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The housing sector

understanding part L - A government initiative to provide a better understanding of the regulations was informative but should have been held sooner

The 'Achieving Energy Efficiency in New Housing' day school organised by the BRE Energy Conservation Support Unit (BRESCU) to discuss Part L1 of the building regulations was a very enlightening event.

Presumably the government, recognising its absolute laxity on promoting or delivering information to architects on the changes, finally realised that it had to do something.

Hopefully the series will be repeated, but even now it is too late for many.

The objective was to examine the housing element of the revised approved document, but also to explain some of the technological requirements and assumptions behind the changes.

Cruel to be kind Clive Clowes of the Housing Corporation boasted that 'the Housing Corporation is endeavouring to take waste minimisation and saving the planet quite seriously', such that it will be demanding 'even higher standards of compliance' than the new Approved Document Part L1 in its forthcoming updated design guidance. He noted that contractors would get 'short shrift' if completed buildings failed the air-infiltration tests and be required to 'put it right'.

Since it is an organisation that follows its design criteria to the letter, I can only begin to imagine the nightmare for some contractors. 'Some may learn the hard way, ' said Clowes, 'but they'll only make a mistake once.'

Phil Jones from the Welsh School of Architecture noted that European Directive 2004 is the driver for future change, and that there may be significant legal duties on architects over and above those contained within the revised document Part L1.

The new Part L now applies to material alterations, replacement of windows (glass and frame combined) and the boiler's commissioning information (which must be handed to the client). 'Reasonable' requirements will pertain so that work on historic buildings complies. On this last point, Ian Orme of Rickaby Thompson Associates noted that 'reasonable' may be interpreted differently by conservation officers and building control officers, but that decisions w ill have to be reached.

Theoretically, new buildings will be 25 per cent more energy efficient, but build costs will be between £600 and £1,400 more for a traditional construction family home.

Elemental method In a very informative talk, Robert Bilbie raced through the main changes to the document and some of the methods for calculating adequate U-values.

Housing must be shown to achieve compliance through either the elemental method, the target U-value method or the carbon index method.

The elemental method is the easiest - simply reading off the tables in appendix A in classic style - but it can be used only if the boiler has certain minimum efficiencies. To find details of all boiler efficiency ratings, visit www. sedbuk. com, which lists 200 mains gas boilers that meet the minimum SEDBUK (Seasonal Efficiency of Domestic Boilers in the UK) rating of 78 per cent (approximately half are condensing and half are non-condensing). For oil boilers, only 10 per cent of those listed are condensing.

Appendix A is 22 pages of U-value calculations and construction specifications demonstrating appropriate thicknesses of insulation.Meeting the new improved standards is a straightforward matter of increasing the thickness of insulation. However, for an insulation with a K-value of 0.04W/mK (approximately the conductivity factor of standard mineral fibre), the insulation thicknesses will be in the order of:

-above flat (concrete) roof - 150mm;

-between joists - 100mm between joists and 150mm above;

-between rafters - 350mm; and lfloors - 109mm for floor slabs, 114mm for suspended floors.

As you can see, the rafter case is bad enough, but the floor requirement is nearly double what is currently required. This will be very difficult to address when carrying out remedial works, so other calculation methods, trading off elements, may be necessary (see below).

External walls of 102.5mm brick, 100mm cavity, 100mm lightweight aggregate block inner leaf (density 1,400Kg/m 3), 13mm plaster inner face and 50mm partial fill (thermal conductivity 0.025W/m 2K) will achieve a U-value of 0.35W/m 2K(although it is a fair bet that the Uvalue of external walls will be reduced to at least 0.3W/m 2K in the next round of revisions scheduled for 2005).

The hype that the new regulations would see the end of timber-frame construction or brick/block construction (depending on which lobby you listen to) and cavity construction were obviously mistaken, but insulation standards are going to have to increase if traditional construction details are to continue. Whether that is with thicker insulation or insulation of the same thickness but better thermal conductivity is open to interpretation (and budget).

Glazing must now meet the required U-value of 2 or 2.2W/m 2K - the U-value of metal windows is slightly more lax than for timber or uPVC to allow for 'additional solar gain due to the greater glazed proportion'.

Target and carbon index The target method allows for more flexibility of design in that you do not have to rely on rigorous compliance with the U-value tables set out above.

Trade-offs can be made between insulation standards and services - lower wall U-values for higher boiler efficiency, for example. It also makes an optional allowance for solar gain.

Even though the SAP calculations do not feature in the new document, you will still have to carry out the calculations to show compliance in accordance with SAP 2001, The Government's Standard Assessment Procedure for Energy Rating of Dwellings. One of the key changes to the assessment procedure, which factors into the U-value calculations, is that there must not be any significant thermal bridging or gaps within the structural elements exposed to the external conditions. To this end, mortar joints, wall-tie conductivity and plaster dabs will have to feature more recognisably in the calculations, known as the combined method. The Robust detail sheets, published by the Stationery Office, are also means by which details can be shown to be compliant (see page 71).

Internal lighting must provide at least one room in three with lighting sockets for fluorescent lamps (note that the hallway, landing and stairs are evaluated as a room for the purposes of this lighting requirement). In essence, a standard 2-D fitting will suffice.

See-through evidence Ian Orme presented some of the instruments of torture that will be used to confirm a building's compliance. The domestic scale fan pressurisation device is a decidedly unimpressive contraption. Assembled in a few minutes compliance will be met if the air permeability of the dwelling falls below the required maximum of 10m 2at 50Pa.

The fan pressurisation technique is applicable to new and existing houses and allows both the air leakage characteristics of the dwelling to be determined and the leakage routes to be traced, using either a smoke generator or a thermal imaging system.

Leakage typically occurs at any of the many penetrations of the external envelope - plumbing services, windows and doors, the junction of the intermediate floors with the walls and at the eaves, for example.

The test is carried out using a fan mounted in a dummy door (the original door remains in place during the test) which is used to blow air into, (pressurise) or suck air out of (depressurise) the dwelling. The air leakage characteristics are determined by measuring the rate of airflow through the fan that is needed to maintain a given pressure differential. The air permeability is given by dividing the air leakage rate at 50Pa by the surface area of the building envelope.

Blowing hot or cold The government's home energy efficiency best practice booklet, Post-construction Testing - a professional's guide to testing housing for energy efficiency, introduces thermography, the process of obtaining images of heat loss from a building's surface and a technique for measuring the U-value of an element on-site.

All surfaces above absolute zero (-273K) exchange radiant energy with their surroundings. The total amount emitted is mainly a function ofthe surface temperature and the emissivity of the surface (its ability to emit thermal radiation). The thermal imaging system senses this radiant energy and converts it in its basic form to a black-and-white image.

Lighter areas on this image represent warmer surface temperatures, darker areas cooler surface temperatures.

Images can then be colour enhanced to improve the definition between areas.

When used to examine a building, the technique can quickly identify areas of unexpectedly high heat loss, such as that caused by a thermal bridge or an area of missing or poorly installed insulation. The survey results provide a permanent record of the pattern of heat losses occurring from the building surfaces, which can be used as a record for checking the performance of buildings of a similar form of construction and informing the design process to help avoid similar defects in the future. Orme warned that a genuine inspection could cost up to £1,500 (a cheaper survey could imply that those carrying it out are not experts in the field, leading to distorted results).

Thermal images of both the interior and exterior surfaces of the building can indicate potential problems within the construction. The image at the top of the page shows the impact of missing blown-fibre cavity wall insulation from the outside of the home. An injection point has been missed by the installer and the insulation does not fill the cavity.

The thermographic technique provides a rapid, non-intrusive method of scanning the building for thermal anomalies and can help improve the performance of the building envelope.

The day school was wound up with a couple of workshops exploring the merits of the Robust Details and the SAP calculations. In all, this was a very worthwhile event, but it's sad the government has waited this long to try to educate those who most need to have information on the changes. It seems that all the seminars programmed for February were sold out months in advance. If they re-run them, try to get a place. Better late than never.

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