Table 15 Thermal Resistances of Air Gaps
|
Unventilated air gaps
|
|
|
Thermal resistance (m²K/W) for
|
|
Thickness
|
Surface emissivity
|
Horizontal
heat flow
|
Upward
heat flow
|
Downward
heat flow
|
|
5 mm
|
High
|
0.1
|
0.1
|
0.1
|
|
Low
|
0.18
|
0.18
|
0.18
|
|
25mm or over
|
High
|
0.18
|
0.17
|
0.22
|
|
Low
|
0.35
|
0.35
|
1.06
|
|
|
|
|
|
|
|
High emissivity plane and corrugated sheets in contact
|
High
|
0.09
|
0.09
|
0.11
|
|
|
|
|
|
|
|
Low emissivity multiple foil insulation with air gap on one side
|
Low
|
0.62
|
0.62
|
1.76
|
|
Ventilated air gaps
|
|
|
Type
|
Thermal
|
|
|
resistance
|
|
Gap between asbestos cement or black
|
|
|
metal cladding with unsealed joints
|
|
|
and high emissivity lining
|
0.16
|
|
|
|
|
Gap between asbestos cement or black
|
|
|
metal cladding with unsealed joints,
|
|
|
and low emissivity surface facing gap
|
0.3
|
|
|
|
|
Loft space between flat ceiling and
|
|
|
unsealed asbestos cement sheets or
|
|
|
black metal cladding pitched roof
|
0.14
|
|
|
|
|
Loft space between flat ceiling and
|
|
|
pitched roof with aluminium cladding
|
|
|
instead of black metal or low
|
|
|
emissivity upper surface on ceiling
|
0.25
|
|
|
|
|
Loft space between flat ceiling and
|
|
|
pitched roof lined with felt or
|
|
|
building paper
|
0.18
|
|
|
|
|
Gap between tiles and roofing felt
|
|
|
or building paper
|
0.12
|
|
|
|
|
Gap between tiles on tile hung wall
|
|
|
(includes resistance of tile)
|
0.12
|
|
|
|
|
Gap in cavity wall construction
|
0.18
|
