Zone 4 DER/Remodel – Insulation & Windows
I’m looking to optimize design for a remodel/DER in zone 4 (Cincinnati, OH) to move towards Net Zero and dramatically improve comfort. All cladding will be removed and exterior insulation will be installed (likely Zip-R). Walls are 2×4 construction. PHG standards suggest R25 walls and R60 ceiling. Building code calls out R 13+5 minimum for the walls and R49 in the attic.
I have been running models in BEopt to decide between Zip-R6 and Zip-R9 for the walls as well as R49 and R60 in the attic. Material cost difference is roughly an additional $500 to upgrade each. I also modeled an efficient double pane and triple pane window. Based on BEopt, there is a negligible improvement in energy savings. The manual J shows no significant change in mechanical sizing.
Outside of energy use, is there any real benefit going to the Zip-R9 and/or R60 in terms of comfort, durability, resiliency, etc that would warrant the additional cost and complexity? Would it be better to put the money towards triple pane windows, or would those be overkill as well?
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Replies
mr_stop,
The problem with these type of questions is there are so many variables, a good case can be made either way - and they unfortunately do to some extent come down to individual preference.
My own would be to not do any of the upgrades, and instead put the effort and money into additional air-sealing. That's will do more to increase comfort, and durability.
Yes, too many variables 😂... It's a very extensive project with significant exterior and interior modifications (it's a borderline tear down) so I'm trying to limit the variables as much as possible. I do have air sealing already planned with a pretty air tight goal.
It has been an interesting study using BEopt at how much I am at the point of diminishing returns once I have reduced air leakage. In fact, there isn't much energy savings adding additional exterior insulation (maybe 5-10%). However, I would like to meet current building code as well as put some added resiliency to the whole assembly with external insulation.
What air tightness are you running the model at? At a certain level these other factors like window U-value and wall insulation become a larger fraction of the overall energy usage.
I'm modeling at 1 ACH50.
mr_top,
The extra cellulose in the attic can be added any time. It may be worth it to bump up the Zip-R. I can't see triple pane windows ever penciling out in climate zone 4.
Thanks. I think that's the route I'm going to go.
Be Opt is right. Once you get near R15 to R20 in your milder climate, there is not all that much extra energy saved by insulating more.
Same with triple pane windows. The one spot where the window upgrade is worth it is if you are in a loud neighborhood. I'm by a semi busy street and when I close the triple pane tilt and turns, the city sound disappears.
P.S. You might also be kicking yourself for not spending that $500 in ten years time when you look back on it. Compared to the reno costs, it is noise in terms of extra cost.
That's what I'm thinking. It's not really about the added nominal cost, but more about dealing with the thicker assemblies.