R-value (insulation) typical straw bale houses have very thick walls and thus are well insulated. Snow is roughly R-1 per inch. Brick has a very poor insulating ability at a mere R-0.2 per inch; however it does have a relatively good thermal mass. Note that the above examples all use the U.S. (non-SI) definition for R-value. When determining the overall thermal resistance of a building assembly such as a wall or roof, the insulating effect of the surface air film is added to the thermal resistance of the other materials. In practice the above surface values are used for floors, ceilings, and
R-value (insulation) +43° C (110° F). Nevertheless, in construction it is common to treat R-values as independent of temperature. Note that an R-value may not account for radiative or convective processes at the material's "surface", which may be an important factor for some applications. The R-value is the reciprocal of the thermal transmittance (U-factor) of a material or assembly. The U.S. construction industry preferes to use R-values, however, because they are additive and because bigger values mean better insulation, neither of which is true for U-factors. The "U-factor" or "U-value" is the overall heat transfer coefficient that describes how well a building