Roofs and flat roofs
What is nail sickness in a slate roof, and can a surveyor see it from the ground?
Nail sickness is the failure of the nails that hold slates, often by corrosion, so slates slip even though they look whole. From the ground a surveyor may see slipped or uneven slates, not the nails themselves. A neat-looking roof can still be losing its fixings.
Last reviewed 24 October 2026. Written for buyers in England and Wales unless this answer says otherwise. No named surveyor has signed this page. It is general guidance, not a report on your house, and not legal advice.
What is the fuller explanation?
A visual home survey looks at the covering from ground level and from any safe vantage the instructions allow. It does not lift slates as standard. Slipped slates, uneven courses and daylight through the loft boards are the clues. The nails are hidden under the lap. Saying “nail sickness” as a fact usually needs a roofer who can see the fixings, unless slates are already on the ground.
RICS describes roof inspections as visual and limited by height, weather and access. A condition rating records the concern. It is not a reroofing specification and it is not a life in years. Ask a roofer what they can see from a ladder or scaffold. Prices for scaffolding and for re-covering vary by roof size and access. Ask them, and do not use a price per slate from a forum.
What should you ask your surveyor?
- Which slips could you see, and could you see the loft underside as well?
- Are you naming nail sickness, or only the risk of it?
- What access would a roofer need that you did not have?
What are the typical next steps?
- Look in the loft for daylight and for fallen nails if the loft was inspected. If it was marked not inspected, say so.
- Get a roofer’s written comment before you turn a rating into a price reduction.
- Do not pay for a full re-cover on the phrase alone if only a few slates have slipped and the nails have not been seen.
Costs vary with the building and with who you instruct. Where this page does not cite a published figure, ask the surveyor, a relevant specialist, or your solicitor for a written quote. Do not treat a forum average as the price.
Also asked about this
Is a slipped slate the same as nail sickness?
No. One slate can slip because a single nail failed, a clip broke, or the wind lifted it. Nail sickness is a wider failure of the fixings.
Does moss prove the nails have gone?
No. Moss holds water and can lift edges. It is not a photograph of the nails.