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Old_school (Old_school)
Senior Member
Username: Old_school

Post Number: 1130
Registered: 01-2009
Posted on Saturday, October 10, 2015 - 05:16 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Moderator/Admin Only) Ban Poster IP (Moderator/Admin only)

In this case, everyone is right. When you foam a roof, you do change the dynamics of the house and the ventilation and air movement. The foam doesn't necessarily "destroy" the old house, but if you stopped a natural air flow that was protecting it, that may "destroy" it. I know when I build cold roofs for houses, I make sure I totally vent the attic space(s) so that the air is free too move in any direction ABOVE the insulation, and I also try and vent down to the walls so that if there is any moisture in the walls, it has an exist point that is less restrictive than the insulated part. Moisture is what pushes off paint from the inside and the paint will push out into the envelope just as easy as it will push the paint off the outside. Moisture and water vapor are the enemies and air movement is the key.

With this in mind, if there was no moisture working its way out of the slate roof, or if you can make it so that it will easily work its way outside in a different manner, the foam will do no harm. The problem is that I almost have to address each house individually and can't give any hard and set ways to do it. I know that doesn't help anyone.!
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Brycenesbitt (Brycenesbitt)
Intermediate Member
Username: Brycenesbitt

Post Number: 35
Registered: 08-2012
Posted on Saturday, October 10, 2015 - 03:12 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Moderator/Admin Only) Ban Poster IP (Moderator/Admin only)

Insulating a ceiling under any sort of roof should be a non-issue for the roof.

At that point you're not affecting ventilation or drying of the roof itself.
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Kwhord (Kwhord)
Senior Member
Username: Kwhord

Post Number: 296
Registered: 10-2006


Posted on Sunday, August 17, 2014 - 08:06 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Moderator/Admin Only) Ban Poster IP (Moderator/Admin only)

Foam kills old houses.
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Steward (Steward)
New member
Username: Steward

Post Number: 3
Registered: 01-2012
Posted on Saturday, August 16, 2014 - 09:52 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Moderator/Admin Only) Ban Poster IP (Moderator/Admin only)

What's your latest opinion on closed cell foam under a solid wood roof deck Joe? I've worked on a number of 100 year old slate roofs that have been foamed and have only found potential minor issues including a little cupping of boards and loose slates that have been pushed up during the installation of foam. Though I haven't run into it yet, I suspect there would be greater chance for rot if there was a leak in part of the roof that sees very little sun, like under a tree that's too close to the roof. Would you still say that an air channel behind rigid foam is ideal? The only disadvantage to that in my opinion is the potential loss of R-value in the creation of that airspace. I would want to limit it to 1".
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Joe (Joe)
Moderator
Username: Joe

Post Number: 815
Registered: 07-2006


Posted on Tuesday, January 28, 2014 - 12:10 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Moderator/Admin Only) Ban Poster IP (Moderator/Admin only)

You should search this message board and read the other posts about insulating a slate roof.

Search button at bottom.
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Hemoon (Hemoon)
New member
Username: Hemoon

Post Number: 1
Registered: 01-2014
Posted on Monday, January 27, 2014 - 09:07 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Moderator/Admin Only) Ban Poster IP (Moderator/Admin only)

I have a room in my house that i am tearing out broken plaster and will insulate walls and drywall. The ceiling is plaster and needs to be removed also, but i have a slate roof. I want to know if its possible to insulate the ceiling of the room. Thanks in advance

Kevin

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