Originally Published: October 4, 2013 6 a.m.
Question: We have completed leakage testing and sealed our home the best we can. What else can we do to improve our comfort and reduce energy use?
Answer: The main areas for home energy loss are air infiltration or air leakage and a lack of envelope insulation. Together, these parameters determine if you have a tight, average or leaky home, and how much energy and money you are losing.
We addressed the effects and importance of air leakage through gaps in the envelope in a previous article (view this story online at dCourier.com for a link). Now we look at the other main heat and cooling loss preventer: insulation. Effective insulation conserves energy by slowing heat transmission, increasing comfort by reducing temperature variations, and lowering noise. It also reduces the size and cost of heating and cooling equipment. However, it must be reiterated that air leakage severally impacts the effectiveness of insulation, so sealing should be addressed before insulation.
Fortunately heat loss and heat absorption are based on the same basic physical effects, that of conduction of heat through materials, convection of heat through air and gases and radiation from the suns rays in the form of infrared and ultra violet heat. Heat always travels toward cold, so in winter heat moves from inside the home to the outside and in summer from the outside inside. The insulation barrier must work in both directions, preventing heat leaving in winter and blocking heat during summer.
A building envelope uses a number of different materials such as wood framing, siding materials, drywall, roofing tiles and insulation to name a few. There are also newer integrated building components such as Integrated concrete forms (modular insulated concrete walls) and structural integrated panels (insulated OSB walls). All these materials are tested for their resistance to heat and radiation flow.
There are two parameters that the energy industry uses to evaluate these materials: R-value, which is the thermal resistance to heat transfer through a material, and U-factor the thermal conductance of heat transfer through a material, U being the reciprocal of R (1/R). The higher R the better and the lower U the better; R is usually specified per inch of material thickness.
For a comprehensive list, visit http://www.greenhomeenergyadvisors.com/articles-and-technical-information/r-value-table/
As an example, the Prescott building code for attic insulation stipulates a minimum R38; therefore, dividing R38 by the R-value of the material selected will determine how many inches will be required. For instance R38 using standard fiberglass batting would be 38/2.8 = 13.5, for open cell foam 10 and for closed cell foam 5.5. Closed cell would seem a no-brainer until you consider that closed cell foam is twice the cost of open cell. So, cost is also a factor in material selection.
For an existing home the current insulation material must be determined and more importantly, establish how well it was installed. If leakage has been a problem then moisture may have degraded the insulation, or the insulation may have shifted leaving major gaps that are not insulated at all and where convection currents bridge the insulation. Many of these issues are behind drywall and not visible. This is where a thermal diagnostic test comes in using an infrared camera that detects and highlights changes in hot and cold areas behind the drywall and other covered locations. Expertise is essential when interpreting these results.
Retrofitting insulation can be a dirty and unpleasant job. These challenges can affect the installation quality, which is essential for performance. For this reason it is important to use a reputable energy and insulation specialist who is familiar with insulation codes and conformance, characteristics and correct installation techniques.
Paul Scrivens of Green Home Energy Advisors can be reached via www.greenhomeenergyadvisors.com. View his blog at www.greenhomeenergyaz.com.