Construction hoarding design is very important as the estimated life of the hoarding will affect the loadings to be used in the design and the types of materials used. Longevity and durability of the hoarding is a design consideration. The life a hoarding shall be specified by the primary developer, end client or if not specified or agreed elsewhere up to ten years.
Designing for wind, crowd and vehicular impact
For most quality Construction hoarding design the important design element is the lateral and horizontal loading from the wind. Subject to the location impact could also come from crowd loading and, or vehicular impact.
Guidance that a minimum notional horizontal line load of 0.74 kN/m shall be considered to act on all hoardings. This load will be considered to act at a height of 1.2m and may be applied from either side of the hoarding. For areas inclined to become overcrowded like pavements, shopping malls, retail areas, stadiums, a larger value of horizontal load should be considered from the public side.
Wind load varies along the length of the hoarding and increases near corners and free ends. The position of a hoarding will also affect the movement of wind around it. For example the wind on a hoarding will pass over it and create both pressure and suction forces on the hoarding, whereas when installed in front of a building the wind is stalled by the building.
The wind will cause either pressure or suction depending on the direction of the wind. In all cases the wind will accelerate near the edges of hoardings and buildings.
If the hoarding is inside or with an enclosed shopping area, wind loading would not need to be considered.
Crowed loading needs to be consideration in populated areas, such as town centres and restricted railway platforms. These loads can be significant, particularly if there is a requirement to resist crowds in stadiums or farm animal crushing loads. Where overcrowding is a hazard, the load is considered to apply from the public side only.
Materials used for Construction Hoarding Design
The most common face material for hoardings is plywood, or oriented strand board (OSB/3). The face material is usually fitted to extent vertically between horizontal rails. External hoardings will require a water resistant wood based product. For strength it is recommended that the minimum thickness of a panel for an external hoarding should be not less than 16mm.
There are certain circumstances that the hoarding will require some fire proofing e.g. shopping centres and underground construction sites.
All fixings need to considered for the duration of the Construction hoarding design and when a long development is expected, the hoarding need to be designed for ease of regular check-ups. Nailed connections are to be avoided as joints tend yo become loose under cyclic loading and deteriorate with age.
The number of fixings should be increased near the ends of hoardings as wind pressure is larger due to the effects of local turbulence of the wind around the ends.
It is suggested that screws, bolts, nuts and washers shall have a protective coating like hot dip galvanised. The use of stainless steel fixings will rarely be warranted on a temporary Construction hoarding design.
Quality hoarding workmanship
The quality of hoarding workmanship should be to recognised works standards. Installers assembling and erecting a quality hoarding should be competent and be aware of correct good practice.
Some examples to be considered would include:
- Where using timber posts in holes with concrete, place the post in first, and then pour the concrete.
- Ensure the direction of the facing material is as correct.
- Fixings are used and fit for purpose.
- Add more fixings and closer post centres near to the ends of hoardings where the wind loads are larger.
Inspection in use
All hoardings should be frequently inspected during their operational life. At the time of installation of the hoarding an initial risk assessment should be carried out. Periods between formal inspections of hoardings should be a maximum of six months. As construction developments are fast changing the hoarding might also change and there for inspections may require to be more frequent. Additional inspections should be carried out after any unusual event such as high winds or impact. The life of a quality Construction hoarding design can be extended by regular inspections and maintenance.