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Insulating exterior walls of an old house by building a dummy wall.

Insulating exterior walls of an old house by building a dummy wall.

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  #1  
Old 01-10-15, 07:56 PM
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Insulating exterior walls of an old house by building a dummy wall.

Greetings all. I'm renovating an old house that has no insulation in the exterior walls. The walls are lath and plaster with newer Sheetrock/drywall installed over it. I don't want to tear out the walls obviously, since it is both plaster AND drywall. So I was thinking about just framing up a 2 x 2 "dummy wall" against the existing exterior walls and insulating that. Fortunately there are newer additions built on all but the front and one side of the house and they ARE insulated. So has anyone done this? I'm mainly concerned about creating a possible moisture problem between the two walls. I would of course use paper backed insulation and could also add a plastic vapor barrier. I've heard a lot of horror stories about blowing in insulation in the exterior walls of old houses and creating a moisture problem. Plus it has nice vinyl siding that I'd rather not remove or cut holes in.
 
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  #2  
Old 01-10-15, 09:02 PM
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Not sure where your hearing those story's about moisture in the walls, unless there's water getting in from rotted window sills I've never seen it before.
The best way in your cause is going to be to have it blown in from the outside.
Vinyl is not drilled, it's simply removed in a few area where the holes need to be.
Very simple job to remove and reinstall with no damage to the siding.
 
  #3  
Old 01-11-15, 04:34 PM
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Installing foil faced rigid foam board over existing drywall

I'm trying to add at least some insulation to the outside walls of an old house that has zero insulation in the walls. The old plaster walls have been sheet-rocked over, so I'm not interested in tearing all that out. Has anyone here Installed foil faced rigid foam board over existing walls? I would then install furring strips over the foam board 16" OC to attach a new layer of 3/8" drywall. Will this create a moisture problem? if not, should the foil side face into the room?
 
  #4  
Old 01-11-15, 05:44 PM
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Not a great plan. I would locate the center of all the stud bays, determine if there is mid blocking in the bays, drill1" holes through the sheetrock/plaster/lath 3" below the ceiling, opening up the guts of the bay, and blow in cellulose insulation readily available at box stores with free blower usage. Then just patch up the holes at the ceiling and wherever there was blocking.
 
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Old 01-11-15, 09:42 PM
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What's on the outside for siding? If it's wood, or vinyl all this insulation inside the walls can be done from the outside.
What your suggesting is going to be way more work then your figuring and almost no gain.
Besides all the time and materials to do the sheetrock all the windows and door trim would have to come off, jamb extensions made, primed and painted, outlet and switch boxes extended out.
Is this house balloon wall construction? If so those walls are open all the way from the basement to the attic.
Adding fire blocking at the top and bottom of the walls will go a long way.
Rim joist been insulated?
How much insulation is in the attic, in your area there should be about R-50 which is 12".
 
  #6  
Old 01-12-15, 06:51 AM
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I was told by an insulation contractor not to add insulation from the outside because I don't have a vapor barrier on the inside, thus creating a moisture problem in the walls. I realize that adding foam board on the inside isn't going to be the same as having insulation in the walls, but I figure it will help some in slowing the transfer of heat.
 
  #7  
Old 01-12-15, 09:09 AM
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Moisture from an uninsulated cavity will be considerably more than a properly insulated one, even without the barrier. Adding foam will encapsulate the moisture in your plaster and sheetrock causing mold. 2" XPS will be about R10, bulky, and expensive.
 
  #8  
Old 01-13-15, 12:42 AM
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I am sorting dealing with the same situation. Wouldn't you like to find the ******* who decided not to insulate exterior walls?




Anyway, there's a frozen pipe in the one I'm dealing with. You're in cold IL and subject to this problem. Listen, if you have water pipes in these walls and insulate only on the side of the pipes that faces the inside, then you would block off all the heat the house has from getting to those pipes. Heat always moves from hotter area to colder and insulation retards this flow.

The best way to keep a pipe from freezing is to only insulate on the colder side of it (the half of the stud bay that faces outside), but insulating both sides of the pipe is common practice and fine and also helps maintain AC in summer, but if you have real drafty siding, then you might want to only insulate the colder side of the pipe, but that usually means taking the whole interior or exterior off.

I posted to your other thread, I don't think it's such a bad idea if you are just screwing foam board to the existing studs and then drywall over that. I wouldn't worry about any moisture build up. People drywall over wallpaper all the time or drywall over existing drywall or plaster lathe that has tons of paint coats that act as a vapor barrier. The only thing is you better make sure you don't hit any wires screwing everything, and also all this work for you will probably only get like R 7 from foam boards and they aint cheap, you can probably for the same price but less work inject foam and get r14+ and if there are pipes in the wall, again, you will insulate on the colder side of them




I highly recommend not using cellulose even though you can rent the machine at most HDepots yourself. You hit a horizontal wire or receptacle box or something and the bay clogs and you might not know it did, or the 100 foot hose clogs and is a nightmare to unclog.

The expanding injected foam you probably need a license to buy locally, you can buy online like foamitgreen for like $500 or something though but I'm not sure if you can pump that into a wall because it has a trigger handle end for shooting directly onto open work, maybe you can attach a hose to the end of it.

If not buying the kit online, then call around prices for having it injected. You can pull the vinyl off in one strip high and one strip low and drill two holes per bay with a hole saw and have it ready for the injector to just come and inject and leave for a lower cost.
 

Last edited by Shadeladie; 01-13-15 at 05:27 AM. Reason: language
  #9  
Old 01-13-15, 01:07 AM
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I am sorting dealing with the same situation. Wouldn't you like to find the ****** who decided not to insulate exterior walls?


Anyway, there's a frozen pipe in the one I'm dealing with. You're in cold IL and subject to this problem. Listen, if you have water pipes in these walls and insulate only on the side of the pipes that faces the inside, then you would block off all the heat the house has from getting to those pipes. Heat always moves from hotter area to colder and insulation retards this flow.

The best way to keep a pipe from freezing is to only insulate on the colder side of it (the half of the stud bay that faces outside), but insulating both sides of the pipe is common practice and fine and also helps maintain AC in summer, but if you have real drafty siding, then you might want to only insulate the colder side of the pipe, but that usually means taking the whole interior or exterior off.

I posted to your other thread about the dummy walls, I don't think it's such a bad idea if you are just screwing foam board to the existing studs and then drywall over that. I wouldn't worry about any moisture build up. People drywall over wallpaper all the time or drywall over existing drywall or plaster lathe that has tons of paint coats that act as a vapor barrier. The only thing is you better make sure you don't hit any wires screwing everything, and also all this work for you will probably only get like R 7 from foam boards and they aint cheap, you can probably for the same price inject foam and get r14+ and if there are pipes in the wall, again, you will insulate on the colder side of them.

I highly recommend not using cellulose even though you can rent the machine at most HDepots yourself. You hit a horizontal wire or receptacle box or something and the bay clogs and you might not know it did, or the 100 foot hose clogs and is a nightmare to unclog.
 

Last edited by Shadeladie; 01-13-15 at 05:27 AM. Reason: language
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