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u-values

Changes to Part L of the Building Regulations

On the 1st October 2010 changes to Part L of the Building Regulations come into effect. Part L deals with how well a building conserves fuel and power.

Whilst garden rooms don’t have to comply with Building Regulations unless they are over 15sqm and used for sleeping accommodation, many garden room suppliers do build their garden rooms to Building Regulation standards – which is a good thing!
Many garden room suppliers state that their buildings u-values (the rate at which heat is lost from a building – which Part L controls)out perform the Building Regulation standards for new buildings, which is a great selling point as it means the garden room will be comfortable to use all year round and cost effective to run.

So what is a u-value? It’s the measurement of the transmission of heat through an element such as a wall, roof or glass. In timber frame construction each element of the wall, such as the exterior cladding, sheathing, studwork, insulation and plasterboard will have a u-value and a garden room designer can work out the combined u-value of the wall, the lower the combined u-value the better performing the wall. U-values are expressed in W/m2 which equals the amount of heat in Watts that is lost per square meter of material. For example a wall with a u-value of 0.30W/m2 will lose 0.30 Watts for every m2 of surface area per degree of temperature difference between the inside and outside of the building.

The changes to Part L from 1st October 2010 lower the target u-values for walls, floors and roofs (remember the lower the u-value the better) meaning that garden rooms built to these new Building Regulation standards will perform even better. Below is a table of the existing u-values for a new build and the figures for 1st October 2010 onwards.

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As a customer it is important that you check the claimed u-values of a garden room with this table, especially if your supplier claims to exceed the Building Regulations for a new build house!

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Not just timber frames

Traditionally garden rooms are made from wood and the construction techniques used are taken from timber frame house building, but new technologies and combinations of materials are being used to build garden rooms.

Materials such as steel, aluminium and PVCU (formally known as UPVC before Europe intervened!) are replacing the use of timber in garden room construction. These materials have benefits over timber in that they are generally quicker to install and need less maintenance than timber. However on their own these materials are generally not as thermally efficient as wood so you need to check with the manufacturer what insulation they use, and in turn what the u-values of the building are.

Building regulations in the UK currently state that walls of a house should have a u-value of 0.27, floors 0.22, flat roofs 0.16 and pitched roofs 0.20,  whilst garden rooms are not bound by building regulations (unless being used as sleeping accommodation) to perform well they should have similar u-values as a house. The lower the u-value the better the thermal performance.

Steel and aluminium normally have a powder coated finish; this is hard wearing and needs little maintenance. In steel and aluminium garden room construction the panels are made from a sandwich of exterior sheet metal – insulation – interior sheet metal, whilst the interior surface is coated in a light reflecting colour such as white or cream you need to be aware that your internal walls will be metal and often have joint covers – not that this is a bad thing!

PVCU doesn’t just come in white but comes in many colours or wood effects and like the metal options it does not require painting. PVCU and modular metal garden rooms are very quick to install – some suppliers can completely install a garden room in just one day!

So if you are looking for an almost zero maintenance garden room take a look at the companies that build in steel, aluminium and PVCU.

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