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Devil in the details

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understanding part L

The government has issued detail drawings which offer guidance on Part L compliance. In our Part L feature (AJ 28.2.02) we challenged readers to criticise them

Top of the class First prize went to Alan Novitzky of Sheffield. His criticism on the errors in the two details, reproduced in AJ 28.2.02, are listed below. The prize went to the first correct answer. Because of the number and speed of responses to this competition, a runner-up prize went to Pam Cole, also of Sheffield.

Winning entry 1.Window shown too far forward to be sure that condensation will not take place at the head and reveals.Rain penetration is also more likely in this position.The window frame would be better tucked into the rebate formed by the outer skin of brickwork, in the traditional manner.

2. The insulation board inside the lintol is insubstantial, liable to displacement and likely to allow thermal bridging.Complete fill lintols would be better.Also, there is no indication that the lintol has a separate dpc laid over it, to conform with good practice.

3. There is no fall shown on the parapet capping with a consequent risk of water penetration at joints.

4. The vapour control layer should be dressed up inside the face of the blockwork and sealed to prevent vapour transmission and interstitial condensation.

5. The relationship of the 'flashing'to the roof membrane and to the angle fillet is unclear.

The angle fillet should be of the same material as the insulation to avoid membrane damage due to differential movement.The membrane should also be dressed up a minimum 150mm behind the so-called flashing.But, if the fillet is timber, as the diagram suggests, there should be a minimum 150mm high curb, fixed to the decking insulation, allowing movement free of the wall.The membrane should be dressed over it, behind the flashing.

Alan Novitzky, Sheffield S17 4HT Runner-up 1.No cavity tray to the parapet wall, or supported dpc below coping.

2. Roof membrane upstand is not a flashing, and the flashing shown is woefully inadequate in downstand length.

3. Vapour control layer should not stop at junction with wall but turn upwards to enclose insulation and be sealed with capsheet.This is an incorrect warm roof detail.

4. Thermal bridge at top of steel lintel, through block to cavity void.

5. Thermal bridge at window head (with such a poor insulation detail to lintel, the window opening should have separate insulation board at head).Use full foamfilled lintels.

6. Wall tie sitting on top of steel lintel flange is a poor detail; the block may not be properly bedded and tend to rock on the wall tie.

7. Lintels require dpc trays in exposed situations.

Pam Cole, architect and architectural technology lecturer, Southampton Institute, e-mail pam. cole@which. net A large number of e-mailed entries are listed on the AJ discussion forum at www. ajplus. co. uk. All of these comments have been forwarded to the DTLR and BRE.

We welcome further comments on the Robust Detail sheets as well as comments on the criticisms.

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