The short answer
Replacing an industrial rooflight means taking out the worn translucent sheet, usually GRP, PVC or polycarbonate, and fixing a new one that matches the profile of the surrounding metal sheeting. Safe access is arranged first, because old rooflights are the commonest fall-through points on a roof. The laps and fixings are renewed and sealed, and the new light is checked for fit and weathertightness. It is often done in a day or two for a single bay, with the building left open to trade.
Why old rooflights fail
A rooflight is a translucent sheet that lets daylight into a warehouse or factory. Many are made of glass-reinforced plastic, known as GRP, or of PVC or polycarbonate. Sun and weather work on them for years. The surface erodes, fibres show through, the sheet yellows and becomes brittle, and eventually it cracks. Pitched laps move as the building flexes, fixings corrode and the seals harden. A light that has gone cloudy cuts the daylight in the building, and one that has cracked lets water in.
There is a safety reason to act as well. A brittle rooflight looks like part of the roof but may not carry any weight, and it can give way without warning. Falls through rooflights are among the most serious accidents in roofing. The guidance on safe access to fragile roofs sets out how people should reach and cross them.
Choosing the replacement
The new light must match the profile of the sheeting around it, whether that is a trapezoidal, corrugated or composite panel, so that it sits flat and laps correctly. If the surrounding sheets are being replaced as well, the new rooflights are specified along with them, and our guide to industrial roof sheeting covers profiles and fixings. Material choices matter. GRP is common and economical, while polycarbonate is tougher and keeps its clarity longer. Some rooflights are specified to a fire rating or to carry a load, and a few are made to reduce the chance of a fall-through. Ask for the product data, and say if the building has special needs such as food production or tall racking.
Quantity and layout are part of the design. Rooflights bring in daylight, which saves lighting costs, but too many hurt insulation and cause glare and overheating. If the roof is being renewed for thermal reasons, the rooflight area is considered as part of the building's energy performance. Your building control body can advise on what it expects.
How the work is done
Weather decides the day. Wet sheeting is slippery and sealant will not stick to damp metal, so lifting is done in dry, calm conditions and any open bay is covered before the crew leaves.
Planning comes first. The roof is surveyed, the safe route is set, and edge protection, crawling boards or a mobile access platform is arranged. Nets or platforms under the roof are used where possible, which also protects the people and equipment below. The existing lights are lifted out carefully, the fixings are removed, and the purlins and the sheeting laps are inspected for corrosion and damage. Sealant tape is laid on the laps, the new light is positioned, and the fixings are driven at the right spacing with sealing washers.
Side and end laps are detailed to shed water, and any gaps at ridge and eaves are closed. Finally the area is swept, the debris is taken away and the light is checked from inside. Where the old roof is made of asbestos cement, the job changes: sheets must not be broken, drilled or disturbed without a proper plan. Our page on asbestos cement roofs on commercial buildings explains the options, and our survey will flag it before anyone goes near the roof.
What it costs and what drives it
We do not publish a rate for rooflights, because the price turns on the number of lights, the profile, the height of the eaves, the access method and the state of the sheets around them. A single bay at a low eaves is a simple job. A long run on a tall building needs a platform or scaffold, and that is often the bigger part of the cost. A fixed written quote follows the survey, once we have seen each light.
Keeping the building open
Rooflight work can usually go on while the business trades. The work is carried out one bay at a time, so the weather never gets in, and noise and falling debris are controlled. Tell us about racking, vehicle routes and sensitive stock, and we will plan the order of work to protect them. Roofs that leak at several rooflights usually point to a wider problem with the sheeting, so a fault tracing exercise is worth doing, as shown in our guide on finding a leak in a warehouse roof.
Our free survey photographs each light and its fixings, which shows you which ones need replacing and which can stay, and the fixed written quote follows from that. If a repair will do, we say so. The rest of our business roofing is gathered under commercial roofing in Basingstoke.
Every roof is different. A free survey with photos settles it for yours.
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