The frame and the envelope under one subcontract

On paper, splitting the steel package from the cladding package looks like good procurement. Two trades, two specialisms, two competitive tenders. In practice it creates one interface — the line where the cladding fixes to the frame — and that line is where most envelope disputes on a steel building begin.

The reason is that the interface is not only physical. The cladding contractor's system assumes a tolerance for the steel it fixes to. The steel contractor works to the tolerance in their own specification. Both can be within their own stated tolerances and still not fit each other, because nobody owned the sum of the two. When the roof then leaks or a panel line runs visibly out of true, each party can point at the other's compliance certificate honestly.

It shows up in sequencing too. Cladding cannot start until enough frame is up and surveyed, and the frame contractor's programme is not usually written around the cladding contractor's mobilisation. Where the two are separate, that gap is nobody's float to manage; where they are one subcontract, it is an internal sequencing problem rather than a claim.

Roofing and cladding systems are named in Masas's ISO-certified scope alongside structural steel and pre-engineered buildings, so the frame and the envelope can come under one subcontract. The ISO 9001, ISO 14001 and ISO 45001 certificates all name construction, installation and erection within that scope, not fabrication alone — one subcontractor carries the package from shop drawings through to handover.

None of this makes the combined route automatically cheaper on the tender return. It usually is not, and a client comparing two numbers on a spreadsheet will see that. What it changes is where the risk sits after award. If the envelope fails, there is one party to call, and no argument available to them about whose tolerance was at fault.

That trade is worth making on buildings where the envelope is doing real work — a long roof run, a large clear span, an insulated store, anything where a leak is expensive rather than merely annoying. On a small, simple, forgiving building, two packages may well be the right call, and it is fair to say so.