Thick masonry walls
Geoff Bamford| Posted inEnergy Efficiency and Durabilityon
I have a friend who owns a 600 yr. old stone house in northern Germany.
In the 70’s, interior 2 x 4 walls were added with open cell white foam board 1″ thick, no vapour barrier and 1/2 drywall.
They are experiencing mould issues at lower portions of interior walls.
Their intention is to open up the walls and seek advice on possible solutions. One thought is to install dense pack cellulose insulation in 2×4 cavities.
My concern with that is temp change in winter could affect integrity of mortar(stone wall) at some point in its cross section.
Any thoughts, recommendations appreciated
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Search and download construction details
Replies
Geoff,
It sounds like there is mold on the gypsum drywall, near the floor. Is that correct?
Mold won't grow unless the surface is damp. The question is, why is it damp?
There are several possible answers or contributing factors.
One possibility is that the owners don't keep the building uniformly heated during the winter. If the lower section of the wall is cold, the cold surfaces can encourage condensation.
Another possibility is that the masonry wall suffers from "rising damp," because there is no capillary break at the base of the masonry wall. This might make the entire area damp.
A third possibility is that there is an air leak that is introducing cold exterior air that is cooling the bottom of the wall.
A fourth possibility is that the house has a masonry floor, or perhaps a concrete slab floor, and that this floor is uninsulated. This would make the bottoms of the walls cold and damp.
To reduce the growth of mold, you want to make sure that part of the wall is warm and dry. That can be accomplished by addressing the rising damp (if the problem exists); sealing air leaks; adding more insulation between the cold masonry and the drywall; adding vertical insulation at the exterior of the foundation; and improving the heating system so that more heat is directed to the bottom of the wall.
Thanks Martin.
If adding more insulation, say rock wool or dense pack cellulose and air leaks have been addressed, would it be advisable to install a vapour barrier on warm side?
Geoff
Geoff,
Is the rigid foam board installed in strips between the studs, or as a continuous layer between the masonry wall and the 2x4s?
It is installed in strips between the studs.
Geoff,
The insulation is installed wrong; a continuous layer of rigid foam between the masonry and the stud wall would have been preferable.
The first step is to seal any air leaks at the perimeter of each strip of rigid foam. This can be done with caulk, canned spray foam, or high-quality tape. For more information on this method of insulating, seeCut-and-Cobble Insulation.
如果这是认真完成,其余的each stud cavity can be filled with a fibrous insulation product. I think that mineral wool would make more sense than cellulose, since mineral wool can tolerate occasional episodes of moisture a little better than cellulose.
In addition, I would pay attention to the advice I gave in my first answer -- especially concerning the need to insulate the perimeter of the floor system (a slab, perhaps?) and to improve the heating system.