CONDUCTIVE LEAKINESS area
(m2)		 U-value
(W/m2/°C)		 leakiness
(W/°C)
Horizontal surfaces
   Pitched roof 48 0.6 28.8
   Flat roof 1.6 3 4.8
   Floor 50 0.8 40
Vertical surfaces
   Extension walls 24.1 0.6 14.5
   Main walls 50 1 50
   Thin wall (5in) 2 3 6
   Single-glazed doors and windows 7.35 5 36.7
   Double-glazed windows 17.8 2.9 51.6
Total conductive leakiness 232.4
VENTILATION LEAKINESS volume
(m3)		 N
(air-changes per hour)		 leakiness
(W/°C)
Bedrooms 80 0.5 13.3
Kitchen 36 2 24
Hall 27 3 27
Other rooms 77 1 25.7
Total ventilation leakiness 90

To compare the leakinesses of two buildings that have different floor
areas, we can divide the leakiness by the floor area; this gives the heat-loss
parameter of the building, which is measured in W/°C/m2. The heat-loss
parameter of this house (total floor area 88 m2) is

3.7 W/°C/m2.

Let’s use these figures to estimate the house’s daily energy consumption
on a cold winter’s day, and year-round.

On a cold day, assuming an external temperature of -1 °C and an internal
temperature of 19 °C, the temperature difference is ΔT = 20 °C. If
this difference is maintained for 6 hours per day then the energy lost per
day is

322 W/°C × 120 degree-hours  ≅  39 kWh.

If the temperature is maintained at 19 °C for 24 hours per day, the energy
lost per day is

155 kWh/d.

To get a year-round heat-loss figure, we can take the temperature demand
of Cambridge from figure E.5. With the thermostat at 19 °C, the

Table E.8. Breakdown of my house’s conductive leakiness, and its ventilation leakiness, pre-2006. I’ve treated the central wall of the semi-detached house as a perfect insulating wall, but this may be wrong if the gap between the adjacent houses is actually well-ventilated.

I’ve highlighted the parameters that I altered after 2006, in modifications to be described shortly.