Replies

1. 
   charlie_sullivan | Jul 27, 2021 06:21pm | #1

   >"it will be more used in summer, but obviously want it to be comfortable for year round use"

   The nature of that limited use in the winter, and what temperature it will be maintained at in the winter when unoccupied might drive a lot of the decision making.

   >"10 kW solar panels"

   Sizing those should come after a lot of other decisions.

   >"Walls of addition: GWB; mineral wool batts; Zip R (2”) sheathing; Obdyke Slicker classic rain screen; cedar shingles."

   Sounds good.

   >"Walls of existing space: GWB; mineral wool batts; existing Plywood sheathing; 2” XPS; Henry Blueskin; Slicker classic rain screen; cedar shingles"

   That will work well, but XPS is a big green building faux pas. The standard North American XPS has huge global warming impact. There are new formulations which aren't as bad (https://www.greenbuildingadvisor.com/article/xps-makers-announce-more-planet-friendly-formulations) but it's better to use an alternative: polyiso, EPS, graphite-EPS ("GPS" or "Neopor"), or mineral wool boards.

   >"is an additional air barrier recommended over the Zip, whether Blueskin, Mento, or other? How much better is Mento vs Zip, for example?"

   Well taped zip by a conscientious crew will be great, better than anything that isn't self adhered.

   >"should I add Intello or similar on the inside?"

   Not needed, but it wouldn't hurt either.

   >Windows: Marvin Elevate double pane casements w LoE-180 (u-value close to 0.20) or Jeld-Wen Siteline Clad-Wood casements.

   >Question: Good enough, or should I look into Zola, Alpen, etc. ? Or

   The first step op would be North American Triple pane low-E, before going to exotics. Triple pane is worth considering for winter comfort but if you aren't particularly concerned about the double pane low-E argon is probably the economical choice, given how cheap solar is. You might want lower solar gain than loE-180 though.

   >Roof Question: recommended air barrier products for existing roof?; and do I need Intello or similar between insulation and GWB ceiling?

   Air tight drywall is probably fine, unless you want to put holes in the ceiling for lights or something.

   >HVAC: Mitsubishi or Daikin 8 zone, mostly ceiling concealed units.

   8 zone is a lot. But it's a little early to be designing this.

   >ERV: Panasonic Intellibalance x 2, one upstairs and one downstairs + a Panasonic whisper comfort spot erv for a bathroom where duct run would be longish.

   Good plan.

   >Existing Fireplace – line inside of brick chimney with 1-2” XPS; Renaissance firebox

   I don't know the details of that system but XPS lining the chimney sounds very unlikely to be code approved or even something that would survive. Presumably they provide installation details with a different insulation system. But also consider carefully what you want the fireplace for.

   >Hot Water – Rheem electric heat pump Water heater (Looked at Stiebel Eltron tankless, but the power requirement swayed me away)

   Tankless electric is a really bad choice--you are making the right choice here. Tankless electric has only disadvantages, even compared to an old fashioned tank, whereas heat pumps are awesome.

1. 
   kr10017 | Jul 27, 2021 06:50pm | #2

   Thanks very much Charlie - very helpful!

   The solar panel sizing I cited is just capacity based on size of roof (about 25 360kw panels). As for lining the brick chimney, thinking of ways to reduce the thermal bridging from this vestigial thing, which exists and is an architectural detail in line with the house’s style and environment, but not very energy friendly.

2. 
   Mark_Nagel | Jul 28, 2021 11:26am | #3

   I'd think that it would be prudent to work up a Model J. Do a baseline to see what the priorities are: things that will get you the biggest returns; although it should seem obvious, there might be some surprises.

   My layman's understanding of window efficiency is that lower u values are more meaningful with larger windows. I am not sure if all manufacturers provide values of glass + frame. Frames can have a substantial impact: higher frame-to-glass area, from my understanding, tends to reduce overall u values.

   Get a more firm grasp on target energy use before committing to solar panels.

3. 
   Jon_R | Jul 28, 2021 11:40am | #4

   Because Zip R isn't exterior insulation, you probably need a Class II interior side vapor retarder to be code compliant. Intello would work well but vapor barrier paint is far less expensive.

   Pay lots of attention to air sealing (and testing to verify it).