By Jay Fox

High-performance building methodologies are continuing to spread throughout the United States. Markets like New York and Massachusetts are leading the way by adopting more stringent building codes that align with Passive House principles, while other states and cities are also seeing an uptick in the number of deep energy retrofits and high-performance new builds. This follows a yearslong push by the high-performance building community, which includes certifying organizations like the Passive House Institute (PHI) and Phius, as well as organizations that promote passive building through education and policy work but do not issue certifications like the Accelerator, the Passive House Network, and numerous state and local Passive House groups like the Phius Alliance New York and Passive House California.

The advocacy work of these groups has been integral to the growth of the Passive House movement, but they have not acted alone. Architects, engineers, and builders have been crucial to cutting new paths, while manufacturers have regularly worked with these teams and institutions like PHI and Phius to create real-world solutions to design problems. More than just providing the necessary components to build to Passive House levels, manufacturers have worked hand in hand with these groups to create the high-performance windows and doors, advanced mechanical systems, and the elements of high-performance wall assemblies that make Passive House buildings possible.

High-performance components like these help create the airtight assemblies that are necessary for energy-efficient building, but they also perform another crucial duty: they manage moisture. Moisture control is absolutely critical for the long-term viability of new projects or retrofits, particularly if they are timber framed. If these assemblies are not allowed to dry, the damp environment can introduce a host of problems that adversely affect performance, as well as occupant health and comfort. Consequently, accurate data about how products manage moisture in real-world scenarios through hygrothermal analysis is absolutely vital. To ensure this kind of analysis can be conducted on components, manufacturers need to submit their products to rigorous testing by third-party.

In keeping with Partel’s long-standing commitment to advancing the adoption of Passive House building, the company recently announced that many of their key products are now listed on the official WUFI® database. The specific products that have been added to the database include internal vapor control membranes (IZOPERM PLUS, IZOPERM PLUS ECO, IZOPERM PLUS A2), external vapor-permeable membranes (EXOPERM MONO 150, EXOPERM MONO DURO 200), and intelligent vapor control membranes (VARA PLUS). Each of these components plays a central role in creating airtight assemblies that protect against water infiltration and help manage moisture.

By having access to third-party verified data about these products, designers who rely on Partel components can create more accurate models and perform independent hygrothermal analyses, resulting in more durable and higher performing building. 

For thicker wall assemblies, which are common in Passive House construction, hygrothermal analysis is particularly important. As noted by Mundt-Petersen (2013), “There is a higher risk of moisture‐related damage in thicker insulated walls. However, this risk can be reduced by choosing more suitable designs in which well‐ventilated air gaps behind the claddings and exterior vapor‐permeable moisture proof thermal insulation boards are of great importance.”

For retrofits, the juggling act is even more difficult as teams must work with the existing fabric of the building and adapt to conditions that are unique to each project. As the Passivhaus Trust notes in Moisture & EnerPHit: Good Practice Guide, “Although there are some rules of thumb that can be very useful, and established approaches generally accepted to be moisture-safe, designers should be careful to avoid oversimplification. It is therefore essential to embed a whole building approach into the design and construction processes.”

Even though Passive House retrofits have the power to dramatically reduce energy consumption and improve health and comfort, failing to respect the existing fabric can radically alter the flow of moisture through the existing assembly, creating new problems or exacerbating existing ones. Without a whole building approach and accurate hygrothermal analysis, assemblies can become repositories for excess moisture, leading to a variety of structural problems, including:

·         Freeze-thaw damage to masonry

·         Corrosion of metallic components

·         Reduced performance of insulating materials

For timber-frame buildings, which are extremely common in retrofits and made up 94% of new U.S. single-family home construction in 2024, excess moisture can lead to rotten wood, resulting in cosmetic damage, reduced load capacity, and eventually compromises to the structural integrity of buildings. Well before failure happens, excess moisture in timber assemblies can lead to the growth of mold. More than just posing a threat to the building’s fabric, mold can affect the respiratory health of occupants and exacerbate chronic conditions like asthma.

More Accurate Modeling with Partel

Better design and technique can mitigate these risks, and better design starts with accurate modeling and data. Partel’s line of membranes and tapes already have a sterling reputation due to their quality and durability. By being listed in the WUFI database, designers can independently model and analyze the hygrothermal behavior of assemblies that contain Partel products with verified data, resulting in healthier, more durable, and better performing buildings.

You can also check out the WUFI site for technical data sheets, manuals, literature, and to learn about workshops. You can also visit Partel's website to explore their WUFI-ready library, download material data sets, and start modelling with confidence.

REFERENCES

Mundt Petersen, S. (2013). Moisture safety in wood frame walls: blind evaluation of the hygrothermal calculation tool WUFI 5.0 using field measurements and determination of factors affecting the moisture safety. [Licentiate Thesis, Division of Building Physics]. Byggnadsfysik LTH, Lunds Tekniska Högskola.

Cambray T, Price S, Megagiannis K. (2023). Moisture and EnerPHit: good practice guide. Passivhaus Trust.