In Canada, there are two methods that can be followed to ensure a log home meets mandated (national or provincial building codes) energy efficiency requirements: a prescriptive method and a performance based method. The prescriptive method clearly sets out minimum standards for each component and they must be met. No measurements or modeling is required which in turn makes it easy to follow. The performance method has thermal performance minimums and how these are to be met are up to each builder – a full selection of building products and practices can be used as long as they can meet the performance requirement. Proving compliance requires computer modeling and/or other calculations and testing to be performed.
The EnerGuide Rating System (ERS) is the performance modeling tool used in Canada for determining energy efficiency and Hot2000 is the software used to calculate estimated energy consumption for a home. This consumption is compared to a benchmark consumption value and an ERS rating, ranging between 0 and 100 is given to a home. The 2012 National Building Code of Canada (NBCC), which many of the provincial building codes are based upon, proposes that a new home must achieve a minimum ERS 80. Achieving such a rating can be accomplished by ensuring a home has adequate insulation in the walls and attic, energy sufficient windows, exterior doors and that the house is well sealed to retain heat. As well, a house should incorporate energy efficient mechanical services and appliances such a high efficiency space heating, hot water heater and heat recovery ventilator.
ERS is capable to quantify energy saving effect of high efficiency mechanical systems and renewable energy systems (photovoltaic, ground source heat pump, etc.). However, provinces may set minimum requirements for performance of building envelope. For example, British Columbia requires that a house achieves ERS 80 by the features incorporated in the building envelop alone. Similarly, the U.S. Department of Energy requirements as outlined in their 2012 International Energy Conservation Code (IECC) also does not allow mechanical and renewable trade-offs.
From a log home perspective, the impact of not permitting trade-offs is significant. Log walls, as part of the building envelope, have difficulty meeting the minimum prescriptive requirements for R-value. In the energy calculation their lower R-value creates an energy deficit that needs to be compensated by other parts of the building envelope in order to achieving an ERS 80. Using thicker logs and/or logs of a less dense wood species (Cedar versus Douglas-fir for instance) will improve the energy performance ratings. However, extra insulation in the attic, foundation, use of triple glazed windows and heat recover ventilation may be necessary to achieve compliance with the new energy requirements.
The energy consumption requirement of housing is continually being ratcheted down in both Canada and the U.S. In the US, it is expected that the 2015 IECC energy consumption requirement will be 50% less than the same requirement set in the 2006 IECC. Log home manufacturers must continue to improve the performance of their homes by making them more air tight using gaskets and paying attention to all connections between logs and other assemblies.
Working with the energy auditors from the start of the building process is the best way to determine the optimal choices for the building envelope and the mechanical systems. Conduction a blower door test early after lock up will detect areas of potential air infiltration and provide effective means of addressing them before the home is completed.
For more information on this topic, contact Dalibor Houdek (780) 413 9031, firstname.lastname@example.org