Cavity and Loft Insulation

A quarter of heat is lost through the roof in an uninsulated home.

Insulating your loft, attic or flat roof is a simple and effective way to reduce heat loss and reduce your heating bills. Loft insulation is effective for at least 40 years and it should pay for itself many times over.

Choosing loft insulation

If your loft is easy to access and has no damp or condensation problems it should be easy to insulate. It is possible to do it yourself.

If access is easy and your loft joists are regular, you can use rolls of mineral wool insulation. The first layer is laid between the joists – the horizontal beams that make up the floor of the loft – then another layer is laid at right angles to cover the joists and make the insulation up to the required depth. This can be done by someone competent in DIY or a professional installer.

Storage space

If you plan to use the loft or attic for storage, you will want to lay boards over the joists. Unfortunately, if you only insulate between the joists before doing this, the insulation won’t be thick enough.

To get enough insulation, you can raise the level of the floor so you can fit enough mineral wool beneath the new floor level. You can do this by fitting timber battens across the joists, or you can buy purpose built plastic legs that fit on the joists and support the new floor. It’s important to leave a ventilated air gap between the insulation and the boards to prevent condensation on the underside of the boards.

Make sure you don’t squash the mineral wool when you fit the boards on top as this this will reduce its insulation value.

Room-in-roof

If you want to use your loft as a living space, or it is already being used as a living space, you can insulate your room-in-the-roof by insulating the roof itself rather than the loft floor. This is typically done by fixing rigid insulation boards between the roof rafters. Boards must be cut to the correct width so that they fit snugly between the rafters. They can then be covered by plasterboard. Rafters aren’t usually very deep, so to get the best performance you may have to insulate over them as well, using insulated plasterboard. If there isn’t room to do this, make sure you use the highest performance insulation board.

Walls in the roof space and around dormer windows should also be insulated. This is typically done with rigid insulation boards.

In all cases adequate ventilation should be maintained to the rafters.

Inaccessible loft spaces

If your loft is hard to access, you can have blown insulation installed by a professional, who will use specialist equipment to blow loose, fire-retardant insulation material made of cellulose fibre or mineral wool into the loft. This doesn’t usually take more than a few hours.

Flat roofs

A flat roof should preferably be insulated from above. A layer of rigid insulation board can be added either on top of the roof’s weatherproof layer or directly on top of the timber roof surface with a new weatherproof layer on top of the insulation. This is best done when the roof covering needs replacing anyway. If your flat roof needs to be replaced anyway you must now insulate it to comply with building regulations.

It is possible to insulate a flat roof from underneath, but this can lead to condensation problems if not completed correctly.

Installing flat roof insulation could save you similar amounts on your heating bills to loft insulation. The savings will vary depending on how much of the property has a flat roof.

Damp lofts

Insulation stops heat escaping from living spaces, so it will make your loft space cooler, which could introduce or worsen existing damp or condensation problems. If you are installing loft insulation yourself, please keep in mind that you may need to increase ventilation. Get professional advice before installing insulation to see if you can fix any damp problems first.

Is installing insulation a DIY project?

If your loft is easy to access, does not have damp problems and is not a flat roof, you could probably insulate it yourself.

Room in roof insulation can be installed by experienced DIY-ers. In cases where there are damp problems or a more complex insulation system is needed, a professional installer should be used.

Flat roof insulation always requires professional insulation. Damp roofs require professional assessment before work can be carried out.

Finding an installer

The National Insulation Association (NIA) is a member organisation for the insulation industry in the UK. Members agree to follow a code of professional practice to ensure that customers who use them receive excellent customer service. You can use their website to find an NIA installer near you.

For further information, call the Home Energy Saving Advice Service on 0300 123 1234 if you are in England or Wales.

If you are based in Scotland, call Home Energy Scotland on: 0808 808 2282. You can also visit Historic Scotland’s Technical Conservation knowledge base for information on how to insulate traditionally constructed buildings.

If you are in Northern Ireland, please call 0800 1422 865.

Pipes, water tank and loft hatch

Insulating between the joists of your loft will keep your house warmer but make the roof space above colder. This means pipes and water tanks in the loft space could be more likely to freeze, so you will need to insulate them. If your water tank is some distance from the loft hatch, you will also need something to walk on for safe access.

The cooler air in your insulated loft could mean that cold draughts come through the loft hatch. To prevent this fit an insulated loft hatch and put strips of draught-excluding material around the hatch edges.

Cavity Walls

About a third of all the heat lost in an uninsulated home escapes through the walls.

Heat will always flow from a warm area to a cold one. In winter, the colder it is outside, the faster heat from your home will escape into the surrounding air.

In general, houses built from the 1990s onwards have wall insulation to keep the heat in, but if your house is older than that it may not have any wall insulation. If this is the case then you may be losing a lot of heat from your home, as heat can escape more quickly through uninsulated walls. Most types of wall can be insulated in one way or another. If you have a typical house with cavity walls, you could save up to £150 per year in heating bills just from insulating the walls. The first thing you need to find out is what sort of walls you have.

Jump to: Cavity and solid walls, Non-standard wall types, Commonly asked questions, More information

Cavity and solid walls

Houses in the UK mostly have either solid walls or cavity walls:

A cavity wall is made up of two walls with a gap in between, known as the cavity; the outer leaf is usually made of brick, and the inner layer of brick or concrete block.

A solid wall has no cavity; each wall is a single solid wall, usually made of brick or stone.

Working out your wall type

If your house was built after the 1920s, it is likely to have cavity walls. Older houses are more likely to have solid walls.

If you can see the brickwork on the outside of the house, look at the pattern of the bricks. If your home has cavity walls, the bricks will usually have a regular pattern:

If your home has solid walls, the bricks will have an alternating pattern:

If the brickwork has been covered, you can also tell by measuring the width of the wall. Examine a window or door on one of your external walls. If a brick wall is more than 260mm thick then it probably has a cavity; a narrower wall is probably solid. Stone walls may be thicker still but are usually solid.

Non-standard wall types

If your house is a steel-frame or timber-framed building, or is made from pre-fabricated concrete different rules apply for insulation.

Generally these houses don’t have a cavity to fill, but it may be possible to insulate them in the same way as a solid wall. However, you may need a specialist company to insulate a non-standard wall. For further advice or to find an installer who can help you, contact the National Insulation Association.

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