Building Construction Handbook, Eighth Edition

Typical values in: m^2 K/W

Internal surface resistances (Rsi):

Walls † 0 123

Floors or ceilings for upward heat flow † 0 104

Floors or ceilings for downward heat flow † 0 148

Roofs (flat or pitched) † 0 104

External surface resistances (Rso):

Sheltered † town buildings to 3 storeys.

Normal † town buildings 4 to 8 storeys and most suburban

premises.

Severe † > 9 storeys in towns.

> 5 storeys elsewhere and any buildings on exposed

coasts and hills.

Air space resistances (Ra):

Pitched or flat roof space † 0„180

Behind vertical tile hanging † 0„120

Cavity wall void † 0„180

Between high and low emissivity surfaces † 0„300

Unventilated/sealed † 0„180

Emissivity relates to the heat transfer across and from surfaces by
radiant heat emission and absorption effects. The amount will
depend on the surface texture, the quantity and temperature of air
movement across it, the surface position or orientation and the
temperature of adjacent bodies or materials. High surface
emissivity is appropriate for most building materials. An example of
low emissivity would be bright aluminium foil on one or both sides
of an air space.

Surface Exposure

Sheltered Normal Severe

Wall † high emissivity 0„080 0„055 0„030

Wall † low emissivity 0„1 1 0 0„070 0„030

Roof † high emissivity 0„070 0„045 0„020

Roof † low emissivity 0„090 0„050 0„020

Floor † high emissivity 0„070 0„040 0„020

Thermal Insulation, Surface and Air Space Resistances