Why hygrothermal concerns are critical, and why the WUFI 1D workshop is indispensable

Lisa White, PHIUS+ Certifier, is today’s guest blogger

One of the pre-conference sessions at this year’s conference is an intensive 2-day session focused on the importance of hygrothermal modeling, the building science behind it, and using WUFI 1D to perform hygrothermal modeling. It runs October 15-16 in advance of the core conference.

In today’s guest blog, Lisa White—a PHIUS+ Certifier and CPHC—explains why hygrothermal modeling is critical, and the benefits of familiarizing yourself with the WUFI 1D modeling tool.

As designers build to passive building performance levels, choosing the right assemblies for projects is more challenging than ever. It seems that we have all recognized the importance of modeling the thermal performance of assemblies—we do this in the static side of WUFI Passive or in the PHPP. Thermal properties are, coincidentally, the only values that the static energy model for certification is concerned with. We’re asked to enter the R-values of each layer of our envelope assemblies—cellulose, framing, OSB, polyiso, etc. That’s it.

But when it comes to high performance, multi-layer assemblies, thermal performance is not, by any means, all that PHIUS+ certifiers are concerned with. And it shouldn’t be all that designers are concerned with, either. The hygric performance is just as important, if not more. A hygrothermally sound assembly ensures long term thermal performance, as well as durability.

When PHIUS evaluates a project for PHIUS+ Certification, we look at both the thermal and moisture performance of the envelope. A project may meet passive building performance criteria based on the energy model, but that’s not the end of the story. In cases that stray from accepted building science principles, in order to assure performance, quality and durability, the PHIUS+ process requires deeper look at the moisture performance of the assemblies. This assessment is done using WUFI 1D – a program for heat and moisture analysis of building envelope enclosures.

The WUFI 1D assessment allows us to analyze if the assembly will perform well, and therefore meet certification requirements, or whether it needs modification. In a small handful of projects, moisture performance alone has prevented a project from being certified. An assembly with poor hygrothermal performance compromises indoor air quality and structural durability, and may cause the buildup of mold and rot which poses health risks. Whether you’re certifying a project or not, this tool and assessment is still incredibly important.

Determining the hygric performance of assemblies becomes even more important when dealing with all North American climate zones—from cold and dry, to hot and humid. No assemblies perform identically in each climate zone. WUFI 1D allows you to model your assembly, and run comparison cases, in a particular climate, based on hourly climate data and conditions.

Retrofit cases pose an even more crucial need for hygrothermal assessment; in most cases, it’s required for PHIUS+ Retrofit Certification. In most retrofit cases, it is impossible to create the ‘perfect wall’ or even sometimes to follow basic building science principles. Existing conditions can limit the variability of the assembly—sometimes sometimes designers are forced to deviate from general guidelines. Using WUFI 1D, a designer can compare and rank different options for assemblies, based on long term hygrothermal performance, in a particular climate.

A tremendous additional benefit to becoming familiar with WUFI 1D is that this program is tied directly into the dynamic side of WUFI Passive. The WUFI 1D preconference session provides significantly more information related to inputs for the WUFI plus side of WUFI Passive, and key abilities to analyze the results. The WUFI 1D preconference sessions will focus on these skills to a greater degree than and in greater detail than is possible in the WUFI Passive trainings, and will be extremely useful in navigating the dynamic analysis of your projects.

All in all, to uphold quality assurance and quality control in PHIUS+ Certification, we analyze both the moisture and thermal performance of your project. This is the only way to ensure a durable, high performance building with superior indoor air quality.

Consequently, we encourage you to take advantage of the WUFI 1D preconference session. The two leading experts on WUFI 1D – Achilles Karagiogis (Owens Corning) and Andre Andre Desjarlaisa (Oak Ridge National Laboratory)  – will lead the trainings. They’ll provide a fundamental understanding of the building science behind hygrothermal analysis, and you’ll learn how make the most of WUFI 1Ds capabilities. Both capabilities will serve you well as you design passive and other high-performance buildings.

And, if you already are confident with your hygrothermal chops, consider taking the WUFI Passive workshop. Visit the conference links below for more information.

Register (general public)

Register (PHAUS Members)