Pushing Passive House into building codes: creating an enforceable standard ASHRAE draft standard briefly available for comment

13 October 2023 by Jason Quinn

Years of effort volunteered by engineers and Passive House professionals has produced a draft ASHRAE standard now released for public review and comment. It is an ambitious and potentially transformational effort to translate Passive House methods of energy reduction and design into Building Code language. 

In theory it should make getting to Passive House-like performance cheaper and easier for designers, developers and builders—which in turn means more affordable and more Passive House-like buildings being constructed right around the world.

Here’s what ASHRAE has to say about the purpose of this document (I’ve paraphrased for brevity):

ASHRAE 227 provides requirements for the design of buildings that have exceptionally low energy usage and that are durable, resilient, comfortable, and healthy. Applicable to both new and existing buildings intended for occupancy, this standard provides requirements for the design, construction and plans for operation of the: building envelope, heating and cooling equipment and systems, ventilation systems, service hot water systems, interior and exterior lighting systems, and plug and appliance loads.

“[It’s] an effort to make the concepts and techniques of passive building [sic] shine through a different structure for compliance, verification, administration and enforcement—a structure that works more like other energy codes and less like proprietary certification programs (of Phius and PHI),” according to Phius senior scientist Graham Wright’s summary of the project.

That way, building consent authorities can lift all or part of the standard and adopt it into their local/regional building code*—and enforce it—without requiring the use of specialist software and highly trained certifiers. In a nutshell, it’s a laudable attempt to push all the lessons we’ve learned doing Passive House into building codes, not just in North America but worldwide.

ASHRAE has taken an approach that may alienate some Passive House professionals but our common goal will be accomplished if it leads to many more, much better buildings. Every existing performance standard was used as source material. The document had to fit with all other ASHRAE standards and be expressed in language that could be enforced in a building code. It’s a big mission that has been underway for four years. 

The draft contains both a prescriptive and performance path, so that not every building will  need to be energy modelled. That’s because building consent officials can’t abide black box software that produces magic numbers as evidence of compliance, so alternatives to energy modelling (where possible) make outcomes easier to express in a language suitable for adoption into building codes. ASHRAE also can’t require use of proprietary software or systems, so all the necessary equations are contained within the standard itself.

The outcome thus far is a compliance path that was dubbed by committee members as a ‘choose-your-own-adventure’: a single building can use the prescriptive path for one part and then the performance path for another. It ends up somewhere between energy modelling and schedule methods in terms of complexity.

Figure: BSR/ASHRAE Standard 227P Passive Building Design

The ASHRAE standard’s hybrid path is inherently flexible and we hope will lead to very good outcomes—but it’s been a hard nut to crack. (I’ve been a member of the committee since it was founded, although the meetings scheduled for US time zones have started brutally early in New Zealand and my contribution has been minor compared to others.)

By comparison, Passive House takes an energy modelling and research approach. The prescriptions for single and multi-family homes for instance are now well understood. But novel buildings with highly unique requirements, like swimming pools/leisure centres and hospitals, require custom energy metrics. They are developed after years of research, creating pilot projects that investigate the best way to proceed. Other specialist buildings demand the same kind of investment. That’s slow and expensive. The ASHRAE committee is attempting to avoid this additional time and expense but still accomplish great outcomes.

At time of writing, the ASHRAE standard is in the Advisory Public Review stage. This runs until 13 November 2023 and you can download the draft for free until that date. Then it will go into another editing process, be released for review again and then finally emerge into the world for sale as an official standard. 

Be warned, at 200 pages of dense text, this is not a light read and will be a slog for those unfamiliar with USA building regulations. The most important New Zealand audience for this document is the folk at MBIE and I do hope that relevant people there give this the consideration it deserves and glean ideas we could use in Aotearoa.

Useful resources for New Zealand designs

In terms of cherry picking the good stuff useful to individual designers in Aotearoa, I draw your attention to Section 7, which contains

  • building enclosure design requirements checklists, 
  • a very clever simplified annual method for residential appliances to limit plug loads, which is notoriously difficult (MBIE, please review this for applicability here!), and 
  • hot water and lighting metrics that could easily map over to New Zealand building code requirements

and also Appendix A, with its table showing deemed-to-comply generic moisture-managed wall and roof assemblies by climate zone. People have been asking for this information for ages and now I can finally share it. Go download the draft!

New Zealand’s climates range from 3A to 5A in the USA categorisation system (see pp 131-133 and pp 145-147 of the draft standard).  

  • Almost the whole North Island is 3A, bar Palmerston North and Taupō (4A) and Waiouru (5A). 
  • Most of the South Island is 4A, except Queenstown and Invercargill (5A). 

Detailed determination of the climate zone outside of the USA can be found in Section, or use ASHRAE 169 table A-6. Approximately 30 different locations in New Zealand are included in A-6 but there is no adjustment for altitude and Standard 169 costs money to access.

ASHRAE’s draft standard specifically strives to be useful and applicable not just in North America but around the world. As an example, in Section 6.13, it allows either the use of Source Energy Factors (only relevant to the American electrical grid) or Primary Energy Renewable factors (good for the rest of the world). The PER factors are from PHI and should match the current PER numbers in PHPP10—New Zealand and Australia are included.

Reference buildings—done right

This ASHRAE standard proposes a reference building approach but in the European style rather than how it’s typically been (mis)used in the USA and New Zealand. Our H1 accounts for complex buildings using reference buildings but it encourages bad habits because it “incentivis[es] inefficient design practices and poor energy modelling practices” as one expert described it. I won’t launch into a discourse about how this country’s H1 reference method ignores steel beams and concrete floor plates, because I have already (read here). 

The USA/NZ approach is to use a theoretical reference building that is the same shape and which uses Code-minimum assemblies. What it does in practice is reward inefficient form factors. The European approach tries to prevent this unwanted consequence by using a statistical reference building that is an average performance across all existing housing stock. 

In the ASHRAE standard, the reference building is one that performs at a Passive House level and which has a reasonable form factor. It is the same size (but like in the European system, not the same shape or orientation) as the proposed building. 

As Appendix F notes, “the requirement to limit heat transmission in section 5.2.2 was derived from a reanalysis of the average R-value of the optimized study buildings used to set the Phius 2018 and 2021 performance criteria”. (Phius of course is the other US Passive House industry body, the one not aligned with PHI.) 

Here are some of the benefits of the approach proposed by the ASHRAE committee.

  • It allows the standard to apply to any size building. 
  • It permits doing away with absolute energy metrics, which can vary by building type. 
  • Buildings will not necessarily have to be modelled using specialist software.
  • Novel use case buildings will be easier; they won’t require a pilot project with PHI.

The disadvantage is there are a number of assumptions made in creating the “optimized study building”’ aka reference buildings. These are underpinned by a value judgement that is not obvious. It’s no different from other standards in that regard.

Here’s the draft standard (remember the 13 November free download deadline).
BSR/ASHRAE Standard 227P Passive Building Design

*Fun fact: There are over 20,000 “permitting jurisdictions” in the US; each state has its own building code, which can usually be added or otherwise changed at city or even township level. There are thousands of sets of building requirements aka codes. Dive down into that rabbit hole here.