Insulating an exterior wall

[Ditch Doc]

Hello all,

I live in an old farmhouse that is roughly 100 years old. Right now, my exterior walls are uninsulated, with aluminum siding installed over old wood siding and there is drywall on the interior. In a week or so, I will tear out the drywall, re-wire and add insulation. I will not know exactly what I'm facing until the drywall is down, but I believe that it is a mix of modern 2x4's and rough cut, some may be 16 on center, but I'm betting most are 24".

I have been searching for a good way to seal for air and water vapor while insulating. I know that the vapor barrier goes to the warm side. Here in Raleigh, NC, it stays hot and humid from about May until September. We run the heat from about October through March. Spring and fall stay wet. I'm going back and forth between a couple of ideas...

1) laying a layer of 1/2" rigid foam between each set of studs, sealing the edges with canned foam, then laying a layer of R-15 paper-backed fiberglass batting with the paper facing the room. Drywall over this.

2) leaving out the rigid foam and laying the batting with the paper facing the room, followed by a layer of poly sheathing over the studs. Tape openings. Drywall over this.

Which way would be effective, but not breed mold?

 

[DC73]

A few random thoughts.

Walls have to be able to breathe to at least one side. Most building scientists are rethinking vapor barriers. Most prefer vapor retarders to vapor barriers and the proper application is highly dependent on your climate. This site is good for a lot of things but there really are no building scientists here that I know of. You'll tend to get responses based on the climate of the person responding.

Do yourself a favor and visit GreenBuildingAdvisor and pose your questions in their Q&A forum which is frequented by building scientists. Those guys love old houses. Pay particular attention to a guy named Dana D. if he still posts on the site. GBA also has several articles that have been written about vapor barriers that should prove useful.

Another good source for research is BuildingScience.com.

Consider mineral wool insulation which is fire resistant, sound resistant and blocks the flow of air better than fiberglass. More costly than fiberglass but less than spray foams. I think its worth it.

Good luck,

DC

 

[8man]

DC makes a good point. The wall needs to breath to one side or the other depending on temps and humidity. You don't want to **** moisture into the room on a hot day with the AC trying to pull the humidity out of the house. Talk to a local HVAC company, go to a new home under construction and see how they are "sealing" the wall and with what. That would help.

Here, I'd line the cavity with Tyvec or a similar product by weaving it around the studs and nailing it to the studs on the side on the inside where you can reach it. Then use unfaced insulation and close it up.

The problem areas will be around windows and doors where you need to seal them to keep away leaks. That will take some more thought.

Good luck.

 

[theoldwizard1]

Hire a spray foam company and have them spray on a 1" layer. You get both a vapor barrier and some insulation.

After that, choose whatever kind of insulation you want; fiberglass roll or batts, "wet" cellulose or dry blown in cellulose or fiberglass afetr the wall board is back up.

 

[DC73]

Hire a spray foam company and have them spray on a 1" layer. You get both a vapor barrier and some insulation.

After that, choose whatever kind of insulation you want; fiberglass roll or batts, "wet" cellulose or dry blown in cellulose or fiberglass afetr the wall board is back up.

This could be a good option but make sure to use closed cell foam and not open cell. Also, check with the building experts because in some climates, 1" might not be enough to avoid condensation issues.

DC

 

[theoldwizard1]

This could be a good option but make sure to use closed cell foam and not open cell. Also, check with the building experts because in some climates, 1" might not be enough to avoid condensation issues.

Concur on the closed cell, but as long as all cracks are sealed I don't see condensation being an issue.

 

[DC73]

. . . I don't see condensation being an issue.

It has to do with the temperature of the interior surface of the foam. If the foam is not thick enough in a cold climate, the interior temperature of the foam could be at a low enough temperature for condensation to occur on the surface of the foam especially if the house is well sealed and the interior humidity is sufficient.

DC

 

[zable9]

A few random thoughts.

Walls have to be able to breathe to at least one side. Most building scientists are rethinking vapor barriers. Most prefer vapor retarders to vapor barriers and the proper application is highly dependent on your climate. This site is good for a lot of things but there really are no building scientists here that I know of. You'll tend to get responses based on the climate of the person responding.

Do yourself a favor and visit GreenBuildingAdvisor and pose your questions in their Q&A forum which is frequented by building scientists. Those guys love old houses. Pay particular attention to a guy named Dana D. if he still posts on the site. GBA also has several articles that have been written about vapor barriers that should prove useful.

Another good source for research is BuildingScience.com.

Consider mineral wool insulation which is fire resistant, sound resistant and blocks the flow of air better than fiberglass. More costly than fiberglass but less than spray foams. I think its worth it.

Good luck,

DC

Those references are good stuff...IMHO....