Loft Insulation

Loft Insulation

Roof insulation

Modern houses are built with loft insulation, but older properties may be losing a quarter of their heat through the roof. Installing or topping-up insulation in a standard loft is an easy and cost-effective way of making a home more energy-efficient. 

Types of loft insulation

For an accessible loft, the most straightforward method is to lay loft rolls of mineral, glass or sheep’s wool between and over the ceiling joists to a depth of 270mm. A layer is placed between the joists then another is laid at right angles to cover them.  For topping up, the appropriate depth of loft roll is simply laid on top of the existing material.  The loft door can be insulated, but it is better to replace it with an insulated trap door.

The second method, blown installation of fire-retardant mineral wool or cellulose, is for roof spaces with difficult access. The process usually takes no more than a couple of hours.

Finally, for flat roofs, expanded polystyrene insulation boards can be attached on or beneath the roof. These can be a bit more expensive and complicated to install, and can lead to condensation problems, so installation is best left to a professional.


If the loft is used for storage and there is insufficient joist depth to accommodate the insulation, there are two solutions. The first is to infill between the joists with loft roll and then lay insulation boards and chipboard loft boards across the top. Alternatively, the level of the loft floor can be raised to accommodate two layers of loft roll, by fitting battens across the joists and nailing chipboard loft boards on top.

For either method, a gap should be left between the loft insulation and the boards to prevent condensation and compression of the loft roll, which will reduce its efficiency.

Loft conversions

The floor of an existing loft conversion can be insulated to keep the rest of the home warm, with loft roll added between pitched roof rafters and insulation boards to false ceilings, walls and dormers to keep the loft room itself cosy. A 50mm gap is needed between insulation boards and roofing felt for ventilation.

Other things to remember

For DIY, choose products with an ‘Energy Savings Trust Recommended’ logo, insulate pipes and tanks and do not install loft roll beneath the cold water tank. Remember to wear protective clothing and a mask.

If the space is used to store perishables like photographs or clothes, the roof should also be insulated to keep more heat in the loft.

An insulated loft needs to be adequately ventilated around the eaves to prevent damp. If there is an existing damp problem it is best to get professional advice.

Costs and savings

270mm of new loft insulation could yield annual savings of £225 for a detached house or £135 for a three bedroomed semi-detached. The cost would be £395 or £300 respectively. It may be possible to get grants through the Energy Company Obligation (ECO) towards the costs. Check with your energy supplier.

Keeping your walls warm

wall insulation

Escaping heat is one of the most important considerations when improving the energy efficiency of your home and your EPC score. Approximately a third of the heat loss from a brick-built home disappears through the walls, so installing wall insulation will reduce losses and save money on energy bills.

It will also make your home feel more cosy and help to prevent condensation on the walls.

How to find out if your house is suitable

The first question is whether your house has solid or cavity walls, as this determines the type of insulation that is appropriate. Pre-1930 properties generally have solid walls of a single layer of bricks. Later houses are more likely to have two layers of bricks separated by a cavity.

The width of the wall is another good indicator. Brick walls less than 270mm thick are probably solid.

Next, check whether your walls are already insulated. If your property is less than 20 years old it was probably insulated when it was built, three-quarters of houses with cavity walls are insulated. If you are not sure, an installer can drill a small hole in the outside wall to check.

Less than 5% of houses with solid walls have been insulated, despite them leaking twice as much heat as cavity walls.

What is involved?

Cavity walls are insulated by injecting foam or mineral beads into the gap through small holes drilled in the outside wall at 1m intervals. The holes are then filled to match the existing mortar.

Experienced installers can complete the straightforward process in three or four hours, depending on the size of the house.

Solid walls can be insulated externally or internally. External insulation involves fixing a layer of suitable material to the wall, then covering it with a weather-proof render or cladding. A wide range of finishes is available.

For internal insulation, boards or stud walls with a backing of mineral fibre or sheep’s fleece are fitted to the inside of the external walls of each room. Internal insulation is disruptive, requires skirting boards and electrical fittings to be removed, and a re-plaster and redecoration of the room. It will also slightly reduce the room size.

How much does it cost?

Budget £500 for cavity wall insulation in an average three-bedroom house. External solid wall insulation can cost anywhere between £8,000 and £15,000 for a three-bedroom house.  Insulating the same property internally will typically cost between £4,000 and £13,000.

How much money will I save? 

Adding cavity wall insulation to an average three-bedroomed semi-detached house could save £150 a year through reduced energy bills and will pay for itself within four or five years. Solid wall insulation in a similar sized house could save up to £300 a year, but the higher up-front cost means that the payback period may be longer.

Fitting wall insulation also adds value to a house, and it is an effective way of raising your home’s Energy Performance Certificate (EPC) energy-efficiency rating.

Installation grants may be available from the Energy Company Obligation scheme. The rules change frequently, so check with your energy supplier or the Energy Saving Trust website for the current situation.