With its thick walls of solid wood, a log home is one of the best-insulated buildings in which you could choose to live. But the nature of a log home’s construction also presents a unique challenge: the opportunity for air to pass through the gaps between the logs.
Fortunately, air infiltration is a challenge that’s easily met, thanks to caulking, the general term for the seals that are introduced between logs. With the right caulking method, or “caulk joint” as it is generally termed, a log home can achieve thermal efficiencies to rival those of any building method.
Two key elements are essential to effective caulking. First, the caulk used must form a “wet” seal, one that adheres to the wood surfaces rather than just filling the gaps between them. And second, it needs to be elastic (a quality sometimes referred to as “memory”), either stretching or compressing as the shapes of the logs themselves subtly move through natural expansion or contraction.
With those elements met, four principles govern the most efficient caulk joint design: caulk depth, points of adhesion, a caulk “well,” and the conditions under which the caulk is applied. Each principle is fairly simple to grasp, and understanding them all will help anyone buying, building, or restoring a log home make the right energy-efficient decisions.
In general, the depth of caulk in a joint is more important than the width of the caulk’s application. Why? Put as simply as possible, the most critical factor is that the caulk have enough mass at any given point to absorb any movement in the logs. As a rule, whatever its width, the depth of a caulk joint does not need to be any more than 1/2 inch or any less than 1/4 inch. (See figure 1, which illustrates how a thinner cross-section results in less stress on the joint.). Also, a deeper joint is preferable to one that is too thin.
Adhesion to three or more points, by contrast, would cause the caulk to be pulled in multiple directions, thus increasing the likelihood that the seal will break away from one or more of the points of adhesion. (See figure 3, which illustrates how such ruptures can occur under three-point adhesion.) Placing a backing rod inside the well.
With this principle in mind, any backing materials included in a caulk joint should provide a surface to which the caulk does not adhere. Doing so allows the caulk to remain at its most elastic.
Superior caulks have enough elasticity to absorb 25 to 50 percent of the total movement in the joint they fill. To allow for that movement, caulk joints require “wells,” spaces that allow the joint to absorb that movement.
Obviously, the greater the movement expected in a particular joint, the larger its caulk well should be. Log homeowners can also take comfort from the fact that high-quality caulks currently being sold are capable of absorbing far greater movement than that for which they are rated.
With this principle in mind, it is wise to select a caulk with properties that best suit the range of local climate conditions, and to apply it at the most stable, least extreme point in the climate cycle. But smart log home builders will also apply caulk at optimum times; for example, sealing caulk joints on the cooler side of a home will work most effectively on a warmer day, while those on the side of a home that gets more direct and prolonged exposure to sunlight would best be sealed on a cooler day.
Keep these guidelines in mind, and you’ll thus enjoy the maximum benefits of log homes’ superior insulation and energy-saving capabilities.