Next energy saving project? 1982 home
I am curious what you would do…
Family of 4 living in a 1982 two story house plus basement in NC. 3300 sqft.
Cathedral ceiling living room; two attics at either end of the house. One above the two upstairs bedrooms and one above the master bedroom next to the living room.
We’re using a single Bosch heat pump to cool/heat all three floors.
Ductwork is new but unfortunately both attics have ductwork in them.
$210 electric last month (1854 kWh) which puts me right at the average of our comparison group of homes provided by Duke Energy.
Most recently we had open cell sprayed in the garage as the master bedroom is above it. I also wanted garage fumes blocked from infiltrating the house.
I am trying to decide what project should be prioritized next.
1. Replace 80 gallon electric water heater (energy guide of $620) with a 50 gallon (energy guide $420)
2. Replace 80 gallon electric water heater (energy guide of $620) with a 50 gallon heat pump tank (energy guide $120)
3. Spray foam roof deck in both attics with 5.5″ open cell. That’s only R18 but the contractor insists on the added air sealing capabilities when I asked for R30 ( ~8 ” of open cell). Concerns are roof leaks, thermal bridging of rafters
Remove old insulation on attic floor
4. Rigid foam board sandwiched between roof rafters, seal with spray foam cans, then another layer of foam board on rafters held in place by strapping.
Seal gable vents.
Remove old insulation on attic floor
5. Remove old blown in fiberglass insulation on attic floor, seal all openings with spray foam cans and then fill in with cellulose R30 levels. Install insulated attic ladder/opening
6. Install PV system on roof portion of living room. Due to the cathedral ceiling I can’t easily add insulation but the PV system would be structured with larger style panels to cover as much of the living room roof surface as possible to get some additional shade on the roof.
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
Hi StefanKe.
Prioritizing energy improvements can be challenging. When I had a home that needed lots of similar work, I always did the next thing that my budget and skills allowed, but installing PV was never a possibility, so that was off the table.
In that way, what jumps out at me on your list is to air seal the attic floors. I'd try to save the blown in fiberglass and add more insulation, if you can shuffle it around while you do the air sealing work.
I think you'd need someone to do some energy modeling to tell you if and when it made sense to add the PV system vs. some of the other potential projects.
I’ll second what Brian said about air sealing the attic floor as your next project. There are a lot of potential gains from doing that.
If you’re thinking of using #4 to create an unvented roof, don’t. Cut and cobble is not a good idea with unvented roofs since you can’t trust it to stay sealed.
If you go from an 80 gallon water heater to a 50, you might notice the change in terms of running out of hot water. That might be something to think about.
The solar project is probably the highest cost project on your list. You may also run into structural issues supporting the system depending on your roof (surprise cost stuff).
I’d look at other air sealing work too. Rim joist air sealing projects usually aren’t too expensive and can really help tighten up a house. Crawl space encapsulation projects and insulating crawl space and/or basement walls is another potential energy saving project. All of the air seal and insulation projects tend to improve comfort too, so they have additional benefits beyond just increased energy efficiency.
Bill
>"Spray foam roof deck in both attics with 5.5″ open cell. That’s only R18 but the contractor insists on the added air sealing capabilities when I asked for R30 ( ~8 ” of open cell). Concerns are roof leaks, thermal bridging of rafters
Remove old insulation on attic floor"
---------
>". Rigid foam board sandwiched between roof rafters, seal with spray foam cans, then another layer of foam board on rafters held in place by strapping.
Seal gable vents.
Remove old insulation on attic floor"
That would likely increase energy use, if the ducts and attic floor are reasonably air tight.
If insulating at the roof deck with only R18 do NOT remove the insulation at the attic floor, except where needed at the roof edges to create the near-perfect air seal.
As others have noted, cut'n' cobbled foam is risky, and time consuming. The thermal bridging rafters also rob it of it's potential- it's far better to put the high R/inch expensive (environmentally and financially) foam in a continuous layer below the rafter edges, and leave the rafter bays empty. Do the math:
https://www.finehomebuilding.com/2017/07/10/closed-cell-foam-studs-waste
>"Remove old blown in fiberglass insulation on attic floor, seal all openings with spray foam cans and then fill in with cellulose R30 levels. Install insulated attic ladder/opening"
If going that route, unless it's full of rodent crap, just move only the insulation as-necessary for air sealing over the lighting cans, flue/stack/electrical/duct boot penetrations, and the seams of partition walls to the ceiling gypsum, etc, then blow cellulose OVER the pre-existing fiberglass to a combined depth of 11-14". As little as 3" of cellulose over the top makes up for any deficiencies of low density fiberglass, restoring it to it's fully rated performance. You may not have enough headroom to get 14" of insulation all the way out over the top plates of the exterior walls, but that's how much it takes to hit current IRC code minimum in the climate zone 4A & 5A (the cooler half of NC), but 11" (~R38 after it settles) is enough to make it the zone 3A portion.
The difference in cost between R30 and R50 is much smaller than you might think, and the difference between R30 and R38 is smaller still, especially if it's an over-blow rather than a full replacement. And it's WAY cheaper than insulating at the roof & rafters, no matter what method is use.
Brian's suggestion about air sealing the attic floor is right- that's really Job #1 and the best bang/buck, followed closely by air sealing (and insulating) the lowest level of the house, whether it's a full basement, crawlspace or slab-on grade. The highest and lowest leaks in the house are the most important, since that defines the total stack effect pressures that drive outdoor air infiltration rates. Verifying/rectifying any air leakage in the new duct system & air handler unit comes next, since even a perfect duct design duct leakage creates room to room air pressure differences that will drive outdoor air infiltration whenever the air handler is running.