Insulation questions answered

Discover the most effective insulation for your home, making it more comfortable and energy efficient – as well as saving you money

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Options for lofts

Q: I don’t know when the insulation in my roof space was installed. Is it worth replacing it?

A: ‘As much as a third of the heat you pay for could be escaping through your roof. However, according to the Government, you can cut your heating bills by up to 20 per cent through effectively insulating your loft, resulting in a typical annual saving of £250,’ says Neil Marshall, chief executive of the National Insulation Association (NIA).

Loft insulation can be installed between and over the ceiling joists/loft floor (for a ‘cold roof’ used for storage), or in line with the slope of the rafters (for a ‘warm roof’ suitable for loft conversions). If your loft is easy to access and has no damp or condensation problems, installation should be an easy and inexpensive process, and DIY may be an option. The loft in an average-sized home could be fully insulated for around £200, as a cold roof, and it will remain effective for at least 40 years. There are also schemes offering free loft insulation – many via major utility companies. If your loft space is difficult to access, you can have blown insulation made of cellulose fibre or mineral wool installed by a professional. This doesn’t usually take more than a few hours.

Rooms in the roof

Q: What’s the best insulation type to create a liveable loft space?

A: ’If the loft is to be used for living space or you have rooms partly in the roof space – as in a dormer bungalow – the insulation is placed in line with the rafters or at loft room ceiling height. To prevent the build-up of damp, a clear ventilated space needs to be left under the roofing felt, or a breathable membrane used with a ventilation void to allow air movement,’ says Neil Marshall. ‘Boards will be cut to the right width so they fit snugly between the rafters, and then covered by plaster or timber boards. As rafters aren’t usually deep, installers may have to insulate under the rafters as well, to meet the requirements.’ There are several types of insulation that could be used, most often rigid cellular insulation, combined with insulation- backed plasterboard, and sometimes multi-layer foil-based materials. Bear in mind that your loft size may be reduced as a result of adding insulation to the walls and roof.

Cavity wall solutions

Q: The insulation in my 1970s home has never been updated. What can I do to improve its thermal efficiency?

A: Homes built after 1930 are likely to have cavity walls, constructed with inner and outer leaves and a gap in between, to prevent rain penetrating the interior. Properties built from the 1990s are likely to have cavity- wall insulation (CWI) fitted in this void, but those constructed before the mid-1980s may not.

Cavity walls lose less heat than solid walls, and are much easier to insulate. CWI fills the void between the wall leaves, retaining warmth and reducing energy loss. To find out whether your home already has CWI, you can either ask a registered installer for a boroscope inspection, or ask your local authority’s building control, which may have a record.

‘Insulation is one of the most cost-effective ways of reducing energy consumption, with CWI providing the perfect solution for many households. Around 33 per cent of a building’s heat is lost through uninsulated walls, but by simply installing CWI, savings of up to £250 per year can be achieved,’ says Neil Marshall. ‘CWI usually takes less than a day to install and, with all the work done from the outside of the building, the disruption to the household is minimal.’

The installation will not affect the appearance of your property; small holes are drilled into mortar joints of external walls and the insulation material (usually blown mineral wool, blown polystyrene beads or urea-formaldehyde foam) is injected into the cavity. The holes are then sealed to match the existing mortar. Look for an installer that offers a 20- to-25-year guarantee on their work. Not every home is suitable for CWI, especially those in areas prone to wind-driven rain, so the work is controlled by building regulations and the local authority must be notified.

Choices for walls

Q: I’ve bought a Victorian house to renovate. Can I add insulation without spoiling its integrity?

A: ‘Around one third of heat loss from an uninsulated house is through the walls, so improving their insulation levels can significantly improve energy efficiency, reducing heating bills and improving comfort,’ says experienced renovator Michael Holmes.

‘Most homes built before 1930 will be of solid-wall construction, made from brick, stone or blocks, with no cavity. The options are to insulate the inside of the building, typically behind plaster or plasterboard with a vapour membrane below, or to add insulation to the outside, typically covered with a new coat of render.

‘Insulating internally usually means having to replace the services, such as heating, plumbing and wiring, and features such as mouldings and window boards,’ continues Michael.

Exterior wall insulation (EWI) will usually alter a property’s appearance, so check if planning permission is required. Due to the level of work involved, it’s more often done when major refurbishments are already planned. The insulation will be at least 5-10cm thick, and its application generally involves a frame being fixed to the wall to hold solid materials, with render or cladding placed over the top. This will increase the depth of the wall, and may encroach onto paths or drives, affecting guttering and drainpipes.

EWI costs several thousand pounds to install, depending on the size of your property, but the Energy Saving Trust estimates that a detached four-bedroom home could save up to £460 per year on heating bills. ‘There are many benefits of EWI, including the fact that no living space is lost. There is little disruption to the homeowners, as the work can be carried out while they are there, and there is minimal maintenance once installed,’ says Neil Marshall.

Insulating the floors

Q: Could I save on energy bills by adding insulation under the floorboards?

A: The Energy Saving Trust advises that insulating the floors of upstairs rooms may be unnecessary if they are above heated spaces. Do consider insulating any floors over unheated spaces, though (such as garages), as you’re likely to be losing a lot of heat. Older houses are more likely to have cold and draughty suspended timber ground floors, and insulating under the floorboards could save you around £60 to £75 a year.

‘Suspended timber floors can be insulated by placing rigid insulation board between the joists, supported by nails or timber battens, or by placing mineral wool bats supported by plastic meshing, to ensure the joists are still ventilated to prevent them from rotting,’ explains Michael Holmes. ‘It is a good idea to put a breathable membrane over the top of the joists to prevent draughts while ensuring the space is ventilated. If there is a cellar or void beneath the property, it may be possible to insulate a timber floor from underneath, but in most cases it will be necessary to lift the floorboards and to fit insulation from above.’

Many newer homes will have a ground floor made of solid concrete, which can be insulated, but this can be a costly process as it will raise the floor level, necessitating adjustments including flooring, skirting boards and door levels. It may be worthwhile if extensive renovations are already planned, using a rigid foam insulation layer laid on the concrete floor with a damp-proof membrane.

In older houses, flagstones may be laid directly onto compacted earth. In this situation, where major renovation work is being undertaken, limecrete (NHL) based insulated solid-floor systems can be used, which allow the floor to breathe but provide thermal insulation and damp-proofing. A solid concrete floor with a damp-proof course is not usually suitable for old solid-walled buildings, as it can lead to rising damp by forcing ground moisture to the base of the walls.

Preventing heat loss

Q: Can simply draught-proofing my house make a real difference?

A: ‘A typical home loses up to 20 per cent of its heat due to uncontrolled air leakage through gaps, and draughts can cause major discomfort. There are many materials available to help prevent air leakages, including brushes, sealants and extruded strips of profiled foam and rubber. Good-quality draught-proofing materials will carry the BS 7386:1997 approval mark and will not only prevent heat loss and save energy, but will also increase comfort levels while guarding against ingress of bad weather,’ says the NIA’s Neil Marshall.

An easy way to further draught-proof your home is to seal gaps between floors and skirting boards, and around windows. Blocking up gaps that let in cold air means you’ll save warm air and use less energy to heat your home. It can cost just £10 to £15 if you do it yourself with a sealant gun from a DIY store. Draught-free homes are comfortable at lower temperatures, so you’ll be able to turn down your thermostat. Be careful not to block ventilation, needed in an old structure to keep it dry – for instance, subfloor air bricks and fireplaces. If airtight new windows and doors are fitted, ventilation to compensate for uncontrolled infiltration (draughts) will be needed to avoid condensation.