Energy Efficiency of Log Homes

Sure, everybody loves their rugged beauty, but what is the energy efficiency of log homes? How can a stack of logs keep out the cold? Won’t I be wasting my hard-earned cash trying to keep this house warm? A good resource is the Thermal Bypass Checklist Guide put out by Energy Star.

R-Value

First a little bit about R-values. The R-value of a material refers to its resistance to heat flow and was adopted in the 1970s during the first energy crisis as a simple way to compare energy efficiency.

So we commonly see R-value ratings for things like fiberglass batt insulation, where:

• 3 ½” (2 x 4 wall) is rated at R-13
• 5 ½” (2 x 6 wall) is rated at R-19

But in the laboratory where they do the rating, the fiberglass batt is actually enclosed in plastic, completely stopping any air flow (unlike the real world) and the difference in temperature that is measured is only 10 degrees (again, vastly different from comparing outside and inside temperatures of a house in New England in the winter, for example, where the temperature differential might be 70 degrees or more).

This is a complex issue that cannot be reduced to one simple metric such as R-value.

Thermal Mass

Log homes take advantage of what is referred to as “thermal mass” effect, using the heat capacity of the wall. That is, the mass of the solid wood absorbs and holds the heat and slowly releases it over time.

Studies done for the Department Of Energy (DOE) and the Department of Housing and Urban Development (HUD) by the National Bureau of Standards compared energy costs between houses insulated with fiberglass to a value of R-13 and log homes built with 7” thick square logs. They showed that the two homes used the same amount of energy, even though the stick-framed house had a nominal R-value 17% higher. 

The energy efficiency of log homes can be as much as 15% better than conventional stick-framed houses.

Prevent Air Infiltration

One very important factor to get right when building log cabins is the prevention of air infiltration. Some of the ways to do this are:

• Sealing between the logs using a ribbon of caulk or foam
• Carefully caulking the corners where the logs come together
• Sealing the windows and doors and other penetrations in the exterior skin with expanding foam or caulk
• Insulating the edge of the concrete (if built on a slab) with, for example, Styrofoam XPS or extruded polystyrene
• Using good insulation in the cabin roof (especially if they are cathedral ceilings)
• Using sill seal between bottom log and foundation and between bottom plates and floor decks
• Providing a clear ventilation path for the roof without exposing a path for interior air (and heat) to escape
• Use the proper log fasteners to secure logs

These are all good ways to boost the energy efficiency of log homes and reduce your monthly energy bill, since the DOE estimates that 44% of your total utility bill pays for heating and cooling of your home. Your log home will feel more comfortable and long-term maintenance will be reduced.