It has recently come to our attention that the British Board of Agrément is taking action to clarify its position on some waterproofing materials certified for zero falls roofs. Exposed zero falls roofs, where the waterproofing is not protected or part of an inverted roof system, are no longer the industry accepted solution they once were.
AccuRoof and zero falls roofs
When the updated British Standard BS 6229:2018 ‘Flat roofs with continuously supported flexible waterproof coverings’ was issued in 2018 we wrote this article about it, explaining how a zero fall roof is now defined as a ‘roof with a fall between flat and 1:80’. The new guidance had the aim of eliminating back falls and ponding water.
Before the update, single ply roofing systems were regularly built with flat (ie zero falls) gutters, even though gutters were recommended to be a minimum 1:80 finished fall. It is now quite common for whole roofs with an exposed membrane to be constructed with zero falls, because they take up less space.
More and more roofing systems have been released with third party approval for zero falls. An increasing number of products are now on the market with BBA certificates that state that they can be used in zero falls situations, and the certificates do not specify that they should only be used in a non-exposed situation.
However, with some exceptions (such as blue roofs, for example), AccuRoof’s approach is that getting water off a ‘flat’ roof is a very good idea, and with the right design advice taken up early enough, that shouldn’t be difficult for specifiers and contractors to achieve.
What’s wrong with exposed zero falls roofs?
A zero falls roof with exposed waterproofing, even with a design fall in compliance with the recommendations of BS6229:2018, will be more prone to some ponding water being present.
If the membrane is not protected or part of an inverted roof system, this ponding water will be visible, which is unsightly.
But ponding water is a red flag for other reasons:
- Safety: During twice yearly inspections or maintenance, operatives should not be walking in exposed ponding water which creates a slip hazard, especially in cold weather.
- Environmental Hazards: Ponding water attracts detritus, stagnation and breeding insects.
- Leaks: Ponding water can create additional damage if for any reason the membrane is compromised.
This is why AccuRoof have always recommended that zero falls are only used for protected and inverted roofs, where these hazards can be eliminated by the presence of protective layers.
What’s New?
The British Board of Agrément (BBA) are now informing manufacturers that during their renewal process for BBA certificates, their certificates will be changed to confirm that waterproofing recommended for zero falls cannot be left exposed, and should always be part of a protected or inverted roof configuration.
This aligns with the LABC Zero Falls Roof Guidance from 2021 which states that:
1.4 The waterproofing system must be a BBA certified monolithic liquid applied hot/cold system or hot melt system certified as suitable for zero-falls applications.
1.5 The system must be inverted type roof (i.e. not warm roof with an exposed waterproof membrane).
Advice to Specifiers
A zero falls roof system should always be part of a protected or inverted roof installation.
If you want to use zero falls, only use a system with third party accreditation for protected or inverted roofs.
Talk to us for advice on zero falls roofs. There are a number of systems we can recommend. For example, IKO’s Hybratech and Metatech are examples of liquid waterproofing systems which have new BBA certificates that confirm they should always be part of a protected or inverted roof installation.
