Colorcoat® Column:Integration of rooflights with pre-finished steel cladding systems
In-plane rooflights can easily be included into profiled pre-finished steel roof systems requiring no modifications to the secondary steelwork and can supply light deep into large single storey buildings. Natural lighting, as well as providing benefits to the building occupants, can reduce energy costs and CO2 emissions, provided a balanced approach is taken to solar gain, heat losses and lighting levels.
What factors do I have to consider when installing rooflights?
The building designer needs to consider each building individualy as the operating conditions and building construction can greatly affect the requirements.
Rooflights can provide very significant savings in artificial lighting and associated CO2 emissions but only if they are installed in conjunction with an efficient automatic control for the electric lighting and cleaned on a regular basis.
The U-value of rooflights is significantly worse than the surrounding insulated cladding and more heat can be lost through the rooflights than through the entire insulated roof cladding. This has to be balanced against useful solar gains and reduced artificial lighting requirements.
Higher performing rooflights are available which can significantly reduce heat losses, however these are more expensive and this needs to be balanced against saving from other building envelope or service enhancements.
24 hour operations and introduction of high bay racking, within a building will greatly reduce the effectiveness of rooflights and increase use of artificial lighting.
How do I take these factors into account when modelling the building?
The introduction of rooflights can have a very significant effect on the CO2 emissions of a building, both in terms of compliance with Part L and actual building operations.
SBEM using the national calculation methodology (NCM) is a Part L “compliance modelling tool” and should not be used for “design modelling”. It calculates the CO2 emissions for an empty building using defined operating parameters. These parameters may be very different from those under which the building will actually operate and the results may therefore be quite different from operational performance. The NCM does allow direct comparison of the performance of similar buildings and this can be used to calculate energy performance certificate ratings for the buildings.
Where hours of operation and operating conditions are significantly different from those defined in the NCM and where high bay racking is likely to be installed, it may be beneficial to carry out specific design modelling to optimise lighting parameters for the actual building operations.
Even when specific “design modelling” has been undertaken it is a requirement of Approved Document L to meet the criterion for CO2 emissions which must be done by compliance modelling using the NCM.