Base wall drafts

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  #1  
Old 01-30-10, 07:41 AM
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Base wall drafts

I posted a little while back about heavy drafts in the home. We couldn't heat too well with the wood furnace and we air sealed the attic which made a world of difference. We now are running into the issue of a heavy constant draft at the base of the walls. The walls were insulated and a vapor barrier was put up, but the base of the wall cavities were never sealed, which is our problem. We have carpet and drywall in place but the drafts are very bad for our comfort and heating. Is there any way to seal the base of the wall cavities without removing drywall? I'd be willing to do it but I would rather find some other way if possible. I didn't know if I could drill small holes in the base of the walls inbetween the studs and inject large expanding foam and hope for the best. Or would I have to remove drywall? The walls are built on top of beams. The house is 150+ years old. Also whats the easiest way to tackle outlets? If I injected foam into the cavities, how much would it take? Thanks.
 
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  #2  
Old 01-30-10, 08:35 AM
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This will take a bit of detective work, but if your walls rest on the sub-floor (under the carpet) and the sub-floor rest on the beams, then you will want to seal the bottom of the walls against the sub-floor. You may have to remove the baseboard, remove a half inch of sheetrock if needed, and caulk or foam the bottom of the wall. This will seal both the sheetrock to wall frame and the bottom of the wall to the floor.

I have seen expanding foam injected into small areas of wall cavities to fill voids detected by infrared cameras. So your idea of foaming the bottom of the cavity might help, but don't go crazy as the high expansion foam can push too hard on the walls. Also, can foam does not like the cold.

As for the electrical outlets and all other electrical boxes, they should be sealed where ever they are, inside walls included. Once air enters a wall cavity, it can flow between the framing and the studs with ease. My choice is to cover each box with contact paper and cut out for the specific device. Then trim the outside so it is hidden behind the cover plate. The principle is, if you eliminate the exit/entrance hole, you eliminate the air moving in that direction. Cold air from where ever it is entering a wall cavity just won't flow to that light switch if there is no longer an exit.

They also make a pour in, slow rise foam for cavity fill. The temperatures would concern me, but it stays liquid longer and might therefore flow into the bottom area better. I have never used it, so no real first hand experience.

A quick temporary fix might be some rope caulk. It can be squeezed into place and removed next summer for more permanent repairs.

Bud
 
  #3  
Old 01-30-10, 09:31 AM
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One of the problems is its a balloon framed home. I don't know how the walls are setup. They were bare in the back room about 5 years ago and I never paid attention on how they were tied into the base of the walls. When I sealed in the basement at the beam and where the joists went into the beams, the air then decided to travel up and out in the living space.
 
  #4  
Old 01-30-10, 10:01 AM
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Is there any insulation in the walls? If none, then the idea of adding some can foam may be best. The other option would be to blow in soma cellulose. Dense pack cellulose does a very good job of blocking air flow.

Do you know what is on the outside of the house. If it is board sheathing, the gaps could present a problem with foam expanding right out through the walls.

A typical balloon construction would be wall studs supported on a beam in the basement resting on the foundation. Up a few inches, they would attach a plate to the studs to form the perimeter of the first floor and connect floor joists caross the span. That would leave the drywall resting on the floor as the only air seal, not very good.

What can you see/reach from the basement? Can you reach up and into that cavity? Or have you sealed that?

Bud
 
  #5  
Old 01-30-10, 11:49 AM
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The walls were filled with urea formaldehyde foam in '78. Then about 10 years ago when the living room was drywalled, the foam was removed and fiberglass put in its place. There was maybe a 1/2 gap looking into the cavity from the basement. The outside of the home was originally dutch lap wood then a layer of tar paper was placed over that and asbestos was put over top that later on. The exterior walls are slightly cool, the bottom of the walls are cold, and thats where the air is entering the home.
 
  #6  
Old 01-30-10, 01:42 PM
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I suspect it is the fiberglass allowing cold air to drop to the bottom of the cavity and seek an exit into your home. I've been known to tape extensions onto those plastic straws to help put that foam where I want it. Is that 1/2" gap near where you would want to seal? If it is, you could apply a reasonable quantity of foam and then block the exit from below with something cut to fit. That would force the foam to expand into the cavity and not just fall out. It won'r like the cold, but it will expand. You could try a section and check it the next day for improvement.

Just to add to your to-do list, if you ever decide to replace the siding, plan on adding some rigid insulation before the new siding goes up. I have completed the front and will eventually do the entire house with 3 1/2" of rigid under new siding. I'm adding new windows as I go, but could re-use the old if I wanted. I'm setting mine to the outside and re-trimming inside. Home energy magazine has a two part article about an energy guy adding 4" of rigid out in Helena. With one wall done, I can tell you it does make a huge difference. The insulation and siding go all the way down to the foundation, so cover the entire area you are dealing with.

Just what you need, more to do, but sometimes having the option avoids doing things half way with half way results.

Bud
 
  #7  
Old 01-30-10, 01:43 PM
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I did some investigating and heres what I found. I looked in an area of the home that had the lathe and plaster gone by the floor, under an old window. There isn't a subfloor, but just 1 layer of flooring. The flooring goes almost up to the wall studs then stops. At that point, the studs are toenailed to the top of the beam. At the point where I looked at how it was built, there was a 1/2 gap to the exterior of the home where the original siding was, and I seen light there. So basically the exterior sheething needs to be sealed at the beam??? I thought about sealing the drywall to the flooring with foam, but I don't know if that would send the air up into the wall where it would come out somewhere else. Where I need to seal, the walls all have drywall, plastic then insulation. I'm stumped. On top of that, the lathe board is in my direct path.
 
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Old 01-30-10, 02:20 PM
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Well, you are not stumped, it's just that the project is a lot bigger than you had hoped. I audited a home with old board siding, lots of air leakage, and the walls were really dumping the energy. He went with 2" of rigid over the entire house. Just finished. Big job, excellent results.

I don't have a perfect solution, but here is one trick I have used. Around windows and doors where the gap is too small for my foam gun to get in there for a good fill, I use a 5/16" drill to drill a hole every inch. I then insert the foam straw and fill. I work my way around and get a very good seal all of the way around the window. Of course I am using the low expansion foam for windows which might be an option for you if you are concerned about expansion out through the walls. They also make a zero expansion foam, ie DAP, that expands out of the straw, but that is it, so little or no pressure to expand after installation. They take more cans, but the foam stays put.

I have a length of 1/4" copper tubing that happens to be a press fit over the plastic tube for the can foam. I tape it so it doesn't accidentally come off, but it is strong enough to push back into the wall to put some foam right at the outside. Angle your holes to where you want them, or make them a bit larger so you can force the tip around. 1/2 day, all cleaned up, cured the next day and ready for a quick coat of mud. The wife wanted to paint anyway .

Bud
 
  #9  
Old 01-31-10, 06:08 AM
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If I can't get into the wall cavity too much, would sealing the drywall to the floor help? I'm hoping it would cause a dead air space in the wall. Our trim is almost 10" tall, so I should be able to remove some drywall to get in there.
 
  #10  
Old 01-31-10, 07:40 AM
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A word of caution.

If the volume of air within a confine remains constant then the amount of air coming in at your base boards is equal to the amount of air leaving the house. Air sealing always seeks the cause for air infiltration. There are several causes for air infiltration such as air leakage and pressure differences. While the object here is to reduce energy costs and improve comfort in our homes there are limits in doing so. One thing that guides professionals in this industry is known as "ASHREA Minimum Ventilation Guide". What this does is help us determine the minimum amount of air exchange for a particular house in order to sustain a "Healthy Indoor Environment".

Houses with wood burning stoves must have a higher rate of air exchange than houses without one. The reason for this is known as the "Combustion Triangle". There are 3 things needed for combustion; Fuel, Temperature and Oxygen. The latter comes from the air within the house. The amount of needed to burn wood varies depending on how big a fire you have in your fireplace/stove. But to illustrate the amount of air needed for combustion is 1 cubic foot of natural gas requires 15 cubic feet of air to completely burn. This amount is doubled if the appliance has an atmospheric draft flue. What this basically means is the amount of air needed for burning wood is equal to the amount of air needed to maintain chimney draft. As in the case with the natural gas this atmospheric draft gas appliance would require 30 cubic feet of air to 1 cubic foot of gas for it to operate safely.

Again, air sealing always seeks the cause for air infiltration and if the cause for the drafts at your base boards is the wood burning appliance I would be remiss if I did not caution you about air sealing these areas.
 
  #11  
Old 01-31-10, 07:45 AM
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The woodfurnace is in the basement. Which has no returns for the ducting to act as negative pressure. The basement is pretty leaky and we never have any problems with backdrafting, or smoke spillage. The living space is seperate from the woodfurnace. If needed, I will add make-up combustion air for the furnace. Our home is not tight by no means.
 
  #12  
Old 01-31-10, 08:51 AM
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Interesting

One thing I wondered is there are also open cavities in the walls in the ceiling of the basement. But when insense sticks are held to them it blows down instead of up? Is this cold air coming down through the walls?

End quote
 
  #13  
Old 01-31-10, 09:12 AM
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I wasn't sure why the air was coming down some walls and up in others. There are small openings to the basement on interior walls that blow down instead of up. Some go up, some down. The exterior walls have a ton of air coming in at the base in the floor above the basement. Almost like having a fan on at the base of the wall. I've been trying to seal the basement where the interior walls are and exterior walls. I think I got everything, or close to it in the attic that I could find.
 
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