Achieving compliant balcony edge drainage for the updated NHBC Standards with the AliDeck System of Aluminium Decking and AliClad Flow Soffit Cladding
The information below refers to the 2022 NHBC Standards. For our latest updates, click the link visit our NHBC Standards 2024 page.
With the start of a new year comes new resolutions, aspirations and, for the construction industry, a new set of NHBC Standards for balcony drainage.
The National House Building Council (NHBC) is the UK’s largest provider of new home warranties. Around 80% of new homes built each year receive a 10-year NHBC warranty and approximately 50% of all new-build properties in the UK are directly inspected by NHBC Building Control Services Ltd.
As part of their inspection and warranty process, NHBC produce a detailed and comprehensive document each year that is applicable to any developments started in that 12 month period.
NHBC Standards 2022 is a weighty 430 pages long, covering all aspects of construction of new-build properties and outlining the requirements for receiving a warranty. Chapter 7.1 of Standards 2022 is devoted to “Flat roofs, terraces and balconies” and contains much important information for those involved in balcony design and construction, including clear direction on achieving compliant balcony drainage.
As in NHBC Standards 2021, it is stated that a “drainage system of outlets and downpipes should be… provided to all flat roof, balcony and terrace areas”, providing clarity that water management on balconies is an absolute requirement to achieve an NHBC warranty.
An interesting development in the 2022 Standards, though, is the subsequent new advice regarding edge drainage. In Standards 2021, NHBC did allow for edge drainage to be utilised in balconies but only with a string of caveats that must be met, quoted in full for reference;
Balconies and terraces which project no more than 2.5m from the face of the building may be drained over a perimeter edge into open space provided the run-off does not cause damage or staining to surfaces below, or damage or erosion to landscaping, or nuisance to people using or visiting the building. The drained edge should start at least 400mm away from an adjacent wall and be at least 25mm below any spill over level into the building e.g. underside of any door thresholds into the building. Concentrations of edge flow should be avoided, and water should be dispersed as evenly as practicable. Edge drainage should not be adopted over private gardens, streets, public pathways or over building entrances unless a suitable canopy or alternate protection is provided. The collecting surface should have no other surfaces relying upon it for drainage. The edge drainage should project and turn down to form a drip edge at least 30mm beyond the adjacent vertical surface.
Standards 2022 rewrites this section entirely, removing the mentioned caveats and providing a clear outline for permissible edge drainage, as follows;
A design approach for free draining balconies can be accepted if rainwater will always be routed away from the building to drain via a suitably formed soffit drainage tray that directs water to run outwards over a continuous formed perimeter edge.
There is brief further text to this that notes “where this drainage design is installed for stacked balconies on multi-storey elevations – the rainwater will tend to cascade down from these edge drainage slots as water runs off each balcony”, but this seems to be provided only as a point for consideration rather than any kind of preventative caveat. The new section concludes with the requirement for adequate ground drainage to prevent ponding or flooding of water at floor level.
This simpler approach to balcony edge drainage is a positive and practical step forward for NHBC’s consideration of balconies. With these concise requirements now in effect, the specification of effective and compliant drainage for projecting balconies in particular has just become much more straightforward.
Indeed, our AliClad Flow balcony soffit cladding system is the ideal, off-the-shelf solution to meet this new guidance. With the interlocking AliClad Flow boards forming a soffit drainage tray and laid to a recommended 1:80 fall away from the building to a perforated edge gutter, effective edge drainage is achieved.
Looking at both NHBC Standards 2022 and BS8579:2020, the guide for the design of balconies and terraces, it is now clear that edge drainage for balconies is perfectly permissible, with no major caveats other than BS8579 stating a maximum projection of the edge-drained balcony from the building of 2.5m, which is significantly further than is typical for residential balconies.
To discuss your balcony project and explore your options for NHBC and BS8579 compliant edge drainage please call the AliDeck team on 01622 235 672 or email info@alideck.co.uk.
