If you have a small child, chances are you have watched Sesame Street, with Murray who presents the Letter of the Day…or is it just us here at Harrington Construction who get the joy of watching episodes of Sesame Street?
Well let us play the R game for construction, can you name some R things on a job site? Don’t be shy.
Rip Saw, Rafter, Rail, Ramp, Rake, Rendering, Rise/Run….. R Value.
There it is…. a term that gets thrown around just as much as Net Zero, Sustainability and many other construction terms that are of current focus in the building world. But what does it mean?
The R-Value is used to describe Thermal Resistance, or a solid materials resistance toward a conductive heat transfer. More easily said: how well a material prevents heat loss. Usually this term is sided with insulation, however windows and doors have R ratings too (actually, windows and doors get a U Rating along with the R-Value and the system of testing is based also on the thermal transfer of the material.). We know that thermal conductivity is the property of a material to conduct heat, but when thinking in terms of construction materials we are also looking at how well the insulation, insulates against cold or heat. Yes, cold too. As discussed on Energy Vanguards blog: http://www.energyvanguard.com/blog-building-science-HERS-BPI/bid/59419/Big-News-The-R-Value-of-Insulation-Is-Not-a-Constant, when evaluating types of foam and insulation; testing is done with cold on one side and heat on the other. This gives an accurate picture, and by that I mean a test using numbers, that shows how well the material is performing at minimizing heat loss. The better the R-Value, the better your home is performing at energy conservation. This in turn helps with energy bills and the level of thermal comfort you feel in your home.
Materials tested get R-Values placed on them. You may hear someone say; that insulation has R-13, that door R-20. Feeling curious about other R Valued construction materials? Check out this table put together by ColoradoENERGY.org: http://www.coloradoenergy.org/procorner/stuff/r-values.htm
The US Department of Energy published a table, showing the recommended total R-Values for homes. The R-Values are broken up in to eight zones of the nation based upon energy costs, insulation costs, heating and cooling demands and projected energy costs/savings for those areas. Depending on where you live, you will insulate your home differently. A person living in zone 1 (the tip of Florida) uses/installs insulation differently than a person living in say zone 7 (Minnesota). See the chart here: http://www.applegateinsulation.com/Product-Info/Technical-Pages/249732.aspx
When building a highly efficient house, such as a Passive House (which is something we like to build) our goal for the building is a very high R-Value. How do we achieve a high R-Value? We super insulate the wall cavities between the exterior and interior wall and attic spaces, we install triple pane windows (these have High R and Low U ratings), we air seal around gaps, and install moisture barriers. These building practices help create a home that is comfortable in temperature despite the temperature outside.