Your responsibility under Part L 2006
From April 6th 2006 the latest revision to Part L will have a major influence on the very nature of rooflight design, construction and, incorporation. In summary, the thermal performance of the whole constructed building envelope has been upgraded by reducing the permitted 'U' values for each thermal element, including ‘controlled fittings’ such as doors, windows and rooflights.
How to comply
There are some key details that will affect the rooflight element of your project designs which are detailed as follows:
L2A & L2B—New and Existing Buildings, Other than Dwellings.
• The percentage of roof area that must be given over to rooflights is prescribed at a minimum of 10% under the new Part L changes and, could be as high as 20%.
• The 20% area will only permissible if there is a provision within the design of the rooflight for limiting solar overheating—usually shading, solar control glazing or simply the orientation of the unit.
• The 10% figure assumes a light transmission of 70%—if lower, then the area devoted to rooflights must be increased proportionately.
• Generally, rooflights will be required to have a ‘U’ value of 2.2 W/m²K or better, including the upstands, which were previously excluded.
• Finally there will no longer be a ‘trade off’ against other parts of the roof, except under special circumstances.
L1A & L1B—New and Existing Dwellings
• All ‘U’ values quoted refer to the ‘whole’ unit including upstand.
– New build—rooflights must have a ‘U’ value of 2.2 W/m²K or better
– Refurbishment—New controlled fitting must have a ‘U’ value of 1.8 W/m²K
– Replacement—must have a ‘U’ value of 2.0 W/m²K
• Adequate levels of daylight must be provided as detailed in BS 8206.
General
• All rooflight units, regardless of design and use will be required to achieve an ‘Air Infiltration’ performance of better than 10m³/h/m².
• All rooflight units must be designed without cold bridges.
