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

Link to Town Building Department website…

REMP (Renewable Energy Mitigation Program)

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…


SBR (Sustainable Building Regulations)

Link to SBR Commentary…


Residential Type I (single-family)

Link to code language…

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


Commercial Type II (multi-family and commercial)

Link to code language…

Most likely will require at least a COMcheck report for permit application submittal.


We do that…

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 Energy Conservation Code Hub for; the western slope of Colorado; Aspen, Telluride, Mountain Village, Town of Snowmass Village, Basalt, Carbondale, Pitkin and Eagle County…


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.

Link to Colorado Energy Conservation Code Hub for; Aspen, Basalt, Carbondale, Eagle County, Pitkin County, Town of Snowmass Village, Town of Telluride and the Town of Mountain Village

Aspen Colorado’s energy code amendments

Spoiler Alert! The City of Aspen has customized their energy code. This blog is about the residential code, I’ll tackle the commercial modifications later.

See the amendments text adoption here…Ordinance 40-2016

Link to Aspen’s Community Development Department…

What are the significant changes?

  1. The first change to the code drops the prescriptive allowable fenestration U-factor to .28.
  2. If submitting under the total UA trade-off compliance option, you will be required to go 2% beyond the passing line, in order to compensate for the fenestration glazing U-factor change.
  3. The option for exhaust-only occupant ventilation and air-cycler systems have been taken away, as balanced heat recovery systems are made mandatory. The HRV or ERV must have an efficiency of at least 65% and its fan powered by an EMC motor. All fans are required to meet a higher standard of efficacy; CFM/watt.
  4. Air sealing is still required, but infiltration (blower door) testing is not required.
  5. Mechanical sizing (ACCA Manual J calculations) is not required.

Here’s the interesting part, the City of Aspen, Climate Zone 7, has sought to simplify the code by deleting the IECC ERI compliance alternative and replacing it with their own version. It’s called the Simplified Equivalent Compliance Alternative. Dwellings must meet the following criteria to comply with this alternative.

  1. Equivalent space cooling energy. The ratio of the air conditioning capacity to conditioned space is less than or equal to 12,000 Btu/hour per 1,000 square feet.
  2. Equivalent space heating energy. The ratio of the space heating system capacity to floor area of conditioned space is less than or equal to 32,000 Btu/hour per 1,000 square feet.
  3. Equivalent hot water. The distance from the hot water supply outlet to hot water pipe to the hot water entry to a room where hot water is used shall be no more than 10 feet. This shall apply to the kitchens, bathrooms with showers or tub, and rooms with a clothes washer.
  4. Equivalent lighting. Lamps over 15 watts shall be CFL, LED, or have an efficacy not less than 90 lumens per watt. Or, at least 90% of the lamps or fixtures shall have an efficacy not less than 75 lumens per watt.

This code change deletes equipment sizing, infiltration testing and energy modeling; the very tenets of the energy rating paradigm. I like the simplicity, but I fear it is too simple. I guess time will tell how Aspen fairs under this code.

Confluence Architecture & Sustainability can provide third-party insulation and air barrier inspections, and certification of compliance with the other provisions of this code.

Jump to Energy Conservation Code Hub for; the western slope of Colorado; Aspen, Telluride, Mountain Village, Town of Snowmass Village, Basalt, Carbondale, Pitkin and Eagle County…


PHEV (Plug-in Hybrid Electric Vehicle)

Confluence already uses an electric car for site visits in the valley; 2013 Nissan Leaf.

But it won’t make it to our HERS Rating inspections and blower door tests in Telluride, Mountain Village, Steamboat, Vail Valley and Summit County.

So we have added a PHEV (Plug-in Hybrid Electric Vehicle) to the “fleet”.

A 2018 Toyota Prius Prime…

2018 Prius Prime

2018 Prius Prime

Some features…

  • Hybrid Synergy Drive with Electronically controlled Continuously Variable Transmission
  • 55 city/53 highway MPG
  • 133 MPGe
  • 640-mile EPA-estimated total driving range
  • 25-mile EPA-estimated EV Mode driving range


Energy & Sustainability Services

Recently more jurisdictions have adopted the 2015 IECC or the IgCC and we have been helping several architects & designers with energy and sustainability code compliance.

Go custom! You don’t have to follow the recipe. Make the energy code work for your project.

Farm out the energy work to Confluence. We will be responsible for any or all of these, bring value to the performance of the building, and take the load off of your hands:

  • Energy code compliance
    • Infiltration (blower door) testing
    • Assembly UA trade-off (calculation software)
    • Total UA trade-off (REScheck or HERS Rating)
    • Performance path compliance (REScheck or HERS Rating)
    • ERI path compliance (HERS Rating)
  • Code compliance/optimization and Construction Documents
    • Ventilation calculations
    • Sealed crawlspace & ventilation details
    • Continuous Insulation details
    • Back-ventilating siding and attachment details
    • Efficient framing details
    • Fenestration flashing details
    • Radon mitigation details
    • Thermal and pressure envelope delineation
    • Vapor retarder specifications
    • Air-sealing details
  • Local/municipal Green/Efficient Building Checklists
    • Carbondale, Basalt, Town of Snowmass Village, Telluride, Mountain Village
  • Above-code/Net Zero design and certification
    • LEED, Passive House, HERS Rating, etc.

Very Large Residential and Commercial Infiltration Tests

Confluence can perform very large residential and commercial infiltration tests, or blower door tests.


We set up eight fans in three doorways for this test at Habitat For Humanity’s new ReStore warehouse In Glenwood Springs, Colorado. Although, not the biggest test we have conducted. That honor goes to a 56,000 square foot house built for a Saudi Arabian Prince in the Starwood neighborhood near Aspen, Colorado.



Recent work…

We have recently gotten the chance to photograph some recently completed work.

The Basler Residence at Elk Springs, Garfield County, Colorado…


And this storage banquette…

Here’s a house going up in Oak Meadows…



How much solar do I need to power an Electric Vehicle?

Nissan Leaf

I don’t understand MPGe. A better metric would get me closer to knowing what I really want to know; how much does it electricity does it take to charge my car’s batteries? How far will that get me? What does it cost? How much solar do I need to offset the power consumption of an EV?

We’ve been driving our 2013 Nissan Leaf for one and a half years now and I have some data… the metric that makes the most sense to me is miles/Kwh. We live in a climate that is less than perfect for electric cars; little too hot in the summer, little too cold in the winter and lots of mountains. But still we average 4.5 miles/Kwh annually. I can’t find much difference in efficiency between the different makes and models of EVs. It seems to have much more to do with your climate, geography, topography, and a driver’s tendency to show passengers how fast an electric car will take off from a start. In 2016 we drove 12,108 miles. Assuming 4.5 miles/Kwh, then 2,691 Kwh went into powering the car.

Our solar array is officially rated at 3,240 watts. It was predicted to make us 4,753 Kwh annually, but in 2016 it gave us only 4,000 Kwh (16% less than estimated). The solar guys say this is because their software doesn’t de-rate for “losses” like; snow on the panels, age, azimuth and orientation. Sounds like a weak excuse to me; regardless, 4,000 Kwh is what we get.

The solar panels made enough power to push the car 4,000 x 4.5 = 18,000 miles. Each one of our twelve panels made us 1,500 miles worth of driving electricity. We drove only 12,108 miles, so the rest went into powering the house. To zero-out our total electric consumption, we would need to make a total of about 8,000 Kwh of power, or have a 6,500 system. 2,700 Kwh for our 12,000 miles of driving (34%) and 5400 Kwh for the house (66%).

So, how much solar do you need to offset your drive. Impossible to calculate for sure, but here’s starting point…  wattage of PV array required = (miles driven annually / 4.5 miles/Kwh) X .8  If you have a lead foot, get a couple more panels.

If we bought the electricity to drive the car 12,108 miles (2,691 Kwh x $.138) it would have cost $371. It would cost me about $1,000 for the gas to drive our 2005 Subaru Outback the same distance. Solar is good when offset your home electric uses, but when it keeps you from buying gas- it pays back three times faster! And don’t get me started on maintenance and repairs; oil changes, transmission oil, power-steering fluid,  fan belts, timing belts, head gaskets, catalytic converters, mufflers, oil filters, air filters, fuel filters, hoses, plugs, tubes, valves, sensors, etc. EV’s still have/need; insurance, tires, shocks, air conditioners, windshield wipers, windshield washer fluid, brakes and brake fluid. But I really don’t miss the regular stops at the gas and oil change stations and repair shops. If you have the means and it fits your commuting- buy one! You’ll love it.

Couple creates a deep-green, DIY home in Satank, Colorado

This is a re-posting of an article from Roaring Fork Lifestyles magazine.


Check this Tumbler scrapbook about the construction process, very interesting.


Confluence Architecture & Sustainability was the HERS raters for this home. The HERS is an outstanding -10! The negative means is actually beyond net-zero, it is net-positive. As in, the occupants of this home should never have to pay for heating, cooling, lighting or hot water. Attention to detail got this house crazy air tight. Even with salvaged windows and doors, Steven was able to get this down to .69 ACH50. I’m sure it would have bested Passive House requirements (.6 ACH50) if not for the less-than perfect windows and doors.

Congratulations Steven and Bailey- you have a beautiful, high-quality home. Here are a few teaser photos…

The "Hainestead"