Mold risk reduction strategies for builders

ABSTRACT

This paper describes a builder's guide to reducing mold risk. The guide was developed as a part of a 30-month program sponsored by the California Energy Commission's Public Interest Energy Research program and the Gas Research Institute to conduct a detailed investigation of residential building construction practices and innovative building assemblies that are resistant to mold formation and growth. The guide emphasizes a three-part strategy to reduce mold risk. The strategy is based on the history of mold problems in California buildings. The three-part strategy is applied to the development, design, installation, and ownership phases of residential construction. The discussion includes recommendations, supporting data, and references to other guideline information pertinent to mold-resistant construction.

INTRODUCTION

Modern residential and commercial construction practices have increased the overall building energy efficiency but have also resulted in conditions that may be conducive to rapid microbial and mold growth. Mold can grow almost anywhere and requires only air, water, a food source, and moderate temperatures to thrive. Under the correct conditions, new mold growth can occur in as little as 48 hours. Modern building envelopes are more airtight than past designs. When water intrudes into envelope cavities in a sustained manner or does not dry quickly, mold may propagate due to trapped moisture. Damp conditions in envelope cavities and the resulting mold growth compromise building envelope energy efficiency, damage building materials, and affect the health and productivity of occupants. Once mold growth occurs, it is costly to remove and can result in expensive litigation. By understanding the building construction parameters affecting mold growth, it may be possible to mitigate or prevent mold growth, thereby limiting heating and cooling energy losses, reducing building remediation costs, and avoiding human exposures.

The Energy Efficient Mold-Resistant Building Assemblies for California Homes program was a 30-month project funded by the California Energy Commission (CEC) and the Gas Research Institute (GRI) to conduct a detailed investigation of residential building construction practices and innovative building assemblies that are resistant to mold formation and growth. The project team included six research organizations, two California builders, 18 participating manufacturers, and a Project Advisory Committee (PAC) comprising product manufacturers, building scientists, participating utilities, participating builders, and state agencies. Based on input from CEC staff, the project team, PAC members, and building industry experts, the highest value areas for this project to address with laboratory testing were secondary water-resistive barrier (WRB) design options (especially around windows), concrete slab installation practices and materials (especially vapor retarder location and fill materials), and drying times for built-up wall assemblies. The majority of the project tasks consisted of laboratory and field studies of building assemblies that are important for keeping building materials dry and, therefore, free of mold growth (Leslie 2006). In addition to that work, the project team developed a Builder's Guide based on the current understanding of experts about ways to prevent mold problems in new residential construction (Harriman and Leslie 2006).

This paper summarizes guidance about ways to prevent mold problems in new residential construction. It represents judgments of the authors culled from a wide variety of experts about what currently constitutes useful advice to developers, designers, builders, and owners about how to reduce the risk of mold growth in new homes.

OBJECTIVE

The objective of the Builder's Guide was to develop guidelines on mold-resistant building components, assemblies, and construction practices for new residential buildings.

MOLD RISK REDUCTION STRATEGY OVERVIEW

The Builder's Guide describes a three-part strategy to reduce mold risk. The strategy is based on an understanding of mold problems in California houses and how such problems can be avoided:

* First, keep most of the water away from the house through a few critical landscaping and drainage decisions made by the developer, designer, builder, and owner.

* Second, keep the rest of the water out by ensuring the roof, walls, and foundation shed and exclude water consistently while draining it away from the house.

* Third, limit mold growth while moisture dries out by stopping water leaks and spills from spreading indoors and by choosing materials and assemblies that are less prone to moisture retention or mold growth when challenged by occasional wetting.

The Builder's Guide consists of the opinions and judgments of a wide variety of experts. These go well beyond the specific topics researched in the laboratory and demonstration homes. The Builder's Guide is considered a good beginning rather than the last word on this highly complex topic. It's also useful to keep in mind that this guide has no force of regulatory authority. It represents the judgments of the authors about what currently constitutes useful advice to developers, designers, builders, and owners about how to reduce the risk of mold growth in new California homes. The guide is arranged according to who's likely to be making each decision and when.