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understanding part L

AJ Interiors

The revised edition of Building Regulations Approved Document Parts L1 and L2 come into force on 1 April. Over the next 17 pages we look at some of the key issues for architects First things first. The revised Building Regulations Approved Document Part L (L1 for domestic, L2 for non-domestic), comes into force on April Fool's Day this year. Though there has been much talk of the transitional provisions, these do not substantially reduce liability for those of you designing buildings at the moment. As a general rule of thumb, if you have not yet submitted your scheme for Building Regulations approval, you should be designing for compliance with the new regulations, rather than the current ones. Any scheme not receiving full Building Regulations approval by 1 April will need to comply with the new regulations.

Parts L1 and L2 cost £12 and £15 respectively, with a further £27 needed to get hold of the support document Limiting Thermal Bridging and Air Leakage: Robust Construction Details for Dwellings and Similar Buildings , otherwise known as Robust Details .

This supplementary document describes good practice, thermally efficient detailing, although it tends not to concern itself with other issues of good practice detailing, so care should be taken with replicating them exactly.

Lean mix mortar in the cavities, for example, is not shown raked, DPCs do not extend beyond the face of the brickwork and sill drips are inadequate. Furthermore, insulation is shown to be crammed into the most desirable, but improbable, spaces.

If architects submit details in compliance with Robust Details , then pressure testing for domestic scale projects (less than 1,000m 2)need not be done at the end of the job, although social housing bureaucrats will inevitably want belt and braces. On a positive note, it is currently assumed that the submission of a letter of intent, stating that construction details will be in accordance with the Robust Details guidance, will be deemed to satisfy the statutory duty. The issue of design intent versus workmanship on site is key, but it would seem that the architect may not be under such an onerous duty after all - much of the liability in this scenario falls onto the contractor.

Block construction Air-pressure testing is done, on a domestic scale, by blocking up all trickle and fan vents, air bricks, chimneys, plumbing traps and so on, then pressurising and depressurising the building (see page 68).However, after showing compliance, these openings are unblocked and the building presumably reverts back to its leaky self. Half of the housing stock being built at the moment would fail this air-infiltration test.

The other aspect of the regulations seems to be a licence to print money on behalf of computer-calculation software providers.

While the elemental and target methods of calculating U-values for domestic dwellings (and the elemental and whole-building analysis for non-domestic buildings), are not particularly difficult, they will still need existing software to be upgraded.

While the carbon index (CI) method for calculating U-values in domestic dwellings allows the greatest design flexibility, it involves very complicated mathematics and will need dedicated software. The carbon emissions calculations, which may be applied to non-domestic dwellings, are well nigh impossible without expert intervention.

Advice on calculating the carbon performance rating for offices is contained in BRE Digest 457, although it is not a read recommended for the faint-hearted.

Other things to bear in mind include: if calculating on the basis of the elemental method, glazed areas should not be more than 25 per cent of the floor area (calculated from inner faces of walls, excluding internal walls but including service ducts and so on), although less than 17 per cent may be deemed insufficient for a comfortable environment. In dwellings, one in three light fittings should be for low-energy luminaires, regardless of whether the client wants them or not.

Throughout the document, seemingly hard and fast rules have provisos. For example, Part L2 stipulates the maximum areas of windows 'unless compensating measures are taken'.

Although this provides opportunities to maintain a certain amount of design freedom, the amount of human energy expended in exploring all of the calculation options contradicts the remit that the regulations will conserve fuel and power.

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