GI Metal Decking Sheets: How to Choose Profile, Thickness and Span

Start with the floor system, not the sheet catalogue

GI metal decking is part of a floor or roof assembly, so the first question is what the deck must do in the finished structure. On a composite floor, the profiled steel deck can act as permanent formwork during the concrete pour and may also participate in the composite slab system after the concrete has cured. That means the profile, thickness, support spacing, concrete depth and attachment arrangement have to be considered together rather than as separate purchasing decisions.

For UAE contractors and procurement teams, the most useful starting document is the structural drawing or BOQ. It should identify the deck type or profile, support direction, span or beam spacing, slab information and any connection requirements. If the design calls for SRK Steel's GI Decking Sheet - 45/150 and 75/305, send the exact profile reference shown on the drawing rather than asking for a generic 'decking sheet'.

Steel deck design guidance also treats allowable span and load as design questions tied to deck properties and construction loading. That is why a supplier quotation should not be used as a substitute for structural design approval. The project's engineer or approved manufacturer load data should remain the controlling reference for span, shoring and load capacity.

1. Confirm the decking profile and rib geometry

Deck profile affects how the sheet sits on the supporting steel, how concrete is placed around the ribs and how the finished floor system is detailed. Two profiles can look broadly similar while having different rib depth, pitch and side-lap geometry, so a verbal description is not enough for a controlled RFQ.

SRK Steel lists 45/150 and 75/305 GI decking sheet profiles. Treat those as profile identifiers to be matched to the project drawing. Do not assume that one profile is automatically 'stronger' or suitable for a longer span simply because it is deeper; thickness, steel grade, support spacing, construction loads, slab configuration and attachment all influence performance.

When replacing an already specified deck with an alternative profile, send the consultant or structural engineer the proposed technical data before ordering. A dimensionally similar sheet is not automatically an approved structural substitute.

2. Specify thickness clearly and avoid gauge ambiguity

Thickness is one of the first commercial variables buyers compare, but it is also one of the easiest places for quotations to become non-comparable. State the required base-metal thickness in millimetres where the project documents allow it, and make clear whether the stated value includes or excludes coating. If a drawing uses gauge terminology, include the corresponding project specification rather than relying on an assumed conversion.

A thinner sheet can reduce unit weight and price, but selection should be based on the approved floor design and handling requirements. During erection and concrete placement, the deck must perform under temporary construction conditions as well as in the final slab system. The structural designer or approved deck tables should determine whether the proposed thickness is suitable.

For procurement comparison, place profile, thickness, coating and sheet length on the same line item. That makes it much easier to identify a quotation that has changed one technical variable while appearing to offer the same product.

3. Review span, support spacing and temporary construction loads

Span is not a catalogue preference. It is the distance the deck must bridge between supports under the conditions defined by the design. During construction, wet concrete, workers, equipment and local point loads can govern the temporary condition before the slab gains strength. The Steel Deck Institute, for example, treats allowable spans and construction loading through design standards and load tables rather than a single universal rule.

Before sending an RFQ, record the beam or joist spacing from the drawing and identify whether temporary shoring is part of the design. If the required span is close to a published limit, the engineer should review the condition rather than asking the supplier to 'increase the gauge' informally.

Projects using decking in commercial construction or industrial warehouses often have different bay layouts, pour sequences and access constraints. Sharing the actual support plan lets the supplier understand the commercial scope even though structural approval remains with the project design team.

4. Confirm galvanized coating and exposure requirements

Galvanized coating protects the steel surface, but the required coating level should come from the project specification and service environment. Do not write only 'GI finish' if the consultant has stated a coating mass, material standard or corrosion category. Put the requirement into the RFQ exactly as written so all bidders price the same finish.

Exposure also matters during storage and construction. Deck bundles that remain outdoors before installation should be stored and covered in a way that avoids trapped moisture and contamination. On coastal or high-humidity projects, the consultant may have additional requirements for material, coating or handling; those should be resolved before purchase, not after delivery.

If the floor package also includes coated sheets, purlins or roofing products, the Galvanized Steel category can be used to coordinate related product enquiries without mixing their specifications into the decking line item.

5. Coordinate decking with shear studs, concrete and openings

A metal deck package rarely ends with the sheet itself. Composite floor systems may also involve shear studs, edge trims, pour stops, reinforcement, openings and penetration details. The parties responsible for each item should be clear in the BOQ and quotation.

Where shear studs are specified, provide the stud diameter and height, welding or installation responsibility, quantity and drawing reference. Do not assume that the stud schedule can be derived from deck area alone. Stud spacing and location are structural-design items.

Large openings, service penetrations and changes in deck direction should be identified before material is released. A late opening can affect sheet layout, trimming and support details. The steel deck should therefore be coordinated with MEP and structural drawings before final cutting lengths are confirmed.

6. Plan sheet lengths, laps, handling and delivery sequence

Sheet length affects site handling, transport, lifting and the number of joints. Ordering every sheet at one standard length can create unnecessary cutting or handling problems if the structural bays differ. A deck layout or cutting schedule is useful on larger floors because it connects quantities to actual zones.

For multi-level projects, ask whether bundles need floor-by-floor identification or phased delivery. A lower material rate can lose its advantage quickly if bundles arrive in the wrong sequence and have to be moved repeatedly on site.

Delivery planning is especially important for active UAE projects with restricted unloading windows, tower-crane schedules or limited laydown space. Include delivery city, site access notes, preferred bundle weight where relevant and programme dates in the RFQ.

Common mistakes when buying GI decking sheets

The most common error is treating decking as ordinary corrugated sheet. Other mistakes include comparing quotations with different thicknesses, omitting coating requirements, ordering before the support layout is frozen, assuming the supplier will design the span, and forgetting shear studs or edge details until the main sheet order is already placed.

Another frequent problem is sending only the total floor area. Square metres are useful for early budgeting, but they do not define profile, thickness, sheet lengths, span or cutting sequence. For a firm project quotation, attach the latest drawing or BOQ revision and identify any information that is still provisional.

If the deck selection is part of a broader roof or secondary-steel package, our C Purlins vs Z Purlins guide explains a similar principle: the project geometry and engineer's design should drive the section choice, not a generic product preference.

What to include in a GI decking sheet RFQ

A useful RFQ should state the project location, deck profile, base-metal thickness, galvanized coating or material specification, sheet lengths, quantity, support spacing or drawing reference, slab/deck system notes, shear-stud requirement, certificate or submittal requirement, delivery sequence and target date.

If the design is still developing, label provisional quantities clearly. SRK Steel can review commercial product availability and RFQ completeness, while the consultant or structural designer remains responsible for approving the structural deck system.

For a broader procurement template, use the Steel RFQ Checklist for Contractors before issuing the enquiry.

Frequently Asked Questions