Hi, I need some advice on whether to insulate a cavity wall in a 1910 brick home. Its is 3 wythe brick with approx 1&1/2″ air cavity between the inner wythe and outer two wythes. Plaster is directly on the inner brick. Its not a modern (1930’s or newer) cavity wall because there are no weep holes or other channels to drain the cavity. In England, Australia, NZ they insulate cavity walls with Rock Wool or UF foam. The National Park Service’s web site says don’t do it. I want to insulate with foam such as Tripolymer, which is permeable. The cavity is the condensation plane. I am concerned about moving the freezing point of water vapor from the cavity to the outer wythes, thereby causing spalling. I live in Southern Minnesota, a relatively cold and dry winter climate. I have asked this question on many boards and energy web sites and few have answered. Any help would be greatly appreciated. Thank you.
Bob Winzenburg, North Mankato, MN
Replies
The moisture comes from within the house area. (bathroom, kitchen, humans)
If you can actually fill the cavity with low expansion foam, you will effectively prevent moisture from entering the outer layer of brick and causing any problems.
Having said that, filling the cavity to 100% is highly unlikely.
You may want to consider installing baseclad on the inside of the house instead and move the entire brick wall to the cold side or outside the envelope.
Gabe
Gabe,
The moisture comes from within the house area only during the heating season. He didn't say if he had AC. In the summer, in northern Minnesota, with AC, moisture is outside in.
Brick is premeable and holds a lot of water. The summer scenario, worst case, if it rains and then the sun shines is the brick gets wet, the moisture goes through the brick, hits and air space, goes to the next brick wall (with nowhere else to go) and continues through the wall until it can exit or is condensed on something like the inside of a vapor barrier. This is a classic problem with insulating and air conditioning old structures.
If you stick something relatively impemeable in the path, like foam, do it only in the ineer space and to vent the outer space to allow the moisture to escape.
Joe Listurbek (sp?) wrote an excellent article in the current ASHRAE Journal on just this issue.
He also didn't say what was on the interior of the three whythes. Makes a difference.
Tim
I agree that the cycling damage would only occur in the winter so I will only comment on this portion of the equation.
There's also a huge amount of missing information that would dramatically effect the outcome of any fixes that we could suggest.
So what do we know for sure.....
MN is cold in the winter.
Old clay brick are very porous as is the mortar.
An old clay brick laying on the ground will totally turn to powder in a decade or two.
That same old clay brick will last a century or two if suspended above the ground.
Why....because it's allowed to dry in between rains.
These things we know.
What we don't know as you pointed out was the type of heating in the building. If it's moist heat or dry electric heat without a humidifier makes a huge difference in the humidity available to enter the wall from within.
What we don't know also is the interior wall system or covering so we don't know if moisture is free to enter if it existed.
Having said all these things I think a safe bet would be that if you could ensure that moisture couldn't enter the brick envelope from the inside, most of the issues would be put to bed.
Filling any blind cavity is quesswork. Foams, even low expansion foams have strong adhesive qualities that make filling gaps difficult without exerting a lot of lateral pressures on the structure.
That's why I suggested installing a continuous layer of SM on the inside so that you would get not only a good insulation value and VB but would put the entire brick wall envelope outside where it belongs in this case.
Gabe
Gabe,
"I agree that the cycling damage would only occur in the winter so I will only comment on this portion of the equation."
I want to make sure that all portions of the equation are considered. Too many times, one side gets considered and one side gets ignored. Then damage is done. I would imagine this is part of the great VB debate.
"That same old clay brick will last a century or two if suspended above the ground. Why....because it's allowed to dry in between rains."
But, by simply keeping the bricks on the cold side, you're missing half of the process. I am concerned that you have prescribed a good way to grow mold. Old masonry buildings don't generally have a lot of indoor air quality problems...until somebody comes along and changes things. Adding a vapor barrier without providing the vapor a way out is a bad idea. When you put a vapor barrier in the flow path of moisture, you reduce the capacity of the "sponge" to dry. By half. Moisture from rain, vapor, etc., will pass completely through a masonry wall with a plaster interior and be on its merry way out the widows and doors and whathaveyou. Inside-out or outside-in. It works the same both ways, until you stop it. Then what is it going to do? Turn around and go back out? Eventually, it will, maybe, but not until some has condensed in places you don't want it or found another, unwanted place to go.
"Having said all these things I think a safe bet would be that if you could ensure that moisture couldn't enter the brick envelope from the inside, most of the issues would be put to bed."
I disagree. For half of the year will have created a whole new set of issues.
Tim.
Are you on some type of medication? There's no freeze thaw cycling in the summer and therefore no spalling damage in the summer.
An oil based paint on plaster is a VB for the majority of the existing wall surface.
Adding SM on the inside doesn't change anything other than makes the entire wall assembly consistent and warmer for the occupants.
Life is easier to understand if you don't search to find complication where it doesn't exist.
If your understanding were accurate, there wouldn't be a building left standing after a decade of exposure to winter freeze thaw cycles OR everyone would freeze to death in buildings that were completely open to the outside air.
KISS isn't just an acronym it's a fact of life.
Gabe
I give you guys some more info. Home walls are 3 wythe, with an air space of 1&1/2" between the inner wythe and outer two wythes. Fairly soft brick and mortar, but in good condition. Interior finish is some sort of plaster or cement plaster applied directly to the inner wythe. Wall surfaces are either painted or papered. All three floors are cast in place concrete. Most interior walls are solid brick as they are weight bearing. The interior finishes and millwork cannot be changed as they are original and in good condition. Windows are double hung, single pane, with exterior storms. There is lots of air leakage at the present. Blower door test yielded 9 ACH at 50 pascals. We are working on that aspect. I was considering using Tripolymer (a phenolic) since it is already expanded at the gun and should fill the cavity better than a foam that expands as it is installed. It is fairly permeable, with a perm rating about 16, I think.
Our climate is cold in winter and hot/humid in summer. VB would be the paint or paper on the walls. Most of the inflitration in this kind of house would be in the breaks in the envelope, such as windows, chimneys, chases, etc.
Heat is single pipe steam with cast iron radiators. AC is both central and window units on the 3rd floor. Hope this additional info helps.
The problem with "any" infill/cavity situation is that you're working blind and you don't know the actual quality/quantity of the coverage.
The problem is compounded by the adhesive qualities of foam. In other words it sticks to the wall face before going to it's intended location. Leaving large voids in the building envelope.
I just finished 80,000 sq. ft. of foam insulation under all conditions and I don't work blind. If I can't see it, I cover it, period.
I understand your cast iron units would have to be moved to allow the 2" SM to be installed on the exterior walls with an additional 5/8" for the drywall, BUT the end result would pay back in a big way.
I would cover the walls with FR21 Bakelite which is both a vb and adhesive, apply the SM directly to it, glue the drywall to the SM and when completed you have a continuous vb, insulation and sealing system in one shot without any bridging or gaps.
Then your only problem would be those windows and chases.
Gabe
Refer to the following web site. http://www.cavclear.com They're headquartered East of you. I understand this is for re-skinning or new construction but you'll see the need to provide drainage of the cavity wall. I believe if you fill the cavity with foam or wool you may have air quality and structure issues.
FYI only. I doubt you have plaster on your brick for the moisture problems mentioned. More then likely you have a portland stucco with a very fine sand, and maybe no added sand on the finish coat. Probably a two coat system also.
Just my opinion, but I would insulate the cavity.
Don
Edited 12/22/2002 9:18:33 PM ET by Don C.
Edited 12/22/2002 9:22:01 PM ET by Don C.
Didn't know you were still wondering about this. Owens corning makes an insulation especially for filling cavity walls. More then likely the other companies do also. Have you looked into the different insulations available?
Don
I am aware that they make a rock wool for blowing in cavity walls. This is done in England. I haven't found an installer in this area that will do this. Thanks.
That doesn't surprise me unfortunately. Have you tried any of the manufacturers directly? Many of them offer training on new products and techniques and then maintain a database on those qualified to do the work. I have a friend that installs nu-wool insulation but he mostly does university sized pool houses, field houses or anywhere there is a bad echo. Because what he does is not done by many, traveling a state or two for him is not unusual. When you do something unique, traveling just goes with the territory.
Don