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Old_school (Old_school)
Senior Member
Username: Old_school

Post Number: 765
Registered: 01-2009
Posted on Tuesday, January 17, 2012 - 10:03 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Moderator/Admin Only) Ban Poster IP (Moderator/Admin only)

Pdcryan. What you describe will work just fine. If you are going to use a spray on insulation,(I would recommend this) you may just want to strike a line about 1 1/2 inches down from the deck boards and drive some spikes part way into it. Then rip a sheet of styrofoam the width of the rafters and push it right against these nails. You will have a 1 1/2 airspace and a good surface to spray the insulation. Just do the whole attic like that and then have them spray the urethane to fill the rest of the void.

If you do that, I would also vent this whole system to the top 3 feet of the peak and install some rafter ties with the same styrofoam attached to them. Continue the spray right on the bottom of that. This will be your "attic" Install some gable vents on either end, with perhaps a fan on one of them. I would carry the "attic" right down to the floor. Just make sure you have a continuous vent on the soffit and that the air can flow from there into the 1 1/2" space between the rafters. You will want to make sure that none of the urethane gets into those cavities as it can expand and close them off.

If you install a fan on one of the gable vents, you should make the other gable vent smaller so that the fan will have to pull air from the soffits to balance the air pressure. You want the air to draw from all over. Done properly, you will have great airflow and no ice what so ever. It will be cool in the summer too. that is important for living when it gets hot.
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Pdcryan (Pdcryan)
New member
Username: Pdcryan

Post Number: 2
Registered: 01-2012
Posted on Tuesday, January 17, 2012 - 08:02 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Moderator/Admin Only) Ban Poster IP (Moderator/Admin only)

Thanks! Re the soffits, I meant that we would have knee walls a few feet out from the eves that would give us some space to crawl around and look for a leak it water was getting through the slates and running down the baffles.
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Lv_pa (Lv_pa)
Intermediate Member
Username: Lv_pa

Post Number: 40
Registered: 05-2007
Posted on Tuesday, January 17, 2012 - 11:29 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Moderator/Admin Only) Ban Poster IP (Moderator/Admin only)

BTW, I didn't understand your last paragraph about soffits having space between the walls, can you elaborate on that?
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Lv_pa (Lv_pa)
Intermediate Member
Username: Lv_pa

Post Number: 39
Registered: 05-2007
Posted on Tuesday, January 17, 2012 - 11:27 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Moderator/Admin Only) Ban Poster IP (Moderator/Admin only)

My roof looks exactly the same from underneath-- some call it "skip sheathing" when you have those laths with large gaps in between. (However, since I'm re-roofing, I have had to add 1x6 fill-in boards in some areas to give extra support for nailing slates, and also for nailing roof brackets for climbing the roof.)

So far I've put in soffit vents on one side and am planning to add ridge vents and baffles and insulation under the slates, as you described. I think they have styrofoam baffles at Home Depot for this purpose, or maybe you can just make them out of cardboard or something.

As for insulation, the way I understand it, the basic choices are open-cell or closed-cell. Open-cell is like fiberglass batts, loose-fill, etc. where air actually can get through, so you also need a vapor barrier. Closed-cell is sprayed in, and is more expensive, but has a higher R-value per inch, and air cannot get through it so you don't need a vapor barrier.

You may want to check out this article about insulation:

http://www.kyfoam.com/r-fairy-tale-cp.htm

I can also give you some names of insulation contractors in the Lehigh Valley, PA area-- I don't know if central Jersey is within their service region, though.
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Pdcryan (Pdcryan)
New member
Username: Pdcryan

Post Number: 1
Registered: 01-2012
Posted on Monday, January 16, 2012 - 08:40 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Moderator/Admin Only) Ban Poster IP (Moderator/Admin only)

Long time follower of these threads - but thus far I haven't really found a good answer to our problem. Sorry if this is a repeat question that I missed! (BTW, my copy of the print bible is on route, so if there's a good section in there that someone could point me do, that would be helpful).

We have a 110-ish year old PA slate roof that is in relatively good condition in Central New Jersey (at least I've convinced myself it's in good shape - it's water tight, after all - except for one of our yankee gutters). Our walk up 3rd floor is currently unfinished, gabled on 3 sides and ripe for adding a few bedrooms. Our slates are attached to furring/batten strips mounted perpendicular to our rafters - and completely exposed from the underside (ie, no roof decking or sheathing to speak of).

http://www.maryandryan.net/2012/01/slate/ has a few pictures

We want to finish, insulate and heat this space. My thought had been to add some type of baffles between the rafters so that the slate can vent both vertically (thanks to the baffles) and horizontally (thanks to the battens), and then use closed cell foam on the inhabited side of that assembly to get the R-value we need. Either plywood or perhaps rigid foam insulation would be used for the baffles to protect the slate from the foam and permit ventilation in that air space. I suppose a ridge vent or vents in the gables would then be needed - along with soffit vents?

If anyone has thoughts on a best practice for this type of application - I'd love to know. In my scenario the soffits would have a few feet of space between our walls that would be accessible for periodic inspection to see if we had any leaks. Any thoughts - or recommendations for New Jersey slaters who would be interest in helping repair/consult would be most appreciated!

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