A panel that performs perfectly indoors can be off site and across a car park after one bad night outdoors. Wind does not test the strength of the sheet so much as the fixing arrangement and the edges, and those are what need specifying for an external installation.
Wind behaves differently on flat panels
Wind loads are suction as much as pressure. A panel fixed at its edges can be pulled away from the structure rather than pushed against it, particularly at corners and eaves where uplift concentrates. Any flat surface mounted slightly away from a backing behaves a little like a sail, and the fixings have to resist both directions.
Fixing density and edge restraint
Most failures start at an edge or corner and then propagate, because once one fixing releases the load on the neighbouring ones roughly doubles. Increase fixing density towards edges and corners rather than spacing uniformly, and use washers or load-spreading plates – a screw pulled through a panel edge is the standard failure photograph.
UV and weathering
Polypropylene degrades under ultraviolet exposure unless stabilised. Standard material chalking and embrittling over a season outdoors is normal, not a defect in the batch. Where an installation is intended to last more than a few months outdoors, specify UV-stabilised material and accept it costs more – replacing hoarding mid-programme costs considerably more.
Thermal movement
Panels expand and contract measurably between a cold night and a sunny afternoon. Rigidly fixed with no allowance, they bow, oil-can and eventually pull fixings through. Allow clearance at joints and use slotted or oversized holes where possible so movement is absorbed rather than resisted.
Inspection and storm procedure
Somebody needs to look at external protection after bad weather, and somebody needs to be able to take it down or reinforce it quickly. Write the threshold into the RAMS – above a given forecast wind speed, inspect before works start – and make sure the person responsible knows they are responsible.
Public interface
External hoarding is also a public-facing barrier. It must remain secure, must not present sharp edges or protruding fixings at pedestrian height, and usually has to satisfy whatever the local authority requires for hoarding at the boundary. Treat it as a structure rather than as covering, because in a public place it is one.
What a fixing schedule looks like
Practical arrangements usually fix at perhaps three hundred to four hundred millimetre centres in the field of a panel, tightening to around one hundred and fifty millimetres along edges and towards corners, with load-spreading washers throughout. Exposed sites and large panels need more; sheltered locations and small panels need less.
Whatever the schedule, somebody competent should review it against the actual exposure rather than against a standard detail drawn for somewhere else. Most hoarding failures investigated afterwards turn out to have used a perfectly reasonable schedule intended for a considerably more sheltered location.
Corner detail on external runs
Corners take the highest uplift and are where external failures begin. Add an extra fixing line close to every corner, consider a continuous angle trim to tie two faces together, and check corners first after any significant wind event. A few additional fixings there prevent a disproportionate share of failures. Where the requirement is a barrier rather than a covering, see temporary partitions and barriers.
What we can do
We supply honeycomb panels in UV-stabilised grades for external use, and we will say clearly when a job needs properly engineered hoarding rather than panels. Send the location, exposure and intended duration and we will advise – including where the honest answer is buy something else.