Purlins, metal roofing and cladding, and deck slabs

Metal roofing and cladding decide how watertight, how well insulated and how durable a factory building is. World Steel controls every layer, from purlins and roof sheets to insulation and composite deck slabs for mezzanines and plant floors. This article sets out the fabrication and installation sequence and the main inspection points.

Purlins, metal roofing and cladding, and deck slabs, photo 12

1. Purlins

Purlin coil delivered to the workshop is checked for thickness before roll forming.
Roll formed on a purlin machine; each piece is labelled with its type, length and position.
On site, thickness and type are checked against the drawings again before installation; sag rods are fitted as designed.

2. Roof and wall sheets

Step	Work	Control
1. Roll forming	Sheets longer than can be transported are roll formed on site.	Profile, thickness and coating as specified.
2. Lifting	Use purpose-made sheet clamps to lift sheets without denting the ribs.	Never drag sheets across the roof.
3. Laying	Move sheets into position and lay them in the designed direction; for standing seam roofs, close the seams with a seaming machine.	Straight ribs, side laps, fixing to the purlins.
4. Flashings	Fit eaves, gutters, ridge caps, gable flashings and details round vents and skylights.	Seal every junction.

3. Insulated metal roof (typical build-up)

Erect the Z purlins.
Lay the mineral wool insulation.
Fix cement board as the support layer.
Bond the bituminous waterproofing membrane.
Fix the clips for the standing seam sheets.
Install the top roof sheets.

The exact build-up (thickness and density of the insulation, membrane type) follows the approved design.

4. Deck slabs

Lay deck sheets on the steel beams and fix them as designed; close the rib ends and slab edges so no grout is lost during the pour.
Fix slab reinforcement and spacers; check temporary propping (if the design requires it) before concreting.
Pour and cure as for a normal concrete slab.

Safety when working on the roof

Safety nets under the roofing area; lifelines along the roof.
No work in rain or strong wind; no loose sheets left on the roof at the end of a shift.

Common mistakes

Mistake	Consequence	Prevention
Purlins of the wrong thickness	Roof sag, insufficient capacity	Check thickness in the workshop and on delivery
Ribs dented when lifting	Leaks at laps	Use sheet clamps; never drag sheets
Missing sealant at flashings, ridges and roof penetrations	Local leaks	Accept flashing details before scaffolding is removed
Deck rib ends not closed	Grout loss, honeycombed slab soffit	Check before the pour

Reference standards

The edition in force when the contract is signed applies.

TCXDVN 170:2007 Steel structures – Fabrication, assembly and acceptance – Technical requirements
The approved installation instructions of the roof sheet manufacturer