Nail Sickness: What It Is and What To Do
Nail sickness is the corrosion of the iron nails fixing roof tiles or slates, causing them to slip after 80–120 years. It is the most common re-roofing trigger on Chichester's Victorian and post-war housing, and is diagnosed by close inspection of nail heads and slipped tiles.
Nail sickness is the most common reason for roof replacement on Chichester's post-war housing stock, and it is affecting a large number of properties simultaneously — the 1960s to 1980s estates in Portfield, Donnington and Tangmere were all built within a similar period, so their galvanised nail fixings are all corroding at roughly the same time. If you live in one of these districts, understanding nail sickness and recognising its signs could save you from an unexpected emergency.
What Nail Sickness Is
When concrete interlocking tiles or clay plain tiles are fixed to a roof, they are nailed to the timber battens with galvanised steel nails. On roofs built before approximately 1990, these nails were typically zinc-galvanised mild steel. The galvanising provides corrosion protection, but it does not last indefinitely — particularly in environments where moisture and salt air accelerate the electrochemical process. After 35 to 50 years, the galvanising has been consumed and the underlying steel begins to rust.
As the nail corrodes, it loses cross-section and eventually the tile it fixes is held by nothing more than the overlap of the tile course above and the friction of tile against batten. This is what roofers call nail sickness: the nail has corroded to the point where it no longer provides meaningful fixing. The tile is now vulnerable to any wind uplift that exceeds the modest gravitational and frictional forces holding it in place.
Ferrous nail fixings used before the widespread adoption of non-ferrous alternatives typically reach end of service life at 80 to 120 years depending on exposure.
— BS 5534 Code of Practice for slating and tiling
How Nail Sickness Progresses
Nail sickness does not announce itself dramatically. It progresses slowly and invisibly until a weather event brings it to your attention. The sequence is typically as follows:
- Individual tiles begin to slip slightly down the pitch — just a few centimetres, barely noticeable from the ground
- After a moderate wind event, one or two tiles are found in the garden
- A repair is carried out — new tiles fixed with new nails — and the problem appears solved
- Six months later, more tiles come off in the next storm — a different pitch this time
- The pattern accelerates: each storm removes more tiles because the nail corrosion is now at an advanced stage across multiple pitches
- Eventually the repair cost within a single year exceeds the cost of a planned re-roof, and the decision is forced
The tragedy of nail sickness is that homeowners who have been through the above sequence typically spend £800 to £2,000 on reactive repairs over two or three years before accepting that a full re-roof is necessary — money that was effectively wasted. Identifying nail sickness early and making a planned decision about replacement is significantly more cost-effective than reactive repair.
Nail Sickness in Chichester: Which Districts Are Affected
Portfield and Donnington
These two post-war districts east and south of the city centre have the highest concentration of nail-sick roofs in the Chichester area. The estates were built primarily in the 1960s and 1970s with concrete interlocking tiles on galvanised nails — now 50 to 60 years old. The proximity to Chichester Harbour adds a salt-air dimension that accelerates nail corrosion compared to equivalent properties further inland. We have re-roofed hundreds of properties in these districts and know the typical tile profiles, batten condition and fell deterioration patterns well.
Tangmere
The former RAF station estate in Tangmere is slightly younger than Portfield and Donnington but is now approaching the same threshold. Nail sickness is the primary roofing issue we see in Tangmere, and ridge tile mortar failure — which often accompanies nail sickness as a secondary indicator of a roof approaching end of life — is near-universal on properties that have not had recent attention.
St Pancras and Whyke (Slate Roofs)
Nail sickness on Welsh slate roofs in the Victorian terraces of St Pancras and Whyke operates differently. The original iron nails on these properties corrode at a slower rate than galvanised fixings on concrete tile roofs, but they are also 120 to 130 years old. Re-nailing — replacing corroded nails on slates that have not yet slipped — can extend the life of these roofs by 20 to 30 years without full re-slating. We assess which option is appropriate at the survey.
Diagnosing Nail Sickness: What We Look For
A close-range inspection from a roof ladder is required to properly assess nail sickness. From the ground, only the most advanced cases — significantly slipped tiles, obvious gaps in the covering — are visible. From the roof, we can see: nail heads that are visibly rusting or missing; tiles that move when pressed lightly; tiles where the nail hole has elongated through years of micro-movement; and felt underlay condition, which deteriorates in parallel with the nail fixings and is an important secondary indicator of overall roof age and condition.
We include a nail sickness assessment in every free survey carried out in Portfield, Donnington, Tangmere and other post-war districts. If we find widespread nail sickness, we will tell you clearly and give you the honest comparison between continued repair and a planned replacement.