A quarter of heat is lost through the roof in an uninstalled 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.
If your loft is easy to access and has no damp or condensation problems, it should be easy to insulate – and in most cases, 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.
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.
An alternative way to insulate your loft is to fit the insulation between and over the rafters – these are the sloping timbers that make up the roof itself. You can use rigid insulation board, carefully cut to size, or you can have foam insulation sprayed between the rafters.
Whichever approach you use, you will need a specialist professional to insulate your roof – this is not a DIY job.
Some companies may offer to fix your damaged or leaking roof by spraying foam insulation directly onto the underside of the roof without first fixing the problem. We do not recommend that you do this. As with any type of insulation, you need to make sure that the roof is dry and in good condition before any insulation is added.
If you want to use your loft as a heated room, then you need to take a slightly different approach, and create a proper room in the roof.
If you want to use your loft as a living space, or it is already being used as a living space, then you need to makes sure that all the walls and ceilings between a heated room and an unheated space are insulated.
Make sure you insulate all the areas of wall and ceiling round any dormer window, and that you use high performance glazing for the window, or for any skylights.
As with warm loft insulation, this is not a DIY job. You will need a professional installer to ensure that the insulation is appropriate and complete, and that adequate ventilation is provided where needed.
If your loft is hard to access, you can have blown insulation installed by a professional, who will use specialist equipment to blow appropriate insulation material into any awkward space. They may use mineral wool fibre, treated cellulose or polyurethane foam.
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.
Get professional advice before installing insulation to see if you can fix any damp problems first.