or just a great HERS / ERI score.

It’s not easy to show energy code compliance in climate zones 6 and 7. Especially if you’re working in a jurisdiction that has adopted above-code requirements. Designers here’s an exercise to help get your design on its way to IECC compliance and beyond. On your next project, before starting your typical design process, rough out a schematic design, but forget all clients wishes, ARC guidelines, height limits, etc. and design for energy conservation by substituting the following parameters…

Envelope

1. Make the thermal envelope a simple, regular volume.
2. Share assemblies with other structures, when possible, but make that party assembly very airtight.
3. Follow the prescriptive code for air barriers and insulation levels.
4. Maximum 20% glazing; 20-30% glazing; plan for really, really good windows, over 30% plan for great triple-pane windows.
5. Put as much of the insulation on the outside of the assembly as you can, or frame with Efficient Framing techniques or use alternate techniques that reduce thermal bridging like; ICFs, SIPs, Larson trusses, adobe, strawbale, etc.
6. Make the roof within 20° of optimal pitch (10:12 to 14:12) and orientation (160°-200° south) for solar, free from obstructions and penetrations.
7. Use passive solar heating techniques when possible; insolation managed by proper overhangs and low-e coatings on glazing.

Equipment

1. Plan for no gas or propane, all electric house.
2. Use no snowmelt.
3. Locate the mechanical room, in the core of the house, minimize distribution runs. Give plenty of room to equipment for service. Easy access; no hatches, ladders or crawling.
4. Locate the outdoor side of the heat pump equipment. Protected from snow and ice.
5. Don’t use site-built forced-air ductwork if you can avoid it. Radiant or ductless preferred. If not, don’t combine ductwork with garages, ventilated attics or ventilated crawl spaces. Insulate it and seal it very well.
6. Plan for a stand-alone occupant ventilation system, with occupant controls and easy access for filter cleaning; not in a crawlspace or attic. Ducting this is okay.
7. Heating; use GSHP (ground source heat pump) if you can. If not, use ASHP (air source heat pump) and passive heating techniques.
8. Cooling; skip it altogether if you can. If not, use ASHP, evaporative and passive cooling techniques.
9. Hot water; use thermal solar per-heat if you can. If not, use HPWH (heat pump water heater). Ducting this is okay.

Electric

1. Use no heat tape.
2. Use ENERGY STAR appliances. Keep refrigeration loads as low as possible. Induction range and convection oven.
3. Plan for low flow plumbing fixtures and fully insulated lines.
4. Plan for DWHR (drain water heat recovery)
5. If hot water runs are still long enough to require recirculation, use a smart pump with occupant sensors in the bathrooms and a temperature sensor to control the pump runtimes.
6. Maximize the PV array size.

Designers: Now you have a schematic design optimized for potential energy conservation. As you move on to your typical design process, keep this design in the background. Know that the more your design develops away from the energy conservation architype, the harder it may be to reach specific performance goals.

Note to Structural Engineers: Your challenge is to help the Architects keep as much steel and wood out of the thermal envelope as possible. Support several inches of Continuous Insulation, even behind stone veneer. Keep the foundation completely covered in insulation, even at patios, doors and behind stone veneer.

Note to Mechanical Engineers: Your challenge is to help the Architects reduce all equipment loads, reduce runs and maximize efficiency. Investigate new technology and equipment and learn how to work with it. And help us all reduce a house’s dependence on gas.

What do we need in place to ensure a successful transition to the 2021 IECC?

Designer and plans examiner education

Architects, mechanical and structural engineers need to be taught high-performance construction techniques. An IECC compliance sheet needs to be created and submitted with Construction Documents. This will help front-load the submittal documents with a more developed mechanical system, air sealing details and specifications. Plans examiners need to learn how to recognize energy conservation issues from drawings a flag them for correction before permit issuance. Once something like a weak party wall assembly is permitted, we’re on the defense for the rest of the game.

General and subcontractor education

Contractors need to know what passing work looks like, preferably before they fail an inspection. The half-dozen raters in the valley cannot be the sole education force for thousands of contractors in the valley. GCs need to know how to interact with a rater; what to include them on, what do they need to see, when to call, etc. Subcontractors need supplemental training on ERV installations, air sealing, Radon barrier installation, etc. New technicians need to be trained on heat pump equipment. I don’t believe there are nearly enough qualified people to install all of the heat pump systems we need to install in the near future. And if it is not done perfectly, the equipment won’t live up to its potential.

Homeowner education

Homeowners need to left with a document that explains how to work the house. Most homeowners seem to be clueless about how to operate an ERV for example. If a homeowner never adjusts the ERV flow or disables it completely, or never changes the filter- we may have done more harm than good in the end. Is the filter replacement schedule being posted? Outdoor reset sensors are now required- are the reset temperature curves being programed before the occupants move in?

Product availability

Builders tend to use the products that the local suppliers carry. We need to start building with products that are not typically stocked in the valley to my knowledge. Specifically I am thinking of items like; airtight electrical boxes, drywall clips, HPWHs (heat pump water heaters), small disposable spray foam kits, liquid flashing, high-performance ERVs and ventilation controllers, vapor-retarding latex primer, etc. Somehow, we need to lobby all of the hardware stores and lumber yards to consistently stock these essential products before significant demand is here.

Enhanced inspection schedule

Rater inspections need to added to inspection checklists, far too many projects go uninspected simple because Raters are not notified of the construction schedule. Ratings only technically require two field inspections, but the reality is that two is not enough. Additional inspections should be required.

1. Pre-test ducted systems at rough-in, prior to insulation, using 2021 IECC standard, even if all ductwork and equipment is in “conditioned” space.
2. Blower Door & IR Camera at rough-in, post spray foam in roof and walls, but prior to installation of blown-in or batt insulation. If the home has a vented attic, do visual walk-thru with insulator to identify additional air sealing required, then use Blower Door: 1) As soon as drywall ceilings are hung and fire taped, but prior to hanging drywall on walls. Or 2) As soon as all the drywall is hung, finished, and painted; but before any cabinets or trims are installed.
3. Insulation Inspection when all insulation is complete

Rater-Building Department coordination and cooperation

Raters and Building Inspectors should have a clear understanding of who is checking for what. In the course of rating a house, we check and test a multitude of things; insulation installation quality, infiltration rate, ventilation rate and watt draw, duct leakage rate, pipe insulation, etc. Typically, JHAs ask me only for a certificate and a blower door test report. Getting an infiltration report without a ventilation report, really doesn’t give you the whole story. So far, ventilation is often being done fairly poorly in the field. There is massive confusion between occupant ventilation, crawlspace ventilation, spot ventilation and make-up air supply. I’m afraid we may see an epidemic of mold erupt in our valley in the near future. And lung cancer caused by Radon.

If the JHA does not ask me for the reports, then I assume they are doing those tests and inspections themselves, or they have a departmental policy not to enforce those parts of the IECC.

Final inspection, confirmed rating certificate and CO

Raters are often unmercifully pressured to cough up a certificate immediately at final. Raters need to have a complete, finished house to do our final inspection and test out; PV on the roof, ERV commissioned, every last piece of pipe insulation installed, door handles on and trades out of our way for testing. After our inspection, it takes a day to update the model and submit all of my paperwork. The it takes a day or two for the Rater to get the final certificate from their provider and transmit it to the General Contractor. GCs need to build this time into their schedule, it is not an instantaneous process.

If your jurisdiction is adopting the IECC, and if you expect projects to use the ERI path, chapter 406, for energy conservation compliance. Or possibly you are looking to modify the rules or goals to accelerate the energy-efficiency or carbon reduction goals of your community? Then there are a few ground rules you should establish ahead of time, so everybody is on the same page.

Raters need to know exactly what was adopted, how special cases are handled and policies surrounding ratings. Below is a list of things that should be thought of before embarking on an adoption…

1. IECC code year adopted?
2. Adopt HERS or ERI rating?
3. If HERS, what is the required score?
4. If ERI, are test results required to be submitted?
5. If ERI, what is done if test results do not comply?
6. If ERI, what is done with mandatory items that do not comply?
7. What is policy, how do you handle atmospherically detached ADUs?
8. What is policy, how do you handle remodels?
9. What is policy, how do you handle additions?
10. What is policy, how do you handle off-grid houses?
11. What is policy, if scores at final do not reach the goal?
12. What is policy, in multi-family, is whole-building infiltration testing allowed? Or must units be tested for compartmentation?
13. What is policy, withhold the TCO & CO until the confirmed rating certificate is issued?

HERS or ERI… To boil it down, the main difference here is that a HERS ratings don’t enforce the IECC. Whereas the ERI version has the Rater checking for mandatory IECC requirements and performing the required testing. AHJs that are relying on Raters as an extension of their own inspection staff, need to have an understanding of what Raters are looking for and what they are not. For instance, a Rater has to perform their own pipe insulation inspection, but they would have no reason to check the vapor retarder, snowmelt controls or pools and spas. Even if a Rater inspects and fails an IECC item, it doesn’t necessary mean that information will automatically be transmitted to the building department. It’s possible that the pipe insulation might fail the Rater’s inspection and pass the building department’s inspection, or visa-versa. HERS ratings scores are always more flattering than ERI scores. And HERS ratings come with a colorful certificate that gives a dollar amount of estimated savings. HERS ratings don’t have any pass/fail thresholds, so their flexibility can easily be used for existing and non-conforming homes. A HERS rating doesn’t require any construction inspections, although the score will benefit if the insulation is inspected, and it turns out to be better than default, which is “poor installation, grade III”. The HERS rating score (not ERI) will appear on the RESNET Registry, which is the database for the MLS (Multiple Listing Service). So if you go with ERI, it will not match the score listed on the MLS.

ADUs and other kinds of out buildings… Ratings don’t deal well with attached or unattached ADUs, guesthouses, party barns, etc. I recommend making a proactive statement in your adoption about how these kinds of things will be handled. Ignore ADUs entirely? Make ADUs stand on their own additional rating? Just an infiltration test for out buildings, no rating?

Remodels and additions… When a Rater inspects a project with existing assemblies and unstickered windows, they must assume the worst. The project will have a hard time making a good score with existing assemblies holding them back. Raters cannot rate just part of a house and ignore part. I recommend additions would be allowed to submit prescriptively, or are required to meet a less stringent score than new construction.

Compartmentalization…  I recommend making a proactive statement in your adoption about infiltration testing in multi-family buildings. Whole-building testing of multi-family buildings has been permitted in the past. Whole-building testing does not test the party wall, corridor wall and floor/ceiling assemblies. If individual unit testing is expected, then make that very clear up front. Typically party assemblies are not designed to create an airtight barrier between units. The unit-to-unit air leakage will make every unit perform poorly on the infiltration tests.

TCO before Confirmed rating…  It would be good to have a policy on whether or not projects can get a TCO before the Confirmed rating is issued. The pro is flexibility. For example, I have had projects lately that had major delays getting their solar installed. I am not able to final a job until the PV is on the roof and functioning. But a house can obviously be occupied safely without solar. Cons are that if people get to move in before I finish my inspection and testing, I often have access problems and new liabilities as a jobsite converts into someone’s home.

Plan for what happens when a project does not meet it’s score requirement… An ERI score is a moving target, it will fluctuate throughout a construction project. Details and specs become available, changes and substitutions are made, inspection and test results become available, etc. I always try to build in a small point buffer to offset any score creep, but invariably some projects will land above their target. Some jurisdictions will say that the project needs to do what is necessary to gain the missing points. Sometimes that works. I have been able to ask builders to upgrade a hot water recirculation pump at final to make up a couple of points. But pretty quickly we run out of options for making points that don’t involve taking the house apart in some way, significant occupation delays, etc. This puts a lot of pressure on the Rater as this starts to get into real money fast. And a Rater does not have the authority or protections of an agent of a governmental jurisdiction. Raters aren’t enforcement officers. There needs to be a way out of this situation. Some jurisdictions use a fee-in-lieu of points model. I suppose that is a reasonable way to go, probably with some limitations.

Thirteen facts about Raters and ratings every jurisdiction should know…

1. Ratings are great for comparing the performance of simple, common, no-frills houses; production homes. The further from “average” the house is, the less reliable the rating is. I would not recommend using ratings alone to cap the energy consumption of custom luxury homes. Even if the software manages to compensate for the volume and glazing ration differences, once you start putting what are essentially commercial mechanical systems in a house, all bets are off.
2. Rating software is much more sophisticated than something like REScheck, but not sophisticated enough to really handle a complex mechanical system with complex controls and operation. Especially dual-fuel houses.
3. Rating software is not like mechanical system design software or Manual J & S software, like Wrightsoft or Elite. Rating software does not how to make “zones” comfortable, so I find it underestimates cooling loads in heavily glazed rooms.
4. Rating software simultaneously checks the energy model for compliance with 36 different codes and programs including; 2006 IECC Prescriptive to 2021 IECC ERI, ENERGY STAR, LEED, 45L Tax Credit, etc.
5. Ratings affect the construction schedule. As a job starts to wind down, there is often much pressure on a Rater to final inspect, test-out and produce a confirmed rating. Ratings cannot be finaled until the house is completely finished; solar installed, door hardware and thresholds installed, ventilators running, appliances etc. It takes at least two business days to get a final certificate from RESNET after a Rater makes the final inspection, builders often neglect to build this time into their schedule.
6. Ratings are not black and white. Different software and different Raters may get slightly different results. The more complex the house, the more ratings will vary.
7. Ratings don’t include all of the energy used in a project. Be cognizant of what is included in a rating and what is not. If you are trying to create a “total energy budget” for a house, know that ratings look only for specific items. People tend to ignore the little asterisks next to the HERS index utility bill estimate that says “*relative to an average U. S. home”. A model Renewables Energy Offset Program would need to catch, not just snow melted driveways and outdoor pools, but also everything about the house that is above “average” in order to have a comprehensive accounting of projected energy usage. And that “average” house is looking at a national scope, I find that almost all of the single-family houses I rate in Colorado are above average in the amount of energy that gets used beyond the scope of a rating. For instance rating do not capture… Anything outside the thermal boundary of the living spaces of the house, like; heated garages, ADUs, out buildings, pools, pool houses, fountains, patio kitchens, patio heating, snowmelt, hot tubs, etc. Items inside the house that a rating will not capture; make-up air for a large kitchen hood or draft inducer for a fireplace, steam showers, humidifiers, oxygen concentrators, elevators, radon fans, multiple redundant appliances, redundant heating systems, whirlpool tubs, pools, supplemental ventilation or dehumidification for pools, etc. We know from study by a local engineering firm (Resource Engineering Group, Crested Butte) that these items, that differentiate an average house from a custom luxury house, are the very things that make these houses exponentially more energy consumptive. Ignoring the burden of the luxury items is really a form of discrimination against anyone trying to build an average house.
8. Ratings are very harsh on uninspected existing assemblies and unstickered windows. If a project covers insulation before I get to inspect it, I am required to assume the worst, and grade the insulation at the worst possible installation level; poor installation. This can add several points to the final score, even though the insulation may have been great. It would help Raters immensely if jurisdictions would stamp the drawings with something like, “Confirmed rating required for CO. Contact the Rater of Record at start of construction, before insulation is installed, after insulation is installed and at substantial completion.”
9. Ratings don’t necessarily push projects to electrification. Ratings are based on dollars, not carbon. Ratings don’t know how clean or dirty the local electrical grid is. Science tells us that we should discourage the use of fossils fuels in new construction and embrace electrical technologies. If you want to incentivize electrification, then something more than a standard rating is required.
10. Ratings are typically full of assumptions and the Projected level. Raters usually get Design Development drawings without PV design, appliance schedule, glazing specs, etc. The rating will gradually get more accurate as the project develops.
11. Home Energy Raters are all certified by RESNET (Residential Energy Services Network) at least until another certification group emerges. Once certified, they can perform HERS, ERI ratings and issue IECC compliance documents. With a little more training and testing, they can issue ENERGY STAR documents. With a little more training and testing, they can become a Green Rater and issue LEED documents.
12. Rater certification and maintenance is not easy. Raters have to take classes in Building Science and how to use the software. Then pass the tests. Then you have to intern on a number of probationary ratings, all before you start work. It takes a load of expensive equipment to actually perform ratings- usually have about $25,000 worth of equipment in my car. I have to pay dues to a company to provide QA (Quality Assurance) which means they review my work answer questions and process the record keeping. Every year I pay for that company to send a representative to one of my jobs to do a live rating review on the spot. Every three years I have to complete 18 hours of continuing education. Plus annual equipment calibration, insurance, vehicle and computer overhead.
13. Raters have no power of enforcement on their own, other than the fear of a non-compliant score. No power to compel document changes, no power to reject work, no power to withhold a CO. If energy conservation measures are to be enforced on a project, then a Rater needs to be supported by the AHJ.

Below is my model code adoption language. Please use it, customize it and evolve it…

HERS model adoption language

1. The AHJ will stamp the rating type, goal and any other special requirements on the cover sheet of the record documents kept on site.
2. New construction projects, gut remodels and atmospherically detached Accessory Dwelling Units shall achieve a HERS score of 50 (Climate zone 7).
3. Addition projects shall have a Home Assessment made of the existing structure and recommendations undertaken. New work to follow Prescriptive requirements. Final infiltration test not required.
4. Multi-family units shall undergo compartmentation testing, whole-building tests will not be accepted.
5. Off-grid houses shall follow the Prescriptive path.
6. CO shall not be issued until confirmed rating is issued. A TCO may be issued for house that have completed testing but the confirmed rating is delayed for extenuating circumstances.
7. If a site is deemed unsuitable for PV; projects may calculate how much solar is required and install that amount off-site. Or PV may be purchased at a community solar farm. Or the PV may be donated to another building in the community.
8. Projects with non-compliant HERS scores shall; calculate how much additional PV it would take to make the score complaint and donate $7.00 per watt to a local community solar cooperative.

2021 IECC ERI model adoption language

1. The AHJ will stamp the rating type, goal and any other special requirements on the cover sheet of the record documents kept on site.
2. New construction projects and gut remodels shall achieve a 2021 ERI score of 60 without PV and a 2021 ERI score of 53 with PV (Climate zone 7).
3. Atmospherically detached Accessory Dwelling Units shall achieve a 2021 ERI score of 53 (Zone 7).
4. Addition projects shall have a Home Assessment made of the existing structure and recommendations undertaken. New work to follow Prescriptive requirements. Final infiltration test not required.
5. All ERI requirements of 2021 IECC Table 406.2 shall be met. The AHJ shall be responsible for all inspections in enforcement of the IECC.
6. Infiltration, ventilator efficacy and Total Duct Leakage test result reports shall be submitted.
7. Ventilator flow test result reports shall be submitted. Non-compliant ventilation flows shall be rectified and re-tested. In the event of the test not being able to be executed for technical reasons, ventilation flows may rely on manufacturer’s data plate specifications.
8. Multi-family units shall undergo compartmentation infiltration testing, whole-building tests will not be accepted.
9. Off-grid houses shall follow the Prescriptive path.
10. CO shall not be issued until confirmed rating is issued. A TCO may be issued for house that have completed testing but the confirmed rating is delayed for extenuating circumstances.
11. If a site is deemed unsuitable for PV; projects may calculate how much solar is required and install that amount off-site. Or PV may be purchased at a community solar farm. Or the PV may be donated to another building in the community.
12. Projects with non-compliant ERI scores shall calculate how much additional PV it would take to make the score complaint and donate $7.00 per watt to a local community solar cooperative.

Please note that I work in the mountains, custom luxury home market- climate zones 6 and 7. This could all change quite a bit in another part of the country. I don’t know a thing about termites, exterior vapor retarders, radiant barrier, etc.…

Thank you,

Mark McLain

Architect

ICC/HERS Compliance Specialist

ICC Residential Energy Inspector/Plans Examiner

RESNET Certified Home Energy Rater

BPI Building Analyst Professional

BPI Multi-family Building Analyst Professional

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

Ratings are a great tool for evaluating the projected performance of unbuilt houses. Many good points; they get projects into a simple energy model that can be used to Value Engineer the most cost-effective version of the proposed house, they put another set of eyes on the work- looking specifically for energy conservation issues, etc. But they do have their shortcomings. Here are a few places I can think of where other jurisdictions have had problems with the application of their adoptions recently…

HERS (Home Energy Rating Score) or ERI (Energy Rating Index)…

Be specific about the adoption language regarding the yardstick you want to measure by. In 2015 HERS and ERI scores were the same. In 2018 HERS and ERI adopted different base standards, and now the scores do not align. ERI scores are harder to reach than HERS scores in 2018 and 2021. The other core difference between the two; ERI reports come with a list of “mandatory” items that have to be done per the IECC (International Energy Conservation Code) ; like pipe insulation. If I fail someone on a poor pipe insulation job, it will show up as a big red problem on the ERI report. HERS doesn’t have any “mandatory” items, no pass/fail. You can get a HERS score no matter what. I can give you a HERS score on an existing house, even though I can’t inspect the pipes.

Accessory Dwelling Units and other kinds of out buildings…

Ratings don’t deal well with attached or unattached ADUs, guesthouses, party barns, etc. I recommend making a proactive statement in your adoption about how these kinds of things will be handled. Ignore ADUs entirely? Make ADUs stand on their own additional rating? Just an infiltration test for out buildings, no rating?

Remodels and additions…

When a rater inspects a project with existing assemblies and unstickered windows, they must assume the worst. The project will have a hard time making a good score with existing assemblies holding them back. Raters cannot rate just part of a house and ignore part. I recommend additions would be allowed to submit prescriptively, or are required to meet a less stringent score than new construction.

Compartmentalization…

I recommend making a proactive statement in your adoption about infiltration testing in multi-family buildings. Whole-building testing of multi-family buildings has been permitted in the past. Whole-building testing does not test the party wall, corridor wall and floor/ceiling assemblies. If individual unit testing is expected, then make that very clear up front. Typically party assemblies are not designed to create an airtight barrier between units. The unit-to-unit air leakage will make every unit perform poorly on the individual infiltration tests.

Issue TCO (Temporary Certificate of Occupancy) before Confirmed Rating…

It would be good to have a policy on whether or not projects can get a TCO before the Confirmed rating is issued. The pro is flexibility. For example, I have had projects lately that had major delays getting their solar installed. I am not able to finish a job until the PV is on the roof and functioning. But a house can obviously be occupied safely without solar. Cons are that if people get to move in before I finish my inspection and testing, I often have access problems and new liabilities as a jobsite converts into someone’s home.

Missed inspections…

If a project covers insulation before I get to inspect it, I am required to assume the worst, and grade the insulation at the worst possible installation level. This can add several points to the final score, even though the insulation may have been great. It would help raters immensely if jurisdictions would stamp the drawings with something like, “Confirmed rating required for CO. Contact the Rater of record at start of construction, before insulation is installed, after insulation is installed and at substantial completion.”

Have a plan for what happens when a project does not meet it’s score requirement…

A rating score is a moving target, it will fluctuate throughout a construction project. Details and specs become available, changes and substitutions are made, inspection and test results become available, etc. I always try to build in a small point buffer to offset any score creep, but invariably some projects will land above their target. Some jurisdictions will say that the project needs to do what is necessary to gain the missing points. Sometimes that works. I have been able to ask builders to upgrade a hot water recirculation pump at final to make up a couple of points. But pretty quickly we run out of options for making points that don’t involve taking the house apart in some way, significant occupation delays, etc. This puts a lot of pressure on the rater as this starts to get into real money fast. And a rater does not have the authority or protections of an agent of a governmental jurisdiction. Raters aren’t enforcement officers. There needs to be a way out of this situation. Some jurisdictions use a fee-in-lieu of points model. I suppose that is a reasonable way to go, probably with some limitations.

Have a plan for what happens when a project does not meet test requirements…

Several tests may be run in the course of a rating; infiltration, duct leakage, ventilation flows, ventilator watt draw, etc. An ERI report will show tests that did not comply with the IECC, but with a HERS rating the test reports may not be automatically supplied with the confirmed rating certificate. The test results will be incorporated into the model, but there is no pass-fail threshold related to the IECC. Recommend deciding ahead of time if test reports will be collected and reviewed. Is there going to be some consequence for failing IECC tests? Are they expected to be remediated and re-tested?

Be cognizant of what is included in a rating and what is not…

If you are trying to create a “total energy budget” for a house, know that ratings look only for specific items. People tend to ignore the little asterisks next to the HERS index that says “*relative to an average U. S. home”. A model Renewables Energy Offset Program would need to catch, not just snow melted driveways and outdoor pools, but also everything about the house that is above “average” in order to have a comprehensive accounting of projected energy usage. And that “average” house is looking at a national scope, I find that almost all of the single-family houses I rate in Colorado are above average in the amount of energy that gets used beyond the scope of a rating. For instance rating do not capture… Anything outside the thermal boundary of the living spaces of the house, like; heated garages, ADUs, out buildings, pools, pool houses, fountains, patio kitchens, patio heating, snowmelt, hot tubs, etc. Items inside the house that a rating will not capture; make-up air for a large kitchen hood or draft inducer for a fireplace, steam showers, humidifiers, oxygen concentrators, elevators, radon fans, multiple redundant appliances, redundant heating systems, whirlpool tubs, pools, supplemental ventilation or dehumidification for pools, etc. We know from study by a local engineering firm (Resource Engineering Group, Crested Butte) that these items, that differentiate an average house from a custom luxury house, are the very things that make these houses exponentially more energy consumptive. Ignoring the burden of the luxury items is really a form of discrimination against anyone trying to build an average house.

Ratings don’t understand batteries, whole-house generators or houses that are not connected to the electrical grid…

It doesn’t come up much, but just beware that houses that don’t fit into the rating box very well, may require/deserve an alternative approach to show compliance.

Electrification…

Ratings are based on dollars, not carbon. Ratings don’t know how clean or dirty the local electrical grid is. Science tells us that we should discourage the use of fossils fuels in new construction and embrace electrical technologies. Ratings don’t necessarily push new construction towards electric as a fuel. If you want to incentivize electrification, then something more than a standard rating is required.

Thanks,

Mark McLain

Architect & Sustainability Consultant

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

Confluence Architecture was instrumental in turning an old 1970 energy hog home into a an efficient, low energy use residence.   The project qualified for $12,000 in  grants from CORE and $7,092 in rebates from Holy Cross Energy.      The home is fully electric and uses air-source heat pumps for heating and cooling.  It is projected to be net-zero. Confluence was responsible for planning, architecture and energy modeling on this home.

Before

After

EV+PV

There is much to like about Electric Vehicles (EVs). There is much to like about Solar Photovoltaic power collection (PV) too. But when you put the two together, something extra happens… You can now think of your solar system as being paid off, not by offsetting the cost of the electricity that runs your house, but by offsetting the cost of the gas you’re not buying.

Below, I am going to list the real-world drive data from our two company cars, a Nissan Leaf EV and a Prius Prime PHEV (Plug-in Hybrid Electric Vehicle). Sorry hybrids, you don’t get to play this game. Then I’ll list our real-world solar array data and calculate the value of the electricity we have harvested from our PV array. And answers some important questions; How much PV do I need to offset driving an EV or PHEV?

3.24 kW PV array:

Number of panels:                           12

Power per panel:                              344 watts

Annual production:                         4,128 kWh

Cost after rebates:                          $5,796

Thermal solar panels on lower roof, PV array on upper roof

The calculations will vary, of course, from place to place and car to car and driver to driver. These cars live in Carbondale, Colorado. The climate is pretty good for EVs; not too hot, not too cold. Typically highway driving punctuated by small towns. The road is never level, up valley, down valley, up the hill, down the hill. We run Blizzak winter tires for about five months, and Michelin Energy-savers the rest of the year. I’m no engineer; there is much rounding and estimating used in these calculations. For projections I will use these fuel values:

Street value of a kWh:                    $.11 (summer 2019)

Street value of a gallon of gas:    $2.60 (summer 2019)

Total annual value of electricity produced by PV based on utility cost of kWh:

Total:                                                $520

Confluence company cars at local EV event.

2013 Nissan Leaf EV, 24.0 kWh battery

Miles driven annually:                     13,000

Miles/kWh: (average)                      4.4 miles/kWh

Total kWh consumed:                      3,022

Percentage of public charging:      10%

kWh provided by PV:                       2,720

Leaf consumes:                                 66% of our production

Leaf consumes:                                 8.0 panels

Miles per panel:                                1,463

Confluence company cars at local EV event.

2018 Prius Prime PHEV, 8.8 kWh battery

Miles driven annually:                      19,000

Hybrid ratio:                                       50% EV : 50% ICE (Internal Combustion Engine)

MPG:                                                    80.5

Gallons of gas:                                   118

Cost of gas:                                         $307

Miles/kWh:                                        5.4 miles/kWh

Total kWh consumed:                      1,713

Percentage of public charging:       10%

kWh provided by PV:                       1,542

Prius consumes:                                 37% of our production

Prius consumes:                                 4.5 panels

Miles per panel:                                 2,111

Total annual value of electricity produced by PV based on gasoline offset:

If 22,500 miles were driven in a gas drive vehicle (e.g. 2005 Subaru Outback, 32 MPG)

Gas offset EV portion of Prius:      $772

Gas offset Leaf:                                 $1,056

Total value of gas offset:                 $1,828 (703 gallons)

Every solar PV panel you put on your roof will push your EV 1,500-2,000 miles.

So, the bottom line is that our PV system makes us $520 worth of electricity annually, not bad. It would pay itself off in about 11 years at that rate. But when we put that electricity into an EV, it saves us from buying $1,828 worth of gas over our old ICE car, which translates to a 3.2 year payback!

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.

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.

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.

https://www.appliedbuildingtech.com/fsc/calculator

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

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

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

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.