Replies

1. GBA Editor
   Brian Pontolilo | Jul 17, 2019 12:40pm | #1

   Hi DakotaGreen.

   There are many ways to successfully build, insulate, and air seal walls and roofs in your climate and you will soon get lots of opinions from GBA users. If you are hoping to build a net-zero-energy house however, you should be working with an architect, builder, or energy-rater who can help you model the appropriate levels of insulation and air tightness balanced with the amount of renewable energy that you will need to produce on site. That is an oversimplification of the equation, of course. Solar gain and shading, performance specs of windows and doors, insulation values at the foundation, rim, etc. all play an important role. And the needs and cost of mechanicals are also part of the equation.

   This article may be helpful when it comes to the net-zero-energy equation: https://www.greenbuildingadvisor.com/article/revisiting-net-zero-energy

   The point is, that to look at the wall and roof assemblies in isolation is not so useful. And even to know which of a few ways to assemble the walls and the roof, is the smartest and most cost effective way to go will depend on cost and availability of certain materials in your area as well as what methods your builder has the most experience with.

   Here you can see how this discussion has played out on GBA in the past:
   https://www.greenbuildingadvisor.com/article/comparing-high-performance-wall-options

   This has

2. 
   Jon_R | Jul 17, 2019 02:23pm | #2

   Roof option #1 has a poor internal:external perm ratio and doesn't have enough foam to prevent sorption/condensation at the inner surface of the foam. Also see here for why soffit vents shouldn't be centered in the soffit.

   For both walls and ceiling, try for a 1:5 internal:external perm ratio. Anything that warms wood sheathing is a plus (even 1.5" of EPS which shouldn't be so hard).

   I hope your builder is experienced with producing very airtight buildings. Spray foam is not necessary to achieve this.

3. 
   Andrew_C | Jul 17, 2019 03:12pm | #3

   There are larger concerns, but there are many alternatives to canned lights that perform the same function better without the guaranteed air leakage and insulation defects.

   I'll echo Brian - you'll save a lot of money and grief paying for expertise in the design phase, rather than trying to correct things later, or spending a boatload of money on a new house and being disappointed.

   Building a new house is exciting, I hope you have fun, just cautioning you to get the design completely detailed before breaking ground.

4. GBA Editor
   Martin Holladay | Jul 17, 2019 05:13pm | #4

   Dakota,
   Here is a link to one more article that you may want to check out: "Building a Low-Cost Zero-Energy Home."