Houses in a cold climate should have a minimum of r 49 in the attic which is equivalent to approximately 16 of fiberglass insulation.
Best r factor for attic insulation.
In particularly cold climates you might go up to r 60.
Existing 3 4 inches of insulation.
Along with knowing the r value of a particular insulation it is also important to calculate the r value of a total system.
R values for each type of insulation.
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In comparison an inch of blown fiberglass insulation has an r value of 3 1 3 4 and an inch of blown cellulose in an attic has an r value of 3 2 3 7.
Achieving greater r values in attics the higher the r value the better the thermal performance of the insulation.
An insulation r value chart or table can assist you with the calculation to ensure your attic or wall r values are adequate for your particular zone.
Warmer climates only require an r 38 or higher or about 12 or more.
Find your zone on the map and then use the chart to determine the level of insulation you need to properly insulate your attic walls floors and crawlspaces.
Let s say the insulation you ve selected has an r value of three per inch.
Recommended insulation levels for retrofitting existing wood framed buildings.