Zip vs Zip-R walls; too hard to analyze
我花了很多时间阅读许多articles on GBA and elsewhere re insulation, HRVs, wall assemblies, etc. When I present some ideas to my builder, I’m met with the harsh reality of a building boom in Kansas City and the unwillingness of framer subs to do anything different, i.e., 2×6 24 OC or foamboard exteriors, etc. If I want foamboard, my only realistic option is Zip-R, which is quite expensive. I’m Zone 4, on the border of Zone 5, so let’s call it Zone 4.5.
4×8, 7/16″ OSB is $14. Basic 4×8, 7/16″ Zip is about $24. Add 1/2″ of R-3.6 polyiso and the price incredibly increases $25 to $48. Add the next 1/2″ polyiso (R-6.6) and the increase is $9 resulting in $58. The next 1/2″ (R-9.6) increases by $5 to $62 and lastly, another 1/2″ (R-12.6) adds another $5 to $67.
R-3.6 is out as the dew point will be too low. If I do the R-6.6, it will add $6,630 to basic Zip. I’m looking at about about 195 wall sheets (4×8). These are material prices only.
OSB $2,730 + 970 Tyvek = $3,700
Zip $4,680
Zip R-3.6 $9,360 (dew point too low)
Zip R-6.6 $11,310
Zip R-9.6 $12,090
Zip R-12.6 $13,065
With the Zip-R 6.6 or above, I could do R-11 to R-15 fiberglass (mostly 2×4, some 2×6 studs), blown or batts. We plan on living in the house for the next 25-30 years. I need some advice here on what to do. Should I stick with OSB or plain Zip and put the insulation money elsewhere? If it’s worth the big jump to Zip R-6.6, then should I then go for the smaller incremental increase to R-9.6 or R-12.6? Figuring out the payback is too much for my liberal-arts major brain. Thinking about R-49 blown for the attic, not sure about the vaulted great room.
The house is a reverse 1.5 with walkout basement. Concrete foundation is 12 ft high and one ft thick. Siding will be stucco. One potential cost saver with the Zip-R might be the following: one side of the house is unfinished storage on the bottom with a suspended, tandem garage on the top. The garage is unheated and will likely have R-11 or 13 fill walls. The storage underneath will be all concrete bunker. Could this side of the house just be regular Zip? Might save $1,500-2,000. Thanks.
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
Bruce:
Alison Bailes of Energy Vanguard recently ran an analysis on different wall assemblies. (https://www.energyvanguard.com/blog/my-24-hour-mistake-2x4-wall-calculations) Be sure to see the earlier post he references as well.
You might also want to check out the Bonfiglioli method (http://www.finehomebuilding.com/2014/11/26/breaking-the-thermal-bridge). It might be an easier sell in your market.
Last, if you really want to go beyond code, you might want to consider doing a double-stud wall. This approach seems to be a much easier sell when talking to regular builders.