U-values (W/m2/K) | |||
---|---|---|---|
old buildings | modern standards | best methods | |
Walls | 0.45-0.6 | 0.12 | |
solid masonry wall | 2.4 | ||
outer wall: 9 inch solid brick | 2.2 | ||
11 inch brick-block cavity wall, unfilled | 1.0 | ||
11 inch brick-block cavity wall, insulated | 0.6 | ||
Floors | 0.45 | 0.14 | |
suspended timber floor | 0.7 | ||
solid concrete floor | 0.8 | ||
Roofs | 0.25 | 0.12 | |
flat roof with 25 mm insulation | 0.9 | ||
pitched roof with 100 mm insulation | 0.3 | ||
Windows | 1.5 | ||
single-glazed | 5.0 | ||
double-glazed | 2.9 | ||
double-glazed, 20 mm gap | 1.7 | ||
triple-glazed | 0.7-0.9 |
outside of the building
Since energy is power × time, you can write the energy lost by conduction
through an area in a short duration as
energy loss = area × U × (ΔT × duration),
and the energy lost by ventilation as
1⁄3 NV × (ΔT × duration).
Both these energy losses have the form
Something × (ΔT × duration),