loft insulation
A home without insulation in the roof loses a huge amount of heat unnecessarily. According to the Energy Savings Trust, adding loft insulation can result in savings of up to £180 pounds per year, which means that the cost of getting it installed will have been covered within two years. And you may even be able to get a grant to help you pay for the installation.

How much you could save

Loft Insulation
(0 to 270mm)
Loft Insulation
(100 to 270mm)
Approximate saving per year Up to £180 £25
Installation cost Around £300* Up to £300*
Time taken to pay for itself Up to two years Up to twelve years
DIY cost From £250** From £150**
Time taken to pay for itself From two years From five years
Carbon dioxide saving per year Around 730kg Around 110kg

These estimates based on insulating a gas-heated, semi-detached home with three bedrooms, showing savings when you insulate an uninsulated loft, and when you top up 100mm of insulation to 270mm. (The recommended depth for mineral wool insulation is 270mm but other materials need different depths). *Average unsubsidised professional installation costs, loft top up assumed to be up to £300 although these may vary. **DIY costs are based on average retailer costs for insulation up to 270mm or more, based on a 44m2 loft.Information source: www.energysavingtrust.org.uk

More good news is that adding loft insulation is in most cases a fairly straightforward task that can be handled by those with only minimal DIY experience.

Here is a guide to laying insulation to create cold and warm roofs in a standard pitched-roof house.

Cold roof or warm roof?

There are two ways you can insulate a roof, and the way you choose will depend on what you intend to use your roof space for. A cold roof is one in which the insulation material is laid between the ceiling joists, just above the top floor. The actual roof space is left cold, hence the name, and as a result using this kind of insulation method means that the roof can only be used for storage. If you want a loft space that can be used as a room, you will need to place the insulation in between the rafters. This is known as a warm roof.

Insulating a cold roof

insulating a cold loftThe most common type of insulation for cold roofs is blanket insulation. It is sold in rolls that come in different widths, so you should be able to find a roll that fits well between the joists in your loft. Make sure you have measured the length of the space that needs to be filled before buying the roll. Once you have cleared the floor of your loft, roll out the blanket of insulation material, using scissors to cut the ends. It is also a good idea to lay another layer on top of the first that also covers the joists. The recommended depth is between 25 and 27 centimetres. Also, don’t forget to add some form of insulation to the loft hatch. A good way to do this is to fix a layer of polystyrene to the top of the hatch.

blown fibre loft insulation

Other types of insulation for cold roofs include loose-fill and blown fibre. Loose-fill loft insulation comes in bags and is a good choice if you have irregularly spaced joists or obstructions in your loft, but you will need to wear protective clothing when pouring it out. Blown-fibre loft insulation is probably the best option for insulating roof areas that are difficult to access, but it will need to be done by a professional, and it is a little more expensive than other types.

Insulating pipes and tanks

pipe insulation
In a cold roof you will also need to make sure that pipes and tanks are properly insulated, this means covering them with an appropriate material. The loft will get very cold in winter and warm in summer and leave your pipes vulnerable. Tanks should have their sides and tops covered, but not underneath, as they will need some warmth from below.

Insulating a warm roof

warm roof insulationTo create a warm roof, it is necessary to insulate the sloping surfaces of the roof with rigid sheet insulation, also known as board insulation. This type of insulating material is often made with cork, straw or wood board, and is generally a little more expensive than cold roof insulation materials as it has a higher insulating value per unit thickness. It is possible to get sheet insulation that is fire-resistant, and there are also varieties of moisture resistant sheet insulation. The boards can be cut to fit or bought pre-cut. It is very important that the boards are cut to exactly the right width so that they will fit snugly between the rafters.

warm loftInstall the insulation boards so that they are flush with the bottom of the rafters, but not filling the rafters’ depth. It is very important that there is space between the insulation and the roof slats to avoid condensation. Once the sheet insulation has been laid, you can cover it and the rafters with plasterboard to create a clean finish. Using insulated plasterboard will give an extra layer of insulation.

Other kinds of roofs

Houses that have dormer roofs and flat roofs represent more of a challenge to insulate. Very often insulation is added from the outside by adding a rigid insulation board on top of the roof’s weather-proof layer. It can also be done from inside, but in both cases it is a job that will need to be done by a professional.