November 06, 2013
The Thermal Efficiency of Chink Joints
In today's economy energy efficiency is a subject that most people are aware of including log homeowners and those people contemplating the purchase of a log home. With this in mind we occasionally get asked about the R value of our chinking and/or backing materials since many people assume that they provide some insulation value to the exterior walls. In point of fact neither thePerma-Chink nor the backing material contributes any significant insulation value to a wall. Whatthey do is eliminate outside air infiltration into the home. This has a much greater impact on the overallenergy efficiency of a home than adding a minor amount of insulation to a wall.
The next question is what can be used in the void between the exterior and interior chink joints toincrease thermal efficiency? Surprisingly the answer for many situations is nothing. Look at Diagram1, it is a cross section of a typical stud bay without any insulation in a stick-built home.
During the winter the outside wall gets cold while the inside wall stays warm. The air next to the insidewall heats up and rises to the top of the bay. This sets up an air circulation flow where the heatfrom inside the home ends up warming the outside wall thus increasing the energy usage within thehome. During the summer the circulation flow is reversed and the hot air next to the outside wall endsup warming the inside wall. The objective of placing insulation between the studs is to eliminate this aircirculation flow. But what is there in insulation that reduces the conductivity of heat from one side to theother? Surprisingly the answer is air. Air is a very poor thermal conductor. The prime objective in mosttypes of insulation is to entrap air in small cavities so that it can't circulate. However the matrix thatholds these small air cavities does conduct heat. Since some insulation matrixes conduct heatbetter than others, it's what differentiates the R value of the various types of insulation likefiberglass, cellulose, styrene foam, etc. But it's the dead air spaces that do the work.
When we take a look at the cross section of a chink joint, Diagram 2, what do we see between theexterior and interior backing materials -- dead air space. For chink joints less than three inches widetrying to gain thermal efficiency by filling the void between the outer and inner log surfaces is futile andmay even be self-defeating. Perhaps if you have a six inch chink joint and live in Alaska it may beworthwhile to insulate this space since it is large enough and temperature difference between theexterior and interior surfaces great enough to start an air circulation flow pattern. But if you live in amoderate climate zone and have a two to three inch chink joint it's probably not worth the cost and effort.
During the winter the outside wall gets cold while the inside wall stays warm. The air next to the insidewall heats up and rises to the top of the bay. This sets up an air circulation flow where the heatfrom inside the home ends up warming the outside wall thus increasing the energy usage within thehome. During the summer the circulation flow is reversed and the hot air next to the outside wall endsup warming the inside wall. The objective of placing insulation between the studs is to eliminate this aircirculation flow. But what is there in insulation that reduces the conductivity of heat from one side to theother? Surprisingly the answer is air. Air is a very poor thermal conductor. The prime objective in mosttypes of insulation is to entrap air in small cavities so that it can't circulate. However the matrix thatholds these small air cavities does conduct heat. Since some insulation matrixes conduct heatbetter than others, it's what differentiates the R value of the various types of insulation likefiberglass, cellulose, styrene foam, etc. But it's the dead air spaces that do the work.
When we take a look at the cross section of a chink joint, Diagram 2, what do we see between theexterior and interior backing materials -- dead air space. For chink joints less than three inches widetrying to gain thermal efficiency by filling the void between the outer and inner log surfaces is futile andmay even be self-defeating. Perhaps if you have a six inch chink joint and live in Alaska it may beworthwhile to insulate this space since it is large enough and temperature difference between theexterior and interior surfaces great enough to start an air circulation flow pattern. But if you live in amoderate climate zone and have a two to three inch chink joint it's probably not worth the cost and effort.
