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Frequently asked questions for loft conversions

Convert or extend?

Q Is it better to convert a loft, or build an extension?

A This depends on the particular circumstances. Loft conversions can be complex and expensive, but they are usually less costly than extensions – and do not take up garden space!


Q Will the converted loft have to be insulated?

A Yes. Loft conversions are treated as 'material alterations', and building regulations specify minimum insulation standards for exposed walls, roofs and new windows.

Q How much insulation should be included?

A Adopt the Best Practice insulation standards set out in Table 1. This will reduce heat losses, and so reduce fuel use, energy costs and carbon emissions.The cost of the extra insulation can be recovered through savings on the price of a smaller heating system. It may even be possible to retain the existing boiler.

Q Will I be able to insert enough insulation into the existing pitched roof construction?

A Yes, if you use the right insulating materials, and insulate both between and beneath the existing rafters.

Q Is there a risk of condensation with an insulated pitched roof?

A The risk of condensation is effectively eliminated if a vapour barrier is included on the warmer side of the insulation (before the linings are fixed) and a 50mm wide ventilated gap is maintained above the insulation (beneath the tiles and felt).

Q What about 'breathing roof' construction?

A This is really 'vapour balanced' construction; it is vapour permeable and so does not need to be ventilated.The existing roofing felt is replaced by a waterproof but vapour-permeable 'breather membrane' (note that the tiles and the existing felt have to be removed, and the tiles re-fixed).The vapour barrier and the 50mm ventilation gap may then be omitted, leaving more space for insulation.

Q Is it necessary to insulate the gable end walls?

A Yes, gable walls should be insulated to the Best Practice standards set out in Table 1.This can usually be achieved internally by means of insulated 'dry-lining'. Chimney breasts and piers should also be insulated, to eliminate thermal bridges.

Q Is insulation effective?

A Yes, if it is properly installed.Architects and builders should understand the need to eliminate 'thermal bridges' and to achieve a good standard of airtightness.There should be no gaps in the insulation at the junctions of walls and roofs, or around openings. All windows, including rooflights, should be properly sealed into the walls or roofs, and the places where services (pipes and wires) penetrate through walls and floors should also be sealed.

Glazed openings

Q Can I have the roof extensively glazed?

A No.Windows are a major contributor to heat loss, and therefore to energy consumption, fuel costs and carbon emissions.An extensively glazed loft conversion is likely to be difficult and expensive to heat.

Windows should only be large enough to admit adequate daylight, and the area of north-facing glazing should be minimised. The building regulations specify the maximum ratio of window area to new floor area (25 per cent).

Q What about south-facing roof windows?

A South-facing roof windows do trap useful solar gains, but contribute to summer overheating. South-facing glazing should include blinds to provide shading from high-angle summer sun. Highly-glazed southfacing rooms must be well ventilated.

Q Should I specify high-performance glazing?

A Yes, if possible. Double- or triple-glazing with wide gaps, a low emissivity coating and gas filling will reduce heat losses, and thus reduce energy consumption, fuel costs and carbon emissions. Comfort will improve through reduced down-draughts and decreased risk of internal surface condensation.


Q Does the converted loft have to be ventilated?

A Yes.There must be provision for background, rapid and (in 'wet areas') extract ventilation.Trickle ventilators and opening windows meet most of this requirement. For wet areas, there are several controlled ventilation options, including energy efficient extract fans, heatrecovery room ventilators and passive stack ventilation.


Q Will the existing heating boiler have to be replaced?

A Not necessarily. If the converted loft is well insulated and airtight, there may be little or no overall increase in heating demand, and the spare capacity in the existing boiler may be sufficient. This can be confirmed by calculation.

Q What if the existing boiler is not adequate?

A If possible, the existing boiler should be replaced by a new condensing boiler, of appropriate output and with a seasonal efficiency not lower than grade B (86 per cent). A condensing boiler will offset additional heat demand, so fuel costs will not necessarily increase significantly.

Q Are condensing boilers expensive?

A Condensing boilers are a little more expensive than conventional boilers of equivalent output, but they are much more efficient. The additional cost is usually recovered through reduced heating and hotwater bills within 2-3 years, and the boiler should go on saving money for at least another eight years.The carbon emissions from condensing boilers are also much less than those from conventional boilers.

Q Will I have to upgrade the heating controls?

A If good controls are not already installed and the boiler is replaced, then they will have to be upgraded.The final system must be fullypumped, and include a programmer, room thermostat and hot water cylinder thermostat.The room thermostat must be interlocked to the boiler so that the boiler does not fire when there is no demand for


Q Should I include a room heater in the loft conversion?

A An efficient gas-fired room heater is sometimes a good alternative, or supplement, to central heating. Electric room heaters are efficient, but they are also expensive to run and have high carbon emissions.


Q What type of lighting should I install?

A Energy efficient lighting with compact fluorescent lamps (CFLs) is much less expensive (over the life of the lamps) than conventional tungsten lighting, even though more expensive initially. Energy efficient lighting significantly reduces electricity use and associated carbon emissions. The Energy Saving Trust (EST) manages a labelling scheme for products of proven energy efficiency.The scheme currently covers a range of lighting fixtures and fittings.These products carry the Energy Efficiency Recommended label. Currently endorsed products can be found at

Q How can I achieve the desired lighting effect with CFLs?

A A large range of CFL lamp types can be obtained, including spot lamps, candle lamps, and coloured lamps of every description. Multitube lamps light up instantly and quickly reach their full brightness.

Special dimmer switches are available for use with CFLs.

Professional assistance

Q Who can help me with all this?

A Choose an architect and builder carefully. Ask them if they know how to design energy efficient roofspace conversions, and whether they have completed any. Ask them if they are familiar with this guide, and with the other guides listed below. If in doubt, contact the local Energy Efficiency Advice Centre (EEAC) via the Energy Saving Trust's

Energy Efficiency Helpline on 0845 727 7200.































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