Flat roofs are often used in the built environment, and they are a common feature in mission-critical projects such as data centres, transport hubs, hospitals and research facilities. In these locations, performance, reliability and durability are essential – any failure can have serious consequences.
That’s where BS 6229 comes in. This British Standard provides best-practice guidance for the design, construction and maintenance of flat roofs, helping to reduce risk and improve performance.
The standard was updated in 2025 to reflect changes in construction methods, materials and performance requirements. At Jones Weatherproofing, we keep a close eye on developments like these, and we are committed to ensuring our liquid-applied weatherproofing system is in line with the latest industry recommendations.
In this guide, we take a close look at BS 6229:2025 – what it is, what changed in the latest update and what those changes mean for architects, designers, contractors and weatherproofing teams.
What is BS 6229:2025?
BS 6229:2025 is the code of practice for flat roofs with continuously supported flexible waterproof coverings.
It provides guidance about how flat roofs should be designed and constructed. and it aims to mitigate risks such as poor drainage, inadequate ventilation and ineffective vapour control. Because BS 6229 considers the complete lifecycle of a flat roof, it also includes guidance on inspection and maintenance.
The guidance included in BS 6229 will be useful for anyone involved in the design, specification, installation or maintenance of flat roofing, including:
- Architects and designers
- Specifiers
- Contractors and installers
- Weatherproofing specialists
- Maintenance service providers
- Building owners
- Construction product manufacturers and suppliers
What types of roof constructions are covered by BS 6229:2025?
The standard applies to all flat roofs that use continuously supported flexible waterproof coverings. This includes roofs supported by:
- Heavy structures such as concrete slabs
- Lightweight decks (metal or timber)
It also covers curved roofs with a pitch of up to 10 degrees.
What has changed in the BS 6229:2025 update?
Following a five-year review process, which involved input from across the roofing sector, the latest version, BS 6229:2025, was published in December 2025. It replaced the previous version, BS 6229:2018.
The update aims to improve flat roof performance, determine responsibilities and increase safety. It includes revisions to Clause 4 (design), Clause 5 (materials) and Clause 7 (care and maintenance). Terminology and definitions have also been clarified to help improve understanding across the roofing sector.
Matt Jones, commercial director at Jones Weatherproofing, explains that some of the changes are critical to the weatherproofing, “In terms of flat roof weatherproofing, some of the key changes to BS 6229 are about deck preparation and surface quality,” he says.
Deck preparation and documentation
The updated standard highlights the importance of careful deck design and preparation. It now requires a level survey and documented handover for decks or slabs
“This helps ensure that defects are identified early and that responsibility is clearly defined,” Matt says. “Knowing the condition of the roof deck can affect the way we approach weatherproofing, so the information these surveys provide can be instrumental in keeping the structure and its contents protected,” he adds.
Surface regularity
The surface quality is another important factor in long-term roof performance and weatherproofing.
Matt explains, “Uneven roof surfaces can lead to ponding or cause stress points in roofing membranes, so the surface quality of a roof is key in how weatherproofing performs long-term.”
Surface regularity (SR) classes describe how flat a roof deck is, based on defined tolerances. SR1 is the highest standard, while SR2 is generally acceptable for most roofing applications. The updated standard places greater emphasis on specifying and verifying surface regularity.
“An irregular surface doesn’t necessarily mean a roof can’t be effectively weatherproofed,” Matt adds. “The SR classes help the weatherproofing team better understand the flat roof’s specific requirements.”
Other changes to the new BS 6229:2025 include:
- Roof falls and drainage – To support drainage on flat roofs, there is now a minimum 1:80 finished fall for general roof areas and internal gutters. The standard gives additional detail about prefabricated and site-formed falls. It also clarifies responsibility for back falls, which should help to improve installation practices and ensure that flat roofs don’t have unintended back falls.
- Blue roofs – Blue roofs are designed to temporarily store rainwater and release it in a controlled way. BS 6229:2025 provides new guidance based on recent blue roof innovations and flat roof water management.
- Thermal performance – The new guidance includes a 2.5% insulation increase for inverted warm roofs. This aligns with other energy efficiency targets, such as Approved Document L: Conservation of Fuel and Power.
- Condensation control – The updated standard addresses condensation risk in accordance with BS 5250:2021, the code of practice for the management of moisture in buildings.
- Fire safety – Fire performance has been reinforced in line with building regulations, including updated combustibility requirements within the roof build-up and clearer expectations for assessing fire performance. The revised standard also states that cross-laminated timber (CLT) decks should be avoided where possible, due to concerns around its fire behaviour, as well as moisture management and long-term durability. Where CLT is used, careful design and risk management are essential.
The update also highlights the importance of:
- Efficient information exchange between project teams
- High-quality installation standards
- Effective maintenance planning
Together, these changes should help to improve the quality and performance of flat roofs across the UK.
Learn more about BS 6229:2025
To view the full version of the BS 6229:2025, the standard can be purchased from the British Standards Institute. The National Federation of Roofing Contractors (NFRC) has also produced a 16-page guide to the updated standard.
At Jones Weatherproofing, our team has implemented the changes to BS 6229:2025 across all of our projects, and our weatherproofing experts are available to provide advice and guidance on meeting the latest requirements.
Get in touch to discuss how Jones Weatherproofing can support the weatherproofing of your upcoming projects.
