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Opinion on adding foam board insulation on the interior over existing drywall.

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CaptainRon

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Discussion starter · #1 ·
Greetings all.

I'm doing a small remodel on a 100 year old home to use as rental property. There is zero insulation in the walls. The walls have the original lath and plaster with 1/2" drywall over that. I really don't want to tear all that out and open the walls. I'm not a big fan of blowing in insulation from the outside. For one, it's too expensive for this project and I know there can be issues with putting insulation in the walls of old houses because there's no vapor barrier behind the plaster. I know there are many opinions on the subject. I've opened the walls of old houses before to find the insulation wet and moldy due to the lack of a moisture barrier on the inside. I thought perhaps I could install 1" foil faced foam board over the existing walls, fur it out and install 3/8" drywall over that. I know the R-value would be minimal, but it's better than zero R-value and should help at least some to slow down the heat transfer. My concern is, will this also create a moisture problem. Will moisture be trapped between the foam board and the new sheetrock? Any and all opinions would be appreciated. Thanks.
 
Discussion starter · #6 · (Edited)
"You need to convince me that you are really a contractor, then I will offer my advice."

Well, I'm not exactly sure how I can convince you, but I've been a contractor for 30 years. I was a sub-contractor for a home builder early on in my career for 8 years before I went on my own. I do small residential remodels (kitchens, baths, etc.) but mostly manage rental property, doing the maintenance, repairs and turn overs. I own a few rental properties myself and just picked up this house I'm working on now.
 
Discussion starter · #7 ·
jaydee said:
Blow insulation from inside
Click to expand...
My concern with blowing in insulation whether it be from the inside or the outside is the issue of creating a moisture problem since there's no vapor barrier behind the plaster. I have seen evidence of this problem when I've opened up walls in older homes that had insulation blown in. I realize there are opposing opinions on this.
 
#8 ·
I would be afraid ,witout knowing more about the house,of moisture getting trapped between the foam and drywall.You will also have to extend all the jambs and outlets 1 3/8".Sounds like a lot of work for minimal gain.IMO
 
Discussion starter · #12 ·
mako1 said:
I would be afraid ,witout knowing more about the house,of moisture getting trapped between the foam and drywall.You will also have to extend all the jambs and outlets 1 3/8".Sounds like a lot of work for minimal gain.IMO
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Hey there. You're actually in my town. Yeah, I realize I'll have to extend some outlets and it would only affect one window which I just replaced, so it's not trimmed out yet. And actually, it's not all the exterior walls. The house has had much newer additions added to two sides of it, so those walls became interior walls. I also thought by adding furring strips over the foam it would create an area of dead air space between the sheetrock and foam that would add additional R-value to it.
 
#13 ·
CaptainRon said:
My concern with blowing in insulation whether it be from the inside or the outside is the issue of creating a moisture problem since there's no vapor barrier behind the plaster. I have seen evidence of this problem when I've opened up walls in older homes that had insulation blown in. I realize there are opposing opinions on this.
Click to expand...
The issue isn't lack of a vapor barrier but rather air leakage & screwy flashing details, well and high indoor humidity, plumbing leaks, ancient wiring...
 
#14 ·
Opinion On Adding Foam Board Insulation On The Interior Over Existing Drywall.

Yank the interior finish and insulate it right. Like mentioned it is air leaks and not so much vapor barrier that cause issues. You can do a pretty good job of air sealing and insulating if you gut the interior and do it right. I wouldn't even consider what you are thinking. Complete waste of time.
 
Discussion starter · #17 ·
mako1 said:
"Hey there. You're actually in my town"
If your last name is Miller I'm actually 2 blocks from your shop.Just trying to think of contractors here named Ron.
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No, that's not me. My company is CU General Contracting. I've been in business in Champaign/Urbana for about 30 years. Most of my work now is on rental property. Repairs, rehabs, etc. I realize what I'm purposing to do is far from the optimal solution, but I just hate tearing out old plaster walls, especially when they've also been covered with drywall. And when you get old and have achy joints, you get lazy : )
 
#20 ·
I'm assuming this is balloon framed.

Step 1: get rid of any water leaks / moisture sources

Step 2: air seal. Keep in mind, some of the old plaster interior and exterior walls will be open clear into the attic

Before step 3, make sure you don't have knob and tube in the walls. Also make sure you know how ceilings are handled - you can have some major difficulties blowing into ceilings.

Step 4 : blow the walls OR put the foamboard on the outside OR trench all the ceilings and put the foam board continous on the inside walls (except for the subfloor, etc.

If all you need is a vapor retarder, use a vapor retarder paint on the exterior walls - tear out just to put a 6 mil plastic sheet in place is a little overkill, IMO.

There is no cheap, easy, fast solution. Putting the foam board on the inside pretty much keeps you from blowing the walls later.
 
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