What are Ideal R and U Values for Walls in Green Architecture

The thermal performance of a building material is indicated by R and U values and are used in the building of green architecture.

R and U Value Defined

R represents the resistance of heat flow. The greater the insulating value and heat resistance, the higher the R value. The direct opposite are the U values which represent the same heat resistance and insulation qualities but in this case, the lower the U value, the better the insulating quality. A high insulating value (high R value) means less money and resources need to be spent on heating and cooling, making a building made of high R value materials more environmentally sustainable.

Traditional building materials such as stone, steel and wood have relatively high heat transfer and such have a low R value. As we know, air is a great insulator, so newer building materials such as rock wool, which contain a lot of air pockets have a high R value. Rock wool/stone wool has 20 times the insulation value of brick (the same thickness).

Thermal Conductivity

The goal of newer building materials is to trap air and bring the thermal conductivity to as close as still air as possible. Vacuum insulated panels have the highest R-value. 

Thermal R Values of Common Building Materials and Green Architecture

Typical R values for common building materials are as follows:

  • Brick—R-0.2
  • Straw bale—R-1.45
  • Fiberglass loose fill—R-2.5
  • Poured concrete—R-0.08
  • Extruded expanded polystyrene (XPS) high-densityR-5
  • Vacuum insulated panel—R-30