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Prevention of Air and Water Infiltration in Log Homes

12-3-2014 10-24-53 AM

Log and Timber Homes Council White Paper addressing infiltration, sealants, compatibility with wood treatments, and durability. Download the White Paper Prevention of Air and Water Infiltration: A Systems Approach.

An average log home has nearly 1-1/2 feet of joint for every foot of log in the walls. If the wall is 12 log courses high, there may be a half-mile of joint to seal. Keeping those joints sealed from the elements is the major priority and challenge for every log home producer and builder.

A well-sealed log wall minimizes air infiltration that can affect thermal performance as measured by higher energy costs. Protecting joints from water is the key to the endurance of the structure, and this protection includes windblown rain. The happiness and well-being of the homeowner and the continued growth and success of the log home producer and builder will ultimately revolve around the design and quality application of the sealing system.

A properly sealed log home also makes surface maintenance much easier. When the seal is inadequate, moisture may enter the log wall via normal flow down the face of the wall, capillary action, or due to wind pressure. The moisture can collect on a surface of a log or migrate to other areas of the wall. In some cases, this moisture can be drawn into the wood to an outer surrounding surface warmed by the sun. When certain coatings or sealers are applied to the exterior surface, an undesirable buildup of moisture can occur under the finish. The consequence of this moisture buildup is a costly maintenance process where the finish and any damaged wood is removed and the wall refinished.

The key to success can be found in the concept “system”. That’s because no one component alone can promise to deliver a successful seal between individual logs. Instead, a combination of these elements working together is necessary to achieve a consistent, durable seal. The system components include joinery design (e.g., patterns for applications of a sealant like caulk or foam gaskets), log shape, proper installation, and other elements that will be discussed in this paper.

The approaches to sealing a log home are as varied as the log home producers in existence today. The fact that there is not one universal log sealing design (i.e., triple, double, single tongue and groove; Swedish cope; spline and miter; chink; etc.) confirms that there is no single method of sealing. The single common denominator that delineates and distinguishes a quality manufacturer from a competitor is the seal at the log joint within the context of a “sealing system”. The proprietary nature of the sealing system is recognized in the graphics in this paper. For more specific details, please refer to the information provided by the log home supplier.
The basic sealing system checklist should include the following considerations:

  • The properties of the logs (section properties, stress grade, mechanical properties of the species used)
  • The moisture content of the logs
  • Type and placement of sealant materials and fasteners
  • Joint design
  • Accuracy & consistency in the milling process
  • Construction techniques
  • Building design and location
  • Weather conditions during the building process

Successful log building systems have considered all of the variables above. The log producer, the building designer, the sealant manufacturer, the fastener manufacturer, the construction crew, and the homeowner all play important interrelated roles in the sealing equation.

The degree of sealing success with minimal field complaints will greatly depend on how critically each of the individual sealing elements are evaluated, managed, and coordinated by all concerned.

The strength of the log sealing system will always rely on the integrity of the individual parts and their ability to work together.

As proof of the success of a sealing system, ask the log producer/builder about their history with blower door testing and/or infrared photography. These are critical elements verifying HERS ratings by BPI or RESNET certified energy auditors and are incorporated into the ENERGY STAR® certifications. Such testing/certification continues to demonstrate that log homes can perform at very high levels = low energy consumption.

Download the White Paper Prevention of Air and Water Infiltration: A Systems Approach.