Nail Sickness: When to Repair and When to Replace

What is Nail Sickness?

Nail sickness is the corrosion of the steel nails that fix concrete or clay interlocking roof tiles to the timber battens beneath. Every interlocking tile is fixed with two nails that pass through a pre-punched hole at the tile’s headlap. When those nails corrode, they expand as they rust, splitting the nail hole in the tile. The tile loses its grip and begins to slide down the roof plane, initially stopping when it catches on the tile below, but eventually slipping past it if the neighbour nails are in the same condition.

Steel nails in roofing applications have a design life of approximately 40–50 years in moderate UK climates. Devon’s above-average rainfall and the high humidity of the Exe Valley and coastal areas at Exmouth and Topsham shortens this to 35–45 years on many properties. Roofs installed in the 1960s and 70s across Exeter’s estate suburbs — Whipton, Pinhoe, Wonford, Pinhoe — are now at or past this threshold.

How to Spot Nail Sickness on Your Roof

The most obvious sign is tiles that have slipped from their original position. Look for tiles that are sitting lower than their neighbours, creating a step in the tile pattern. On a heavily nail-sick roof you may see multiple tiles displaced in the same section, which indicates the nails in that area have failed at roughly the same time.

The British Standard for slating and tiling, BS 5534, requires corrosion-resistant fixings such as aluminium or stainless steel — steel nails used before its wider adoption are the root cause of nail sickness.

Source: BS 5534

A subtler sign is a small pile of broken tile material in the gutters or on the ground directly beneath a roof section. When a corroding nail expands and splits the tile hole, the tile head can fracture across the fixing point. The fragments fall and collect at the eaves.

If you can access the loft safely and have a torch, look at the felt from underneath. If you can see daylight through the roof plane — blue sky visible between tiles — tiles have moved enough to create gaps. If the felt shows water staining or softening in specific areas, those areas correspond to tiles that have been displaced long enough for rain to reach the secondary weatherproofing.

The most reliable assessment is a survey from the roof itself. A roofer can test nail condition by applying gentle upward pressure to individual tiles at representative points across the roof plane. Tiles that respond to this pressure have corroded nail fixings. Tiles that resist indicate sound or partially degraded nails.

Why Nail Sickness is So Common in Exeter’s Suburbs

The estate housing built across Exeter and surrounding Devon towns in the post-war decades — the 1950s through to the late 1970s — used concrete interlocking tile almost universally. These tiles were a significant improvement over the clay plain tile and Welsh slate of the previous era: cheaper, faster to lay, more consistent in quality, and available in volume for the mass house-building programmes of the time.

The steel nail was the universal fixing. Stainless steel nails, which resist corrosion indefinitely, were available but cost more. The volume house-building sector used standard bright steel throughout — it met the specification of the day and performed within its design life. The problem is that the design life has now expired.

Devon’s climate accelerates the process. The county’s above-average rainfall means roof coverings in Devon see more moisture cycling than equivalent properties in drier regions. The Exe Valley creates a humidity funnel that affects Exeter, Tiverton, Crediton and surrounding towns. Coastal properties at Exmouth, Dawlish and Topsham experience salt aerosol that accelerates corrosion further. A nail that might last 50 years in a dry English Midlands climate may fail in 35–40 years in Devon.

Is your Devon roof showing signs of nail sickness? Call 01392 759 295 for a free survey. We assess the full extent, tell you honestly where on the repair-vs-replace spectrum you sit, and quote both options so you can make an informed decision.

Repair vs Replace: The Honest Assessment

The repair-versus-replace decision on a nail-sick roof is not about the age of the roof or how many tiles have slipped so far. It is about the extent of the condition across the roof plane and the cost trajectory over the next 5–10 years.

Repair is the right answer when: Nail sickness is confined to a specific section of the roof — typically a single slope or a defined area where the nail specification was weaker. When less than 20–25% of the roof plane tests as mobile under hand pressure, targeted re-nailing with stainless fixings and tile replacement is good value.

Replacement is the right answer when: Nail sickness covers more than 30% of the roof plane in a consistent pattern across the whole surface. At this point, every tile is in the same condition — the ones that haven’t moved yet simply haven’t been nudged by wind or frost. The repair cost over 5 years — attending to successive tile failures across the whole roof — typically approaches or exceeds the cost of a planned replacement.

The crossover point is usually clear in the survey. We tell homeowners honestly which side of it they are on.

What a Re-Roof on a Devon Nail-Sick Property Involves

A nail sickness re-roof is a full replacement: strip the existing tile, inspect and replace battens where rot or splitting is found, lay new breathable underlay, fix new tile with stainless ring-shank nails on new battens. The concrete or clay interlocking tile being replaced is generally still structurally sound — it is the fixings that have failed, not the tile itself. Modern concrete or clay tile on stainless fixings gives a roof with a 40–50 year low-maintenance life ahead of it.

For Devon properties, we always specify stainless ring-shank nails rather than the smooth-shank equivalent. The ring-shank provides significantly better pull-out resistance than a smooth nail, and combined with stainless steel corrosion resistance, represents the most durable fixing available at modest additional cost over standard product.

The programme for a standard 3-bed semi is 4–6 days. Batten replacement takes additional time if the battens are extensively deteriorated, but on most Exeter estate properties installed with preservative-treated timber, the battens are in better condition than the nails.