A mezzanine is a part floor built inside a tall building. It’s one of the cheapest ways to add usable space, because the roof and walls are already there. But it’s a structure in its own right, and getting the design right starts with what it will carry.
Every mezzanine must be engineered #
All mezzanine floors need engineering design. The floor has to be strong enough for the load it will carry. It also has to be braced so that, with that load on it, it resists an earthquake without collapsing onto people below or damaging the building.
What’s it for? #
- Light storage: boxes, spares and seasonal gear.
- Heavy storage: stock, parts and pallets, possibly loaded by forklift.
- Offices or staff rooms, where people work every day.
Each use has a different design floor load under the loading standard, and the engineer designs the structure, connections and footings for it. Tell us the real use. A floor designed for an office isn’t designed for pallets of stock.
Floor loads: from light storage to commercial #
In a rural building used for occasional storage, a mezzanine can be designed quite light, based on the weight and how it’s spread across the floor. In a commercial building, the engineer will design to a floor load rating in kilopascals (kPa). That usually starts at about 2.5 kPa and is often around 5 kPa for dedicated storage or shelving. We’ll talk this through with you and settle what applies to your use.
Steel or timber framing #
We help design both steel and timber-framed mezzanine floors. Most of our clients choose steel, because it integrates seamlessly with our steel structures. A typical Steelspan mezzanine has steel joists with plywood flooring on top. The plywood sheets have shiplapped or tongue-and-groove edges and are glued and screwed down. The underside is usually strapped with timber or steel, then lined with fire-rated plasterboard for fire protection.
Deck options #
| Deck | Suits | Notes |
| Timber or particleboard flooring on steel joists | Light storage, offices | Light, quick to build, easy to fix things to |
| Steel grating or plate | Plant platforms, industrial storage | Durable; grating lets light and air through |
| Concrete on steel decking | Heavy storage, forklift-loaded areas, offices needing acoustic separation | Heaviest and strongest; needs a stronger frame and footings |
Freestanding or supported by the building? #
Most mezzanines in portal frame buildings stand on their own columns, so the main frame isn’t carrying extra load it wasn’t designed for. If you plan a mezzanine from the start, the building and mezzanine can be designed together.
Height above and below #
You need comfortable standing room above and below, plus space for lights, sprinklers or services. That often decides the building’s wall height, so plan it before the building is designed.
Stairs, balustrades and safety #
The Building Code requires barriers where people could fall 1 m or more, so a mezzanine needs a balustrade along open edges. Stairs need to meet the access rules for rise, going and handrails. Loading gates or pallet gates keep people safe when goods are lifted up.
Fire and consent #
A mezzanine is building work and needs building consent. In commercial buildings, it affects escape routes and fire design, and an office mezzanine may also bring in accessibility and energy-efficiency (H1) requirements. A private mezzanine in a farm building is quite different from one in a commercial building. In a commercial building, the underside of the mezzanine and all of its supporting structure typically need at least a 30-minute fire rating. If offices above are enclosed, the escape stair down is normally required to be fully fire-rated as its own enclosure, so occupants can get out safely. It isn’t as simple as popping a mezzanine into a commercial building, and we can help you untangle these requirements.
Talk to Steelspan #
Tell us what the mezzanine will carry and who will use it, and we’ll design it with the building. Use our Easy Shed Quote or call 0800 787 726.
