Phius Updates Its Standard

At Phius, our mission is to make high-performance passive building mainstream. To do that, we created the Phius standard to guide builders in the successful design and construction of passive buildings. The new Phius 2021 standard marks an important evolution in fulfilling that mission by focusing on further reducing emissions and facilitating scaling up.

Wide recognition of the impact of buildings on the environment has led the market to focus on and emphasize both building electrification and achieving net zero energy. The focus on building electrification acknowledges that renewable energy resources can only power electrical loads in buildings and cannot “net out” the impact of on-site combustion of natural gas. So, we must electrify if we want to reduce emissions associated with operating buildings. The net zero energy concept attempts to reduce building impact by “netting out” the building’s energy use with the same amount of renewable energy production, on an annual basis. At Phius, we believe that passive building is the right foundation for both concepts, and that Phius certification is the quality-and-conservation first approach to all-electric, net zero building.

As in the past, the Phius standard remains grounded in ensuring the quality, durability, health, and safety of the building. For residential construction, it builds upon the existing third-party certification programs ENERGY STAR, the U.S. DOE’s Zero Energy Ready Home, and the U.S. EPA’s Indoor airPLUS. Phius 2021 also includes a new quality assurance program for non-residential buildings.

Beyond covering the fundamental quality elements of a building, the Phius standard specifically focuses on optimal investments in passive conservation measures. With Phius 2021, there are now two pathways to achieving the standard: a performance and a prescriptive one. Under the performance path, heating and cooling load performance targets are set based on both a peak (worst case) condition and on an annual basis. The new prescriptive path can be met using specified individual component measures (more on this below). These passive guard rails remain at the center of all paths for Phius certification. They come with non-energy benefits such as comfort, reduced noise, resilience during outages, and load and demand flexibility for the renewable grid.

After passive conservation strategies have been employed, Phius emphasizes the use of active conservation strategies to further reduce operational energy use. If aiming for zero net energy, on- or off-site renewable energy must be used to net out the annual energy use.

Phius 2021 builds upon these key concepts to bring emissions down and scale up.

Emissions Down

At Phius, we know the ideal target for net energy use or emissions is zero. And, even further than that, the architectural, engineering and construction (AEC) community needs to consider the impact of the materials and systems in our buildings, as well as the emissions associated with the supply chains needed to deliver the building from cradle to cradle. However, Phius’ focus remains on reducing operational emissions and delivering a quality building, as we firmly believe that is the foundation on which all other considerations should be built.

The well-known Phius performance path now has two levels related to overall building impact: the CORE target to acknowledge aggressive load reduction and energy conservation and the ZERO target to build upon CORE but also fully electrify and net out operational energy use with renewable energy.

In addition to banning on-site fossil fuel combustion for the ZERO tier, the 2021 standard has added other provisions to reduce emissions and support decarbonization efforts. For CORE projects that choose to use combustion, electrification readiness requirements are enforced to ensure that the building is prepared to electrify in the future.

On top of this, all residential projects have requirements for electric vehicle (EV) readiness, ensuring the project is ready to support a future where vehicle charging with renewable energy is possible.

And lastly, the proxy used to assess building impact (source energy) reflects a future electric grid scenario. This lowers the calculated impact of electricity use and creates a more level playing field for electric equipment use versus natural gas, incentivizing project teams to electrify systems now.

Scaling Up

In the past, the Phius standard guided investment in passive conservation strategies by setting aggressive performance targets and requiring energy modeling to design and verify compliance with these targets. While this method has been effective and provides flexibility for designers to find their most-cost effective solutions, we questioned whether the overhead and skills needed for modeling were a barrier to the wider use of the standard.

Could we use our experience to develop a path without required modeling that would make the standard more accessible, without compromising the integrity? The answer was yes—if we limit the scope.

In November 2020, we introduced a pilot prescriptive path followed by a comment period. After reviewing and addressing the community’s constructive comments, we launched the Phius 2021 CORE Prescriptive standard in March 2021. The scope is limited to single-family detached and attached housing.

We consolidated all we have learned from successful single-family passive building designs over the life of the certification program and formulated it into a digestible recipe for widespread adoption. The standard takes a hybrid approach with prescriptions for both envelope and mechanical elements of the building and allows for some performance tradeoffs within those categories. It comprises three types of requirements: Universal, building-specific, and climate-specific.

Universal: These requirements apply to all projects, and most of the program requirements fall into this category. These are items such as banning fossil-fuel combustion, an airtightness threshold, maximum limit on window-to-wall ratio and maximum floor area based on planned occupancy, compact form regulated by the maximum envelope-to-floor area ratio, designing for limited moisture and condensation risk, thermal bridge elimination, third-party co-requisite programs, etc.

Climate Specific: These requirements are critical for appropriate passive building design. They include setting minimum thermal performance for the opaque and transparent enclosure, guardrails to limit window solar gain with guidelines on SHGC and overhangs, and minimum efficiencies for ventilation recovery and active heating/cooling systems.

Building Specific: These are the active conservation regulations that impact operational energy like the efficiency of the water heater, major appliances, and lighting. There are two compliance paths in this category: one based on meeting the prescribed efficiency of each individual component and the other using a performance tradeoff between equipment to out-perform the component-based approach, on a predicted annual energy use basis.

A handful of new resources were developed to support the prescriptive path. These free tools can be utilized to support the design of high-performance homes, whether the project chooses to pursue certification or not.

The Phius CORE Prescriptive 2021 Zone Table is probably the most broadly applicable resource. It provides a single zone table outlining the climate specific project requirements, displaying the range of thermal and mechanical equipment performance requirements based on the edges of the climate zone. This is especially useful for those designing in different cities across a zone; the conservative end of the range can be applied to all projects in that zone instead of looking city by city.

The Phius CORE Prescriptive 2021 Snapshot is similar to the zone table, outlining mostly climate-specific requirements and some building specific requirements. Instead of zone-by-zone, the requirements are based on the individual city (climate data set). The snapshot is recommended for anyone designing a single-family home: throw in the general building size and climate zone and use the requirements as a starting goal for design, whether or not any Phius certification is being pursued.

The most comprehensive tool is the full Phius CORE Prescriptive 2021 Path Checklist, which is used to support full compliance with the standard. It has useful tools built in, like an effective R-value calculator, whole-building UA tradeoff calculator, moisture design criteria for the opaque enclosure, condensation risk assessment for fenestration, and the appliance, hot water, and lighting performance tradeoff calculation.

The following resources are also available: Phius Certification Guidebook, Multifamily Resource Site, Commercial Resource Site, & Professional Certification and AdvancedTraining

As with the 2021 updates, the Phius standard will continue to evolve to support our mission both by widening our reach and expanding our lens. Be on the lookout for updates such as the Phius Retrofit Pilot program — a full decarbonization metric for retrofits, separate from our existing REVIVE retrofit certification program — and PhiusGEB (Phius Grid-Interactive Efficient Building), which supports grid friendliness characteristics such as aligning loads with variable renewable energy, load and demand flexibility, smart systems, micro-grids, and direct current.

As the Phius standards continue evolving, we look forward to working with the passive house community to bring emissions down, and scale up — together!