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.

Rolls of InsulationUntil relatively recently insulation found in the average home was minimal; a 100mm (4") depth of glass fibre blanket in the loft was the norm for many years and, prior to that, even just 25mm (1") was acceptable.

In the last 20 years, with increased concern about the environment, much has been done to improve matters and the current Building Regulations stipulate many areas which must be insulated, and to what degree, in a new build. For example, the current specification for loft blanket insulation is for a 250mm (10") depth. Wall cavities too must now be insulated with rigid sheet insulation material.

Floors must include an insulation layer, usually in the form of a 50mm (2in) layer of flooring grade expanded polystyrene in a solid floor. A suspended wooden floor will have rigid insulation material mounted between the joists.

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.

Loft InsulationPart 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.

Calculation Examples

A 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

A room (7m x 4.5m) in a bungalow with 2 external
walls, a patio door (4m x 2.2m) and a window
(1.5m x 1.5m), insulated to the latest regulations,
with a 20°C temperature difference, will lose
around 900W - equivalent to a 1 bar electric fire.

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.

Although individual heat loss figures are 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 will be needed to keep it at a steady temperature.


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Springvale manufacture a wide range of products for the construction industry. We have thermal insulation systems suitable for use in floors, walls and roofs. Foundation protection materials & tools are available for civil engineering and groundwork applications. Website




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