The scale of the domestic low energy challenge

In my last post I gave some values for the key statistics required for a building to meet the PassivHaus ultra low energy standard. Now I’m attempting to put that up against what I expect to be the status of our new home, and current Energy Saving Trust recommendations and the current Building Regulations.

This post is devoted to giving you some figures ready for the discussions that will follow.

The ‘new home’

An introduction to its structure would be a good start. The building comprises two parts. An original bungalow built in the 1930s with a pitched, tiled roof and a later extension with mostly flat roof and a section of polycarbonate roof  built in the 1960s. Both ‘feature’ unfilled cavity walls. The old building has wooden suspended floors and the new is almost entirely concrete solid floor. Double glazing was installed throughout in the 1980s, but there is some evidence it is beginning to fail.

There is a fibreboard lined space in the loft with a thin scattering of roof insulation on the unenclosed section. Insulation in the flat roof is unknown, but there’s not much height for any real thickness. It has gas fired central heating with a large and old boiler.

Not sounding too promising at this point.

Side Note: In 2010 the UK Building Regulations have been tightened in their latest release (April) Part F deals with ventilation, and is heading towards PassivHaus style full ventilation, and the values on Part L (energy efficiency) have been tightend. Further tightening is coming in in October 2010.

Special note:- To avoid repetition all U values are in W/m2/oC.

‘Opaque’ U values (walls, floors and roofs)

Walls Roof (Pitched) Roof (Flat) Floor
PassivHaus Super insulation levels – U values for walls, floors and roofs All to be 0.15 W/m 2/ oC
New home 1.6 1.9 1.5 0.7 Suspended

0.45 Solid

EST 0.25/ 0.6 0.16 0.25 0.25
Bldg. Regs 0.3/ 0.35/ 0.7 0.16/ 0.16/ 0.35 0.2/ 0.25/ 0.35 0.22/ 0.25/ 0.7

New Home. These values are average figures for typical similar construction methods.

EST = Energy Saving Trust. Figures Source – CE83 from the Energy Saving Trust, page 6

Bldg. Regs = Building Regulation 2010 Part L. The three figures here are for Best Practice/ If Conversion / If Refurbishment

‘Opening’ U values (windows and doors)

Windows Doors
PassivHaus 0.8
New home 2.0 2.2
EST 1.3 to 1.6 Solid – 1.0

Half glazed – 1.5

Bldg. Regs 1.8 Solid – 3.0

Half glazed – 2.2

New Home – Source: CE83 from the Energy Saving Trust, page 9, similar values from Reduced Data SAP – collected data asset FAERO Defra 2006

EST states “BFRC Class ‘C’ or better”. This equates to 1.6 down to 1.3.


Test Air change
PassivHaus 0.6 h1 0.4
New home >7?
EST 5 3
Bldg. Regs 5 3

Test is carried out at a pressure of 50Pa. The figure is in m3 per hour per m2 of floor area.

“Air change” is the approximate number of air changes per hour that the figure equates to.

Appliances and Lighting

Appliances Lighting
PassivHaus All appliances to be A+ rating minimum Low energy luminaires
New home Wide variation, many not known 75% to 80% incandescent lamps
EST All appliances to be A or A+ rating 75% to 80% low energy luminaires
Bldg. Regs 75%+ of lights must be ‘low energy’

Definition has been increased to 45 lumens per watt (from 40).


Appliances Alternates
PassivHaus No specific recommendation Various
New home An elderly gas boiler and radiators with simple time clock and room thermostat controls. There is no pipe insulation on the visible runs For future consideration
EST High efficiency condensing boiler with separate hot water store and modern controls including individual Thermostatic Radiator Valves (TRV).
Bldg. Regs Gas boilers must be ‘condensing’ type and ‘A’ rated (> 90% efficient).

Thermal Bridging

Thermal bridging occurs where two insulated areas meet, or don’t meet, leaving a poorly insulated gap. For example, these can occur at the junction between the top of a wall and the ceiling. Heat loss through such bridges can be far greater than their relatively small area would lead you to believe.

PassivHaus No thermal bridges.

The PassivHaus methodology is built around attention to detail so as to eliminate thermal bridging through design and quality construction.

New home As you will have seen from the above figures, it is almost all thermal bridge anyway!
EST Similar principles to the PassivHaus, taking trouble to design out as many as possible.
Bldg. Regs Psi value of 0.04 w/m.k

Where next?

The next stage is to examine an order of priority. This will be determined somewhat by the priority order that emerged from the initial analysis but with a heavy overlay of practicality and budget. There are some works that will be very disruptive, and it would be best to see if those can be undertaken before we move in. Others will have dependencies and need to have a logical order so that work does not have to be done more than once.

Leave a Reply