Critique for gut-job re-do — insulation
I’m working on a gut job rehab of a property I bought in Houston, TX. (Hot Humid, AC 9 months of the year). It is 1965 construction 2 story. First story is brick veneer with an air gap and exterior drywall over stud framing. Second story is vinyl siding over vertical wood siding with deteriorated 30# felt over stud framing. Roof is approximately 18 years old, typical redo for Houston… they removed cedar shingles and put down 1/2″ plywood deck with asphalt shingles. It was insulated with 1.5″ rock wool and there was evidence of moisture accumulation on the interior side of the exterior drywall.
Slab has a vapor barrier, but is gaining moisture from the ground somehow…..
My goal is to have a comfortable house that has low energy costs planned on a 15 to 20 year ownership cycle.
Right now I am planning to do closed cell foam in the exterior walls, convert to a closed attic with open cell on the roof deck and use ducted mini splits for zoning purposes.
The vinyl siding is going to go away. I will either keep the wood siding or apply tyvek and fiber cement siding. There are some flashing issues where the upstairs walls meet the first story roof. Minor leak under the right wind driven rain conditions.
I plan to apply the foam myself and I already own the equipment to do it and am certified to handle the materials and have a local distributor lined up to purchase from. I will be applying some open cell in selected areas as a sound deadener (like on the bottom of the upstairs floor).
I chose closed cell in the exterior walls to provide an air and moisture barrier. I would use open cell, but I am concerned with moisture migrating in and staying there. Short of removing the brick I can’t fix the exterior envelope. Either way I stack it, I am in for two sets of material to insulate this house properly, so shifting one set to closed cell lines up nicely with the exterior walls and isn’t that much more expensive as I am applying it myself and own the equipment.
I replaced the windows with Plygem units from Home Depot that meet the energy star requirements for my region on emissivity and solar gain.
Issues and Questions:
– I am trying to calculate the benefit of installing a 5v style metal roof against asphalt shingle. The roof is 20 years old and has some flashing issues and 2 areas with minor leaks. That’s enough for me to replace it as part of the scope of this project. I have installed utility style (corrugated) metal roofs and built a metal building before, so I’m not new to metal working. I’ve also done 3 tab shingle roofs. My working theory is that a metal roof will cost about 25 to 50% more than a good quality 3 tab roof (Owens Corning Duration or similar). That savings will be paid back in insurance discounts and energy savings by going with a silver, Galvalume, or light grey roof. White would be ideal, but I have trees and that will get the white roof dirty.
– I considered a R style corrugated roof on wood stringers on top of the deck and then doing a radiant barrier under it. That is easy and low-risk but I can’t find any references on doing that. It makes sense that the radiant barrier would be highly effective in this style and then I’d be free to put whatever color I want in.
– HVAC equipment has to stay in the attic due to 8 foot ceilings. Therefore I think it makes sense to cathedralize the attic with spray foam.
– Any thoughts on the first story wall assembly open cell vs closed cell? Specifically – will open cell in a hot humid climate with air conditioning on one side suck in and retain moisture from the exterior? The exterior drywall is not taped/sealed.
– I’ve searched for a model assembly to use, but can’t find anything that matches this construction style with a retrofit.
GBA Detail Library
A collection of one thousand construction details organized by climate and house part