Ian Dryden, National Specification Manager Bituminous Membranes at SIG Design and Technology, discusses best practice for incorporating modular rooflights into flat roofs with Architecture Today’s Technical Editor John Ramshaw.

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Modular rooflights provide a relatively easy and inexpensive method of bringing daylight into buildings. However, as with many seemingly simple design items, there are a bewildering array of different products and systems to choose from. Ian Dryden, National Specification Manager Bituminous Membranes at SIG Design and Technology, in discussion with Architecture Today’s Technical Editor John Ramshaw, explores best practice for incorporating these essential devices into flat roofing projects.


SIGnature Glasslink factory glazed modular rooflights can span up to 3.8 metres with unlimited length

What is a modular rooflight and what are the main types available?
Modular rooflights come in standard sizes and are designed to be easy to install by roofing contractors and competent trades people. They are usually made from polycarbonate or glass. The latter tend to be specified for their superior sound insulation and solar control, as well as aesthetic performance. They are also chosen for applications where weight and access are not issues, and where the rooflight needs to be within 1.5-metres of a compartment wall.

Domed polycarbonate modular rooflights are particularly suited to completely flat roofs down to a zero-degree pitch, where clear glazing is needed but heat gain is less of a concern, and refurbishment projects where weight is an issue or the roof is completely flat.

Clear polycarbonate rooflights installed in a green roof

What considerations should be made for the roof pitch?
Modular rooflights are designed to be installed at the same pitch as the roof, which in the case of SIG’s SIGnature range can be from 0-15 degrees. Glass units used on flat roofs should always be installed with a pitch of at least two degrees to eliminate ponding.

What about thermal performance?
All our SIGnature glass rooflights exceed current Part L requirements (minimum 2.2W/m²K). Triple-skin polycarbonate dome rooflights will also comply with Part L, whereas double-skin units will not.

These polycarbonate rooflights have been damaged by UV light making them unsafe and in need of replacement

Is weight an issue?
Polycarbonate rooflights can always be installed by hand. By contrast, some glass units can weigh up to 300kg necessitating crane installation, which in turn can result in access problems. By splitting large glass rooflights into smaller modules it is possible to making fitting both easier and safer.

What are the main safety issues with regards to glass rooflights?
It is important to protect people both above and below the rooflight. As such, the unit should be non-fragile (to stop people accidently falling though it) and incorporate a laminated – not toughened – glass inner pane (to prevent shards of glass falling on building occupants if it is shattered). Unlike some competitor products, all SIGnature rooflights are non-fragile and have laminated inner panes.

Modular glass rooflights installed over a classroom 

Are there particular issues to consider with rooflights on schools?
We’ve come across several factors which are particular to schools, including refurbishment projects. First, there is the risk of pupils getting on flat roofs and falling through rooflights. Aside from the potentially tragic consequences of this, the school would be liable. Specifiers should make sure that the rooflight manufacturer meets the new standards for triple-skin on polycarbonate models, as well as laminated inner leafs on glazed units. However, many schools will avoid glass altogether.

Second, a lot of schools have benefited from turning rooflights into internal access hatches. This avoids scaffolding or ladders, which prevents pupils from being able to climb up onto (and fall off) roofs. An internal hatch also provides secure access, which allows a school to use in-house maintenance for inspections if it wishes. It is also worth mentioning that natural ventilation is a growing issue in schools post COVID, so specifiers and their clients could consider opening rooflights to improve ventilation.


Modular glass rooflight installed in a domestic extension 

How can SIG help specifiers choose the right product?
SIG has launched the SIGnature Rooflight Configurator, which is designed to make rooflight selection simple and straightforward. Specifiers first choose the type of rooflight that best suits their needs. Then they select the required specification in terms of size, kerb, tints, opening options, ventilation requirements, etc. Additional information is also available on screen about further options for each rooflight configuration. When the specifier is satisfied that the product they’re looking for is available, they can make an enquiry about it or download the appropriate brochure.


Typical rooflight upstand detail for warm roof incorporating SIGnature Torch on System

In terms of product range, SIG supplies a wide range of different rooflights, including fixed and opening polycarbonate domes and pyramids, glass units in standard and linked modules, as well as access hatches and smoke vent domes. Added to this, some of our modular rooflights are available on 48-hour delivery.

Contact Details
Find out more about the SIGnature Rooflight Configurator at bit.ly/RooflightConfigurator. As well as providing easy ways for you to choose modular rooflights, SIG Design and Technology can also assist with bespoke rooflight designs. For more information, please visit the SIG Design and Technology website.