Chicago Regulation Change Provides Opportunity for Phius Professionals

Al Mitchell

Al Mitchell

Phius Technical Staff Member Al Mitchell wrote this week’s blog post, which discusses the recent change in regulations related to coach houses in Chicago, and how designing these new buildings to Phius standards is a win-win for all parties.

The City of Chicago has lifted a nearly half-century ban on accessory dwelling units (ADUs), opening up a door for some people to build additional units on their property. The pilot program for ADU construction pertains to rentable units, occupiable by relatives, tenants, or even to be used as additional space from the primary home. There are two types of ADUs acknowledged by this regulation: a detached dwelling unit, such as a coach house or apartment on top of the garage, or a conversion unit, such as a built-out attic or basement.

However, there are a handful of caveats to consider. First, the allowances for ADUs, whether coach houses or conversion units, are limited to select pilot zones. There are five pilot zones: North, Northwest, West, South, and Southeast. These zones cover portions of 25 of the 77 Chicago community areas. Each area has a few special requirements for different types of ADU. For example, the North and Northwest zones can have a coach house built on the property before a primary house is built, while the other three zones require a primary house to be built on the lot before a coach house can be built. In the West, South, and Southwest zones, buildings must be owner-occupied in order to add a conversion unit. All ADUs in Chicago are to be rented for a minimum period of 1 month, and there is a requirement for a certain number of affordable units on larger properties where more units can be added.


Blog Pic 1This offers a great opportunity for people to add value to their property, create flexible living spaces (especially to take advantage of the benefits of multi-generational housing) or build a unit that can provide additional income for the owner while providing right-sized, cost-effective housing for another person. Approximately 70% of the lots in Chicago are 25 feet wide and face broadside south, making the applicability of this format broad. The aim of this blog is to make the case for building these newly allowed accessory dwelling units following the Phius passive building standards to create comfortable spaces, save energy and operational costs, and provide spaces that can weather inclement weather conditions, especially during a failure of space conditioning.


Conversion units like the ones proposed in Chicago, would likely require a complete building retrofit to achieve the maximum cost and energy saving potential. This study is going to focus on detached coach houses, of maximum permitted dimensions. This comes at an apt time for Phius, as 2021 has marked the release of a user-friendly and streamlined prescriptive compliance path, as well as the performance target curves have been reworked to include allowances for small living spaces (in response to the tiny home craze).

Looking at coach house potentials, four cases were selected for evaluation. Three of the cases represent a single-story unit, one in the place of the garage, one pushed forward with open parking on the alley, and one built on top of the garage. The fourth case is a two-story coach house with no garage. The smaller units are studios, with no bedroom considered, one occupant, and the two-story coach house has one bedroom and two occupants. The standard kit of appliances is a dishwasher, refrigerator, and an induction range. Electric resistance water heaters are used in the base cases and a split heat pump system provides space conditioning.

The base cases follow code minimum constructions and windows per IECC 2018.  An envelope airtightness of 0.31 CFM50/sqft was used to match typical construction. The Phius CORE Prescriptive Path follows the prescriptive requirements per Chicago – Midway airport, and uses the default airtightness of 0.04 CFM50/sqft. The prescriptive path windows are whole window U-Values, and are set based on the required prescriptive comfort standards. Per the water heater efficiency requirements, the water heater was upgraded to a small heat pump water heater. The performance path uses 0.06 CFM50/sqft as the required airtightness metric, and follows the same window set as the prescriptive path. A heat pump water heater was used.  The other opaque assemblies were backed off from the conservative prescriptive path to meet the required calculated targets. Please reference the table below for the envelope performance specs in the study.


Case Wall R Roof R Slab R Window-U Airtightness CFM50/sf
IECC 2018 18.4 44.0 10.6 0.3 0.31
Phius 2021 CORE Prescriptive 40.0 71.0 21.6 0.16 0.04
Phius 2021 CORE 26.8 52.0 17.2 0.16 0.06
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The cases designed to Phius standards prove to reduce the space conditioning loads significantly, as shown in the Space Conditioning Results Chart. These outputs are specific per area, making it easy to compare different building sizes. Per the Source Energy Chart, the Prescriptive and Performance averages save 35% and 30% respectively. These source energy savings directly reflect the anticipated savings on an electrical power bill for the tenant of these coach houses.

Coach houses built to these passive building guidelines project significant energy savings that will directly benefit the occupants of these buildings, on top of the other comfort and passive survivability (what happens during a power failure – stay tuned for a part two blog). The required upgrades to meet the performance path is principally based around better windows and airtightness, saving on other insulation requirements per the prescriptive path. 

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The Phius Difference: Custom Energy Design Targets for Heating and Cooling — The Key to Zero

Katrin Klingenberg -- Co-Founder & Executive Director, Phius (Passive House Institute US)

Katrin Klingenberg — Co-Founder & Executive Director, Phius (Passive House Institute US)

The Klingenblog’s namesake, Katrin Klingenberg, wrote this week’s blog, examining custom energy design targets and how Phius’ approach to them sets the organization apart in the quest for Zero.

Designing zero energy and zero carbon buildings today can be cost effective if guided by the appropriate targets for investment in efficiency first. These targets are cost-optimized limits on heating and cooling loads.

The limits on heating and cooling loads are set to guide the design to a cost-optimal investment in passive conservation strategies: insulation (the appropriate amount, properly installed), dedicated continuous air, water, and vapor control layers, mitigation and avoidance of thermal bridging, high-performance windows (with appropriately tuned solar gain) and dedicated balanced ventilation with filtration and energy recovery. These principles ensure building resilience, health, comfort, safety and durability.

The cost optimization to set the targets focused on achieving the highest source energy savings (relative to a code baseline) for the least total cost (including the up-front cost of energy-saving measures, and ongoing operational costs). It factors in the cost of materials and the cost of energy supply in each particular region to calculate the sweet-spot. At some point, up-front conservation measures don’t pencil, and that’s when any additional investment should shift to active conservation strategies or active renewable energy generation systems.  These climate-optimized, project-specific targets for thermal performance define the cost-effective sweet spot on the path to zero.

The thermal performance targets are known in the industry as “Annual Heating Demand” and “Annual Cooling Demand.” They are expressed in kBTU per square foot per year or — in the metric world — in kWh per square meter per year. They are, in concept, similar to the Energy Use Intensity (EUI), but refer to the delivered heating and cooling energy required by the building. These annual space conditioning demands can only be met with passive measures and dial in the thermal performance of the building. Once those are met, a conservation-first focused total energy budget is set to guide investment in active measures. This limit is also project-specific, and can be expressed in the EUI we are all familiar with — the amount of energy used by a building per unit of floor area per year, including space conditioning and all other energy uses. That EUI can be converted into an emissions equivalent as needed to determine offsets needed to achieve zero carbon. Voila! It’s that easy!

Phius is the only building certification program that has developed such design and certification targets. They are available on the Phius website in an easy-to-use calculator. Choose climate, enter building square footage and occupancy, and you get your optimized design parameters! They are also built into the easy-to-use design and certification tool, WUFI(R)  Passive.

Before supercomputing, managing such a complex, dynamic system of variables to generate custom targets as a designer was impossible. The task of energy optimization was handled by specialized engineering firms doing the modeling — a costly and external process. Small budget projects such as single-family and small multifamily projects could not take advantage of it. Even larger projects often took the prescriptive path to eliminate the cost of custom optimization. 

Today, the reliable and detailed accounting of emissions in the building sector is necessary on a per-building basis. Many cities have passed climate action plans with extremely specific emissions reduction targets to meet over the next few decades. The Phius standard now provides an easy-to-apply, cost-effective design, and certification methodology alongside accurate accounting of carbon emissions for any building in the building sector.

With some training, architects can now easily perform these calculations themselves and build it into their design workflows right from the beginning, making sure their design is on track from start to finish.

The framework for the Phius standard today was conceived in 2015, updated in 2018, and refined again in 2021. Many municipalities have leaned on and incentivized the Phius framework to meet their climate action plans. At the forefront was New York State Energy Research and Development Authority (NYSERDA) in the State of NY. They designed a proof-of-concept program early on called Buildings of Excellence. The agency now offers cost and performance data for representative groups of completed projects using varying techniques for low energy design and accounting.

C3RRO, a third-party consulting firm under the leadership of Florian Antretter, has graphed the NYSERDA cost and measured performance data for various approaches and graciously made it available to Phius for publication. The results are proving the concept. 


As envisioned, the Phius Standard, design, and certification methodology has led to projects that not only perform the best, but are also constructed at minimal additional upfront cost. (PHI projects that use a single target for heating and cooling limits in all climates also perform reasonably well but are more expensive to build).

The new comprehensive guidebook explaining the Phius Standard design and certification methodology is now available here.

We are well on our way to (Phius) ZERO emissions!

It’s Here! The Phius Certification Guidebook v3.0

SONY DSCIn this week’s blog, Phius Associate Director Lisa White introduces the Phius Certification Guidebook v3.0 and explains how to get the most out of the newest guidebook iteration.

The Phius Certification Guidebook is the one-stop-shop for all things related to the Phius project certification program.

The guidebook contains information ranging from Tips for Designing a Low Cost Passive Building to Energy Modeling Protocols and What to Avoid. It continues to evolve alongside Phius’ growing certification program and standard updates. 

Guidebook CoverOne great reason to certify a project is to share knowledge with the passive building community, which accelerates growth. This guidebook is the keeper of that knowledge as well as lessons learned from the expanding base of certified projects. The Phius Certification team receives a myriad of questions from project teams related to unique circumstances and first-time design decisions that often require developing new guidelines and protocols to be applied on future projects — and those end up in the Guidebook. On top of that, the detailed review of projects throughout design and construction illuminates opportunities for the certification team to improve the guidance we provide to our constituents.

Version 1.0, released five years ago to support PHIUS+ 2015, clocked in at 87 pages. Version 2 followed to support PHIUS+ 2018 at 157 pages, and the most recent update, Version 3, supports Phius 2021, with 190 pages. The guidebook is a key resource for Phius professionals — but we’re often told it’s too long! I’m certain it can feel much shorter, and be incredibly useful, if you know how to navigate it. Anyone can get around a big city with the right map!

View this Table of Contents: Updates Summary which outlines what is new and updated in v3.0.

The document is split into 8 main sections followed by appendices.

The Sections

  • Sections 1 & 2 contain high-level information that is invaluable to first-time project teams and building owners/clients.
  • Section 3 is arguably the most important section, outlining all the certification requirements. Under Phius 2021, there are substantial updates to this section, most notably outlining the requirements of the performance and prescriptive paths side by side, as well as comparing and contrasting how each path handles items such as passive and active conservation strategies.
  • Sections 4 & 5 are key for setting expectations and understanding the workflows and fees associated with the certification process. There is a great high-level graphic showing three phases of certification steps at the beginning of section 4.
  • Section 6 is chock full of detailed energy modeling protocol. This section is laid out in order of the WUFI® Passive tree structure, guiding modelers top down with information ranging from early design defaults to detailed inputs for unique situations.
  • Sections 7 & 8 outline monitoring building performance as well as additional certification badges available. 

The Appendices

    • Appendix A is a consolidated resource about renewable energy. It explains how it can be used in the calculation of source energy use, and guidelines for procuring off site renewable energy.
    • Appendix B is likely the most often overlooked section, while also the appendix most referenced in project certification reviews. This appendix outlines the prescriptive approach to achieving moisture control in opaque assemblies. This most recent update splits this appendix into four types of guidelines: general, for walls, for roofs, and for floors. Do yourself a favor and vet the assemblies used on your next project (certifying or not!) against the guidelines listed here.
    • Appendices C & D are carried over from the previous version, outlining how to assess when a cooling system is recommended (App C) and internal load equipment tables for non-residential buildings (App D).
    • Appendices E, F, & G are great resources for the Phius Certified Rater or Verifier.  Appendix E is the Phius Certified Rater/Verifier manual. It outlines detailed technical inspection and field requirements, post-construction requirements, as well as how to maintain or renew the professional credential. Appendix F describes the procedure to prepare the building for airtightness testing, while Appendix G provides the onsite testing requirements for multifamily buildings.
    • Appendix H describes the Phius 2021 target setting updates, similar to what was found in the previously released “Standard Setting Documentation”
    • Appendix I is new to this version, and holds important information — most notably tips for passive building design about keeping costs low, assembly & window selection, and ventilation systems.
    • Appendix J talks about Co-Generation on-site, and how it affects the source energy factor for natural gas or grid electricity used on-site (depending on how the co-gen is prioritized). This is carried over from a previous version.
    • Appendix K is brand new, outlining definitions and requirements for electric vehicle charging infrastructure to supplement the requirement outlined in Section 3. EV capability is required in some fashion for all residential Phius 2021 projects.
    • Appendix L is also brand new and only applies to Phius CORE projects, as it describes electrification readiness requirements for combustion equipment. As a reminder, fossil-fuel combustion on-site is only permitted for Phius CORE projects, and not allowed for projects pursuing Phius ZERO or Phius CORE Prescriptive.
    • Appendix N closes out the document with normative information. Most notably, N-7 describes many of the underlying formulae for the Phius CORE Prescriptive path which is brand new to Phius 2021. It also contains the formulas and calculation methods used for lighting and miscellaneous electric load calculations, for example.

General Tips

  1. Utilize the Table of Contents and click to the section you need.
  2. Use the ‘find’ function (Ctrl+F) when in doubt of where to look to search for keywords. If taking this route, take note of what section your results are in – for example, is it a requirement or just informative?
  3. Bookmark the Guidebook link! (And follow Phius’ newsletters to be sure you’re aware when new versions are released).
  4. If you are the…
    1. Building Owner/Client — read Sections 1.1-1.4 and Appendix I-1 and review the graphic on the first page of Section 4.
    2. Project Team Member — read through Section 3 one time in its entirety if Phius Certification is a goal of the project. It’s only 18 pages, there are tables and pictures, and you can make it an excuse to have a beer.
    3. Project Submitter — read through Section 4 one time to set expectations, you will be happy you did. Also note Section 2.2, “Yellow Flag” items.
    4. CPHC / Energy Modeler — bookmark Section 6 for reference as you work through the WUFI Passive model.
    5. Phius Certified Rater/Verifier — bookmark Appendix E & F.
    6. One who loves the nitty gritty of passive building — print it, read it cover to cover.

Each iteration of the Guidebook reflects the aggregate knowledge gained by your efforts. Thank you! Feel free to use the comments section below for suggestions and questions.

Help Wanted: Identifying conditions that can complicate retrofits

32tev__gPhius Senior Scientist Graham Wright weighs in here with a guest post about some on-the-ground research he did regarding retrofits. Graham conducted a brief street-view survey of residential housing in Portland, Oregon (Glenfair, Glendoveer, Rockwood neighborhoods), and documented conditions that would complicate panelized retrofit solutions. He invites you to do the same in your neighborhood, and to submit what you find to advance research on panelized retrofit solutions.

It looks like I will be pivoting to concentrate my work on retrofit for a while. This is in connection with the Advanced Building Construction Initiative (ABC) of the U.S. Department of Energy. Under the program, RMI was funded to set up a collaborative and phius is a member. The vision shared at the recent summit is to figure out how to decarbonize ALL BUILDINGS by 2050. A study of the building typologies is underway, led by NREL.

It is already clear that single-family detached houses are the vast majority of buildings by number, they probably also dominate the aggregated “thermal loads” of heating, cooling, and hot water that comprise most of the energy/emissions savings opportunity.

The NREL data set does not have all the building properties that one would need to identify the technical barriers to deep energy retrofits. There is general awareness on the ABC team that the U.S. housing stock is very diverse and that this is a challenge to the concept of industrialized retrofit. So to get a better sense of this I spent a couple of hours looking at houses within walking distance of where I live in east Portland, Oregon. I looked for conditions that would complicate an exterior panelized envelope insulation retrofit, or that would complicate air-sealing. I looked at 33 houses and noted 30 separate conditions. These are assigned four-letter codes as shown in the table below. Some were much more common than others, such as attached garages, and some were so universal I did not even list them, such as gutters/downspouts.

My takeaway from this excursion was that the number of conditions that one would need to have a plan for is large but not endless. There are obviously some missing, such as balconies and widow’s walks. It’s not a large sample and I could only see one or two sides of the houses from the sidewalk. Many of the houses pictured are on crawl space foundations as indicated by vents, and that could also be considered an air-sealing complication, though I did not call it out here.

Here’s a slide show with problem conditions annotated:


Please send photos of houses near you! If possible, annotate conditions as I have in the gallery, using  the codes in the table below, or adding other conditions not listed, that also seem troublesome from the point of view of exterior retrofit and air-sealing.

Here are the problem conditions I classified, along with the number of cases I identified on my walking tour:

ACOD – air conditioner outdoor unit (3)
AGAR – attached garage (10)
CATV – cable tv line (1)
DISH – satellite dish (5)
DRYV – dryer vent (2)
E@RF – electrical mast through the roof (8)
EMTR – electrical meter (3)
EOUT – electrical outlet (1)
FENC – adjacent fence (13)
FCHM – fireplace chimney (17)
GCHM – gas appliance chimney (5)
GMTR – gas meter (3)
HOSE – hose bib / reel (3)
MLCA – mature landscaping close aboard (9)
MSXT – masonry extension from wall (5)
OV@R – overhang attached at roof (5)
OV@W – overhang attached at wall (5)
PBVT – roof plumbing vent (3)
PBCO – plumbing clean out (1)
RFVT – roof vent (4)
SKLT – skylight / sun tunnel (3)
SOFF – overhang with soffit (3)
STOV – wood/pellet stove chimney (1)
TCOM – telecom or mystery wall box (7)
THIC – change in cladding thickness (5)
TITE – can’t add wall thickness (20)
WART – wall art (1)
WBOX – window box (2)
WING – wing or fin wall (1)
XTLT – exterior light fixture (12)

PHIUS+ 2021 Source Energy Factor for Grid Electricity

PHIUS+ 2021 will include a change to the source energy calculation for grid electricity to more accurately reflect future grid conditions and better weigh the impact of electricity versus natural gas use on site.

In past versions of PHIUS+, the source energy factor for grid electricity was defined by the Energy Star Portfolio Manager and was determined based on past generation and consumption data from the EIA. The calculation methodology accounts for the total primary fuel needed to deliver heat and electricity to the site, including conversion losses at the plant as well as transmission and distribution losses incurred to deliver electricity to the building. Under PHIUS+ 2018, the source energy factor for grid electricity for the U.S. was 2.80, which was an average of the EIA reported data from 2012-2016.

With the release of  PHIUS+ 2021 the calculated factor for the United States grid electricity is 1.73 which reflects a 2050 outlook. 

Figure 1: U.S. power sector evolution over time for the NREL Mid-case scenario

Figure 1: U.S. power sector evolution over time for the NREL Mid-case scenario

Calculating a future source energy factor for the United States electric grid electricity required the combination of three data sets: 

(1) The projected future electricity generation mix, which was taken from NREL’s Mid-Case Scenario for 2050.

(2) Fuel conversion energy factors per generation type from the EIA.

(3) Total system losses from transmission, distribution and storage, taken from eGRID2018 and NREL’s future grid mix scenario.

A detailed description of the calculation methodology and corresponding data sources can be found in the PHIUS Tech Corner article. Read the full article here.