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Covering an exterior plaster wall with 2x4 framing and drywall

Covering an exterior plaster wall with 2x4 framing and drywall

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  #1  
Old 06-11-20, 08:47 AM
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Question Covering an exterior plaster wall with 2x4 framing and drywall

I've got a dilemma on my hands here.
I'm a home remodeling contractor for 25 years, we recently finished a "flip" house for a customer. The house is balloon framed, ( stud cavities go from sill plate to attic ). on the exterior of the house we have vinyl siding over 1/2" fanfold insulation which is over old wood shiplap siding and then 1" planking which served as the sheathing back in the 30's, those planks are attached to the dimensional 2"x 4" studs which once again, run the entire height of the home. The existing walls are wood lath and plaster. We, as we have many times before left the plaster up and framed new 2 x 4 walls against the existing plaster ran our new wiring insulated with 3-1/2" fiberglass insulation, installed 1/2" drywall taped and coated 3 coats spackle one coat latex primer and 2 coats of latex paint. I now have a code enforcement official telling me that mold will grow on the surface of the plaster and I have to remove the drywall, insulation and old plaster and fill all wall cavities with fiberglass insulation. I've been through the IRC code book and cannot find anything that supports his, for lack of a better word, theory . He's always been a decent guy and very professional. On a few occasions I've made small changes that I knew weren't code, but made him feel better, but this one is going to cost a few thousand dollars. He is supposed to email me something that backs his statements.
Anyone have any suggestions here? The walls are sealed up properly from the inside.
 
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  #2  
Old 06-11-20, 10:38 AM
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The existing walls are wood lath and plaster.
Is there any insulation in the existing wall?

If not then the wall, all the way to the interior plaster would be exposed to outdoor temps, meaning your new wall and insulation would be the vapor retarder and any moisture that passes would then dissipate to the exterior!

Unless plaster acts as a moisture barrier I dont see how you would get condensation on that surface.
 
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Old 06-11-20, 10:53 AM
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Don't know but you have me interested. Let us know what you find out.

Probably something in "R402.4.1.1 AIR BARRIER AND INSULATION INSTALLATION" that says voids must be filled with insulation. So the original wall should have been insulated. And I agree with him that the plaster would be a condensation surface, but cant find anything in code other than it's not typical wall construction to do it that way.

It would be similar to why basement walls are supposed to have 2" of insulation on them before you put up a stud wall in front of them. It has to do with where the dewpoint will be within the wall assembly. Condensation has to do with temperature of the surface and the dewpoint, not the material per se. The plaster is simply a surface that shouldnt be there as far as the testing and diagrams of wall assemblies are concerned. Bud9051 is a member here that could explain it far better than I could. If he doesnt chime in, try private messaging him.
 
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Old 06-11-20, 04:14 PM
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All I did as a contractor for 15 years was work on 100 plus year old houses and have never once or heard of anyone do what you did.
Not there to see the house your working on, but any I've worked on had no or poorly done blown in insulation done from the outside and no fire blocking in the walls.
Doing what you have done did not address the fire blocking issues, left the outside walls likely uninsulated.
By not taking the time to first remove the plaster and strapping, addressing the fire blocking, add the new wiring then insulating all you did was make the rooms smaller, make far more work building the walls and to make extention jambs.
It would be one thing to add some strapping to the studs to build them out for thicker insulation, but to build a whole new wall is just strange to me.
 
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Old 06-11-20, 05:07 PM
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exceptions

R503.1.1 In the IRC code clearly states that building envelope assemblies that are part of the alteration shall comply with numerous sections of code required during new construction with Exceptions, one of them being:
Where the existing roof, wall, or floor cavity is not exposed
 
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Old 06-13-20, 05:39 AM
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Marq1

There is no insulation in the exterior wall cavity . This home was built nearly 100 years ago, with no signs of mold whatsoever. We even removed a section of exterior wall to enlarge the kitchen area. First we removed the wood siding and 1" planks so that the backside of the plaster wall and stud framing were exposed. Not a hint of mold.
One would think that moisture from the heated side of the plaster would be able to penetrate through to the wall cavity, settle and mold would form. Not the case here. My view is that what we have essentially done is fortified the vapor retardant quality of the exterior walls from the inside and made the dwelling more energy efficient.
 
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Old 06-16-20, 09:41 AM
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I don't know about this kind of situation but I sure am curious about it. Please do not drop out of this discussion until it is resolved. I really want to know what you learn and why and how it all turns out.
 
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Old 06-21-20, 07:52 AM
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tightcoat

After extensive research, and not in any of the plethora of ICC code books I found a very informative publication on vapor barriers, vapor retarders, and the materials that create and are used for them. Green Building Advisor.com
There's also a list of common materials used in construction for wall coverings and their perm ratings which is a materials permeability ( The measure of ease with which water vapor passes through a unit of thickness ).
The existing plaster walls had a perm rating of 12-15 depending on how many coats of paint were on them. At that number, water vapor from the warm interior air was able to escape the building envelope through the plaster and exterior walls. The drywall, Spackle, primer, paint and kraft facing on the insulation drastically lowered the amount of water vapor passing through the existing plaster, making the, for lack of a better word, "situation" inside the building envelope a far less likely place for moisture to hang out and become mold. I've attached a sketch of the wall envelope with the perm ratings of materials that I used. I handed this along with a copy of the publication from Green Building Advisor.com to the code official. He said that he was going to look into it and that his reason for questioning the possibility of mold growth was due to his own experience when remodeling a bathroom with a similar construction to what I did the walls were full of mold.In my thirty plus years in this business I've come across a few situations like this myself. Its usually when a double wall is used to accommodate plumbing in an exterior wall. In this particular application a vapor retarder must be applied to the interior finish in order to slow down the passage of water vapor so that the cavity created can disperse of it as needed in order to avoid the creation of mold
 
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  #9  
Old 06-24-20, 09:19 AM
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So has this been resolved? How? Don't leave us up in the air on this.
 
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Old 06-30-20, 07:19 PM
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resolution

In short, I was able to leave the plaster in tact. The code official took the publication that I had provided and returned the following week without much to say about it. He did however make me remove the drywall and install draft stop which is a whole other topic. The house in question is now more fire resistant than the Sears Tower.
 
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Old 07-01-20, 10:34 AM
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Thanks for letting us know the outcome.
 
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