Basalt, Colorado’s energy conservation code requirements

The Town of Basalt, Climate Zone 6, is currently (June 2019) on the 2015 IRC (International Residential Code) and the 2015 IECC (International Energy Conservation Code).

Basalt has a REMP (Renewable Energy Mitigation Program) that engages anytime exterior uses of energy are used like; snowmelt, pools spas and garages. REMP fees are offset by renewable energy production, fee-in-lieu, or a combination of the two. Link to entire adoption…

Basalt is enforcing separate infiltration tests for ADUs, infiltration limit of 3.0 ACH50 and duct testing when outside the envelope.



Type I (single-family) SBR (Sustainable Building Regulations)

Link to code language…

Points are determined under one of four compliance paths; prescriptive, performance, Net Zero Energy Ready or LEED for Homes.

Link to SBR Commentary…


Type II (multi-family and commercial) SBR (Sustainable Building Regulations)

Link to code language…


Please give us a call and we can help navigate the process in the most cost-effective way. And optimize your construction for performance.



Jump to Pitkin County’s energy conservation code compliance page…

Jump to Aspen’s energy conservation code compliance page…







The underutilized U-factor alternative?

I review quite a few residential IECC (International Energy Conservation Code) submittals, and I would estimate that three-quarters of them are submitted as a straight-up prescriptive submittal. That’s when the table below is followed, without deviation. There is nothing wrong with this approach, but if a little flexibility is required, then leave the R-values behind and look at assemblies as U-factors, that can be morphed and traded around.

Table R402

The U-factor alternative (2015 IECC R402.1.4) is a very powerful and useful method, but I don’t see it get used much.

Table R402 U-factor alternative

I think it can be useful to use a chart like the one below to see building assembly alternatives by U-factor. PDF link…  U-factor alternative assemblies

For instance; can I substitute OVE (Optimum Value Engineering) or Efficient Framing for CI (Continuous Insulation) in zones 6 & 7. The Prescriptive compliance alternative would have at least R5 CI installed on the exterior of the above grade walls. The U-factor alternative says; use any wall with a U-factor of .045 or better. So, at a glance, from the list, I see that I could substitute R3.6 CI (i.e. 1.5” ZIP insulated sheathing) for the R5 CI and bump up the cavity insulation number to R23 and build the wall with efficient framing techniques. Don’t like CI at all? Then substitute an efficient framed wall with the cavities foamed solid to R36. Don’t like CI or efficient framing? Then you could use a 6” SIP, ICF or straw bale. Check the total U-factor of your specific assembly, it could vary from the U-factors on the list by a couple of thousands. Here is a super-good online wall calculator for R-values and U-factors including checks for moisture control.

If you still don’t like the choices that the U-factor alternatives gives, then it is time to move up to the Total UA Alternative, AKA RESchecks (2015 IECC R402.1.5). Often, projects get bumped out of the prescriptive path alternative because the insulation can’t easily be provided in a particular location. Then the Total UA Alternative could be used, because it can trade-off different assemblies. For instance, slab edge insulation, often hard to do at a door threshold, patio or deck attachment or behind stone veneer. The uninsulated slab edge can be “traded” for surplus U-factors on completely different assemblies anywhere in the project.

If you still don’t like the choices that the Total UA Alternative gives, or still having trouble reaching the code threshold, then it is time to go fully custom with the Simulated Performance Alternative (2015 IECC R405) or the Energy Rating Index (ERI) Compliance Alternative (2015 IECC R406). Both alternatives can checked by the software at the same time, but the ERI Alternative is more powerful, because it take into consideration low infiltration rates, high efficacy lighting, appliances and renewable energy sources. The only certified ERI program currently is the HERS Rating.

Please contact us if we can help you comply with the energy code in the smartest possible way.

Carbondale, Colorado’s energy conservation code requirements

Carbondale is currently (June 2019) on the 2009 IRC (International Residential Code), the 2012 IgCC (International Green Construction Code) and the 2015 IECC (International Energy Conservation Code).


Carbondale has adopted the 2015 IECC and has a REBP (Residential Efficient Building Program). The chart below is the crux of understanding the energy code compliance.

Link to adoption…

Carbondale REBP

Link to REBP guidelines and REBP checklist here…

The required points refer to the REBP checklist. Points are earned by including features in the house like; efficient framing, water conservation, chemical reduction, etc. Refer to the guidelines to understand how to fill out the checklist. Extra points are awarded for above code HERS (Home Energy Rating Score), infiltration rates and solar.

Currently (June 2019) the Town enforces the HERS maximum on the chart in lieu of the ERI (Energy Rating Index) path compliance limits as listed in the 2015 IECC. Which is quite a bit easier to obtain than the 2015 ERI limit for zone 6; which is 54 for any sized dwelling. But ERI 54 will never become the limit, because the Town adopted the ERI number from the 2018 IECC, ERI 61. Currently, the Town is not considering ADUs (Accessory Dwelling Units) as their own unit, that needs its own; REBP submittal, HERS rating and blower door infiltration test.

HERS ratings are not mandatory, but it would be unlikely to show 20% better than code with only a Total UA calculation (REScheck). Getting to a HERS of 60 or 70 is pretty easy, even without renewables. If a project is small enough to get through under the Prescriptive path or Total UA Alternative, the project will still need an infiltration test report showing 3 ACH50 (Air Changes per Hour at 50 Pascal) or better. And duct leakage testing if any ductwork leaves the thermal envelope.

Other random amendments;

  1. Carbondale has amended their Climate Zone to 6.
  2. Maximum infiltration rate changed to 5.0 ACH50.
  3. Alternate maximum infiltration rate adopted: .24 CFM50 per square feet of thermal envelope area.
  4. 1.2 CFM/watt minimum efficacy for HRV/ERVs (Heat Recovery Ventilators or Energy Recovery Ventilators) fan motors.
  5. ERI compliance level is modified to 61.

Confluence can perform these tests and produce these compliance reports. Please call us early in the process so we can help you optimize the insulation and comply with the energy code in the most cost-effective way.


Carbondale is on the 2009 IBC (International Building Code), but they have also adopted the 2012 IgCC (International Energy Conservation Code).

Link to Carbondale’s heavily amended adoption of the IgCC here…

Navigating the IgCC is a deep subject, but expect it touch every phase of your project. The code requires above IECC insulation and infiltration mitigation, construction waste tracking and structured plumbing. The code requires third-party inspections and testing for the envelope. Confluence has been the code compliance and envelope consultant for six IgCC projects now. The Town of Snowmass Village has also adopted this code. Please calls us early in the process if you are planning a commercial project in The Town of Carbondale or The Town of Snowmass Village.

Jump to ICC’s overview of the International Green Construction Code…


Jump to Pitkin County’s energy conservation code compliance page…

Jump to Aspen’s energy conservation code compliance page…