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Flue pipe coming through a dark metal roof

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Skylight repairs for commercial roofs, plus the flashings around them

Skylight repairs on commercial roofs usually mean replacing tired clear sheets and fixing the joints around them. We also repair the flashings around plant, flues and pipes, which are just as likely to leak.

Call 027 929 6889

Free quote
Central Auckland based
Written scope before work starts
Photos of what we find

Why clear roof sheets fail

Many shops, factories and warehouses have clear roof sheets set into the metal roof to let daylight in. Most are polycarbonate, and older buildings may have fibreglass. Both are worn down by the sun. Over the years they yellow, cloud over, go brittle and crack, and the laps where they meet the metal sheets can open up.

Clear sheets also move differently from steel as the temperature changes, so their fixings need the right washers and a little room to move. Where the wrong fixings were used, or holes were drilled too tight, the sheet cracks out from each screw.

Old corrugated roof with a clear skylight sheet, seen from above

Signs your skylights need repair

Cracked or brittle sheetsCracks, crazing or pieces breaking off are signs the sheet is past repair and needs to be replaced.
Yellowing and lost lightDiscoloured sheets let in much less light and are usually close to the end of their life.
Leaking lapsWater getting in where the clear sheet overlaps the metal roofing, often from lifted laps or missing seals.
Failed fixingsOld screws and washers around clear sheets break down, leaving holes and cracks at each fixing.

How our skylight repairs work

Make the area safe
Clear sheets are fragile, so we set up protection around them before work starts and keep people off them.
Check the profile
New sheets must match the metal profile around them. We confirm the profile and length before ordering.
Replace and lap correctly
Old sheets come out, new sheets go in with the laps the right way for the weather, sealed where the system calls for it.
Fix with the right hardware
Fixings with suitable washers, in properly sized holes, so the sheet can move without cracking.

Flashings around plant and penetrations

Every flue, vent, pipe, fan and plant stand that goes through a roof needs a flashing. On commercial buildings there are often dozens. They are also the parts of a roof most often changed after it was built, when new equipment goes in and someone cuts a hole and seals it up as best they can.

We see flashings held together mostly by sealant, flexible boots that have split in the sun, back flashings missing on the uphill side of a penetration, and plant stands bolted straight through the roofing. Each of these lets water in sooner or later.

A good repair sheds water around the penetration with properly formed metal or a suitable flexible flashing, with sealant only as a second line of defence. Where a penetration sits across the ribs of the sheet, water coming down from above needs a path around it, not into it.

Old corrugated roof with a roof vent, seen from above

Flashings we repair

Flues from kitchens, heaters and boilers
Extraction fans and roof vents
Air conditioning pipework and plant stands
Pipes and cables from solar or other equipment
Roof hatches and access points
Flashings where the roof meets walls and parapets

If you are not sure which of these is causing your leak, our commercial roof leak detection process tests each one in turn. On large industrial roofs, skylight work often fits into a wider plan, which we cover on the warehouse roof repairs page.

Commercial skylight repairs questions

Why do commercial skylights go yellow?

Polycarbonate and older fibreglass clear sheets break down under UV over the years. They discolour, lose light, become brittle and eventually crack. Once that happens, replacement is usually the only real fix.

Can a cracked skylight sheet be patched?

A small crack can sometimes be sealed as a short-term make-safe. But a cracked clear sheet is weaker and more fragile, so we normally recommend replacing it.

Is it safe to stand on skylights?

No. Clear sheets are not designed to take a person’s weight and falls through them are a serious risk. Nobody should walk on them, and we plan our work so they are protected or avoided.

Do new clear sheets have to match the metal profile?

Yes. The clear sheet has to match the profile of the roofing around it so the laps sit tight and shed water. We check the profile before ordering.

What is a penetration flashing?

It is the weatherproof seal around anything that comes through the roof, such as a flue, vent, pipe or plant support. It might be a formed metal flashing, a flexible boot, or a combination, depending on the size and shape of the penetration.

Can old flashings just be resealed with silicone?

Sealant has a place, but it should not be the only thing keeping water out. A well-made flashing sheds water on its own, with sealant as a back-up. Flashings that rely entirely on sealant tend to leak again once it cracks.

Other repairs we carry out

Grey corrugated metal roof seen from above

Commercial roof leak detection

Tracing where water actually gets in, with staged water testing and moisture checks.

Close view of old grey corrugated roof sheets where they overlap

Rusted roof repairs

Cut edges, laps and fixings assessed, then treated or replaced sheet by sheet.

Large commercial metal roof under a bright sky with a person in the distance

Warehouse roof repairs

Long span roofs repaired around your stock, staff and trading hours.

Edge of a long run metal roof with a tree close by

Box gutter repairs

Internal gutters, outlets, sumps and overflows cleared, repaired or relined.

Replace tired skylights and fix leaking flashings

Tell us how many clear sheets and penetrations are on the roof. We will inspect them and give you a free quote.