The Energy Efficiency of Heartwood Log Homes

Wood has a high thermal mass, which means it holds heat well. Wood is also an excellent insulator. A well-built log home is very comfortable and energy efficient.

We take steps to further eliminate draughts between logs to keep your home snug. First, we use the scribed-fit technique to make the logs fit closely together without need of caulking or chinking. The diagram below shows the construction of the wall and how it rests on the foundation.

At one time, we and most other log home builders used fibreglass insulation as a sealant between the logs. It worked, but there had to be just the right amount placed between the logs so that it would compress to form a gasket, but not so much that it would hold up the log above. A small amount of twisting during the drying process could expose a line of fibreglass to the air inside the house.

A few years ago we started using a strip of Emseal, an expanding foam tape, on the outside edges of the joinery as a supplement to the fibreglass. This foam strip expands from about 1/4" (6mm) to as much as 1 1/2" (38mm). (See diagram above.) If there is any movement of the logs due to settling, the Emseal gasket will expand to fill the space. We have been very pleased with the results, so much so that we started giving a warranty against air and water infiltration on our homes. After attending an International Log Builders Association conference in 1999, and discussing the issue with our colleagues from across the continent, we decided to go the rest of the way. We have now eliminated fibreglass from our log joinery altogether. We now use Emseal on the inside as well as the outside of all notches and lateral grooves. We have found a source of natural sheep's wool, treated with borates, that we are using to block airflow at the door and window openings and around the notches.

In 2002, we built a home for a couple in New Hampshire, using the double Emseal and sheep’s wool sealing system. They applied for certification under the U.S. Department of Energy’s “Energy Star” rating program. Under this program, a house is tested for air infiltration and compared to the exact same house built to current energy efficiency standards. Of course, all aspects of the home’s design were a factor in the results. An efficient and well designed heating/cooling system, extra insulation in the roof, and greater than normal care in sealing around doors and windows, for example, all helped to boost the energy efficiency of the home.

In the end, we were thrilled to hear that this home received the top rating, Five Star Plus, which means that it was found to be 50% more energy efficient than the standard home. We are proud that our log walls were an important factor in receiving this high rating.