CRAWLSPACE ISSUES IN THE NORTHWEST

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1 CRAWLSPACE ISSUES IN THE NORTHWEST Ken Baker, K energy, Association of Idaho Cities Chuck Murray, Washington State University Extension Energy Program Issue Statement With respect to crawl space design and construction, code requirements for energy efficiency, moisture control, radon control and combustion air can conflict. The resulting design strategies tend to favor a solution for one criteria, without full consideration of the others. Consensus on a comprehensive design strategy appropriate for Pacific Northwest homes has not been achieved. Code requirements for crawlspace insulation and ventilation continue to be one of the major code issues in Idaho and Montana. In response to International Residential Code (IRC) language that is vague on methodology, most jurisdictions we have communicated with on this issue have developed and prescribed a conditioned crawlspace approach for builders. This creates inconsistencies in the way crawlspace ventilation is addressed from jurisdiction to jurisdiction. And it has created some degree of frustration for builders and building jurisdictions alike. In Washington State, the energy and ventilation code almost exclusively require unconditioned crawl space construction, proactively avoiding the debate on ways to comply with code when conditioned crawl spaces are utilized. This prescription works well under the current Washington State codes but the state is now in the process of review and adoption of the energy provisions of the 2006 IRC. Adoption of the 2006 IRC will make available the same crawlspace wall insulation and ventilation options that are in the 2003 IRC. Thus, the technical and building science issues that this paper will discuss could soon apply to Washington State, Idaho, Montana, and possibly Oregon. The IRC is developed for use nationally. Construction options included in the IRC do not always provide the best solution for specific climatic conditions. The IRC has been developed with several crawl space options, primarily based on the recommendations of research and advocacy groups located in the Eastern and Southeastern United States. The Pacific Northwest needs to determine which options are most appropriate for meeting occupant health, building durability and energy efficiency goals appropriate for the local conditions. Typical Crawl Space Designs The International Residential Code (IRC) specifies requirements for crawl space ventilation, vapor retarders and insulation. There are two crawl space designs allowed under the IRC, the unconditioned crawl space and the conditioned crawl space. While there are a number of variations to these designs, the basic distinctions are described in Table 1.

2 Table 1:Typical Crawl Space Designs Unconditioned Crawl Conditioned Crawl Insulation R installed in the floor joist R-19 installed on the crawl space wall Ducts sealed and insulated Yes Yes - Maybe? Crawl space ventilation Passive vents to the outdoors, 1:150 Several mechanical ventilation options. Crawl vented to the interior no sometimes Ground moisture control Poly ground cover Better poly ground cover Radon vent system required High radon counties in WA Always in WA Natural vent combustion OK Yes No The following two sketches illustrate the requirements for a unconditioned crawl space and a conditioned crawl space as set forth in the 2003 IRC. Note, that additional ventilation options are available for conditioned crawl spaces. In lieu of the continuously operated mechanical ventilation option illustrated, there is language in Chapter 4 of the IRC that allows for the crawlspace to be used as a supply plenum for the home, or to allow crawlspace ventilation directly to the interior of the house where climatic conditions warrant, or to supply the crawlspace with conditioned air from the furnace. The practical application of these options makes apparent a number of building science and technical issues. Unconditioned Crawl Conditioned Crawl Building Science/Technical Issues for Conditioned Crawl Spaces The building science and technical issues that rise from the application of conditioned crawl space designs include: 1) moisture control; 2) radon control; 3) combustion air for combustion appliances placed in a crawlspace; and, 4) energy efficiency. Of these four issues, moisture control is of primary concern to the building industry. This is probably true because moisture in the crawlspace has been identified as a key factor for mold growth and subsequent health and safety liability issues. Washington State has identified radon

3 as a key issue because of the impact on health of building occupants. Radon control is a primary reason for the current Washington code requirements to use under floor insulation in a first effort to isolate the crawlspace from the living space. Provision of air to combustion appliances in a crawlspace is an issue mostly confined to Montana where furnaces are typically located in the crawl space. Energy efficiency is probably the issue with the least concern to the building community because it doesn t have an impact on occupant health. 1. Moisture Control As stated above, moisture in a crawlspace is a primary issue of concern for builders because it directly correlates to mold, rot and subsequent liability issues. In the Pacific Northwest the dominant source of crawl space moisture is bulk water, not water vapor from indoor or outdoor air condensing in the crawl space. Moisture enters the crawl space because of improper irrigation practices, ground slope, rain runoff, high groundwater tables, rain and snow during the construction process, and leaks in plumbing. These sources can be controlled through proper design but not eliminated. The sources of moisture can not be completely eliminated and some level of ventilation will be needed. We also know that moisture; temperature; food (wood); and mold spores are all necessary components for mold growth. If relative humidity in the crawl space is kept low, mold will not grow. We do not know which ventilation strategy will best fit a comprehensive design approach for energy efficiency, moisture control, radon control and combustion air. The combination of temperature, moisture and food that will feed mold growth is not readily understood. We are aware of no practical guide for new construction that would provide cautions and solutions to new construction practices specific to the Pacific Northwest. Develop a design criterion that is appropriate for crawl spaces in the Pacific Northwest. An easy to read and apply cut sheet on preventing moisture and mold in new construction. It could be a one-page laminated sheet that graphically depicts proper irrigation placement, foundation drainage planes, ground slope, ground cover applications, the need and process for removal of moisture control during construction, and effective ventilation strategies. 2. Radon Control Radon measurements were recorded throughout the Northwest region during the 1980 s and the Environmental Protection Agency has provided very detailed and applicable guidelines and education for radon control and mitigation. Still, the public has a low awareness of the need to build radon control into homes so building jurisdictions and the building industry do not always build in the proper safeguards for radon.

4 The information on radon control and mitigation is readily available from a number of sources as are the means and protocols for testing. A new education effort directed toward the industry may provide some solutions. We believe there is good opportunity here to document utilization of ABS ventilation stacks for the dual purpose of radon mitigation and crawlspace ventilation. This may have an appeal to builders as it could offer a simple and economical method of crawlspace ventilation with radon mitigation as a bonus. 3. Combustion Air for Combustion Appliances Per the mechanical codes, combustion appliances must have a positive source of outside air delivered into the combustion appliance zone. This becomes an issue in new construction where the conditioned crawl space method is opted. Attempted use of this code compliance method may have health and safety impacts on the building occupants violating provisions of the mechanical codes. There are a number of possible code violation or health and safety issues with these choices. The most difficult aspect of this issue is in understanding the impact of one strategy such as mechanical ventilation on the successful implementation of a life-safety requirement and its practical application. For example, will the use of mechanical ventilation depressurize the crawlspace and lead to combustion back drafting? Don t allow combustion appliances in crawlspaces. Or only allow them in unconditioned crawlspaces. 4. Energy Efficiency In a heating dominated climate the effects of ground coupling, or using the crawlspace as a thermal storage device, i.e., conditioned crawl space, will not save as much energy as well unconditioned crawl space. What is the life cycle cost of each crawl space system. Perform a life-cycle-cost comparison between conditioned and unconditioned crawl space. External and LC costs include fan replacement, radon mitigation, moisture control, etc.

5 Next Steps Washington State University has proposed conducting a test study to determine IAQ and economic impacts on four crawlspace ventilation and insulation combinations. The regional team should review the research design and protocol and provide input on regional needs and the study should be conducted. We should identify the most frequently used systems/strategies in the region, identify building candidates that use these systems, prepare and perform a research design, document the selected systems performance, and publish and distribute case studies. Demonstrate and document the performance and economics of a combination radon/ventilation strategy utilizing ABS ventilation stacks. Prepare and implement an educational series for the industry. Conclusion Over the past 20 years the Northwest has led development of energy efficiency and IAQ strategies for residential buildings. This is an opportunity to continue in that leadership role through a proactive approach of information gathering and education.