Many people view the Building Regulations specifications for insulation as a niggling set of rules that add extra cost and trouble to a project - but this is far from true. A correctly insulated home will be more comfortable to live in and, importantly in this age of ever increasing energy prices, less costly to heat. Although saving money is a powerful motivator, the need to conserve energy should be an equally important consideration.

Apart from the building itself, the plumbing within should also be considered for insulating. Almost all modern hot water cylinders come with a pre-formed polyurethane foam jacket instead of requiring the, often badly fitting, lagging jackets that used to be commonplace. All pipework runs should be insulated to avoid unwanted heat loss into under-floor cavities, or the loft space, and to help prevent freezing in winter. Pipe insulation takes the form of extruded tubular foam with a central hole corresponding to the diameter of the pipe. The insulation can either be slid along the pipe before the joints are made or, as it is often pre-scored or pre-slit, can be slipped over the pipe afterwards. While some runs of central heating pipework can be left uninsulated if the heat loss will contribute to the warming of the house, heat loss in hot water supply pipes has the knock-on effect of wasting water when having to repeatedly flush out dead-legs of cold water and should be avoided.

Part L of the Building Regulations - Conservation of Fuel and Power, covers the subject in detail and should also be read in conjunction with Part F (Ventilation) as, although one of the main losses of domestic heat is due to draughts, one should not build a completely sealed box, but one that allows fresh air to circulate. To this end high efficiency heat exchangers are now built into "Heat-recovery ventilation" devices. These expel stale air from the building but not before they have removed any residual warmth and used to it heat fresh air drawn in from outside.

When reading Part L or any documentation concerning itself with insulation, one will come across references to U-values. A U-value is a measure of how much energy a given insulation material will transmit from one side to the other; in practical terms, how much heat the insulator will allow to be lost through it. The lower the value the better the insulation. Part L of the Building Regulations lays down exactly how much heat loss is allowed through the various external parts of a building so insulation material matching, or beating, these U-values must be used.

Although a strict understanding of the maths isn't needed when dealing with U-values it can be interesting to see how these values are related to the real world. U-values are given as W/m² K or, more simply, a measure of the heat energy (Watts (W)) that a given material will conduct away per square meter (m²) and for every degree of temperature difference (Kelvin (K)) between the two sides. Kelvin is a measure of absolute temperature and has identical size units to Celsius - thus 0°C is 273K, 25°C is 298K and 100°C is 373K. Since we are only interested in a temperature difference between inside and outside it can be taken as read that 1° Celsius is 1° Kelvin.

So, for example, a typical double glazed window of 1.5m x 1.5m with a U-value of 2.0 and a temperature difference of 20°C will lose:

      (1.5 x 1.5) x 2.0 x 20 = 90W

By comparison a 4m x 2.4m external wall with a typical U-value of 0.35 will only lose:

      (4 x 2.4) x 0.35 x 20 = 67.2W

Although a little meaningless on their own it's worth remembering that adding a full list of these heat losses together for a room shows just how large a heat source needs to be to keep it at a steady temperature. Another example: A sitting room (7m x 4.5m) in a bungalow with two external walls, a patio door (4m x 2.2m) and a small window (1.5m x 1.5m) and insulated to the latest regulations, again with a 20°C temperature difference, will be losing approximately 900W; the equivalent of a 1 bar electric fire.

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isover offers a large range of solutions for wall, roof and floor insulation with external cladding, cavity fills, etc.

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