Wood has a thermal transmission factor, called k. It is used in calculations to generate the R-value of an assembly, but only certified insulation products have specific R-values. The U.S. Department of Energy (DOE) rates an Eastern White Pine log at R-1.42 per inch which might mean an 8” log would be R-11.4, but that’s not the whole story.
Home Energy Raters do not take into account the thermal mass value of a solid wood assembly.
The DOE has issued a grant to Oak Ridge National Laboratory (ORNL) and the International Mass Timber Alliance (IMTA) to research the energy conserving properties of mass timber. Mass timber can be solid wood like logs and timbers, or laminated wood like glue-lam beams and cross-laminated timber panels.
Work done at the ORNL in Tennessee has proven the following:
A 7- inch thick mass timber wall is 22% more efficient than a stick built structure with R-19 insulation.
Improved thermal comfort with thermal mass (up to 46% fewer uncomfortable hours due to convective air flow). Thermal comfort is the condition of mind that expresses subjective satisfaction with the thermal environment.
Lightweight assemblies (stick built structures) respond over a short time to temperature changes both inside and outside.
Mass assemblies (Log, concrete, brick) respond slowly to changes not only in temperature, but relative humidity. Since mass absorbs and radiates heat and humidity, it tempers the indoor environment.
Peak demand was up to 50% lower with mass wood depending on the month and location.
An example of peak demand is everyone coming home from work at the same time and turning the air conditioning on.
IMTA efforts are continuing as they are building three pairs of 3-meter cubes, one stick built and one of mass timber.
A pair of cubes are set up in Tennessee with more in Texas, and Colorado to replicate a more operational environment.
Over a 2- year period, constant temperature monitoring will take place. The data from these cubes will be used to prove the computer simulations used to design the cubes. The simulations will then be used to generate new thermal codes for mass timber walls.
The IMTA is a not-for-profit,
charitable organization that promotes Mass Wood Construction and
sustainability, energy efficiency, low embodied energy, and carbon
sequestration, by the following engagements.
- Identifying barriers which challenge the use of mass wood construction in residential and commercial applications.
- Pursuing scientific research and testing in collaboration with post secondary institutions, government, and non-governmental organizations.
- Disseminating data pertinent to the development of building codes and energy standards that reflect wood’s value proposition.
