hi,
They make thin foam pieces that you staple to the inside of the roof sheating before you put the insulation up. These foam pieces are as wide as the rafter spacing, and form a channel for air to flow between the top of the insulation and the roof sheathing. They might be called insulation chutes(?). 
Seems like you would also want ridge venting so that the air has a place to flow out, and soffet venting so the air has a place to flow in.

The only vapor barrier should be on the inside (heated side). The roof sheathing, felt paper and shingles will let water vapor through OK.

Gary
www.BuildItSolar.com


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## freeinalaska (Jan 21, 2005)

Solargary has it right on. You need at least an inch of vent between the roof plywood and the insulation. They sell pre-made baffles for this, but the ones I saw were designed to be installed on top of the rafters before the plywood and roofing is installed. I figured this out AFTER I had my roof in place. I got creative and used lathe every 12 inches installed from the underside to create the airspace. A contractor friend of mine said even cardboard would suffice.


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## cc-rider (Jul 29, 2003)

What is the purpose of the air space?? Someone else I asked explained that it wasn't needed.... but I'm still not sure that he knew what he was talking about (but it made sense at the time!)


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## Chas in Me (Jun 19, 2004)

cc-rider said:


> What is the purpose of the air space?? Someone else I asked explained that it wasn't needed.... but I'm still not sure that he knew what he was talking about (but it made sense at the time!)


When you have warm air bumping against cold air, you get condensation. The airspace directly below the roof will cause an air flow. This flow will carry moisture out of the roof area. Makes life a lot happier.


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## wy_white_wolf (Oct 14, 2004)

cc-rider said:


> What is the purpose of the air space?? Someone else I asked explained that it wasn't needed.... but I'm still not sure that he knew what he was talking about (but it made sense at the time!)


Think of it as ventilation space. A typical roof has 2 vapor barriers. One you intentionally put on the inside of the insulation. this is to keep moisture out of the wall. Try as we may this vapor barrier will never be 100% effective. 

The other is created by the roofing material on the outside. These two vapor barriers will lock in any moisture that does get any, causing mold, mildew and every kind of nasty thing to rot away your building. 

The ventilation space is for air flow to carry away the moisture. So you not only need the space, but a way for air to enter and exit, eave and ridge vents should work nicely.


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## kuriakos (Oct 7, 2005)

The airspace and vents also keep the roof cold so snow on it doesn't thaw and then refreeze into ice dams.


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## tiogacounty (Oct 27, 2005)

I've handled a simular situation by installing baffle trays, then 4" unfaced fiberglas. Next I glued and nailed 1" styrofoam to the bottom of the rafters, then a layer of 1/2" drywall. The drywall is inportant as a fire barrier with the foam insulation. Tongue and groove board can be nailed and glued to the drywall surface. This would give you an R value of roughly 20. The place should be nice and toasty, and you can do the T&G boards anytime. Once you have the sheetrock up and taped, it's livable. As another post said, you ABSOLUTELY need a continuous ridge vent and soffit venting. Cathedral ceilings can be difficult to vent, and a gambrel complicates things. Make sure that there is a clear flow of air, above the insulation, in every rafter bay. Good luck.


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## uncle Will in In. (May 11, 2002)

In my misspent youth, I put 6 inch batts between 2x6 rafters with no air vent space. The underside of the sheeting, and the rafters will be soaked with water continualy. It is only a matter of time until the rafters rot out.


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## Cabin Fever (May 10, 2002)

kuriakos said:


> The airspace and vents also keep the roof cold so snow on it doesn't thaw and then refreeze into ice dams.


I agree! In the north country you want the attic or the "breathing room" (as you put it) as cold as it it outside. The only way to do this is with adequate ventilation. If the attic is ventilated it remains cold and consequently, the roof deck stays cold. As Kuriakos said, if the roof deck is warm, snow will melt, then run down the roof, and then re-freeze on the eaves, thereby creating ice dams. Thawed snow (ie, water) backs up on the ice dam and then leaks into the structure.


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## cc-rider (Jul 29, 2003)

Cabin Fever said:


> I agree! In the north country you want the attic or the "breathing room" (as you put it) as cold as it it outside. The only way to do this is with adequate ventilation. If the attic is ventilated it remains cold and consequently, the roof deck stays cold. As Kuriakos said, if the roof deck is warm, snow will melt, then run down the roof, and then re-freeze on the eaves, thereby creating ice dams. Thawed snow (ie, water) backs up on the ice dam and then leaks into the structure.


But that's the problem, CF, there ISN'T an attic. My confusion is still that, if this were a vertical outside wall, I'd stuff it as full of insulation as I could and be done with it. You don't "ventilate" an outside wall, so why would I ventilate a ceiling in a living space? 

I guess I can see both sides of this. Sigh. But which is correct? I don't want the rafters to get wet and rot out, but I also don't want to have to put ventilation (and cold air!) some place that it isn't 100% necessary.


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## seedspreader (Oct 18, 2004)

cc-rider said:


> But that's the problem, CF, there ISN'T an attic. My confusion is still that, if this were a vertical outside wall, I'd stuff it as full of insulation as I could and be done with it. You don't "ventilate" an outside wall, so why would I ventilate a ceiling in a living space?
> 
> I guess I can see both sides of this. Sigh. But which is correct? I don't want the rafters to get wet and rot out, but I also don't want to have to put ventilation (and cold air!) some place that it isn't 100% necessary.


Everyone has given you correct info. The difference between the walls and ceiling is two fold.

Heat rises...
and
Snow sits on the roof.

The sides of your building will never experience the amount of moisture and contact with the elements that the roof does.


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## wy_white_wolf (Oct 14, 2004)

cc-rider said:


> ...You don't "ventilate" an outside wall, so why would I ventilate a ceiling in a living space? ....


The outside wall doesn't have the roofing shingles and tarpaper that the roof does. While walls do have siding it is far from a moisture barrier and allows the wall to breath without the ventelation.


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## cc-rider (Jul 29, 2003)

Ok.... I'm throwing another wrench in the works... I probably should have mentioned this previously.

We don't have any way to put in eave vents. The roof is sealed right to the walls all around. No gaps or places to put vents. 

Also, we won't be there in the winter very often, so it is unlikely that we will have heat in this building. Will that help the moisture issue? (Actually, at this point, there ISN'T a way to heat the building! No electric, no fireplace, no propane....) 

Also, there isn't tarpaper under the roofing. We weren't there to supervise that, and didn't notice until they were done. We even considered hiring someone to tear them all off and redo it, but figured that, since we've already paid for it, we'll just let it go and see what happens. When questioned (an amish crew built this), they said it "allows the roof to breath if we don't put tarpaper on it." Personally, I think they were just being cheap.

So now, in light of the fact that we CAN'T put eave vents in.... what is our best option?


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## Cabin Fever (May 10, 2002)

What they do around here for houses without eaves is to put in roof vents near the bottom of the roof (usually two) as well as near the peak of the roof (also usually two, to make a total of four roof vents). The cooler outside air comes in the lower vents and the warmer attic air goes out the peak vents.

Others put in wall vents in the gable ends of the building.


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## Chas in Me (Jun 19, 2004)

If you're not going to heat the place, there is no reason to insulate. Insulation is to keep heat in.
Just a thought.


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## mtman (Sep 2, 2004)

Chas in Me said:


> If you're not going to heat the place, there is no reason to insulate. Insulation is to keep heat in.
> Just a thought.


if you keep paint in a shed with no insulation it will freez if you keep paint in a shed with insulation it will not freez just a thought


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## mtman (Sep 2, 2004)

Cabin Fever said:


> What they do around here for houses without eaves is to put in roof vents near the bottom of the roof (usually two) as well as near the peak of the roof (also usually two, to make a total of four roof vents). The cooler outside air comes in the lower vents and the warmer attic air goes out the peak vents.
> 
> Others put in wall vents in the gable ends of the building.


thats correct the same princible as a double hung window open the bottom a bit open the top a bit cool air in the bottom warm air out the top keeping your house cooler


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## wy_white_wolf (Oct 14, 2004)

cc-rider said:


> Ok.... I'm throwing another wrench in the works... I probably should have mentioned this previously.
> 
> We don't have any way to put in eave vents. The roof is sealed right to the walls all around. No gaps or places to put vents.


There's always a way. The original design may not allow them so you need to modify it to work. Just like your modifying the attic to be living quarters. Can you post a pick of what you have so we can better advise?




cc-rider said:


> Also, we won't be there in the winter very often, so it is unlikely that we will have heat in this building. Will that help the moisture issue? (Actually, at this point, there ISN'T a way to heat the building! No electric, no fireplace, no propane....)


Still important to be vented. The building will still warm up during the day and lose heat at night, just more slowly. 




cc-rider said:


> Also, there isn't tarpaper under the roofing. We weren't there to supervise that, and didn't notice until they were done. We even considered hiring someone to tear them all off and redo it, but figured that, since we've already paid for it, we'll just let it go and see what happens. When questioned (an amish crew built this), they said it "allows the roof to breath if we don't put tarpaper on it." Personally, I think they were just being cheap.


Ok I looked back and didn't see what type of shingles.

If they are asphalt (3-tab or t-locks), They don't breath and should have tar paper under them.

Wood shingles need to breath and don't have tar paper under them. It is really be important to ventelate under these. Not ventalting under wood shingle or putting them on tar paper will trap moisture under them after rain stroms and make them rot away in a couple of years.




cc-rider said:


> So now, in light of the fact that we CAN'T put eave vents in.... what is our best option?


Again see above.


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## tiogacounty (Oct 27, 2005)

About fifteen years ago there was a debate in the construction industry about tar paper. The manufacturers were trying to void roof warranties if there wasn't any roofing felt under their shingles. After a few lawsuits, some were forced to admit that the only benefit of felt paper is that it provides a secondary protection in the event of shingles blowing off, and really does nothing to alter the shingle warranty. If your roof is installed without paper, don't waste a dime "repairing" something that isn't broken. I built my first house in 1989. I used absolute garbage grade three tab shingles, and no tar paper. It lasted 15 years without a problem. I typically put 30lb felt under shingles now, but it's just for insurance, not because it's necessary. As for your venting question, like I said previously, every single rafter bay needs continous ventilation from the bottom to top. If not, you may start to see sagging sheathing in a few years and eventually you end up with a rotted moldy mess. I've seen it happen. I just spent many days repairing a roof over a cathedral ceiling. Some of the sheathing was so rotted it looked like mulch. The house had very little effective soffit venting and a few "mushroom" vents near the ridge. The place has tens of thousands in damage because of poor ventilation.


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