" and r60 in roof. "

I don't know about resulting allergies, but did you mean ceiling/attic, and not roof? My brother regrets using foam to coat the interior of his roof, it resulted in cooking his roof shingles and it shortened their life by half.

This is a great question, and I appreciate your concern for both energy efficiency and your family's health. Spray foam insulation is often the best solution for achieving high R-values in limited space, especially in 2x6 walls where traditional insulation may fall short. Closed-cell spray foam, in particular, provides excellent thermal performance, air sealing, and moisture control, which can help improve indoor air quality by reducing allergens and pollutants from entering the home.

That said, health considerations are important, especially for families with allergies or asthma. Spray foam contains chemicals that off-gas during installation and curing, which is why proper ventilation and professional application are crucial. Most reputable installers follow strict guidelines, including allowing the foam to fully cure (typically 24-72 hours) before reoccupying the space. Once cured, high-quality spray foam should be inert and not release harmful VOCs. If you have sensitivities, you might want to look for low-VOC or Greenguard-certified spray foam products and discuss alternative options with a trusted installer.

Given your family's health concerns, it may also be helpful to consult with an indoor air quality specialist before moving forward. While spray foam can be an excellent choice for long-term comfort and efficiency, ensuring it's installed safely and correctly is key to avoiding potential issues.

Take a look at some of our services to get an idea of how a professional company can help you and your family to accomplish your goal.

Great discussion, and I hope you find the best solution for your addition!

I don't know what code book you pulled R30 out of but for 99% of America R21 is code when used in 2x6 walls, and do you know why? Because it's all you can stuff into a 5 1/2" deep cavity. The only place in the United States requiring R30 is northwest Alaska and the Arctic slope of Alaska, do you live there? If not someone lied to you.

If you want more than Minimum code you can add 1" of foam board to the exterior of the walls to get R26, or 2" to get R31. Or you can build with 2"x8" studs and fill the cavity with fiberglass or rockwool. The optimum build would be to use two layers of 2x4 walls with a 1/2" air gap between the studs of the 2 walls to decouple the thermal bridge between the wood to the outside with a finished cavity depth of 7 1/2" and use 2x8's for the top and bottom plates. This convenient cavity will allow room for 2" of foam board and high performance R21 fiberglass insulation to get R31, or just 8" fiberglass for R25.

You could also build a single wall with 2x4's and insulate with R13, then stack a layer of 2 string hay bales for another R20 to R30, then build an inter wall with another layer of R13 for a grand total of R46 to R56.

Climate Zone 8 which extends to the northern tip of Canada requires R49 in the ceiling and R13cavity+R10continuous in the walls, per the IRC (or R20+R5 for walls).

Insulation and air sealing has to be detailed ahead of time prior to cutting the very first wall stud. There are too many options of achieving both insulation for thermal comfort and condensation control which may affect framing and finishing the exterior.

Usually, to achieve numbers in extremely cold climates, there will probably be some chemicals used, whether in air impermeable insulation (spray or rigid foam) or liquid-applied membrane (e.g. Zip-R). These can be avoided by using other materials, but detailing of the building enclosure needs to be done ahead of time.