Chimney flashings on new build housing are one of the most consistent sources of post-handover defect claims in the two-year warranty period. The mechanism is predictable. Water finds any weakness in the flashing detail around the chimney and enters the roof structure, showing up as staining on ceilings below, mould in roof voids, or actual visible water ingress during heavy rain.
Why chimney flashings fail on new build roofs
The reason chimney flashings are prone to failure is that they involve multiple materials meeting at multiple angles, all of which have to be weatherproofed against water running down the chimney face and across the roof surface. Lead soakers between courses of tiles. Front apron flashings. Back gutter behind the chimney. Chase cuts into the brickwork. Sealant details where mechanical dressing is not adequate. Each is a discrete workmanship item.
The Lead Sheet Association guidance sets out the standards for each component. Code number for the lead sheet. Overlap dimensions per pitch. Fixing patterns. Chase cut depths. Where the guidance is followed by qualified operatives, the flashings hold up for decades. Where it is not followed, the failure emerges within months.
Globe Roofing's chimney flashing work on new build housing uses qualified leadworkers to LSA standards. The materials specified match the exposure zone. The chase cuts are checked for depth before flashings are installed. The install is documented per plot as part of the sign-off pack. Each of these is a small discipline. Cumulatively they produce a defect rate that is materially lower than the industry average on comparable schemes.
Choosing an installer with trained leadworkers
For developers and QSs, the specific question at tender stage is whether the roofing contractor has trained leadworkers or is using generic roofing labour to fabricate the chimney flashings. The difference in workmanship quality is visible in the finished detail but only if you know what to look for. The difference in warranty period defect rate is significant.
There is a specific commercial consideration worth mentioning. Chimney flashing failures often manifest as internal water damage in occupied properties. The visible damage requires internal remediation as well as the roof-level repair. The total cost of a single chimney flashing failure claim, including internal make-good, can exceed a thousand pounds. Across a portfolio of comparable schemes, the cumulative cost of avoidable chimney flashing failures adds up quickly.
The specification decision at design stage matters as well. Modern breathable underlays interact differently with chimney flashing details than older non-breathable underlays. The soaker sequence around a chimney needs to account for the underlay's water shedding path. Where the sequence is wrong, water finds a route into the roof void even where the visible flashing looks correct.
Chimney flashing on refurbishment work
On refurbishment work, chimney flashing is particularly demanding because the existing chimney structure may have moved or degraded over time. The flashings that were adequate for the original construction may not seat correctly on the current chimney condition. A survey before flashing installation is essential.
For QSs reviewing roofing tenders, the specific question about chimney flashings is worth raising directly. A contractor whose tender addresses chimney details explicitly, references LSA standards, and indicates leadworker qualifications is a different proposition to a contractor whose tender treats chimney flashings as an incremental extension of standard roofing.
The cost difference between correctly specified and installed chimney flashings and the alternative is not large. The warranty period claim rate difference is significant. The arithmetic favours getting it right at first installation rather than paying for claims across the following two years.
Talk to Globe Roofing
To discuss chimney flashing detailing on your scheme on your scheme, contact Globe Roofing on 01223 890727 or email enquiries@theglobegroup.co.uk.
