Effective Moisture Management Strategies

December 4, 2012

Effective Moisture Management Strategies

For several years, NAHB’s Building Product Issues Committee has tracked the adverse effects of unwanted excess moisture in homes. Most of the recurring themes have been identified to be specific to certain regions of the country and certain exterior claddings. Building code requirements have changed in response to the need for more robust weather resistance performance of exterior envelopes. Product specifications and performance requirements have changed as well. But it’s often hard to keep on top of all the code and technology changes that are happening in the industry.

In an effort to help builders avoid the pitfalls of inadequate moisture management in home construction, the Forest Products Lab and Home Innovation Research Labs developed an online video resource. A series of 14 how-to videos that illustrate construction techniques that minimize moisture-related performance issues in the design and construction of wood-framed wall systems are available online. The videos serve as a building science primer for construction elements that can be affected by moisture.

Below are some of the suggestions highlighted in the videos as key areas of focus for managing moisture accumulation and dissipation.

Material Selection

When selecting construction materials, you obviously need to consider the desires of your customers and the needs of your particular climate zone. The rise and fall of temperatures within a certain range for each climate zone should be anticipated and accounted for in your material selection. Be sure to employ the right construction details based on the cladding material type selected and the climate zone. Some products retain water; others repel water. Some products allow moisture to flow through them with ease; others retard the flow of moisture. It is critical to understand how different materials must be assembled in order to prevent moisture problems originating at the foundation, within the exterior walls, or on the roof of the house.

Air Tightness of the Building Enclosure

Depending upon how the air tightness is achieved, moisture issues can arise in tighter buildings, especially when vapor retarders are used incorrectly or when the design requirements of the climate zone are not well understood. Generally, you have to consider managing the heat flow, air flow, and vapor flow within, around, and through the home – these are all interrelated and depend upon the outdoor climate conditions and the indoor environmental control systems.

Flashing Systems

The management of bulk water – rain and other precipitation – is critical to preventing moisture issues in residential construction. Beyond the basic function of a good roof and gutter system, a home requires equally good flashing systems because this is the primary way to prevent water from becoming trapped within the building enclosure. Flashing systems promote drainage of water at construction interfaces – roof and wall interfaces, door openings, windows, utility penetrations, and the foundation. The durability of a typical residential house can be improved with good flashing practices and maintenance, like the ones described below.