Insulating a brick home


Old 05-19-02, 06:40 AM
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Question Insulating a brick home

I posted this over on the Bricks and Masonry forum; thought it should go here as well.
We have a home with 3 course brick walls and concrete floors, circa 1910. There is a 2" air space between the outer 2 courses and the inner course of brick. The walls are plaster applied directly to the brick. I know the air space is for condensation. We live in So. Minnesota, with relatively cold, dry winters. The house is one big thermal bridge. I would like to insulate that 2" air space using tripolymer foam, which is a phenolic foam that is fully expanded at the time it leaves the application gun. The company has done many of these homes. My question is this: Will foaming in that air space cause problems with the brick? Will the moisture moving through the brick freeze and cause the brick to fail? The bricks are quite soft. C.P. Chemical, the maker of tripolymer, tells me that the foam shrinks slightly and should allow condensation to run down the wall of that air space. Any help on this would be greatly appreciated. Thank you.
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Old 05-19-02, 06:35 PM
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Cavity wall insulation

Perhaps the following might be helpful:

The insulation should reduce the heat flow through the walls of the home as well as the transmission of moist air, thus reducing the possibility of high moisture levels in the wall cavity.
Old 05-19-02, 07:17 PM
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Thanks. nm

Old 05-21-02, 09:28 AM
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There are 2 reasons why I would not recommend injecting foam in the dead air space. Diffusion and Equilibrium Relative Humidity (ErH%). Diffusion explicitly implies that all materials will have heat travel through it, if a portion or a side is at a lower temperature. ErH% basically does the same thing except that it applies to % of moisture content in materials. Both even apply to air. Degree of temperature difference will affect the rate of diffusion and the amount of humidity in a material and the air. This not only applies to 2 different materials and the air but will also applies to similar materials like brick to brick.

If we apply this to the brick wall without the foam, as the heat from the house travels through the first course of bricks, it will carry a % of humidity with it. This is one of the causes that makes the air in houses dry during the winter. The 2nd course of bricks will be at a lower temperature than the first course. This will attract the heat coming through the first course. In most cases the cooler brick will absorb the heat much faster than it will the humidity. So the air in the dead space absorbs it. Even if the air became saturated and the humidity condensed in the dead space, eventually the humidity levels in either course of bricks will drop and absorb the moisture.

The heat with a % of humidity continues to travel through the 2nd and 3rd course of bricks to the outside where it is easily absorb by the shear volume of air with a lower temperature and normally with a lower % of humidity.

Injecting foam into this dead air space will impede the process mentioned above and will eventually lead to increase deterioration to the wall which will lead to the structual failure of the wall. I am an Energy Conservationist and we have been blamed on numerous occassions for doing just this. This is well documented by structual engineers and architects throughout this country. I see that many of my collegues have not learned by our mistakes and I do mean ours.
Old 05-21-02, 10:30 AM
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Thanks for the detailed response. In searching...

the web for info on cavity fill, most of the info was in the UK where there appears to be an extensive industry devoted to cavity fill, since they have so many brick homes. The dominant fill material is rock wool or mineral wool. Other materials included U.F. foam (probably illegal here?) and styrofoam beads. I was unable to find any technical info on the subject of the effect of filling the condensation plane or air space with insulation. In fact, I have left requests on the DOE and related web sites and have only gotten general responses about wall insulation. Your post is the only one of many to provide any real food for thought. Again, thanks.
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