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This pattern often indicates that the roof covering is intact but the underlay beneath it has deteriorated and can only manage light moisture before being overwhelmed. It can also indicate that the flashing around a chimney, dormer, or abutment is failing under sustained water pressure. A thorough inspection from a Carterton roofer — including inspection from inside the loft space — is the best way to identify the precise source.

Flashing is the weatherproof material — usually lead, though sometimes mortar fillet or modern alternatives — that seals the junction between the roof covering and vertical surfaces such as chimney stacks, dormer cheeks, parapet walls, and abutments. It fails most commonly through age and fatigue (lead work-hardens and eventually cracks), through inadequate original installation, or through mortar pointing around lead steps crumbling away with weathering. Failed flashing is one of the most common causes of roof leaks.

Roof sagging can result from several causes, including deteriorated or undersized rafters, roof spread (where the walls are being pushed outward by the weight of the roof structure), rot in the timber roof structure due to prolonged water ingress, or removal of load-bearing elements during works. Any visible sagging or distortion of a roof should be assessed urgently by a roofer and potentially a structural engineer, as it may indicate a structural concern requiring prompt action.

Yes, over time. Moss retains moisture and, in freezing conditions, the freeze-thaw cycle can cause tiles and slates to deteriorate more rapidly. Moss growth can also lift tiles and displace them over time. While a moderate moss covering will not cause immediate damage, heavily moss-covered roofs benefit from treatment and removal. Biocide treatments can kill the moss, allowing it to be removed carefully without damaging the tiles.

Ridge tiles are traditionally bedded in mortar, and as that mortar ages and weathers, it cracks and loses adhesion — allowing the ridge tiles to shift, slip, or fall. This is a very common problem on roofs over 15 to 20 years old. The solution is re-ridging — raking out the old mortar, re-bedding the ridge tiles, and repointing to seal the joints. Modern dry-fix ridge systems are an increasingly popular alternative, avoiding mortar altogether and providing a more durable, maintenance-free solution.