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Devil in the details

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understanding part L - A new collection of detail drawings offers guidance on Part L compliance. But are they sufficiently robust to be relied upon?

The loose-leaf binder Limiting Thermal Bridging and Air Leakage: Robust Construction Details for Dwellings and Similar Buildings is published by the Stationery Office on behalf of the Department of the Environment, Food and Rural Areas and the Department of Transport, Local Government and the Regions, and contains 136 'detail' drawings showing how to build to 'higher energy-efficiency standards'.

This is a visual version of an approved document.

Rather than insisting that the guidance be followed, it hints that if its recommendations are adopted then compliance with the requirements of Part L will be deemed to be satisfied. But it is not prescriptive and other methods of compliance will be countenanced if they meet the requirements of the statutory instrument.

Unfortunately, as a set of technical details, they are distinctly unimpressive and make one long for the NHBC Technical Manual standards or Mitchells or Roy Chudley. Though the booklet says that the aim of the details is to 'reduce risks and potential problems that can arise as a result of building to higher energy-efficiency standards', citing the increased possibility of rain penetration, they seem not to have dared to consider aspects of detailing beyond the broader remit of reducing interstitial and surface condensation. And even these details are questionable. Given that the buildings will be warmer and tighter, any weak spots will pose a higher potential for condensation build-up.

The problem for me is that, though they deal with their prime area of concern - ensuring that insulation is as effectively 'lapped' as possible to minimise thermal bridging - they are not sufficiently robust to be copied, or relied upon, and used as working details. Nor do they explore the physics of good detailing. Bring back BRE good practice report Thermal Insulation: Avoiding Risks;

all is forgiven.


Statutory documents available from the Stationery Office (tel 0870 600 5522):

-Building Standards (Scotland) Regulations, Technical Standards, Part J, Conservation of Fuel and Power , 2002 edition lBuilding Regulations Approved Documents L1 and L2, Conservation of Fuel and Power , 2002 edition lLimiting Thermal Bridging and Air Leakage:

Robust Construction Details for Dwellings and Similar Buildings , DEFRA/DTLR, The Stationery Office, 2002 Guidance The government's Energy Efficiency Best Practice Programme Guides (available from 0800 585794):

-'Central heating system specifications', General Information Leaflet 59 l'Energy-efficient ventilation in housing', Good Practice Guide 268 -'Energy-efficient lighting', Good Practice Guide 199 l'Energy-efficient refurbishment of existing housing', Good Practice Guide 155 l'Post-construction testing', General Information Report 64 l'Energy efficiency in new housing', Good Practice Guide 79 l'Controls for domestic central heating and hot water', Good Practice Guide 302 Also -'Thermal insulation: avoiding risks. A good practice guide supporting building regulations requirements', BRE 262, 1994


The first person to write to Austin Williams at the AJ by 10 March, highlighting five non-robust aspects within the above details, will win a copy of a new technical design manual on environmental science.austin. williams@ construct. emap. com Articles l'L is for low heat losses', AJ 3.5.01 l'How much do U-value glazing', AJ 17.1.02

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