Energy Efficiency Best Practice in Housing
Energy efficient loft extensions
This guide explains how to achieve Best Practice standards of energy efficiency. Intended
for designers, builders and homeowners carrying out loft conversions, it deals with:
• insulation in roofs, dormers, gables and chimney breasts;
• energy efficient windows;
• efficient heating;
• controlled ventilation;
• energy efficient lighting.
Domestic emissions arise from the use of energy for space and water heating, cooking, and the use of lighting and electrical appliances. To meet our international commitments and tackle climate change, we must significantly reduce energy related emissions in homes.
- energy efficiency
Loft conversions are important; they can provide new, energy efficient accommodation and can also improve the overall energy efficiency of the houses.
- loft conversion
Converting a loft for energy efficiency
Some conversions are inherently easier to make energy efficient than others.The most efficient forms minimise heat losses by reducing the ratio of heat loss area (i.e. exposed walls and roofs) to floor area. They also allow easy installation of insulation.The main choices are as follows.
Loft insulation is the most cost effective energy efficiency measure and the easiest to install. Standards of loft insulation have increased in recent times. Some previously insulated lofts should be ‘topped-up’ as building regulations now specify a minimum of 250mm thick insulation.
- roof insulation
For an insulated pitched roof (where the insulation is placed between the rafters) the building regulations specify that a 50mm wide ventilation gap must be maintained above the insulation (and beneath the roofing felt and tiles); this is to reduce the risk of interstitial condensation.
- vapour barrier
A vapour-balanced roof construction allows moisture to permeate, removing the need for ventilation of the roof construction. The vapour resistance on the inside of the construction should be five times that on the outside.
The walls and roofs of dormers should be insulated to Best Practice standards (i.e. to achieve maximum U-values of 0.25W/m2K for walls and 0.13W/m2K for roofs) – see Table 1. Since dormers are almost always of timber-framed construction, this will involve a combination of flexible insulation quilt within the frame and thermal lining board on the inside.
- existing walls
When a loft is converted, exposed gable walls and any attached chimney breasts become the external walls of the new living space. Insulation should be installed to achieve Best Practice.
For loft conversions, building regulations in each part of the UK specify maximum allowable areas of glazed openings (windows, doors and roof windows).They also specify maximum U-values for new openings (windows, doors and rooflights). Adopting the higher, Best Practice standards for openings set out in Table 1 will reduce fuel use, fuel costs and carbon emissions.
Housing in the UK has traditionally relied on air infiltration through the building fabric to provide background ventilation.Window opening and the use of extractor fans supplement this when required.
For houses with gas or oil fired central heating, a key issue is whether the existing boiler has adequate capacity to heat the enlarged house once the loft conversion is completed. In many cases, the additional heating load makes it necessary to install a new boiler with extra capacity, at significant cost.
The condensing boiler is the most efficient type available and is becoming the standard choice in most parts of the UK. Further to this, from 1 April 2005, all gas boilers installed in England and Wales are required to be condensing boilers (aside from a small number of exceptions).
- room heaters
If the house whose loft is being converted does not already have a central heating system, it is a good idea to consider installing one (with a condensing boiler). If this is not appropriate or affordable, the new living space may be fitted with fixed individual room heaters.
Building regulations in the UK require that new accommodation (including loft conversions) has some light fittings that will only accept energy efficient lamps. At least one new room in three should have such fittings.
Frequently asked questions for loft conversions