Best use of extra funds for high performance options
We are in the process of building a custom home in Denver Colorado, Zone 5. 4215 Sq Ft. 4-bedroom 4 bath, with a conditioned crawl space. Main floor has an in line living room, dining room, kitchen. Living and dining are vaulted, kitchen and rest of main floor drop to 10 ft. ceilings. Second floor has two bedrooms and bonus room, 9 ft. ceilings. 2×6 construction, zip sheathing on walls, vented roof. Walls will be R-23, Ceiling R-50, Floor R-38. I expect a blower door score of 1.5 ACH50 or better. HERS model states we will have a score of 57. My builder is a custom builder but I’m driving the high-performance aspect of this build.
We break ground in June and still have a couple decisions to make as to where to utilize about $40 to 50K of extra money. Options include the following:
- Upgrade windows from Anderson 100 series (.26 U-Factor) to Alpen Zenith ZR-6 series (.14 U-Factor). This would also include a 16 ft. 4 panel slider in main living room. Upgrade from Windsor Pinnacle Clad (.30 U-Factor) to Alpen Zenith (U-Factor .19). Around $30K increase. Almost forgot, all windows are fixed (thanks Steve Baczek) except the required egress in 3 bedrooms and the master has a door to patio for egress.
- Add closed cell spray foam for a flash and batt insulation on walls and roof. Around $19-25K increase
- Add Zehnder ERV Around $15K increase
- Use Zip R6 or Zip R9 on exterior walls. Around $20K to 25K increase
- Use AeroBarrier. Haven’t had an estimate but the guess is $5 to 10K.
HERS rater stated exterior insulation, Zip R, doesn’t make much difference in score. Windows would probably help HERS score the most, but he hasn’t modeled all the above scenarios.
If there is something else, I should consider please let me know.
Feedback by most to least important is greatly appreciated. My goal is comfort, which I realize is subjective, but I don’t want to experience hot or cold spots and with three children under 6 air quality is important.
Thanks in advance for any feedback.
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Replies
Windows probably will gain you the most, especially if you have a lot of glass area relative to the size of your walls.
I would go with exterior rigid foam over spray foam flash and batt. The reason is that exterior rigid foam can be detailed airtight pretty easily, so it will get you similar air sealing to spray foam in walls, but exterior rigid foam will also help with thermal bridging which spray foam won't. More bang for the buck with the exterior rigid foam, basically.
Aerobarrier would probably be last on my list, with the HRV somewhere in between.
BTW, you mention a "conditioned crawl space", but also R38 in your floor. I'm assuming that "R38" would be the floor over the crawlspace? If that's the case, you should reconsider -- insulate the walls, and possibly the floor, of the crawlspace instead, and do not insulate the floor over the crawl space. You'll get better performance with the crawlspace inside the building envelope this way, which is how it should be for a conditioned crawlspace.
Bill
Thanks Bill. I should have added that the crawlspace walls are insulated R-15 and inside the building envelope. The R-38 floor is for rooms over the garage. A small cantilever floor area on second floor is R-49 floor. Didn’t realize we had a cantilever until all designs were complete and everything engineered or I would have deleted that cantilever.
For me it would be about return on investment the only way I know to understand that question is to model your options in a computer program called BEopt. The program uses your local weather data your inflation guess, your interest rate, and your cost per sqf to build and helps you find the compo that costs the least to build finance and operate over time. Note lots of the default BEopt cost per sqf data has become outdated in today’s market. It was always best to enter your own cost data from your bids.
https://www.nrel.gov/buildings/beopt.html
Please post the drawing for your vented R50 vaulted ceiling. That sounds like quite a design challenge especially if your design has a high fire rating and comes in at an affordable cost.
Walta
I would do the windows and the ERV. I would also reconsider the huge slider and go with fixed glass and French doors. Even the best sliders leak a lot of air.
What about solar panels?