Insulating a 1905 vintage 2-1/2 story
Greetings. I am in the process of “rescuing through renovation” a 1905 vintage 2-1/2 story house in Omaha (zone 5) that was formerly divided into seven apartments. Being that the house was used for apartments for the last 50 years, it has received minimal maintenance. The weak condition of plaster on the inside of the exterior walls have made the decision to gut the walls of plaster and lath a clear choice. I have new windows on order to replace the existing deteriorated windows.
As one can guess, there is no insulation in the side walls. Unfortunately the renovation budget and likely property value can’t justify using double-framed interior walls. Since the walls will be totally accessible I plan to use “flash and batt” insulation to minimize air infiltration and have a wall with something close to an R-20 rating.
My main concern is the roof insulation. The attic has completely finished walls and ceiling and was used as on of the seven apartments. I would say 90% of the attic has finished surfaces. Since I’m gutting the second floor walls and ceiling, and am not sure of the insulation in the roof, which of the following would be the best course?
1 Insulate the ceiling of the second floor so that I’m sure of some level of insulation, Would this require a vapor barrier?
2 Bite the bullet and rip out the ceiling in the attic and insulate. This would probably require closed-cell foam to achieve something close to R-45 to R-50.
3 Do both.
Thank you in advance for any thoughts you may have.
Dick Ryker
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Replies
Richard,
This is how a home of similar vintage in OR was energy retrofitted, in my opinion you are relying too much on expensive foam. Flash and batt is flawed for a number of reasons, non-uniform thickness, difficulty in insulating the remaining stud space, you have not addressed thermal bridging through the framing.
http://www.oursustainablehome.org/
Dick,
The answer depends on whether you need to use the attic space for living space or whether you intend to leave it unconditioned. If a single family is moving into a building that was formerly divided into seven apartments, there is a good chance that you have enough square feet without using the attic.
If I'm guessing correctly, then install insulation in the second-floor ceiling and/or the attic floor.
Thank you for your comments, Doug. One of my concerns is air infiltration. Omaha is notoriously windy in the winter. And it seems that closed cell foam will provide the barrier I need, especially since all the exterior walls will be accessible during renovation., I've considered adding 1" strips of XPS to the studs to act as as a thermal break. The alternative, I suppose, is a secondary 2x4 wall.
Still looking for insight of the roof question!
Thank you Martin.
A strapped wall will help with thermal bridging and add additional R-value while maximizing interior space. If you are going to open up the interior walls completely get all you can from this opportunity. Electrical wiring can and should be brought uo to code.
As for an air barrier, I suppose Airtight Drywall is the safe method for Omaha. Much has been written about the system and details are available, I'm sure GBA has some archives.