There are generally only two types of rooflight used in industrial metal roofing, site assembled and factory assembled


Site assembled, these are built up on site in the same way that the metal roof is assembled, however, in lieu of the insulation quilt a layer of polycarbonate sheet is laid within the void to achieve the required U value and to reduce solar gain.

This type of rooflight should not be used with composite panels.


Factory Assembled , or more commonly called FAIRS. These, as the name suggests are an assembled unit ready to install.

This type of rooflight should not be used with a built up metal system


Some key points :-


Non Fragility

it is essential that a non fragile roof is provided - this is applicable to the main steel roof and the rooflights. Each manufacturer with provide advice on the weights ( strengths) of the materials required.

However, it is imperative that the rooflights are fully and correctly installed and fully fixed prior to netting being removed. On about two thirds of the new buildings we inspect, the rooflights are not correctly installed and are left in a fragile state.

Another issue here is that of longevity. Some manufacturers will offer a minimum period of non fragility ( with obvious conditions relating to environment etc ) , whilst others will only state " when new ". When new is fine to cover the period of construction, but how about future maintenance or inspection visits ?



Often an Architect / Client will specify that they require a 25 year warranty for the roofling and cladding, but then allow the use of carbon steel screws.

Carbon steel screws will only have a warranted life of 10 to 12 years ( less in some environments, and zero when close to the coast ) The use of such screws can invalidate the non fragility expectation of not only the rooflights but also the steel sheeted roof too.



For 25 years Stainless steel screws MUST be used. This is also applicable for buildings close to water and some other environments ( coastal / river etc )

We have known carbon screws rust to the point of failure within about 4 years on a site in Ipswich ( 14 miles in land though still a port )



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