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EXTERIORS
What lies beneath?
Julian Thurbin of Wallbarn explores the key factors to consider when specifying the infrastructure beneath decking or paving that may be hidden, but is essential
A
well-designed, specified and installed decking or paving area can form the crowning glory of an outdoor space. But what lies beneath these new-build or retrofitted spaces is key to ensuring their safety and long-term performance. Many decked, paved or tiled areas are supported by a hidden substructure of pedestals or rails which must be robust enough to withstand loads placed upon them as well as being weatherproof, rot-proof, durable and long-lasting. This is especially important for public areas and if designers expect heavy traffic and/ or planters, street art or heavy furniture on the suspended surface. Substructures must also offer flexibility to deal with deck falls, interruptions in the deck surface, and different surface finishes. Therefore, understanding how the space is going to be used (domestic or commercial; public or private; fire-rated; multiple levels?) lays the groundwork for selecting the most appropriate and cost-effective substructure to support the decking or paving selected.
Paved hard landscaped areas supported by pedestals have slim gaps – millimetres wide – between pavers. These are formed when slabs are clicked into place on special lugs attached to pedestal headpieces. Lugs hold the floor elements in position and the gaps facilitate drainage, with rainfall directed into channels beneath the hard landscaping, either at street or roof level. This system also creates an opportunity to collect rainwater for recycling, on blue roofs for example. Decking will have a joist beneath the boards connected using mechanical fixings/clips. Often the joists will be laid onto adjustable plastic pedestals
Floating floor
Entry level fixed-height solutions to self- levelling, adjustable height, heavyweight and Class A fire-rated pedestals all provide a ‘floating floor’ with uniform flat surfaces separating paving/decking from the base structure, improving drainage and
protecting the surface beneath. Pedestals require no penetrations of roof membranes (there are no mechanical fixings), protect the roof finish, are lighter than bedding into mortar, and provide a quick and cost-effective way to transform areas into usable spaces. Paving can be lifted to allow access to the roof deck if required.
Specifiers and contractors have a wide choice of pedestals, substructure systems and paving/decking finishes. But there are pitfalls to be avoided and key decisions to be made to ensure the required finish and performance is achieved.
Class A?
Is the project at height, and within scope of Approved Document B, and BS 8579, BS 8579:2020 Guide to the Design of Balconies and Terraces? If so, only Class A non-combustible metal pedestals, substructures and fixings, and Class A paving can be specified in order to comply with relevant Building Regulations. There are a number of solutions marketed as ‘fire-safe’ but it’s worth making sure that the system manufacturer/ supplier can demonstrate compliance and that the pedestals do not have flammable elements such as rubber ‘gaskets.’
Understanding how the space is going to be used lays the groundwork for selecting the most appropriate and cost- effective substructure
andscaping & External Works_ Decking -
Wallbarn.indd 1
WWW.BUILDINGCONSTRUCTIONDESIGN.CO.UK
13/06/2024 11:43
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