Log Cabin R-Values, and EZ Log Insulation
When comparing traditional log cabins with EZ Log's new construction systems, many will have questions about r-values and insulation. Because these more contemporary building systems have thinner wall profiles than traditional log cabins, it's natural to imagine their walls offer lower r-values than traditional log cabins. However, double-wall EZ Log options can provide thermal resistance ratings between R-15 and R-30. To help you understand the differences between these two construction methods, we've provided the following information.
The double wall kits available for our residential cabins and homes include 3/4 inch thick, tongue and groove boards which provide an exact match for the appearance of exterior walls when installed horizontally. Also included are metal brackets for attaching vertical studs to the inside of exterior walls. Standard 2x4 studs create a 3-1/2 inch wall space, and this allows a variety of insulation choices. Double walls also create a space for wiring and plumbing options. When combining 70mm EZ Log wall logs, 2x4 interior studs, and 3/4" tongue and groove interior wall boards, a double wall will have a total thickness of approximately seven inches. The combined wood thickness in this wall is 3-1/2 inches, and because the US Department of Energy lists the r-value for most softwoods at 1.41 per inch, this represents an R- 4.9 value. Add this to any of the following insulation choices to find the total r-value for a seven-inch double wall.
R-values for various types of insulation:
Closed-cell spray foam insulation for 2x4 studs adds an R-26 value
High-density fiberglass for 2 x 4 studs has an R-15 value
Medium-density fiberglass for 2 x 4 studs adds an R-13 value
Low-density fiberglass for 2 x 4 studs has an R-11 value
Examples of total R-values for EZ LOG Walls with different insulation types:
The EZ Log double wall with closed-cell spray foam insulation achieves R-30.9
With high-density fiberglass the EZ Log double wall achieves R-19.9
With medium-density fiberglass the EZ Log double wall achieves R-17.9
With low-density fiberglass the EZ Log double wall achieves R-15.9
While it's theoretically possible for round log walls to attain a thermal resistance rating as high as R-30.9, the logs would be nearly 22 inches thick, and weigh nearly *1000 pounds for 20 foot air dried, white pine logs. By comparison, the heaviest wall timber in an EZ Log home only weighs about fifty pounds. We believe you'll find EZ Log's solutions are much more affordable, attractive, efficient, and practical.
While the r-value (or thermal resistance) for a log home can be calculated by log thickness, another factor will come into play - the thermal mass possessed by logs of different sizes and weights.
Large log walls can represent significant quantities of thermal mass, which contribute to energy savings when a log home is configured for passive solar efficiency. This means that logs can store radiant heat from sunlight during daylight hours in cold months, and release this heat into a home at night. However, this effect can prove negative when cooling a home, unless sufficient shade from deciduous trees or extended eaves can reverse the effects of thermal mass during summer months. In either case, thermal mass and a log home's site orientation present more complex considerations than simple calculations based on wood thickness. When building any log home, it's important to consider passive solar effects and thermal mass when deciding its site orientation.
Log homes are typically available with various timber options, from six-inch thick logs to twelve-inch logs. Excluding considerations for thermal mass, if we measure a log home's efficiency by r-value alone, six-inch pine, fir, or spruce logs will have an r-value of 8.46. Eight-inch logs will rate an R: 11.28, ten-inch logs an R:14, and twelve-inch logs an R:17. However, these calculations only work for square logs. Walls built with round profile logs will vary in thickness. For this reason, some calculate thermal resistance for round logs on the width of contact zones between logs, while others base thermal resistance on the average thickness of round logs.
Besides r-values, a very important consideration when building an energy efficient home, is the cost of energy itself. While it may be affordable now, no one can predict what energy will cost in the coming years. So, the investment of time, thought, and a little extra money to achieve good energy efficiency now, may provide significant rewards in the future.
For more information about EZ Log solutions, we invite you to call us with a mobile device by clicking the phone number at the top of this page, and you're always welcome to visit our two outdoor show rooms at the addresses listed below.
NOTE: for additional information about energy efficient buildings, we highly recommend the US Department of Energy's website, which can be found at energy dot gov.
* Calculation based on a pine log measuring 21.9 inches thick by 12 inches tall, weighing approximately 27 pounds per cubic foot. The calculated weight is 985.5 pounds; however, a log with these dimensions may weigh more depending on moisture content.