In July of 2024, the state of New Mexico adopted the 2021 IRC building code. As part of this code change, the insulation requirements also changed. The changes were designed to increase energy efficiency and are now structured based upon the climate zone the home is being built in.
Most of New Mexico’s alpine zones are rated from 5 to 7. With Ruidoso being in zone 5 and Angel Fire and Red River being in zone 7.
According to the new code, the insulation for walls has changed significantly and now requires either an insulation value of R30 in the cavity of the wall or the other option is what is referred to as “R20 + R5 continuous”, what this means is that you can put R20 in the wall cavity but then you must have an additional continuous R5 between the wall studs and the siding.
One of the issues with the R30 option in the wall cavity is that the only real way to accomplish this with 2x6 framing is with closed cell spray foam insulation. Closed cell insulation has a few drawbacks, the biggest one being if there were a leak inside a wall, broken pipe etc.. the issue may not present 
itself until a tremendous amount of damage has been done. Open cell spray foam will allow water to pass through, alerting you of an issue. Closed cell foam has also been known to cause condensation issues in certain environments due to its inability to ventilate well.
The option of R20 +R5 continuous is easily achievable with the use of open cell spray foam in the wall cavity plus the addition of a one inch ZIP panel. A ZIP panel is a structured insulated panel made from OSB with a built in water resistant barrier allowing it to function as wall sheathing, insulation, and a weather resistant barrier. The R20 +R5 continuous option does create additional cost compared to the previous building code, however, some of the cost can be offset due to the fact that the addition of the SIP panel deletes the need for OSB siding and house wrap.
An additional option if you prefer not to use spray foam and want to use the R20 +5 option is to use a product such as Owens Eco Touch fiberglass in the cavity, this product is a high density fiberglass insulation that achieves a R21 rating that may be more economical.
Question? Feel free to contact me at anytime.
Rob Swan
Swan Realty
Whisper Creek Homes
575-770-2958
rob@swanrealtyinc.com