Floor Flatness for High-Bay Racking in Blackburn Warehouses

The standard everyone works to: TR34

Warehouse floor flatness is specified using the Concrete Society's Technical Report 34 (TR34). Racking manufacturers, truck suppliers and insurers all refer to it, so it is the language you need when talking to contractors.

TR34 splits floors into two types. Free movement areas are where counterbalance and reach trucks can drive in any direction, with wide aisles. Defined movement areas are very narrow aisle (VNA) installations, where guided trucks run in fixed wheel tracks. The tolerances for defined movement are far tighter, because a tiny dip under one wheel becomes a large sway at the top of a mast lifting 12 metres or more.

• Free movement classes run from FM1 (the strictest) down to FM3 and below, with the class chosen mainly by lift height.
• Defined movement classes DM1 to DM3 apply to VNA aisles, again graded by lift height, with DM1 typically used where lifts go above around 13 metres.
• Lower lift heights, such as a shallow pallet store below 8 metres, can usually work with a less demanding class.

Which class does your racking actually need?

Start with your top beam height and your truck type, not the floor. A reach truck operation in a typical older unit on Whitebirk or Shadsworth, lifting to 8 or 9 metres, usually needs a good free movement class. A new VNA scheme lifting to 12 or 14 metres in a modern shed near the M65 junctions will need a defined movement survey of every aisle.

Your truck supplier will normally state the floor tolerance their machine needs in its specification. Ask for it in writing. Racking installers will also want to know the floor can take the point loads from base plates, which is a separate question about slab thickness and strength, not flatness.

How flatness is measured

For free movement floors, a surveyor takes readings on a grid across the slab and checks the elevation difference between points 300mm apart, along with wider level variation across the whole area. The results are compared against the limits for your chosen class.

For VNA aisles, a profileograph is run along each aisle in the truck's wheel paths. It records the height difference between the wheel tracks and how quickly that difference changes as the truck travels. These are measured in fractions of a millimetre, which is why older slabs that look perfectly flat to the eye often fail.

What if your existing floor falls short?

Many Blackburn warehouses date from the 1970s to the 1990s and were laid long before today's high-bay layouts were planned. A failing survey does not automatically mean a new slab. The usual options are:

• Precision grinding of VNA wheel tracks, removing high spots so each aisle meets its DM class. This is common and often the most cost-effective route.
• Local grinding or levelling compounds in free movement areas where only certain zones fail.
• Joint repairs, since broken or curled joints are a frequent cause of failed readings and truck damage.
• Lowering the top beam or changing truck type, if the cost of correction outweighs the benefit of the extra height.
• Replacing sections of slab where it is badly cracked, curled or undersized for the new loads.

Costs and planning

Costs depend heavily on floor size, condition and the class required. A flatness survey for a single unit is usually a modest cost relative to a racking project, while aisle grinding is generally priced per linear metre and varies with how much material needs removing. A survey first tells you exactly where the problems are, so you only pay to correct what fails.

Survey before the racking goes in. Grinding aisles under installed racking is possible but slower and more disruptive. If you are building new, specify the TR34 class in the tender documents so the floor is laid to it from day one, rather than corrected afterwards.