It’s a question we get asked a lot from contractors working on commercial and residential projects. As more building owners are looking for ways to maximise space and transform unused areas into vibrant terraces, contractors are having to adjust to the challenge of converting these spaces.
Broadly speaking, the majority of flat roofs are suitable for conversion to a useable terrace, provided the roof deck is appropriate. The roofs of commercial buildings are likely to be constructed of metal, timber or concrete all of which should provide a stable and regular surface with sufficient load-bearing capacity to support the dead and live loads of a terrace in use. We always advise consulting a suitable professional.
Roofs do come in many shapes and sizes, so when we’re asked this question, we start with these design considerations.
Commercial and large multi-residential flat roofs will be either inverted or warm roofs, with the main difference between the two types being the location of the insulation layer.
Buzon pedestals were also specified for the roof terraces on The Broadway – a mixed-use development in central London. This project saw a mix of decking and porcelain surfaces, both installed on an inverted roof system encompassing over 1,300 square metres of valuable outdoor space.
Domestic roof extensions, on the other hand, tend to use a cold roof build up. In this construction the insulation is between ceiling joists, rather than above. Waterproofing is typically applied to a plywood layer which sits above the insulation on a ventilation void made of timber furrings/ battens. It's for this reason that we would not recommend it as a suitable base for a terrace as the hidden furrings can lead to instabiity of the terrace as well as damage to the waterproofing.
Once the suitability of the roof structure is established, the next consideration is how to achieve a level surface for the terrace even if the roof structure itself is laid to falls.
This is where Buzon pedestals come into their own. Any falls or unevenness on the roof deck can be compensated using millimetre-precise slope correction functionality to ensure a perfectly level finish whilst still allowing drainage on the roof to function as designed.
Many commercial sites will also need to maintain access to vital building services via the roof. Elevating the terrace via a pedestal system hides any unsightly pipework and utilities, yet allows for sections of the terrace to be removed when access is required.
Prior to 2019, the National Classification System, BS 476- 3:2004 was used to determine external fire performance for roofs.
This has now been fully replaced by the European Classification System BS EN 13501-5. This classification system comes with five ratings: with BROOF (t4) the highest rating and acceptable on any roof in any situation, regardless of use and proximity to neighbouring buildings. This unrestricted use means that BROOF(t4) is now considered to be the best practice choice for all roof terrace projects.
In order to receive a classification, roof systems are tested (and rated) as a complete build-up, rather than relying on the rating of the individual components or products as is the case with balconies.
The ‘system-led’ approach applied to roof terraces means that all components – from membrane right up to surface material, including the pedestal system – are rated as a whole. As such, the components of the tested system cannot be swapped or replaced for other products, unless the resultant new ‘system’ has also passed the correct testing.
Buzon standard pedestals have been tested with a variety of surface finishes including 20mm porcelain and composite decking with both warm and inverted roof systems from leading manufacturers. Contact us for more information on compliant systems.
The shape, size and material of supporting pedestals must be considered alongside the waterproofing and insulation used on the roof.
Fire-rated metal pedestals carry a higher risk of penetrating the roof membrane because of their sharper edges, while the use of square-based pedestals can cause issues if the sharp-angle corners are allowed to damage the membrane.
To prevent this type of damage, the Single Ply Roofing Association (SPRA) and Buzon recommend using pedestals with a round base and minimum diameter of 170mm to ensure even weight distribution, regardless of the material they are made from. Importantly you may invalidate your roofing warranty if you use pedestals that don't meet those requirements.
In summary, the flat roofs of commercial buildings can provide the potential for some great open spaces, giving an attractive extra amenity for building occupants. While most such roofs will be eminently suitable for a range of surfaces there are important issues to consider at the design stage and we would always recommend contacting suppliers directly for guidance.
Why not speak to one of our experts? Give us a call on +44 020 8614 0874 or get in touch today!