68
EXTERNAL ENVELOPE
is often a key stipulation from planners with any heritage properties, and importantly for a retrofit scheme. It also plays an important role in thermal efficiency. Sitting flush with the roofline reduces the roof window’s exposure to the elements and therefore enables the rooflight to retain more heat. Guidelines for flat rooflights and pitched roof windows are found in Part L of the Building Regs. They specify the appropriate whole window and centre pane U-values for different building environments. Building Regulations make allowances for heritage properties to use centre-pane values for thermal efficiency calculations. However, centre pane values will only measure the glazing’s thermal performance. These values tend to be lower than whole unit calculations since they don’t take into consideration the frame and supporting components. The Rooflight Company discloses both whole window U-values and centre pane U-values for rooflights and skylights, thereby supporting designers in calculating the true performance improvement of a retrofit scheme. Each heritage property possesses its own unique history and charm. Consider the 1839 Derby Roundhouse, once a hub
for steam engine production – the site fell into dereliction throughout the twentieth century. An unusual polygon of sixteen sides, 58 metres in diameter, the space is lit from a dome-shaped roof some 15 metres above the ground. The Grade II Listed Building has been sympathetically restored as part of Derby College.
The roof provided one of the few opportunities to improve the building’s thermal performance. The work involved reinstating a ring of 48 trapezoidal roof lights within the existing timber frame, of which 36 open remotely using electric actuators. As every facet was unique, scanning technology was used to map the entire roof structure and build a 3D CAD model of the rooflight that ensured millimetre accuracy and enabled the construction team to work within the historic constraints of the existing building. The result was a sympathetic renovation, keeping the look and feel of the original building, without compromising on modern performance.
Keeret Eden is innovation manager at The Rooflight Company
ARMATHERMTM
STRUCTURAL THERMAL BREAK
Extension for Tekla Structures that creates Armatherm Thermal Break connection/plate. The component automatically takes the plate
dimensions and holes of the place it is fixing it to.
Request a quote or visit our website: +44 1274 591115
INFO@ARMATHERM.COM
WWW.ARMATHERM.COM ADF06_Armatherm /
Armadillo_HP.indd 1
WWW.ARCHITECTSDATAFILE.CO.UK 07/06/2023 08:39 ADF JULY/AUGUST 2023
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