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Roof and loft

Heat rises, and in an uninsulated home, a quarter of heat is lost through the roof. 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. 

How much you can save

England, Scotland and Wales

Loft insulation (0 to 270mm)

Detached house Semi detached house Mid terrace house Detached bungalow
Potential saving per year £250 £150 £140 £200
Installation cost* £395 £300 £285 £265
Carbon dioxide saving per year 1050 kg 620 kg 580 kg 830 kg
Loft insulation top up 

(100 to 270mm)

Detached house Semi detached house Mid terrace house Detached bungalow

Potential saving per year

£25 £15 £15 £20
Installation cost* £265 £220 £215 £205

Carbon dioxide saving per year

110 kg 65 kg 60 kg 95 kg

Estimates based on insulating a gas-heated home with either a totally uninsulated loft, or topping up existing insulation from 100mm to 270mm. (The recommended depth for mineral wool insulation is 270mm but other materials need different depths). *Average unsubsidised professional installation costs, although these will vary.

Northern Ireland

Loft insulation

(0 to 270mm)

Detached house

Semi detached house

Mid terrace house

Detached bungalow

Potential saving per year £350 £210 £200 £280
Installation cost* £395 £300 £285 £265
Carbon dioxide saving per year 1260 kg 750 kg 700 kg 1000 kg

Loft insulation top up

(100 to 270mm)

Detached house

Semi detached house

Mid terrace house

Detached bungalow

Potential saving per year £40 £25 £20 £30
Installation cost* £265 £220 £215 £205
Carbon dioxide saving per year 135 kg 80 kg 75 kg 115 kg

These are estimates based on insulating a oil-heated home with either a totally uninsulated loft, or topping up existing insulation from 100mm to 270mm. (The recommended depth for mineral wool insulation is 270mm but other materials need different depths). *Average unsubsidised professional installation costs, although these will vary.

Choosing loft insulation

Easy access and regular joists

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 or living 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 do the following:

  • Insulate between the joists with mineral wool and then lay rigid insulation boards on top, with wooden boarding on top of that. You can buy insulation board pre-bonded to floor boarding to make the job easier. Or
  • raise the level of the floor so you can fit enough mineral wool beneath the new floor level. 

Either way, make sure you don't squash the mineral wool when you fit the boards on top as this this will reduce its insulation value. 

If you want to use your loft as a living space, you can insulate the roof instead of the floor 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.

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 make existing damp or condensation problems worse. Get professional advice before installing insulation to see if you can fix the damp problems first.

Installing loft insulation

For a list of insulation installers visit National Insulation Association call the Home Energy Saving Advice Service on 0300 123 1234 if you live in England or Wales, or Home Energy Scotland on  0808 808 2282 if you live in Scotland.

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. Pipes and water tanks will be more likely to freeze, so you will need to insulate them. If your water tanks are 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.