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This article outlines requirements for balcony decking load capacity.

Designing a balcony, terrace or external walkway requires careful assessment of load-bearing capacity. Essentially, it’s a structural consideration that requires the calculation of known and potential loads.

Types of load

When designing a balcony or terrace deck, it’s useful to consider various types of load: the point load, uniformly distributed load, dead load and live (or imposed) loads.

point load is a load applied to a single, specific point on the deck. It is also known as a concentrated load. It could be an object, a person or an action.

A uniformly distributed load (UDL) is a load that is distributed across 1m2 of the deck.

The dead load is the completed weight of a structure before it goes into service – in essence, the permanent components and materials that apply downward pressure. It represents the non-dynamic forces that place continuous force on a structure.

The live or imposed load is the dynamic forces that are likely to occur from occupancy and intended use. They represent transient pressures such as the anticipated weight of people, furniture and moveable equipment.

Live loads depend on structural strength, so it is important to establish as much precise knowledge as possible about the planned use of the decking. For example, a first-floor terrace on a busy city bar is likely to accommodate a much greater live load than a roof access walkway or a small balcony on a one-bedroom apartment.

Dead and imposed loads should be calculated in accordance with BS 6399. The NHBC guidance (2010) states that design should account for point loads imposed by foot traffic and storage of materials.

Choice of material for load-bearing

In recent years, aluminium has become the stand-out choice of material for balcony decking, terraces and external walkways. This is primarily due to new Building Regulations related to fire safety, requiring balcony materials to be on-combustible and A1 or A2 Fire Rated under the Euroclass system (aluminium is A1 Rated). However, another of aluminium’s useful attributes is structural efficiency: as a dead load itself, aluminium is lightweight – requiring less structural support than steel or concrete – yet its load-bearing strength is high.

Load spans and deflection limits

When assessing load-bearing design in relation to your balcony or external terrace/walkway, you should consult the individual manufacturer’s load/span tables for each profile to determine a suitable installation.

Load spans are measured in Kilonewton per square metre (kN/m2). At Neaco, we define our load span figures in terms of Light Duty, Medium Duty and Heavy Duty, determined by anticipated occupancy and use. The load span measurement (or spanning capability) of each profile progressively decreases between Light, Medium and Heavy Duty.

  • We define Light Duty, as 3kN/m2 UDL. or 1kN Point
  • We define Medium Duty, as 5kN/m2 UDL or 1kN Point
  • We define Heavy Duty, as 5kN/m2 UDL or 1kN Point


We provide this data along with deflection limit data. Deflection is the bending or “sag” caused by loading. A deflection limit is expressed as a fraction: clear span over a given number. For example, if a decking has a 1/200 deflection limit and is selected to span 180cm, it will deflect no more than 180/200 = 9mm (or 0.35 inches) under maximum design loads.  

Installing the structure should be in accordance with the manufacturer’s instructions and BS 6399-2. NHBC guidance recommends that the frequency of fixings meet the manufacturer’s recommendations, and be calculated to resist the wind uplift figures derived from BS 6399-2. The guidance goes on to state that structural steelwork should be designed in accordance with BS 5950 and Technical Requirement R5.


Safety is paramount when determining the loading requirements of your balcony or external terrace/walkway. It is important to consult a qualified structural engineer in conjunction with your chosen manufacturer to ensure that the installation is suitable for or all foreseeable use and occupancy. BS 6399 is the key reference for the performance and technical requirements, but expert advice is extremely valuable.

For advice on load-bearing requirements, please contact our product specialists on 01653 695721 or fill in our enquiry form here.