When building using Rough Sawn logs, the size of the logs may vary. This is not a problem, because the dovetail stays constant, only the space between the courses changes. If your logs are exact size the space between stays 1½". Everywhere you fasten the logs together you use blocking to support the logs between courses. One advantage to this system is that wiring can simply be run between courses.
After all logs are stacked, and wiring installed you're ready to install the backer rod. Out of ridged foil backed insulation cut strips to fit between the logs. Fasten the strips to the blocking, and chink over the insulation with a latex based chinking to complete a perfect air tight seal.
