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Every little helps when it comes to reducing CO² emission rates

With dramatic reductions in CO² emission rates in dwellings coming in to force in October 2010, every bit of air leakage counts. Neil Perdell, National Technical Manager at Aico, looks at how plugging the smaller gaps can make a difference.

The Building Regulations Approved Document L1A ‘Conservation of fuel and power in new dwellings’ comes into effect 1st October, adding a significant 25% improvement to annual CO² emission rates from the previous 2006 standards.

Furthermore, party wall heat loss has to be rated at zero. Air flow in the cavity provides a heat loss mechanism – when outside air is able to flow into the party wall cavity a cold zone is created leading to heat flux through the wall sections on either side. These air movements are now recognised as significant and can result in substantial heat loss. To reduce heat loss to zero, the at-first-obvious step is to fill in the cavity, but this may end up contravening another part of Building Regulations – Part E, resistance to the passage of sound.

You can’t get around this particular problem by ‘offsetting’ either – the zero heat loss from party walls is non-negotiable and is in addition to the targeted improvement of 25%.

There are numerous products and design ideas that can help dramatically reduce air leakage through the major ‘offenders’ such as doors and windows. But with an extra 25% improvement required, developers need to go one step further and look to other sources of air leakage in a dwelling. What about air that leaks through holes in the walls made for sockets and switches and for recessed lighting such as downlights and service penetrations? Wherever you make a hole, air comes through, even when a product has been installed in that gap.

Current Energy Saving Trust best practice guidelines recommend a target of three cubic metres of air leakage per hour, per cubic metre of room volume, at the test pressure of 50 Pascals. Testing of typical double recessed sockets and downlights at Chiltern International laboratories show that at 50 Pascals they leak air at a rate of 3.7 and 19.7 cubic metres per hour respectively. Therefore if a room of 22 cubic metres had two recessed downlights and 10 recessed double switch/sockets it would fail, even if the rest of the room had zero leakage, which it certainly would not.

The good news is that the solutions to air leakage are already at hand for both recessed downlights, switches and sockets in the form of downlight ‘loft covers’ which simply sit over the downlight to prevent air leakage and switch / socket inserts which are preformed and are placed within the recessed back box of the switch/socket box. Aico can provide such products in the form of Loftcap loft covers and Firecap switch/socket inserts. The Loftcaps have the added benefit of meeting the Capped F standard, which means it is completely safe to lay loft insulation directly over them, preventing more critical energy losses. This is in line with Building Regulations Part L, which calls for uninterrupted coverage of thermal insulation in loft spaces to minimise heat loss.

Both loft covers and switch/socket inserts are inexpensive and can reduce air leakage by up to 80%. They also offer full fire protection (so are ideal for party walls) when fitted, which is also compulsory in many circumstances.

Although it is fair to say, that the electricians contribution, in the form of reducing air leakage from downlights, sockets and switches, is never going to achieve the new CO² emission rates alone – it is also essential to look at windows, doors and even airtight membranes. However, without addressing the former, developers are unlikely to meet the new regulations. A whole approach needs to be taken if the new emission rates are to be met.

And as a final aside, I should point out that whilst L1A deals with new properties, Reduced Data SAP which is used for Energy Performance Certificates for existing dwellings, is due for revision very shortly and is likely to be aligned with SAP 2009. Here, loft covers in particular provide a simple, convenient and highly cost-effective means of reducing air leakage in existing properties.

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