insulation over plaster and lathe
I have found this discussion on applying insulation directly to plaster walls.
https://www.greenbuildingadvisor.com/community/forum/energy-efficiency-and-durability/17131/insulation-over-lath
My question is, is it always safe to apply rigid expanded polystyrene directly to plaster walls, with furring strips?
The main issue I am aware of is condensation. Could it form between the foam and plaster wall?
I would apply at least 4 inches of rigid foam and 2 inches of mineral wool as a fire barrier. There is loose fill insulation between at least some of the studs.
Is it even safer to build a wall a few inches from the plaster wall, and attach insulation to that? I read suggestions on that for masonry walls, and perhaps it might be a safer option for all types of walls when the construction is unknown.
Thank you.
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Put the foam directly against the plaster wall- a gap would be a potential thermal bypass. As long as the foam &/or interior finish wall is air tight to the interior, there is no way for humid interior air to transport moisture to the now colder plaster & lath.
By itself 2" of rock wool isn't quite thick enough to qualify as as a thermal barrier for fire-code purposes, but half-inch wallboard is.
Thanks Dana.
I plan to put
1) two staggered layers of 2 inch expanded polystyrene with caulked / foamed edges,
2) 1-2 layers of 2 inch Comfortboard,
3) wood panel finish.
Attaching directly to the wall will be easier and more effective, as long as there is not risk. Thanks.