What’s the best way to renovate/rebuild an old south-facing exterior wall?
Hi All – I am a newbie to this group but have considerable building experience remodeling and renovating homes, and completing unfinished properties. Still, I am no expert building contractor.
I just bought an older home in Northern Nevada that was built in the 1970’s. We are South of Reno. It is high mountain desert, very dry most of the year, and around 5000 feet. The map says we are between zones 5B and 6B. The southern exposure of the home experiences huge heat gains during sunny days. Inside temps in the rooms on the south side of the house usually lag the outside temp by no less than 5 degrees F, which means that during 95 degree days the inside temps are 90 when I don’t run an AC. The Hardyboard siding on that exposure is heavily weathered so I do plan on removing and replacing all of that.
The wall construction is 2×4 and consists of drywall over bare studs on the inside and hardyboard over studs on the outside with what appears to be 15# felt paper between the studs and the hardyboard. The space between the 16″ OC studs is insulated with kraft paper faced fiberglass with the paper facing against the drywall.
We have quite a view so all these walls have very large windows. The room with the worst heat gain has the largest: 2 windows that are 60″W x 72″H. The windows are double pane and are probably original argon gas based windows. All of the windows have heavy condensation stains between the panes so its pretty obvious that the seals have been compromised and most likely the argon gas is entirely depleted. I also plan on replacing all of the windows in this house.
Last but not least, this home experiences serious problems with dust infiltration. After a couple of days of high winds (not unusual this year) there is a fine coating of dust everywhere so its obvious that the WRB is failing as far as wind leakage and intrusion is concerned.
I want to bring this wall up to current standards or beyond. I figure why pay a ton for advanced HVAC if the walls are leaking heat (and dust) all year long. I want to start with making the walls as good as possible and with improving the WRB to as high a standard as possible. I have read with great interest everything I could find on this site, especially those articles discussing polyiso, but my reading and studying on the topic has produced as many questions as it has solved:
- Should I sister in 2×6 studs so I have a larger void for insulation or is it more energy effective and/or cost effective to use sheet(s) of 4×8 polyiso between the 2×4 studs and the exterior siding? It seems to me that the 2×6 studs may not be as cost effective because of the additional labor of furring the windows to make them line up with the newly extended exterior. On the other hand, two layers of 3/4 or 1″ polyiso 4×8 sheeting adds its own special problems with mounting and weatherproofing new replacement windows.
- Or, instead of #1 above, would it be better to just replace the fiberglass batts with 16″W polyiso between the studs? Obviously I could get up to 3.5″ of polyiso between the studs but I assume there is a point of diminishing returns where the heat loss transmitted by the wooden studs and fasteners exceeds any gain of additional insulation
- The consummate question would then be whether a combination of the above would be the most energy effective and cost effective? Maybe the 16″ batts of polyiso between the studs (how thick?) plus two sheets of .75 polyiso mounted horizontally under the siding?
- Along with the question of combining solutions and methods: what kind of siding should I consider? I know there are siding solutions that include polyiso or polystyrene cladding on the inside.
- Lastly is the question of repairing/replacing the WRB to resolve the issue of air leakage. I guess the most effective solution would be largely dependent on which of the above solutions for insulation are chosen?
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