Screwed roof or standing seam?

A screwed trapezoidal roof is the economical choice for most sheds and warehouses at a normal slope. Standing seam costs more per square metre but has no fastener holes and no end laps, so it is chosen for low slopes, very long slopes, and buildings where a leak is expensive: food, pharmaceuticals, cold storage and electronics.

Galvalume or colour-coated?

Bare Galvalume is the aluminium-zinc coated sheet as it comes: a light grey that weathers to a matt finish and costs least. Colour-coated sheet adds a paint system over the same base for appearance and extra protection, in seven standard colours. Many buildings take a bare Galvalume roof with colour-coated walls.

How is the building insulated?

With an XLPE or fibreglass blanket laid over the purlins and girts under the sheet, held by the sheet fixings, with its facing to the inside. Where a finished inner face is wanted, a liner panel goes inside the purlins or girts with the insulation between, which also protects the blanket. Cold stores use insulated panels instead.

What about daylight and ventilation?

Translucent daylight panels in the roof profile, turbo ventilators, ridge ventilators, roof monitors and louvers are all set into the cladding and trimmed like any other opening. They belong to the accessories system and are chosen with the cladding, so the purlin and girt spacing suits them.

PEB Cladding System

Cladding system

The skin of the building.

The cladding system is the skin of the building: the roof and wall sheets fixed to the purlins and girts, and the flashings, trims, fasteners, sealants and insulation that turn them into a weathertight envelope.

Everything under the roof, the crane, the stock, the machines and the people, depends on the cladding keeping the weather out. In a pre-engineered building the cladding is a system: profiled sheets roll-formed from high-tensile coated steel, laid to the purlin and girt spacing the frame was designed with, and closed at every edge, ridge, corner and opening by a matching trim.

DSI supplies the cladding with the frame, so the sheet profile, the purlin spacing, the insulation and the fixings are decided together. The roof and wall sheets, the standing seam system where it is specified, and every flashing, fastener and sealant come from one source and go up with the same crew.

Materials

The grades and thicknesses DSI specifies for the envelope. The purlins and girts the sheets fix to have a page of their own.

Roof & wall sheeting: S550 high-tensile steel
Standing seam roofing: 300 MPa, 0.50–0.80 mm core
Bare Galvalume: IS 513, 0.4–0.8 mm
Colour-coated Galvalume: IS 513 (AZ 150), 0.4–0.8 mm
Colour-coated Galvanized: IS 277 (120 GSM), 0.5–0.8 mm

Seven standard colours

The colour-coated range for roof and wall sheet, fascias and trims. Many buildings take a bare Galvalume roof with colour-coated walls.

DSI Leaf Green
DSI Galvalume
DSI Off White
DSI Taurus Blue
DSI Stone Grey
DSI Red
DSI Dark Grey

Colours are screen approximations. Confirm the shade against the sample card before ordering.

Part 01

Roof cladding

Profiled steel sheets laid across the purlins, lapped and screwed down to shed water and resist wind uplift.

The roof sheet is a trapezoidal profile roll-formed from S550 high-tensile steel, bare or colour-coated, in lengths that run from ridge to eave in one piece wherever transport allows. It is laid across the purlins with its ribs down the slope, side-lapped by one rib and end-lapped only where a length has to break, and screwed through the crest of the rib into the purlin with self-drilling fasteners under sealing washers.

The profile does the work. The rib height sets how much water the sheet can carry at the roof slope and how far it can span between purlins, and the high-tensile steel lets a thin sheet span that distance under wind uplift and foot traffic. Sheets are 0.50–0.80 mm core thickness, chosen for the span and the exposure.

Translucent daylight panels in the same profile take the place of a steel sheet where light is wanted. A ridge cap closes the top, an eave flashing and gutter take the water at the bottom, and foam closures fill the profile at both. Insulation, an XLPE or fibreglass blanket, is laid over the purlins under the sheet, or a liner panel is added below for a finished ceiling.

At a glance

Material: S550 high-tensile steel, Galvalume or colour-coated
Thickness: 0.50–0.80 mm core
Fixing: Screwed through the rib crest to the purlins
Insulation: XLPE or fibreglass blanket over the purlins

Drone view straight down onto the white profiled roof sheeting of a DSI building: a gabled roof with ridge, rows of turbo ventilators and skylight strips at every bay — A DSI roof from above: profiled sheeting laid bay by bay over the ridge, with turbo ventilators and skylight strips in every bay.

Trapezoidal profile in S550 high-tensile steel
Bare Galvalume or colour-coated, 0.50–0.80 mm core
Single lengths ridge to eave where transport allows
Self-drilling fasteners with sealing washers through the rib crest
Ridge cap, eave flashing, closures and gutter to match
Translucent daylight panels in the same profile

Part 02

Wall cladding

Sheets fixed to the girts that close the sides and ends of the building, cut and trimmed around every door, window and louver.

The wall sheet is the same high-tensile profiled steel as the roof, fixed to the girts with its ribs vertical so the wall sheds water and the ribs read as clean lines on the elevation. Sheets run from the plinth to the eave in one length where they can, lapped by one rib at the sides and screwed to every girt. A base flashing closes the bottom against the plinth; the eave strut and eave flashing close the top.

The wall is where the building is seen, so the sheet profile, the colour and the way the openings are trimmed decide its appearance. DSI’s colour-coated range has seven standard colours, and a two-tone wall, a band of a second colour at girt level or a fascia in a contrasting shade is only a matter of which coil goes where.

Every opening is framed by the girts and finished with jamb, head and sill flashings, so the sheet edge is covered and water is led out. A liner panel inside the girts, with insulation between, gives an insulated wall with a clean inner face for offices, cold stores and clean areas.

At a glance

Material: S550 high-tensile steel, colour-coated or Galvalume
Thickness: 0.50–0.80 mm core
Colours: Seven standard colours
Build-up: Single skin, or liner panel with insulation between

Three-tone colour-coated wall cladding on a DSI shed: red and silver sheeting above a dark grey band with louvre panels, over a plastered base — Colour-coated wall cladding on a DSI shed, banded in three colours with louvre panels for ventilation along the upper wall.

Same S550 profiled steel as the roof, ribs vertical
Colour-coated in seven standard colours, or bare Galvalume
Base, corner, eave, jamb, head and sill flashings
Full-height sheets from plinth to eave where possible
Liner panel and insulation for an insulated wall
Two-tone walls and contrasting fascias from the same range

Part 03

Standing seam roofing

A roof with no screw through the sheet: panels clipped to the purlins and seamed to each other, for long slopes and low pitches.

A standing seam roof is fixed without a single hole in the sheet. Each panel sits on concealed clips screwed to the purlins, and its upstanding edges are folded over the neighbouring panel’s edges by a seaming machine on the roof. The clips let the panel slide as it expands and contracts, so a length of many metres can run from ridge to eave without end laps and without the fastener holes that leak first on a screwed roof.

DSI standing seam panels are roll-formed from 300 MPa steel in 0.50–0.80 mm core thickness, on site where the length calls for it. Because there are no laps and no exposed fasteners, the roof can be laid at a low slope, which lowers the building and its cladding area, and it stays tight through the thermal movement that a screwed sheet fights against.

It is the roof for buildings that cannot afford a leak: pharmaceutical and food plants, cold stores, electronics and paper, and any building with a long slope or plant on the roof. Insulation and a liner sit below it on the same purlins, and the same flashings and gutters close it as a screwed roof.

At a glance

Material: 300 MPa steel
Thickness: 0.50–0.80 mm core
Fixing: Concealed clips and seamed edges, no exposed fasteners
Best for: Low slopes, long slopes and buildings that cannot leak

Dark seamed metal roof panels with raised seams running down the slope past a rooflight — Seamed roof panels with their raised edges running down the slope, and no fastener through the sheet.

Concealed clips on the purlins, no fastener through the sheet
Panels seamed to each other on the roof
Panels free to move with temperature
Long lengths ridge to eave, roll-formed on site where needed
Suited to low slopes and long slopes
300 MPa steel, 0.50–0.80 mm core

Part 04

Cladding components

The flashings, trims, fasteners, sealants and insulation that turn sheets into a weathertight envelope.

Sheets alone do not make a roof. Every edge, change of direction and opening is closed by a flashing or trim folded from the same coated steel: ridge caps, eave and gable flashings, corner and base trims, jamb, head and sill trims at openings, and apron flashings where a wall meets a lower roof. Foam closures fill the profile under the ridge and at the eave, so wind, dust and birds stay out.

Fasteners are self-drilling screws with sealing washers, sized for the sheet, the purlin and the exposure; stitching screws close the side laps. Sealant tape in the laps and a gun-applied sealant at the flashings finish the weatherproofing. Gutters and downspouts take the water from the eave to the ground, sized for the roof area and the rainfall.

Insulation goes under the roof and behind the walls as an XLPE or fibreglass blanket, with a liner panel where a finished inner face is wanted. Daylight panels, turbo ventilators, ridge ventilators and louvers are set into the cladding and trimmed the same way; they belong to the accessories system and are chosen with the cladding.

At a glance

Flashings: Folded from the same coated steel as the sheet
Fasteners: Self-drilling screws with sealing washers
Sealing: Foam closures, lap tape and gun-applied sealant
Insulation: XLPE or fibreglass blanket, with liner panels

Red and white profiled wall sheeting of a DSI shed running under a red eave flashing, with vertical corner and joint trims and screws along the rib lines — Eave flashing and joint trims folded from matching coated steel, closing the top and the joints of the wall sheeting.

Ridge, eave, gable, corner and base flashings
Jamb, head and sill trims at every opening
Self-drilling fasteners with sealing washers, and stitching screws
Foam closures, sealant tape and gun sealant at the laps
Gutters and downspouts sized for the roof
XLPE or fibreglass insulation and liner panels

FAQ

Questions about cladding.

For the purlins and girts the sheets fix to, see the Secondary System. For the rest of the building, see About PEB.

Screwed roof or standing seam?: A screwed trapezoidal roof is the economical choice for most sheds and warehouses at a normal slope. Standing seam costs more per square metre but has no fastener holes and no end laps, so it is chosen for low slopes, very long slopes, and buildings where a leak is expensive: food, pharmaceuticals, cold storage and electronics.
Galvalume or colour-coated?: Bare Galvalume is the aluminium-zinc coated sheet as it comes: a light grey that weathers to a matt finish and costs least. Colour-coated sheet adds a paint system over the same base for appearance and extra protection, in seven standard colours. Many buildings take a bare Galvalume roof with colour-coated walls.
How is the building insulated?: With an XLPE or fibreglass blanket laid over the purlins and girts under the sheet, held by the sheet fixings, with its facing to the inside. Where a finished inner face is wanted, a liner panel goes inside the purlins or girts with the insulation between, which also protects the blanket. Cold stores use insulated panels instead.
What about daylight and ventilation?: Translucent daylight panels in the roof profile, turbo ventilators, ridge ventilators, roof monitors and louvers are all set into the cladding and trimmed like any other opening. They belong to the accessories system and are chosen with the cladding, so the purlin and girt spacing suits them.

Next step

Tell us what the building has to keep out.

The use inside, the site and the exposure are enough for DSI to specify the roof and wall system with the frame.

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