A factory wall is the cheapest part of a plant to get wrong and one of the most expensive to put right later. It has to keep rain out, transfer wind load into the frame, hold its colour for a decade, and accept every door, window, duct and service the process line will ever need. Settle the specification at order stage and installation is routine work; leave it to whoever holds the drill and every decision gets made twice, once badly and once again for money.

Single-skin sheet or sandwich panel

The steel structure page on this site condenses the choice into one line: wall cladding is steel sheet or sandwich panel, with EPS, PU, glass wool and rock wool as the core options. The hidden decision is insulation, not material. A single-skin profiled sheet weighs 6-10 kg/m2 and carries yield strength between 250 and 550 MPa, so it spans well and installs quickly, but it stops weather, not heat. Any wall that separates an office block, control room or warehouse stock from an unheated bay needs a core: PU where the U-value drives the energy bill, rock wool where fire performance matters, EPS where budget rules and the building is not heated. The TDC51D+Z PPGI page names foamed sandwich panels among its own applications, which is the supply chain confirming that the same prepainted coil feeds both single-skin and cored panel lines.

The frame behind the sheet

Sheet never spans a full storey height on its own. It lands on girts, and girts land on columns, so the cladding specification is really a frame specification. The standard recipe uses Q235B or Q355B welded H sections for columns and beams with Q235 C and Z purlins as the secondary frame. The Q235 H-beam range covers flange widths of 50-400 mm, web depths of 100-900 mm and lengths of 6-12 m at a ±1% tolerance, invoiced by theoretical weight. Where the site punishes bare steel, the same sections come hot-dip galvanized: the hot dip galvanized H-beam series runs from 100x100 to 900x300 mm with flange thickness of 4.5-21 mm, invoiced by actual weight because the zinc adds mass. Round tube does the bracing quietly: A53 galvanized pipe, 1/2" to 36" NB with Grade B at 60,000 psi tensile, handles tie tubes and knee braces and survives the same splash zone as the sheet above.

Coating choice follows the environment

For most inland plants, Z275 galvanized steel coil is the workhorse: zinc from 30 to 275 g/m2, thickness 0.12-2.0 mm, width up to 2,000 mm, thickness tolerance of 0.01 mm, 3-5 t coils, 5 t minimum and delivery in 7-14 days. Quote the coating designation and standard together: the Z80 roofing galvanized coil page shows the same number living in four systems, GB/T 2518, JIS G3302, EN 10327 and ASTM A653M. Under a roof that runs hot, or where the ladder of atmospheres moves toward marine, 55% aluminium-zinc earns its premium. Galvalume sheet carries 2-6 times the service life of galvanized at equal thickness, resists 315 °C against 230 °C, and reflects roughly 80% of sunlight; its own literature ranks service life from rural through industrial to general and then severe marine. The galvalume vs galvanized comparison matters most at cut edges: zinc sacrifices, aluminium only barriers. Coastal sites skip the argument and move to the stainless corrugated roof panel family, which trades coating thickness for a substrate that does not care about salt.

Colour, resin and the fifteen-tonne question

A prepainted wall is a coating-system decision before it is a colour decision. The PPGL coil range runs 0.12-6.0 mm thick and 600-1500 mm wide in 3-20 t coils, with polyester, silicon-modified polyester, PVC plastisol and PVDC resin systems behind colours from plain RAL to wood grain, stone and matte. On the profiled sheet itself the film measures 5-25 µm on the top face and 5-20 µm on the back. Two commercial details catch buyers out. First, "RAL colour or as customer's sample" are two different contracts, and the sample route costs a trial. Second, textured finishes: the wrinkle PPGI line hides oil-canning on wide flat panels, but it carries a 15-tonne minimum per colour and about 30 days production, so sampling one shade is a programme decision rather than a freebie. The JSW PPGI page lists the governing standards, EN 10147, EN 10142, DIN 17162, JIS G3302 and ASTM A653, which should appear on the certificate with the colour.

Profiles, coverage and what the flat width becomes

Profile selection decides span, stiffening and appearance at once. Corrugated galvalume runs 0.151-1.2 mm in flat widths of 914, 1000, 1200, 1220 and 1250 mm, and profiling consumes some of that width: a 1000 mm flat coil of DX52D+AZ covers roughly 875-915 mm once formed, so coverage width, not coil width, sets the panel count. Heavier structural profiles such as the classic rib galvalume panel go to 4.0 mm thick in AZ30-AZ150 on substrates from DX51D to S550GD. Coils for profiling arrive on 508 or 610 mm IDs at 3-5 t, including DX51D+AZ150 and the cold rolled aluzinc range. A fascia or screened elevation changes the maths again: perforated corrugated galvalume panels let air and light through while keeping the profile, with hole pattern and pitch made to order. The roofing sheet category and the PPGI category list the profile families side by side for comparison.

Trims, openings and the details that leak

Walls fail at corners, not in the field of the sheet. Flashings, gutters, soffits and door trims are bent from the same coil, and the steel plate bending service handles knife bends, 180° returns and double-layer folds with unfold-length calculation, the step that decides whether a trim actually covers the joint. Openings need clean apertures: punching for vents and louvres, and the cutting routes split by thickness, mechanical below 10 mm, hydraulic above, CNC turret under 2 mm, laser and plasma where the edge matters. One caution from the coated-sheet trade: plasma and laser edges on prepainted sheet burn the film back from the cut, so exposed cut edges need touch-up or a folded cover strip. Brackets and lintels that weld to the frame come from plate welding, and the full set of services sits under customised processing. Drilling swarf left on a painted wall rusts onto the surface within weeks; sweeping it off the same day is the cheapest maintenance in the building.

What to fix before the order

Six things should be closed before an enquiry becomes an order: single skin or cored panel for each wall type; coating family by the environment ladder; colour by RAL number and the 15-tonne minimum acknowledged; profile and coverage width, not just gauge; girt spacing matched to the chosen span; and the trim schedule drawn as carefully as the sheet layout. Deliveries arrive on 20 ft GP containers of 5,898 mm internal length for panel lengths, with lead times that run 7-14 days for plain galvanized coil, 15-35 days for profiled sheet and about 30 days for textured colour. A wall specified this way goes up once, in the colour you chose, and stays that way.