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 42 years and it should pay for itself many times over.
Easy access and regular joistsThese are estimates based on insulating a oil-heated home with either a totally uninsulated loft, or topping up existing insulation from 120mm 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
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.
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, 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.
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.
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 and you will need to get Building Control Approval. Get professional advice before installing insulation to see if you can fix any damp problems first.