New House Building Envelope
Hey GBA community!
Long time reader, first time poster. We are building our dream home in Steamboat Springs, CO and have a great builder and architect. That being said, I wanted to get some feedback on the build from an insulation factor.
I am trying to keep this simple for all parties and looking for the easiest application of methods with highest ROI on comfort, spend, and simplicity.
We are using all aluminum or fiberglass triple pane windows with u value of <.21 and r values of around r-6. Right now we like Alpen ZR-6 and Quaker CityView collections. Both have great local support which is key.
From an envelope perspective, i am weighing best approach while keeping it simple. Right now, I like using Zip R-9. I would go larger, but see detail issues with windows and cladding.
We currently have 2×6 framing and thinking of supplementing the walls with a “flash and fill” or just using a blown in fiberglass. Builders here don’t seem to like cellulose as it seems to have the reputation of settling here. I plan to have insulated headers as well.
For the roof structure, we have a shed roof with tall ceilings. Min ceiling height is 10′ with it going as high as 15′. We want to insulate the roof with exterior insulation. We will be using a metal roof. Thinking plywood with ice/water and then 2 layers of rigid foam. Then in the interior open cell spray foam.
We will have slab on grade with hydronic heating. The insulation detail here is to use insulated concrete forms with 2 layers of rigid foam or closed cell spray foam which is common here.
So essentially looking for your feedback and guidance on the assembly details noted around:
Main building envelope
Roof detail
Slab detail
Overall, I may be considering the use of T studs, but that might overwhelm my builder. I like the concept of using materials that can be obtained locally. We will also be using a Zhender ERV and air conditioning for upstairs only.
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Replies
I haven't used the T-studs, but I also haven't been paid to hype them, so grain of salt yada yada...
It would seem that the point of Tstuds is to break the thermal bridge, but you're already doing that with Zip-R. I'd say save the money as lumber prices are going back up now and even without that you'll need that money somewhere else in the build budget.
I think the R9 exterior Zip panels will leave you a good bit short of a safe wall without the spray foam. I think R15 is needed in CZ7 if using vapor open insulation between the studs. Flashing and batting may bring you back into safety, but potentially at higher cost. I do appreciate the commonly seen builder's resistance to thicker CI. The screws get longer, more expensive, harder to direct and cladding options can be affected. The R12 Zip has generated threads on GBA about the difficulty in meeting the required nailing, so search the QA for those.
Just the same, T--studs aren't going to help you with the risk of condensation on the inside surface of your R9 Zip. A CLOSED cell flash might get you into the safe zone. Your roof notes don't reveal the total R value of "two layers", so be sure to observe the required ratio of exterior insulation to interior insulation. Dense batts under the roof decking may be less costly than foam. Locally, (8,000 ft, south of you) code requires high temperature ice and water shield over the entire roof under metal. For my own exterior insulated roof we used 8+" nailbase set over roof sheathing that was air sealed with synthetic roofing paper. R-19 batts between rafters, R-52 whole roof value. If there are any problems with the build up, I haven't seen any signs. My one wall check made during an outlet upgrade showed the sheathing to be in perfect shape. I do however have R22+ on the outside.
One thing to consider is the need for ever better vapor control as you skate closer to the minimums for CI. I opted to avoid the need by having a vapor open to inside plan. Hoping that all the trades can do their thing without dinging a vapor barriers integrity is certainly an act of faith.
Your slab should be R-15 and the foam set on washed stone sufficient to keep it up out of water and if your area is subject to radon, deep enough to set the pipes. Your slab inside a ICF perimeter will certainly offer pathways to living space if radon exists. Curiosity question, are you saying spray foam under the slab? Best of luck in these difficult building conditions.
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