February 27, 2003

The moisture vs. energy code balancing act

The Construction Consultants


One of the challenges of today’s construction is dealing effectively with the issue of moisture control and maintaining good indoor air quality.

Builders are required to “tighten” buildings to meet energy code and use sustainable products for environmental health while maintaining structural integrity and meeting consumers’ needs for good indoor air quality.

It has proven to be a delicate balancing act with very little margin for error.

The 2002 energy code requires more insulation in the walls, stricter minimums on window U values and better sealing methods on the heating ducts. Elimination of the code’s requirements for introduction of outside air into the heating unit and for installation of a whole house fan has produced discussion as to the benefits and deficits.

Moisture created inside the home will be expelled to the outside through vapor diffusion, breaks in the envelope or controlled manual ventilation. Most builders agree that the most effective method is with an efficient, controlled ventilation system. However, the builder must rely on the homeowner to understand the critical necessity of ventilation and the importance of the continued use of the system as installed.

The builder’s responsibility for homeowner education has become very important. More and more builders are making a specific point of this issue at the homeowner orientation and providing written materials to the homebuyer.

Builders are moving toward better care of the environment and the products they are using reflect that move. However, there are some tradeoffs. The use of more organic material has produced more mold growth. Removing lead from paint was done for consumer health reasons, but lead was a great mold inhibitor. Formaldehyde gives carpet its “new” smell and helps preserve wood, but has been removed from most products for healthier air quality. Gas appliances and gas heat are energy efficient, but water vapor is a byproduct of gas, putting more moisture in the air. Water-based paints are healthier, but they also add moisture to the air.

Even though mold has been around forever, it has suddenly been getting a fair share of attention. Organic material and moisture or high humidity are the food sources of mold.

Builders are providing more educational material to homeowners about home maintenance for the prevention of mold. However, mold has become more of a presence during the construction phase.

Materials come to the job site containing moisture, and then gather more moisture in the rain. After installation, the drying process can begin, but faster construction methods cause the walls to get closed in before materials dry. Any moisture that had been able to escape into the building or permeate to the outside, is now being trapped by the insulation, exterior weather barrier and siding.

Additional moisture is added by the drywall texturing and painting processes. Mold spores are already present on the materials, and, as mold grows at a rapid rate, it begins to show up more and more during the construction process.

Builders are constantly learning the best methods for controlling moisture and eliminating the possibility of mold growth during construction, including:

  • Keeping materials as dry as possible on the job site to help eliminate trapped moisture.

  • Checking walls and floors before insulation for mold to give the builder a chance to treat any signs before progressing.

  • Making sure exterior walls are reasonably dry before any weather barrier and siding is installed.

  • Running heaters or dehumidifiers during moisture-producing stages of construction to help eliminate any trapped moisture.

  • Cutting foundation vent holes as soon as possible to maintain air flow through the crawl space.

  • Cutting cardboard from the pads in the crawl space and keeping moist dirt away from the bottom of the exterior gypsum board to remove the food source for mold growth during the process.

Tradespeople are not immune to these issues and have been getting better educated along with builders.

Another challenge facing builders is how to keep moisture from entering the walls from the outside. Many different moisture/air barrier products are available with as many different flashing materials. The application method has always been the critical issue, but methods vary and specifications become cumbersome. Maintaining consistency and reasonable scheduling in combination with erratic weather patterns can be quite a challenge.

When addressing indoor air quality moisture/water intrusion, builders must consider each element of construction for materials and process used and whether these materials and processes meet good construction practices, jurisdictional codes and the consumer good.

Consideration also must be given to how the house functions as one unit. That’s quite the balancing act.

Diane Glenn, owner of The Construction Consultants in Bellevue, is a former builder and past president of an Idaho homebuilders association. She is president of the Master Builders Education Foundation and a board member of the Master Builders Association of King and Snohomish Counties. She can be reached at (425) 709-6100 or

Other Stories:

Copyright ©2009 Seattle Daily Journal and DJC.COM.
Comments? Questions? Contact us.