Roof Lantern Drawings. The drawings below illustrate our standard methods of traditional lantern construction. We recommend non-stepped units, i.e. the glass is secured in place with purposely designed channel.
Our default roof pitch is 20º, but we do produce lanterns with steeper slopes. In most situations 20º is perfect to avoid obscuring first floor windows too much.
The flat roof itself is often quite thick, with Building Regulations requiring 150mm PIR insulation on a warm deck. This insulation sits on top of the joists, so the build up of the flat roof is likely to be around 400mm above ceiling level. On top of that there is the kerb upstand on which the roof lantern sits, which is usually required to be a minimum of 150mm, therefore the underside of the lantern is already quite high.
This is our standard section, non-stepped double-glazed units with the ringbeam sitting directly on the kerb upstand.
The internal and external finals as well as the internal cornice are all optional extras.
Some clients prefer the extra detail, others prefer simplicity.
The rafters are typically 45mm x 95mm with 24mm double-glazed units.
Depending on the span and design, hip rafters may be slightly deeper than this. A concealed cable groove can be factory-fitted into a specified rafter to hid the. cables for any electrical roof vents or central lighting.
Triple-glazing has a u-value of 0.7 W/m²K compared to 1.0 W/m²K with double glazing.
Glass units with a 70mm step to top sheet. Once widely used in the industry, stepped units are now less common.
The side windows are made to measure, however a height of less than 300mm is generally not recommended. Whilst it is feasible to fit opening vertical windows, an opening roof window is a more effective and aesthetically pleasing option.
