Heat loss and insulation

The savings and comfort benefits of good insulation, once installed, are continuous. The cost of insulating all or part of the house is soon offset by the savings in heating bills. Other benefits include reduced likelihood of condensation, improved comfort and even a cooler home in summer.

In a typical home, 25 per cent of the heat goes through the roof (more in a bungalow), about 35 per cent through the walls, 10 per cent through the windows, and 15 per cent in draughts, while another 15 per cent is lost into the ground, so that improving insulation leads to significant reductions in heat requirements.

Roof insulation

A layer of mineral fibre insulation laid between joists in the loft will substantially reduce the 25 per cent of heat loss through the roof. The new U.K. Standard is met by a 50 mm thickness but at least 75 mm is recommended. This is close to the standard adopted by most European countries with the exception of Belgium which advises between 150 mm and 200 mm and Sweden and Norway where 250 mm to 400 mm is used.

Mineral fibre insulation comes in rolls and works rather like an eiderdown trapping the air and providing a heat barrier. Cold water tank and pipes in the attic must be lagged as well, but make sure that the underside of the cold water tank is left uninsulated to minimise freezing in cold weather.

Other methods of roof insulation include expanded polystyrene impregnated fibre insulation board, rigid polyurethane and expanded laminated polystyrene/ plasterboard, fixed to rafters, but generally these materials should be installed by professional tradesmen and only flame retardant or self-extinguishing materials. Should be used.

Cost of roof insulation—which can be a fairly simple do-it-yourself job—is from about £30 for the materials.

Wall insulation

The main purpose of cavity walls is to prevent rain penetrating to the inner leaf or wall but it can be made a lot more effective by filling the cavity between the inner and outer leaf with special insulation materials.

The reason a house loses heat through its walls is straightforward. The heat you put into your house heats the whole structure of the place including the inner leaf of bricks. This in turn heats the air and, through natural convection, this air will eventually finish up touching the outer leaf of bricks to which it will transfer the heat. This heat, plus the heat passed from the inside by radiation, gradually escapes so it is the outside air that gets the benefit.

The object of good insulation, there- fore, is to hold the air in the cavity station- ary and reduce loss by radiation. This is done by pumping into the cavity either a foaming resin (ureaformaldehyde) or mineral fibre. It is a simple matter to do this when the house is being built and, now, not all that difficult to do in existing houses. Cavity wall insulation must be under- taken professionally. Holes are drilled in the brickwork joints at regular intervals then either foamed ureaformaldehyde (which sets after a few minutes) or mineral fibre is injected forming a low-density insulating infill. The holes are then re- pointed and the brickwork left with little sign of disturbance. This type of insulation forms a highly efficient heat barrier and if expertly carried out it is most unlikely that any moisture could invade from the outer leaf.

The work of cavity insulation takes about one day and the cost varies according to the size of house. A small semidetached house could be foam-filled for around £130. A medium sized detached house would cost around f150. Injected mineral wool fibre costs slightly more in an existing house, slightly less in an estate of houses under construction.

Existing property with solid walls can also be insulated but not quite so easily. The most effective method is to line the walls with an insulating material combined with a vapour barrier on the warm side to prevent the penetration of warm, moist air, which could otherwise condense on the inner cooler surface. One way of doing this is to fix slabs of glass fibre between battens which are attached to the wall and held in place by the moisture barrier material. Another method is sticking polyurethane laminated plasterboard to the walls. This is usually suitable for older properties being converted or modernised but advice is needed from a building or insulation specialist.


Draughts are not just annoying, they are costing money by increasing heating bills. Just how much can be judged by the fact that an ill-fitting door, front or back, with only a 3 mm (I inch) gap around it is the equivalent to a 174 sq cm (27 sq inch) hole letting in cold air.

Draught excluders—obtainable from most hardware stores—can be fitted to doors and windows very cheaply. Plastic backed foam strips can be easily stuck around window frames and the tougher phosphorbronze strip nailed all the way round the door frame.

Unused chimneys should also be sealed to cut down heat loss by blocking up the fireplace opening and fitting a ventilation cap at the top of the stack. A ventilation grille either in the chimney breast or in the material blocking the fireplace will also be needed to allow air movement which prevents the build up of condensation.

The one danger is of getting carried away and draughtproofing everything in sight. Houses and people need ventilation and to exclude all air ingress will lead to condensation problems as well as personal discomfort. Concentrate on draughtproofing doors to the outside, all windows, and fireplace openings for simple and significant reductions in heat losses.

Floor insulation

Insulation for suspended floors is often neglected yet the saving can significantly reduce the 15 per cent of the total heat loss from a house. Sometimes a thick carpet with ample underlay is satisfactory, but for really effective insulation some form of insulating material, such as glass fibre, should be included below the floor surface. With suspended floors where there is a crawl space underneath, much can be done to cut down the heat loss by lining the underside of the floors with rolls of paper-backed glass fibre or expanded polystyrene sandwiched in building paper.

Care must be taken not to mask the natural ventilation necessary to prevent dry rot or other damage to woodwork. In a room where a carpet is not completely fitted, excessive draughts and air changes often occur through shrinkage between the skirting board and the floor. This can easily be remedied by nailing a wooden fillet to the floor close up against the skirting. Hot water tank If your hot water cylinder has no lagging, heat is lost unnecessarily and money wasted. For without a lagging jacket enough heat for up to 16 baths a week can be lost. Put another way, this is enough electricity to keep one bar of an electric fire going for 80 hours!

Many electric hot water cylinders are supplied already insulated. If not, a 75 mm (3 inch) lagging jacket, or a box filled with loose insulation should be placed around the cylinder. It is very easy to do. Even a well insulated cylinder will give enough warmth to “air” the clothes in the airing cupboard. Hot water pipework, too, should be lagged to reduce running costs further, and also make sure to lag exposed cold water pipes to avoid freezing.

If the tank has really good lagging you have no need to turn the immersion heater off when you are out during the day or overnight (unless you are one of the numerous users of the White Meter or other off-peak tariff). A time switch may give you further economy but the cost of the switch and installation should be set against fuel saving.

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