Question about Plaster walls

est1900December 8, 2007


Does anyone know if plaster is considered a breathable / porous material? Most of the walls in my house are plaster and recently I have noticed that while standing near one of the largest walls in my house that I can feel a breeze on very cold days when the wind is above normal. Its very odd because I don't see any gaps or holes anywhere but without question there seems to be a breeze blowing right through the wall as if there wasn't a wall there at all. Granted, it's not to the point of blowing my hair back or anything but it seems drastic enough to possibly be my primary culprit in the homes very lousy ability to retain any heat in the winter months. The outside of the home is covered in vinyl siding and underneath that are wooden laths. It appears there may be some kind of black tack paper/white Styrofoam as well that I assume are acting as an insulation barrier but itÂs definitely not Tyvek.

My digital thermostat is set to kick the heater on whenever there is a 4 degree difference between the target temp and the actual interior ambient temp. The heater comes on for a few minutes and then shuts off as normal but literally within a 5-10min time frame it is kicking back on again to reheat the house.

I am trying to maintain the homes era correct features as much as possible but if I can't seem to get the home to retain heat better I may have to resort to using modern materials in order to combat the heating costs during the winter months. Last winter my average monthly heating expense was $380 for a 1500 sq/ft home which is pretty ridiculous. I am dreading the thought of what my bills will look like this year now that fuel costs have gone thru the roof.

I originally thought this problem was related to half the windows being only single pane glass with storms but now I am reconsidering this theory. I know there are definite improvements to be made in terms of the windows but at a quoted price of over $900 per window installed (Andersen) I would hate spend that kind of money and still have a cold home because of other issues that I maybe overlooking.

One of my initial thoughts was to get 1 x 3 wood strips and build the drafty wall out a bit by adding a layer of drywall then use a foam sheet insulation of some sort between the plaster and the drywall. Doing this would also fix another issue with this wall which is related to one of the previous owners (ie..brain surgeon) painting over wallpaper covering the entire span.

Any opinions you may have on my situation are appreciated. Thanks

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You are right about the windows. Payback is usually very long and many times wont solve your problem if there are other issues. That Styrofoam insulation probably wasnt sealed correctly and air is getting around it to your wooden lathe. The lathe also has probably many cracks and gaps around it letting air into the wall structure. Do you know what kind and how much of insulation you have in the wall cavities if any and your attic space?
If you can, seal all baseboards with clear 100% silcone caulk both the tops and bottoms. Also caulk any other gaps you find. Seal all penetrations of your upper ceiling to the attic with spray foam or caulk like duct chases plumbing chases wiring etc. Then beef up your attic insulation to the recommended values for your area. In many cold climates they call for R49 in the attic space. I would use loose fill cellulose instead of fiberglass cause it does a better job of sealing and covering everything. Only after all that, think about adding insulation to your walls if theres space for it. Again you can blow in cellulose into the wall cavities by drilling holes and blowing then patching them. Its messy but fairly easy and works.
With your large fuel bills you probably also have an old inefficient furnace. You can upgrade this but will cost you. So to solve your issues go in this order of less costly/best payback to more expensive/longer payback: Air sealing with caulk/sprayfoam and foamboard entire house, increase attic insulation with cellulose, wall insulation, furnace upgrade, window upgrade.
good luck

    Bookmark   December 8, 2007 at 1:20PM
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Solid plaster in good shape will not allow air to move through in any significant amount.
It IS a pretty decent heat conductor though, and if air is getting into the cavities behind the plaster the R value of the plaster itself is nothing to write home about, about R-1 per inch (the same as wood).
If the wall is cold (use some aluminum tape and put a thermistor on the surface to get a decent surface measurement) it will create convection flow as the air chilled by the wall falls down towards the floor.
While cold does not radiate like heat, a cold surface absorbs any heat that is radiated towards it.

    Bookmark   December 8, 2007 at 4:47PM
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Is your attic well insulated? If cold air is in the attic, it'll drop down the wall cavities. I'd leave the windows alone and instead lay rolled insulation on the floor up there, if you haven't already.

    Bookmark   December 8, 2007 at 5:18PM
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Just remember that fiberglass wont do a thing to stop the cold air. If it did they wouldnt use it in some furnace filters. Cellulose is far better at insulating and even slowing the air but you have to actually air seal first with caulk and spray foam. If the walls have no top plates in the attic make some with foamboard and then caulk or foam that as well.

    Bookmark   December 8, 2007 at 5:49PM
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Found this on John Leeke's website....

Attic Insulation: Heat rising through the attic and roof is a major source of heat loss, and reducing this heat loss should be one of the highest priorities in preservation retrofitting. Adding insulation in accessible attic spaces is very effective in saving energy and is generally accomplished at a reasonable cost, requiring little skill to install. The most common attic insulations include blankets of fiberglass and mineral wool, blownin cellulose (treated with boric acid only), blowing wool, vermiculite, and blown fiberglass. If the attic is unheated (not used for habitation), then the insulation is placed between the floor joists with the vapor barrier facing down. If flooring is present, or if the attic is heated, the insulation is generally placed between the roof rafters with the vapor barrier facing in. All should be installed according to the manufacturer's recommendations. A weatherization manual entitled, "In the Bank . . . or Up the Chimney" (see the bibliography) provides detailed descriptions about a variety of installation methods used for attic insulation. The manual also recommends the amount of attic insulation used in various parts of the country. If the attic has some insulation, add more (but without a vapor barrier) to reach the total depth recommended.

Problems occur if the attic space is not properly ventilated. This lack of ventilation will cause the insulation to become saturated and lose its thermal effectiveness. The attic is adequately ventilated when the net area of ventilation (free area of a louver or vent) equals approximately 1/300 of the attic floor area. With adequate attic ventilation, the addition of attic insulation should be one of the highest priorities of a preservation retrofitting plan.

If the attic floor is inaccessible, or if it is impossible to add insulation along the roof rafters, consider attaching insulation to the ceilings of the rooms immediately below the attic. Some insulations are manufactured specifically for these cases and include a durable surface which becomes the new ceiling. This option should not be considered if it causes irreparable damage to historic or architectural spaces or features; however, in other cases, it could be a recommended measure of a preservation retrofitting plan.

Here is a link that might be useful: john leeke's attic insulation

    Bookmark   December 9, 2007 at 1:17PM
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It's not likely that the air is coming directly through the plaster walls, rather that it is coming from near or around the walls.

In my house, I had the gas company come out to do some weatherizing and part of that was air sealing with a blower door test. When the tech turned on the blower door, I was standing in my kitchen near an inside wall. All of a sudden, there was a rush of wind coming at me, which was enough to blow up my t shirt. It was coming from what looked like a solid space between the bottom of the wall, and the floor.

One thing you can do is get a chemical smoker at the hardware store, and do some infiltration tests around the wall, so you can see the pattern of the air currents and determine exactly where the cold air is coming from.

Better yet, check with your local gas or electric utility to see if they are running efficiency programs that you can take advantage of. In my case, the gas utility paid 50% of the costs of insulation, air sealing and weatherstripping.

    Bookmark   December 10, 2007 at 11:15AM
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We had an energy audit done on our ancient house almost fifteen years ago. The results of the blower tests were sobering. The technician told us the amount of cold air leakage from outside was the equivalent of having one of our large windows open all winter. The culprit areas? As mwkbear was those areas around the windows, doors, foundations, electrical sockets, chimneys!

We used tube after tube of caulk as a stopgap measure and when we remodeled out kitchen again last winter, I did the plaster repair work, paying special attention to those areas. They are tight as a drum now. Knowing exactly where the heat is escaping is a very valuable tool and it's quite down to a fine art with the testing equipment available in an audit. I highly, highly recommend them!

We also built a solarium along the entire length of the most exposed wall. It's a dead air space now, has some solar gain, and is heated to a slightly lower temperature than my kitchen and dining room. We also replaced the wavy glass single pane windows with modern tilt-in double paned, and added a cast iron vent free gas grate to the kitchen fireplace hearth. It's an extraordinarily cozy room now instead of an engineering nightmare and impossible to heat.

Our energy used fell at least us a relatively rapid payback for the investment. But, there is no way to measure the increase in comfort.

    Bookmark   December 12, 2007 at 12:11PM
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Hi i recently renovated apartment for new tenant ,and trying to avoid complete ripping of old exterior walls.i got a foam board with aluminum face on both sides ,fasten it do the wall and use 1/4 Sheetrock over it .seams like is working bi course new tenant is not to upset with his gas heating bill .You getting a new wall and some insulation ,depends on thickness of foam board .

    Bookmark   February 10, 2011 at 9:00PM
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I'm glad someone asked this question - I was wondering the same thing. I think it's time for an energy audit...

    Bookmark   February 24, 2011 at 8:18AM
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I testify that our electric bill (we have electric heat (heat pump) and A/C) dropped nearly in half after we did blown-in insulation in our attic, especially dramatic drop in the winter. We did it ourselves(ok my dad did it with me) and were able to get a tax credit for 1/3 of the cost. Cost way less than $1000 for well over 1200 sq feet of attic piled very high.

I'm still working on caulking the windows, but it's something that is CERTAINLY helping. I also need to caulk the windows OUTSIDE.

    Bookmark   February 25, 2011 at 11:01PM
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