R Value Of Concrete Wall Below Grade

Concrete block wall with perlite in cavities r 2 9.

R value of concrete wall below grade.

The r value of an uninsulated 8 inch thick basement wall built using normal weight concrete is 1 35 based on data from the 1993 american society of heating refrigeration and air conditioning engineers handbook. By doubling the thickness of the wall to 16 inches the r value only increases by 0 50. In addition the doe recommends r 10 to r 20 insulation for under a slab which we have not taken into consideration for this article. 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.

The r value listed by pca for a normal weight 144 pcf 6 inch concrete wall is 1 23 and includes inside and outside air film resistances which contribute to overall thermal resistance. Concrete block makes a cost effective and structurally sound wall but it has little thermal resistance. And sheath it with 1 3cm sheets of thermax and 1 3cm sheetrock the total r value would be 14 75. Depending on the density of the blocks an 8 inch thick block wall without any other type of.

Other engineering sources cite the r value of earth as about r 0 25 per inch or double our calculation. The minimum insulation r value recommended by the department of energy for horizontal below grade surfaces in cold climates is r 10 to r 15. In addition to r value stability rigid foam insulations differ in their rates of moisture absorption and their ability to dry. R 0 125 per inch for soil sounds pretty reasonable if we assume about 20 moisture content and if we consider for comparison or a sanity check that the r value of uninsulated concrete is about r 0 8 inch.

By comparison most xps warranties typically cover only up to 90 percent of the published r value to account for the r value degradation that occurs in the field. If you are building your house you have the advantage of being able to insulate properly right from the.