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frankdavis
Posted on Tuesday, January 25, 2005 - 11:10 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Moderator/Admin Only) Ban Poster IP (Moderator/Admin only)

Good morning. I have read all of the relevant posts regarding insulating under a slate roof and I am still not sure what to do. If someone could please provide some insight into the following situation, I would GREATLY appreciate it.

First, I have a 1920's tudor that has a partially finished attic space. A previous owner had put R-19 (5-1/2") insulation underneath all of the rafters, except for the lower portion in the front of the house, in front of a knee-wall. The insulation is stapled so that it is fairly snug against the sheathing, but there is still some airspace in the middle of the bats (centerline between rafters).

My questions are as follows:

1. My house is currently experiencing MAJOR ice damming in the front of the house, but not at all in the back of the house. I am guessing that it is from the heat loss due to the uninsulated portion of the roof?

2. Can I leave the current insulation in place, or do I need to unstaple all of it (huge job) and put in baffles, then re-install the insulation?

3. As a next step, should I install a plastic vapor barrier over the entire underside of the rafters, sealing the joints with tape?

4. I am also planning on insulating on top of the finished rooms in the attic (not done) and on the knee-walls (also not done). Is this a good idea? If I do this, should I just take down the rafter insulation all together?

PLEASE HELP!!! The advice of Joe and of all the other fine slate roofing professionals on this site is greatly appreciated. Thanks for your help in maintaining my lovely old home.

Best Regards-
Frank D.
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Walter Musson
Posted on Tuesday, January 25, 2005 - 04:20 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Moderator/Admin Only) Ban Poster IP (Moderator/Admin only)

Is there access to the uninsulated space behind the kneewall?If so you could insulate that area soon to help eliminate some major loss of heat this Winter and do your other areas in the Spring.
don't forget that some means of soffitt and ridge vent are needed to make even an insulated space work properly,something which you may not have.
Most likely that will need to be done in warmer weather.Does the front face South or West?Sometimes solar gain can melt snow and it will re-freeze later in the day.Provided there is some breathing space you could leave it in place and use the poly barrier.Even when you insulate those other ceilings you can still leave what's there now unless it's sodden.
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frankdavis
Posted on Tuesday, January 25, 2005 - 05:06 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Moderator/Admin Only) Ban Poster IP (Moderator/Admin only)

Walter -

First, thank you for your reply. To answer your questions in order to further discuss.

- Yes, I can get to the kneewall(s). In fact, one kneewall and uninsulated portion of the roofline in question form two legs of a "triangle" in one of the crawl spaces.

- The soffits on the house do not have any vents, nor does the roofline. I had heard that slate roofs naturally "breathe" and that these were not required, but please let me know if this is incorrect.

- The house faces South East and the roofline in question receives a huge amount of sunlight during the day. This may be a large contributing factor to the melt / freeze cycle.

- The insulation is in good shape and there is a small amount of breathing space, so it sounds like a poly barrier might not be a bad idea.

- Finally, I had added snow brakes to the roof this fall due to damaged half-round gutters from sliding snow. This seems to have made the ice damming problem slightly worse, since the snow is now not sliding off the roof.

Thanks again for your input Walter...I look forward to your additional recommendations.

Best Regards-
Frank
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Walter Musson
Posted on Tuesday, January 25, 2005 - 07:29 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Moderator/Admin Only) Ban Poster IP (Moderator/Admin only)

Frank,
Yes a slate roof does breathe to some degree but not enough to conform to modern insulation requirements.You will need to add ventilation of some nature in the warmer times.
Sounds like the insulating and poly vapor barrier will be manageable.
The snow guards don't cause the ice damming,but as you correctly point out they don't let the snow accumulation slide off so all the days heat melts some of the snow pack and some invariably re-freezes as the sun goes down.Snow melts quicker than the ice accumulations so over time the inside heat and the solar gain continue to add more ice.
Have you had water penetration yet?
If not and there is a healthy band of ice you might consider maually and carefully removing some of it.
Best of luck.
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Roofnron
Posted on Tuesday, January 25, 2005 - 09:30 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Moderator/Admin Only) Ban Poster IP (Moderator/Admin only)

Hi Frank, I wanted to throw in my opinion as well.

I think and suggest that all attic spaces have a proper balance of ventilation, no matter the type of roof system. People think of shingles when contractors say ventilation, but it is very important for you attic health. I suggest proper ventilation on all roofs I install. Proper ventilation means intake and exhaust ventilation and never more exhaust then you have intake.

Referring to your second email:

First, can you slide baffles or spacers from the uninsulated attic area in between the insulation and the roof deck? This spacers can be bought at Lowes or Home Depot in the insulation isle. It would be nice if you could so you don't have to remove any insulation.

Second, you should check to make sure your insulation isn't blown or shoved against over the soffit and add intake vents. Check out www.airvent.com. They have good information on ventilation and requirements and an interative tool explaining ice dams. Also - slate roofs do breathe and adding the proper ventilation won't extend the life of the slate. They don't provide the proper balance of intake and exhaust your attic area needs.

Third, poly should only be used on the warm side of insulation. I think, if I am understanding you, it would be a bad idea to add poly to the rafters themselves. You could have a big condensation problem if you do that. Older houses are not tight. You are have warm moist air leaking into the attic, which is helping to cause the ice dams. Unless you are meaning for your entire attic to be conditioned space, similar to a cathedral ceiling. But then you would have to take down all the insulation and install the baffles. The idea of # 4 sounds good, but if the interior walls are already complete you still can't add the monolithic vapor barrier.

Lastly, regarding the snow brakes, have you tried lowering the half round gutter so sliding snow or ice doesn't hit them? The front edge of the gutter should be lower than the plane of the roof. I would agree with you on adding snow brakes to an already ice dam problem might not have been a good idea. I would only use them to protect people at entrances or walkways, not the gutter.

I hope my opinion helps.
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Anonymous
Posted on Thursday, January 27, 2005 - 10:41 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Moderator/Admin Only) Ban Poster IP (Moderator/Admin only)

Remember, a thick snow pack on your roof will act as an insulating blanket. Thus the roof deck will become warmer thanks to that layer of snow and melt the bottom of the snow pack. The run off reaching the cold air at the edge of the roof freezes. Your dam is born. Heat cables will work although they do require energy and monitoring. They must be replaced periodically. They are the cheapest solution to ice dam leaks short of removing the snow after every storm.
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FrankDavis
Posted on Sunday, January 30, 2005 - 02:38 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Moderator/Admin Only) Ban Poster IP (Moderator/Admin only)

Guys -

Thank you all so much for your opinions in this matter. I have not only learned alot, but you certainly are helping me aviod future problems.

I have begun insulating the top(ceiling) and sides (knee walls) this weekend as a way to help minimize heat loss into the attic.

Thanks again!!!
Frank

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