What does the R-Value of home insulation mean?
Wednesday, October 17, 2018
R-value is a measure of “thermal resistance.” Another way to define it would be that R-value is a measure of the ability of the insulation to resist the movement of heat across it from one side to the other. Since heating and cooling account for 50% to 70% of a home energy bill, it’s always a good idea to learn the R-value of the insulation in the ceiling, walls, and (sometimes) floor of a home you are considering buying. A higher R-value translates to better insulation quality and lower energy bills.
Newly constructed homes are required to have a placard just inside the attic access hatch certifying the R-value of the insulation in place. On older homes, we make an estimate of the R-value, based on the the thickness, type, and condition of the insulation, for two reasons: 1) it is usually not marked, and 2) insulation deteriorates and collapses down over time, which reduces the R-value from what it was when originally installed.
One of the things that we also do during each home inspection is an infrared scan of a home’s insulation envelope, looking for areas of missing insulation or gaps in the insulation coverage. Often a former back porch, for example, that has been enclosed into a conditioned interior room will not have insulation in the walls or ceiling--because it was not necessary when the room was built as a screen porch, and the remodeler did not retrofit insulation into the walls and ceiling during the conversion to an interior space. The lack of insulation is clearly visible to our infrared camera.
Here’s a chart for estimating R-value of various insulation materials, based on their thickness.
It’s important to note that the R-value of insulation is reduced if it is crushed or damaged, which can happen when workmen in an attic trample it down while doing a repair.
Here’s links to a collection of some of our other blog posts about INSULATION:
Insulation Chart - InterNACHI
How To Look At A House
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