Note: if you are starting with an un-Insulated space it is very important to read the section below titled "Estimating R Values for Un-Insulated Spaces"
Note: These are all US R values. To convert to SI R values multiply by 0.176. For example US R10 = SI R 1.76. Most Common R Value Upgrades:
(1) adding cellulose over loose fill Fiberglass insulation will also reduce
air infiltration and will reduce currents in the fiberglass that can reduce the
effectiveness of loose fill Fiberglass insulation : For other situations, use the R value table just below to look up the R value for your situation. Note that all R values are in US units. |
ColoradoEnergy.org has a good table of R Values:
You will find R values for most materials, insulations, and windows in the table at this link.
If you are starting with a wall, ceiling or floor that is not insulated, it is important to make a good estimate of the current R value. Its very important to get the R value for uninsulated surfaces as close as you can, as small changes in these values will make for large changes in your heat loss.
Ceiling:
This applies to conventional wood framed ceilings of either the cathedral or attic type.
Attic air film R 0.61 Sheathing R 0.5 SheetRock R 0.45 Inside air film R 0.61 Total R 2.2 The components for a cathedral ceiling with a 1 inch vent space between the top of the insulation and the bottom of the roof sheathing are a little different, but the total is nearly the same. The attic calculation assumes a well ventilated attic.
Walls:
This applies to conventional wood stud walls with interior sheetrock and exterior wood siding:
Outside air film R 0.25 Wood siding R 0.59 Sheathing R 0.5 Inside air cavity R 0.94 SheetRock R 0.45 Inside air film R 0.68 Total R value R 3.4
Floors:
This applies to conventional wood joist floors with 3/4 plywood subfloor covered with carpet and pad over an unheated and ventilated crawl space:
Lower air film R 1.23 Subfloor R 0.94 Carpet+Pad R 1.23 Inside air film R 0.92 Total R value R 4.32 I think that it could be argued that some additional R value could be added for crawl space to account for the thermal resistance of the crawl space walls to the outside -- this would be particularly true for people who close up the crawl space vents during the winter.
Concrete and Block Walls:
Above grade concrete wall including inside and outside air films = R 1.2 for 6 inch, R1.4 for 8 inch
Concrete block wall with air in cavities = R 2.0
Concrete block wall with Perlite in cavities = R 2.9
The reason that it is important to make a good estimate for the current R value for uninsulated spaces is that small changes in R values result in large changes in heat loss when the total R value is low. For example, if you miss the R value by 1 when the total R value is (say) 2.0, this will result in a 50% error in the heat loss. For an insulated space it does not mater so much -- if you miss the R value of an R30 insulated ceiling by R1, its only a 3% error in heat loss.
Gary
Rev. 3/12/06, 3/24/06