Industrial

Low-Pitch Industrial Roofs: Refurbishment Over the Existing Sheets

A warehouse roof is not a big flat roof. It is a different building with a different set of weaknesses, and the thing that changes most is not the material but the arithmetic: everything on it repeats, so every decision is multiplied by however many times the detail occurs. The work is to make the roof already up there watertight again rather than to replace it.

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The short answer: A low-pitch industrial roof is refurbished in place: laps, fixings, gutter runs and penetrations are treated across the existing sheets rather than stripped off. What decides whether that is possible is the condition of the sheet and what still holds it down.

Scale

What changes when a roof is measured in units

On a house you can point at each detail. On a distribution shed they arrive in series: lap after lap, fastener after fastener, and a gutter run from one end of the building to the other. Nothing is complicated on its own, but a fault that is trivial once becomes a programme when it repeats the length of a roof, so the specification reads as quantities of a few operations rather than unique repairs.

Failure

Where a big sheeted roof gives way

Laps. A shallow pitch gives water time to stand in the joints rather than run off, and whatever was bedded into them when the unit went up ages out of the job.
Fasteners and their washers. Every fixing is a deliberate hole sealed by a washer that goes hard with age. They give up quietly and in numbers, and the water rarely shows below the one it came through.
Gutter runs. Splits, failed joints and standing debris put everything the field sheds inside the building instead of into the downpipe. Their length is why they are worth treating as their own item.
Penetrations and plant. Extract, ductwork and their supports each break the sheet, and each was detailed in a hurry.

The edge of the sheet has its own well-known failure and its own page: cut edge corrosion, and how a steel sheet is treated.

Access

Almost nothing up there carries a person

The rooflights are the obvious hazard: they weather, go brittle and give way without warning under anybody who assumed otherwise, and the sheets between them are frequently no better. So nothing is walked on until a survey says it will hold, and that assumption shapes the price as much as the specification, because the way up decides how the work is staged.

The limit

Cement sheeting, and where the work stops

A unit of this vintage may be roofed in profiled cement rather than steel. Where it is, our work stops at the edge of that material: nothing of ours goes onto it, over it or through it, so no repair, no new layer, no fastener and no walkway. Neither will we say what a sheet is made of, because that means testing it properly and a contractor’s guess is no basis for a decision.

What governs it is the asbestos register the duty holder keeps for the building, and the specialist working to that register under the asbestos regulations. We read it before planning, stay out of whatever it puts out of bounds, and change the programme if it changes. Once that material has been dealt with by others, the roof that follows is ordinary work.

Scope

What is ours, and what belongs to somebody else

Re-cladding a whole building. Taking a unit back to the purlins and re-sheeting it is a cladding contractor’s trade. Lifting out the panels that have gone, so what remains can be treated, is ours.
The frame. Purlins, rails and anything carrying load belong to a structural engineer.
Roof-mounted plant. Isolating it, lifting it and setting it back sits with whoever runs it, programmed before we start.
Drainage past the outlet. Gutters, outlets and downpipes are ours; the drain they discharge into is not.

Questions

Frequently asked questions

Can a large sheeted roof be refurbished without stripping it?

Usually, and it is why surveying one properly pays. Where the sheets still hold their fixings and the frame below is sound, the roof is treated in place. Stripping a unit of this kind means opening its inside to the weather, which is the costly part.

How is a roof this size actually inspected?

From a platform and from above, not by walking it. Sheets and rooflights of this age are assumed unsafe to stand on unless a survey says otherwise, so a mobile elevating work platform covers the eaves and gutter lines and an aerial pass maps the field, the penetrations and the plant.

Do you re-sheet the whole building?

No. Re-cladding a unit in new profiled metal is a cladding contractor’s trade, and we say so rather than stretching to it. Swapping out sheets that have failed, so the good roof surrounding them can be treated, is ours, along with everything on the waterproofing side.

The roof has cement sheeting on part of it. What happens?

Nothing of ours goes on that part. We do not judge what a sheet contains, because that is settled by testing rather than by eye, and we neither repair it, cover it nor fix into it. The building’s asbestos register decides what happens there, and we plan around it.

Is a gutter line worth doing on its own?

Often it is the item that repays itself first. A valley or eaves gutter runs the length of a unit and collects everything the field sheds, so when it splits the water goes inside rather than away. We take those runs on with or without the field around them.

A unit letting water in somewhere along its length?

Tell us what the building does, roughly how you get up to it and what sits below. Those three answers shape how we come and look.

Coming out and pricing the work is free; a written condition survey carries a fee, agreed before the visit and taken off the price of the work if you go ahead.