Roofing
Designing Podiums, Balconies and
Green Roofs to meet Building Regulations
Demand for private and communal outdoor space within a buildings design has never been higher, especially in inner city environments where space is limited. Whether a commercial office building such as the ‘Walkie Talkie’ that houses the publicly accessible ‘Sky Garden’, ‘Crossrail Place’, the new terminal at Canary Wharf or a residential development such as Chelsea Creek, facilitating ‘outdoor’ use within the structure of a building is a post millennium requirement.
Whether an accessible green roof, hard landscaped podium or internal balcony these applications all pose the same construction problems: how to waterproof them, how to insulate them, how to meet access regulations and how to build them with minimal risk from other trade activities.
Radmat Building Products, a supplier of many forms of waterproofing system for all types of roof construction would always lean towards an inverted, or protected, roof construction. This is a form of warm roof construction in which the insulation is placed above the waterproof layer with ballast, paving, timber decking or a green roof used to hold the insulation in place.
In inverted roof construction the waterproof layer also acts as a vapour barrier, eliminating the risk of condensation within the roof construction. The insulation provides thermal performance and has the added benefit of protecting the waterproofed surface from impact damage and the elements. Whether gravel ballast, paving, timber decking or a green roof the upper finish layer further protects the insulation and waterproofing membrane beneath. Unlike dark coloured roof finishes the surface materials also contribute to reducing the Urban Heat Island affect, making a positive contribution to a city’s, and the world’s climate.
The limitation in application tends to be the structural load of the system; a loading of 80kg/m2 is typically required to retain the insulation on the roof. However with most inner city developments being concrete framed this is less of a concern.
From a construction perspective the inverted roof can offer a significant programme benefit. Radmat’s PermaQuik PQ6100 is BBA Certified for installation at zero falls, removing the time and cost of adding a screed to falls. This application is completely compliant with Building Regulations provided appropriate checks are undertaken.
BS6229:2003 is the document that the Building Regulations refer to with regards to falls on flat roofs; and BS6229 specifies minimum finished falls of 1 in 80, achieved by designing to 1 in 40. But 2003 was a long time
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ago, and 2016 BS6229 will be updated to include zero falls applications as defined by ETAG 031, ETAG 005 and British Board of Agrément in Building Bulletin 4.
ETAG 031 is a European Guideline published in 2010 that sets the requirements for the certification of zero falls design and calculation, BBA Building Bulletin 4 is a précis of the requirements. Both these documents are recognised by the NHBC and zero falls construction is accepted in their Chapter 7.1 standards publication, updated in November 2015. Reference to zero falls application also appears in the LRWA Hot Melt Code of Practice and the GRO Green Roof Code.
When checking the suitability of a roof for zero falls application it is important to ensure the manufacturer assesses the deflection plan for the deck to identify any low points that are not near rainwater outlets. If the outlets cannot be moved to areas of high deflection then other options should be explored with the manufacturer to ensure the effective dispersal of rainwater.
Once the zero falls design of the concrete slab has been signed off the next consideration is compliance with Building Regulation’s Part L and Part M. Insulation in an Inverted roof has traditionally been thicker than in a warm roof, but as U values increase new products have been developed. Radmat’s ProTherm G Extruded Polystyrene insulation has a 0.034 W/m2K Lambda value, enabling a 200mm thick board to achieve a 0.15 U value. For projects where threshold height compliance with Building Regulation Part M are a focus, ProTherm Quantum Vacuum Insulated Panel system can achieve the same 0.15 U value with only a 40mm thick board.
For assistance in designing your next inverted roof, podium or balcony, or to receive the new RIBA CPD Providers Network accredited seminar ‘Inverted Roofing: a guide to design & specification’ please do not hesitate to contact us.
TEL: 01858 410372 53
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