by
Dr Jianqiang Mai | Managing Director, CHPK Technical Services
The British Standards Institution has published a revised PAS 9980, the code of practice for fire risk appraisal of external walls on existing blocks of flats, and from October appraisals are being carried out under the new guidance. First issued in 2022, the update keeps the core principle that remediation should be proportionate to the actual risk a building presents, not a blanket removal of anything combustible.
That sounds simple. In practice, the detail matters, and small changes in wording can have big consequences for residents, building owners and remediation budgets.
Over the coming months, our technical team will publish a series of short articles, each taking one topic from the revised guidance and explaining what it means on real buildings.
We start with one of the most common questions we are asked: what happens to timber-decked balconies?
Under the revised guidance, the fire performance risk factor of an area of timber decking of around 1m x 2m on a balcony is rated as Neutral, therefore, it may be concluded that the timber deck can be retained. That figure is drawn from fire test research and gives assessors a clearer reference point than the original 2022 wording, which was more loosely defined as timber “of limited extent”.
This is a welcome step. But a number alone does not tell a building owner what to do. The real questions are what the allowance means in practice, and what a proportionate proposal for a given building should look like. Answering those means looking past the headline figure at how each balcony is actually built.
The current guidance does not distinguish between different balcony boundaries, yet the boundaries of a balcony have a significant impact on how fire could spread.
Getting this wrong cuts both ways. Treat a higher-risk balcony as acceptable and residents could be put in danger. Treat a low-risk balcony as unacceptable, and owners and leaseholders could face high, unnecessary cost and disruption.
At CHPK, every appraisal starts with resident safety. From there, we believe the right answer comes from understanding the specific building, not from applying the new recommendations in full as a fixed rule.
In practice, that means we:
This is a more nuanced approach, and it takes more technical work. We think it is the only way to get outcomes that are both safe and fair to the people who live in and pay for these buildings.
A 1 m x 2 m timber deck installed at a corner between two walls can generate a flame height of 1m to 1.7m, thermal radiation to the ceiling of 6.7kW/m2 to 12.8kW/m2, and convective heat transfer from the plume to the ceiling. This can cause direct vertical spread of fire from one floor to another. Consider the fire performance risk factor for this scenario: Negative is appropriate.
By comparison, the same timber deck installed against a single wall will generate a flame height of 0.3m to 0.7m, thermal radiation to the ceiling of 1.3kW/m2 to 2.2kW/m2, plus convective heat transfer from the plume to the ceiling. This is unlikely to cause direct fire spread from one floor to another vertically. Consider the fire performance risk factor for this scenario: Neutral is appropriate.
If your building has balconies with timber decking, do not assume they must all be stripped out, and do not assume they can all stay. The answer depends on how they are built. An appraisal that looks closely at balcony type and position can avoid both unsafe outcomes and unnecessary cost.
Our technical team is happy to talk through how the revised PAS 9980 applies to your portfolio.
