Mezzanine Floor Design & Load Planning

What is a Mezzanine Floor?

A mezzanine is an intermediate platform installed between the floor and the roof of a building, creating extra storage or working space. Mezzanines can be freestanding on their own columns, or integrated with the building's structure. Where existing columns or structural members will be used, they must be verified before they carry any additional load.

Whether a mezzanine is feasible depends on the building's clear height and the space you need above and below the deck. They're commonly used for:

• Additional storage, including racking or shelving on the mezzanine
• Picking and packing areas raised above the warehouse floor
• Offices overlooking the warehouse floor
• Specialised storage for temperature-controlled goods
• Assembly and quality control workstations

Structural Design

Design Loads

The structural designer selects the design loads for the intended use, in line with the applicable design standards. There's no single standard loading figure for warehouse mezzanines.

• Permanent loads: the structure itself, the actual decking and any relevant permanent fixtures.
• Imposed loads: stored goods, people and equipment, appropriate to how the floor will be used.
• Distributed and concentrated loads: these are different design checks. Distributed loads are expressed per unit area, while concentrated loads act at particular points. A relatively modest load can be critical when it's concentrated on a small bearing area.

A uniformly distributed load rating doesn't, on its own, show that a floor is suitable for racking feet, pallet positions or machinery. Those need checking as concentrated loads.

Racking on a Mezzanine

Racking feet impose concentrated reactions on the deck, so racking on a mezzanine must be checked against the floor's concentrated-load capacity, not just its distributed load rating.

Structure and Decking

Mezzanine structures typically use:

• Main beams: structural steel sections carrying the primary loads
• Secondary beams: members supporting the decking
• Columns: vertical supports down to the base, or existing structural members once verified
• Decking: steel, grating, composite or structural-grade wood-based panels, specified by grade, thickness and support arrangement, and suitable for any concentrated loads

The design should check strength, stability, connections, deflection and vibration. Span lengths have a big effect on beam sizes, which in turn affect cost and lead time.

Existing Slab and Foundations

Check that the floor slab and foundations can carry the new column reactions, baseplates and anchors. A floor that looks sound isn't evidence that it can support a mezzanine. Some schemes need new foundations; others use the existing slab once it's been verified as adequate.

Building Regulations and Approvals

A new mezzanine needs Building Regulations approval. Confirm the approval process early. It's separate from planning permission, which some projects also need. The rules differ in Wales, Scotland and Northern Ireland, so check the requirements for your site's location.

Typical Documentation

• Structural design calculations
• Construction drawings and specifications
• Fire safety information: escape routes, fire resistance or protection, alarms and emergency lighting
• Loading information: safe loads and the approved loading arrangement
• Installation method statement

Inspections

Agree the inspection stages and notification requirements with the appointed Building Control body. Depending on the scheme, checks may include:

• Foundations or base: where new foundations are needed
• Structural frame: after the beams and columns are erected
• Decking, guarding and stairs: once they're in place
• Completion: when the mezzanine is finished

Layout and Safety Planning

Headroom

Headroom under and on the mezzanine must suit the intended activity, access, equipment and services. There's no single minimum figure for every case: HSE's guidance on the Workplace Regulations (L24) uses 2.4 m as an illustrative example of room height, rather than a universal minimum.

Headroom for people is a different question from the clearance needed above racking and stored goods, so plan for both. Stairs and escape routes have their own headroom requirements under Building Regulations.

Stairs and Access

Mezzanines need safe access by suitable stairs. Stair geometry, flight lengths, landings, width, handrails and headroom depend on the applicable access and escape requirements. In England, Approved Document K covers this and refers industrial stairs to the relevant standards.

Fire Safety and Accessibility

Consider escape routes, stair arrangements, fire resistance or protection, alarms, emergency lighting and the applicable access requirements at the design stage, not after the layout is fixed.

Edges and Loading Points

Open edges need guarding, with protection against goods falling from the deck, and loading points need suitable pallet or loading gates. HSG76 addresses these risks directly and warns against using chains or tape as edge protection.

Load Placement

Load the mezzanine in line with the approved loading arrangement and any local restrictions. Spreading pallets out doesn't automatically solve a concentrated-load problem, or make racking suitable for the floor.

Handover and Future Use

• Display the safe loading capacity and any restrictions on the mezzanine
• Keep the approved drawings and loading information
• Have the design reviewed before any change of use, racking layout or permitted equipment

For inspections and ongoing safety, see our guide to Mezzanine Floor Safety & Building Regulations.