The thermal performance of a building space depends on the flows of heat conduction, solar radiation and air across the internal surfaces of walls, roofs and floors that enclose that space.
Heat conduction at the internal surface of a building element depends on the level of insulation it offers and its thermal mass.
Conduction in a lightweight building element such as a timber frame wall is strongly related to its R-value (total thermal resistance).
However, conduction in a heavy building element such as a solid wood wall depends on its R-value and thermal mass. Both need to be considered when determining the effect of these types of constructions on building thermal performance.