Green Building, Part 2: Conserving Energy

The highly compelling feature of green building, is not only do you make your building and environment healthier, by being more energy efficient you can save money.  In the following section you can discover some simple and leading edge materials to make your buildings green and delivering savings on energy bills for years to come.

Conserving Energy

U-values measure the loss of heat though a given thickness of material and the lower target U values laid down in part L of The Building Regulations reflect the Government’s commitment to energy conservation. Higher standards for thermal insulation equal lower energy consumption.

SAP (Standard Assessment Procedure) was introduced by the government in 1995 to ensure that all new homes would be more energy efficient. The annual energy cost is assessed per square metre of floor area. The ratings are expressed on a scale of 1 – 1000, the higher the figure the greater the energy efficiency. Although there is no minimum requirement, a rating lower than 60 would need to be improved; for example, by the installation of a high efficiency condensing boiler or 12mm double-glazing.

Construction Brick and Block

Brick and block construction may struggle to achieve target U-Values, especially, if those targets are brought down even lower in the next few years. However useful examples of ways in which the present figures can be achieved are given in part L of The Building Regulations.

It’s known that timber frame construction can meet and exceed thermal insulation requirements but what are the plusses for the bricks and mortar method of construction?

Firstly, solid concrete floors and partition walls are very efficient in their resistance to the transmission of sound and are highly resistant to fire. The inner blockwork leaf of the cavity wall can act as an excellent thermal store in winter, absorbing heat from the house during the day and storing it. This means that when the heating goes off at night, the house will take several hours to cool down as the stored heat is slowly released from the blocks. In summer the interior of the building will stay cooler as the sun’s heat will be cooled before it has a chance to penetrate the inner fabric.

Mortar joints have always been a weak spot for heat loss so to counter this problem thin joint blockwork has been developed by the concrete block manufacturers. A special adhesive type mortar is used to join the blocks creating a much thinner mortar joint which improves the thermal insulation properties of the wall. The technique also allows walls to be constructed faster than using traditional cement mortar.

Solar Gain Protection

It is important to keep the inside temperature of buildings as comfortable as possible without having to use excessive amounts of energy to heat or to cool. Untreated glass allows the heat from the sun to enter buildings and on very warm days can cause the inside temperature rise to uncomfortable levels.

The amount of heat from the sun transmitted through the glass can be reduced in several ways:

  • Blinds/curtains
  • Solar Films
  • Brise soleil
  • Solar Glass

Internal blinds or curtains do not prevent the sun’s heat from entering a building so will be of most benefit if windows can be left open. They do reduce the radiant heat aspect of the sun. Blinds & curtains   protect furnishings from being faded by ultra violet rays.

Draught Proofing

Draught proofing is one of the most inexpensive & effective ways of making efficient use of energy in all types of building. It will often pay for itself within a year.

According to the Draught Proofing Association only 22 million dwellings in this country are adequately draught proofed. In the commercial & industrial buildings sector, the figure is only 10%. Building Regulations require draught proofing on all windows & external doors in new buildings. Existing properties should be to the same standard.

Up to 15% of fuel bills can be saved by fitting high performance draught proofing materials to all external windows & doors.

A 5mm gap, commonly found under a domestic door can let through 80 cubic metres of cold air per hour.


When it comes to environmental issues, glass is not so straightforward. It’s recyclable and contributes to saving electricity by letting light in, but it also lets a lot of heat escape from buildings. Yet with it being hugely popular as a design material for architects, ways are being found to improve the resistance of glass to heat transference.

energiKare™ Single/Spacia by Pilkington

Double-glazing traps a layer of still air between two panes of glass which reduces thermal transmittance. The use of argon gas (which is heavier than air) between panes and the introduction of low emissivity glass into the glazing units have helped to lower heat loss through windows and reduce condensation in buildings.

Replacement windows became an improvement subject to building regulations control since the upgrading of thermal insulation standards (Building Regulations April 2002). When replacing windows, single-glazed windows should be replaced by double glazed windows where ever possible. There will be some exceptions for listed buildings where double-glazing may spoil the aesthetics or historic authenticity of the building. Thermal insulation is increased progressively up to an optimum which is maintained between 20mm & 200mm gap between panes.

It is estimated that around one million replacement window installations happen every year. This would place enormous pressure on local authorities if all of these went through the normal Building Regulations application process. The Glass & Glazing Federation have set up the Fenestration Self Assessment Scheme (FENSA) to ease this burden. Installation companies that meet certain criteria may self-certify that their work complies with the Building Regulations. A sample of the work of every installer will be inspected by FENSA appointed inspectors to ensure standards are maintained. FENSA will also inform local authorities of all completed FENSA installations and issue certificates to householders confirming compliance.

Also see:

Part 1: Materials

Part 3: Electricity and Energy Efficient Boilers

Part 4: Renewables