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Maintenance AdviceMarch 2025
Nail Sickness on Kent Roofs: What It Is, What to Do
Nail sickness is one of the most misunderstood roof conditions we deal with across Maidstone and Kent. It's often invisible from ground level until advanced, and when diagnosed, homeowners are frequently told they need a full re-roof when the reality is more nuanced.
Nail sickness — the corrosion and failure of the iron nails originally used to fix roof tiles and slates — is the defining maintenance challenge for Victorian and Edwardian properties across Maidstone. The town centre, Fant, Bearsted village, Tonbridge and surrounding Kent towns all have pre-1950s roofing at or past the age where nail sickness becomes structural rather than cosmetic.
What Actually Happens
Original Victorian and Edwardian roofing used iron wire nails to fix slates and clay tiles. Iron corrodes. After 80–100 years in the wet conditions of a Kent roof space, these nails have often reduced to a thin shell or disappeared entirely. The tiles then rely solely on their nibs — small protrusions at the head that hook over the batten — to stay in place. This provides almost no resistance to wind uplift or vibration.
The result is progressive, apparently random tile or slate loss across different areas of the roof. This scattered pattern is the diagnostic signature of nail sickness — distinguishing it from localised damage caused by impact, moss-related lift, or mortar failure.
Repair vs Replace: The Real Answer
If nail failure is localised to one slope or a limited area, re-nailing that section with copper nails is viable and cost-effective. Copper nails don't corrode and will outlast the tiles themselves. If nail failure is widespread across the whole roof, a full strip and re-lay is the only lasting solution — patching extends life by two to three years at most before the next batch starts slipping.
Key diagnostic question: Is tile loss occurring in a localised area, or in scattered positions across different slopes? If scattered, get a loft inspection before committing to any repair strategy.
Nail sickness follows a predictable progression that correlates closely with the age of the roof and the original nail specification. Ungalvanised iron nails — used universally on pre-war properties in Maidstone — begin to show significant corrosion from the 60–70 year mark. The nail doesn't fail suddenly; it reduces in cross-sectional area as the iron oxidises, progressively losing its tensile strength. By the 80–90 year mark, many nails on an uninspected pre-war roof have corroded to a fraction of their original diameter. At this point, the tile or slate is held by nib contact alone.
The transition from nail-dependent to nib-dependent fixing doesn't immediately cause tile loss — tiles sitting correctly on properly maintained battens can remain in place by nib contact for years. The acute presentation of nail sickness is typically triggered by a wind event of moderate but not exceptional severity. Tiles that would have been held by corroded nails in 5mph wind move when the wind reaches 20–25mph. This is why nail-sick roofs present with progressive tile loss across multiple storm events rather than a sudden failure in a single severe storm.
Copper Nails: Why They Matter
Modern roofing specification uses copper or stainless steel nails as a matter of course — both are effectively corrosion-proof in the roof environment. When we re-nail or re-lay a nail-sick roof in Maidstone, copper nails are specified throughout — two per tile at the correct gauge for the tile thickness. Copper nails are more expensive than galvanised steel, and significantly more expensive than the original iron wire nails they replace. They are also the correct specification, and a re-nailed roof using copper fixings should not require attention for nail-related reasons for the next 80–100 years.
A re-roof that specifies galvanised steel rather than copper is not wrong — galvanised nails have a service life of 40–60 years and are adequate for new-build and most re-roofing applications. But where the explicit purpose of the re-roof is to address nail failure, specifying copper rather than galvanised builds in the maximum available service life from the new fixings.
Assessment Without Full Access
A reliable assessment of nail sickness extent can be made in some cases without full roof access, through a combination of ground-level observation and loft inspection. From the ground, the scatter pattern of tile displacement — whether losses are genuinely random across the roof, or concentrated in specific areas — provides diagnostic information. From the loft, nails visible through the felt at the back of the tiling can be assessed directly. Significant rust staining on the felt below nail positions, or nails that are visibly reduced in diameter, confirm active nail sickness. Nails that are intact and show no corrosion indicate the fixing system is still sound despite the roof's age — a finding that sometimes occurs on properties where the original tiles were laid on galvanised rather than iron nails, or where a previous re-lay used better fixings.
While nail sickness is most associated with Welsh slate and clay plain tile on Victorian and Edwardian properties, the underlying mechanism — corrosion of iron fixings — can affect other roofing materials where original iron nails were used. On earlier machine-made clay interlocking tiles from the 1900s–1930s, iron wire nails were also used and are similarly subject to corrosion at the 80–100 year mark. On interwar properties across Maidstone — the 1930s semis in Barming, Bearsted and the western suburbs — nail sickness on clay interlocking tile roofs is beginning to present as the same scatter-loss pattern seen on the older Victorian stock.
Concrete interlocking tiles from the 1950s and 1960s were originally fixed with galvanised nails rather than iron — galvanising was standard by this period for roofing nails. Galvanised nails have a service life of 40–60 years depending on the galvanising quality and the moisture environment. On the oldest concrete tile roofs across Maidstone's post-war estates — properties built in the late 1950s and early 1960s — there is a possibility that the original galvanised nails are approaching end of life, though the tile delamination problem typically presents before nail failure on this generation of roof. A survey on a 1958–1965 property in Penenden Heath or Shepway that shows scattered tile loss across different slopes, in the absence of obvious delamination, should include nail condition assessment as part of the diagnosis.
Nail Sickness on Garages and Outbuildings
The focus of nail sickness discussion is usually the main house roof, but the same failure mechanism applies to garages, outbuildings and lean-to structures with clay or slate roofs built in the same period as the main property. Victorian-era garages and coal stores in the rear plots of Maidstone's terraced properties — common in Fant and the inner conservation area streets — frequently have clay plain tile or Welsh slate roofs that have received no attention since construction and are exhibiting advanced nail sickness without the homeowner being aware.
Nail sickness on a garage or outbuilding roof has lower immediate consequence than on the main house — the structural damage from water ingress is less significant, and the internal space is typically less sensitive. But it's worth addressing for two reasons: a nail-sick outbuilding roof in the midst of a period property affects the overall condition presentation of the property; and the tiles and slates that are slipping off a nail-sick outbuilding roof are a potential hazard to people and vehicles below. On steeply pitched Victorian outbuilding roofs adjacent to paths or parking areas, displaced slates and tiles represent a genuine safety risk that's worth addressing proactively.
We survey and quote outbuilding roofs alongside main property surveys across Maidstone — the access is typically straightforward and the quote for a small outbuilding re-roof is proportionally much lower than for the main house. Including the outbuilding in a survey visit adds no cost to the survey and may identify a problem that's worth addressing alongside main property work. Call 0162 229 6232 to arrange a combined survey.
Acting Before the Problem Becomes Acute
Nail sickness is one of the few roofing conditions where acting before acute failure is straightforwardly cost-effective. A roof survey that confirms moderate nail sickness — nails corroded but tiles still in place — gives the homeowner the option of a planned re-roofing project at a time and budget of their choosing. Waiting for nail sickness to progress to widespread tile displacement leads to emergency repairs, potential ceiling water damage, and a re-roofing project that happens on the storm's schedule rather than the homeowner's. The cost of the re-roof is the same either way. The difference is control and consequences. We survey for nail sickness free of charge across Maidstone — call 0162 229 6232.
Nail Sickness: The Key Facts for Maidstone Homeowners
Nail sickness affects pre-1950 roofing with ungalvanised iron nail fixings. It progresses invisibly until it causes scattered tile or slate displacement across multiple slopes. The diagnostic is the scatter pattern — multiple isolated losses in different positions rather than a localised failure in one area. Repair is viable if sickness is localised; replacement is required if widespread. Copper nails are specified for all re-nailing and re-roofing work. Victorian and Edwardian properties in Maidstone — Fant, the town centre, Bearsted village — are at or past the age where nail sickness should be expected on unreviewed roofs. A free survey from us will confirm whether your specific roof has nail sickness and how extensive it is. Call 0162 229 6232.
Frequently Asked Questions
Nail sickness is the corrosion of the iron nails holding slates and tiles, common on Maidstone's pre-1950 roofs. It causes tiles to slip and fall as the fixings lose strength.
The sign is scattered tile or slate loss across multiple slopes rather than one area. From the loft, corroded or rust-stained nails at the tile backs confirm it.
Localised nail sickness can be addressed by re-nailing affected areas. Widespread sickness across the whole roof means a full re-roof is the cost-effective solution.
Copper or stainless steel nails, which are effectively corrosion-proof. A re-roof using copper nails shouldn't need attention for nail-related reasons for 80–100 years.
Ungalvanised iron nails begin significant corrosion at 60–70 years and can lose most of their strength by 80–90. Maidstone's Victorian and Edwardian roofs are at or past this age.