Controlling Moisture: The Key to Good Buildings
From ASHRAE Journal Newsletter, March 8, 2022
Moisture control is key to creating energy-efficient, durable and carbon-neutral buildings.
To help engineers achieve this design goal, ANSI/ASHRAE Standard 160-2021, Criteria for Moisture-Control Design Analysis in Buildings, has been updated. The 2021 edition of Standard 160 revises the definition of the moisture-design reference year, adds a related evaluation criterion and includes a new method for ranking weather years.
Standard 160 specifies performance-based design criteria for predicting, mitigating or reducing moisture damage to the building envelope, materials, components, systems and furnishings—depending on climate, construction type and HVAC system operation. These include criteria for selecting analytic procedures, criteria for inputs and criteria for evaluation and use of outputs.
ASHRAE Standard Project Committee 160 discussed the updated standard with ASHRAE Journal:
Why is it important to talk about moisture control right now?
Everyone wants to trust their homes to be safe, heathy and resilient. Architects and design engineers are critical in designing buildings that are not only energy efficient but also durable and carbon neutral. Moisture control is key to the success of energy efficiency, durability and carbon-neutral designs.
Because ASHRAE SPC 160 deals specifically with design considerations needed to avoid moisture-induced problems, such as biological, chemical and structural damage, paying attention to moisture control is an absolute must in today’s designs.
What were some of the most significant changes to the 2021 edition of the standard?
Significant changes to the 2021 edition include the selection and use of a moisture design reference year in the design for moisture control. This alone is one of the most important upgrades to the standard.
ASHRAE is leading the way internationally for the use of a weather year that is selected based on the damage potential from weather. Before, the selection of the weather year was not specifically based on deep science but on committee consensus as the 10th percentile cold and warm year.
Now, a clear approach is described that is based on extensive hygrothermal analysis. This approach was developed as part of a multiyear ASHRAE Research Project TRP 1325, Environmental Weather Loads for Hygrothermal Analysis and Design of Buildings. This is a major improvement to our standard because the selection of hygrothermal loads now has a scientific backbone.
Do you have any tips for engineers regarding this topic?
This standard embraces a multidisciplinary method for accessing designs on behalf of moisture control. The perspective no longer focuses on the specific threshold of moisture present in an envelope system.
The emphasis shifts to the amount of time water is present, where it accumulates and how it relates to biological efficacy (e.g., mold growth, algae growth, rot), chemistry of the materials (e.g., corrosion, chemical compatibility) and structural impact (e.g., freeze-thaw).
Of course, we are not there 100%, but the committee is working on multiple engineering-based assessment methods. The ASHRAE standard is currently the state-of-the-art standard in design worldwide. Future research is also needed to create more realistic predictions for freeze-thaw assessments and corrosion methods.
What should engineers know about using this resource?
With the new addendum a, we are getting better assessment of the moisture loading from building envelope systems. We have just addressed the use of a weather year that is selected based on moisture loading.
The method described in the standard can be used to select a year from a series of many years anywhere in the world. It is a simple method that captures the characteristics of moisture loading that are important for proper design of buildings.