Common Roof Problems and When to Call a Roofer

A roof is a system of components — tiles or slates, battens, felt underlay, rafters, ridge tiles, hip tiles, valley flashings, lead flashings, gutters, and fascias — that work together to keep water out of the building. When any component fails, water can enter. The challenge is that the point where water enters the roof is often not the same as the point where it appears inside the building — water can travel along rafters, battens, or ceiling joists before dripping through a ceiling.

The National Federation of Roofing Contractors (NFRC) estimates that approximately 70% of all roof repairs in the UK are caused by one of five problems: missing or damaged tiles/slates, failed lead flashing, blocked or damaged gutters, failed flat roof membrane, and ridge tile failure. Understanding these five problems — and how to identify them — allows homeowners to catch issues early and avoid expensive remediation.

The lifespan of a roof depends on the materials used. A concrete interlocking tile roof typically lasts 30–40 years. A natural slate roof can last 80–100 years if the slates are in good condition and the fixings are replaced periodically. A flat felt roof typically lasts 10–15 years. A GRP (glass-reinforced plastic) flat roof typically lasts 25–30 years. A lead flat roof can last 60–100 years if properly maintained.

In Hertfordshire, the most common roof types are concrete interlocking tiles (on houses built from the 1960s onwards), clay plain tiles (on Victorian and Edwardian houses), and natural Welsh slate (on pre-1900 houses). Each has different failure modes and maintenance requirements.

Missing or slipped tiles are the most common roof problem in Hertfordshire — and the most urgent. A single missing tile creates a gap through which wind-driven rain can enter the roof space, saturating the felt underlay and the roof timbers below. In winter, a missing tile can allow frost to damage the underlay, creating a larger area of vulnerability.

Tiles slip or come loose for several reasons. On older roofs, the nibs (the projections on the back of the tile that hook over the batten) can break, causing the tile to slide down. On concrete interlocking tiles, the clips that hold the tiles in place can corrode and fail. On clay plain tiles, the nails that fix the tiles can corrode — a problem known as nail sickness, which typically affects roofs more than 50 years old and can cause large areas of tiles to slip simultaneously.

The fix for a missing or slipped tile is straightforward — a roofer will lift the surrounding tiles, replace the damaged tile, and re-fix the surrounding tiles. The cost is typically £150–£500 per tile, including the call-out charge. If nail sickness is identified, the entire roof may need to be stripped and re-tiled — a significantly more expensive project (£8,000–£20,000 for a typical semi-detached house) but one that is necessary to prevent widespread tile loss.

You can check for missing tiles from the ground using binoculars, or from inside the loft on a bright day — daylight visible through the roof covering indicates a gap. Check after every significant storm, as wind can dislodge tiles that were previously secure.

Lead flashing is the lead sheeting used to seal the junction between the roof covering and vertical surfaces — chimneys, parapet walls, dormer cheeks, and the abutments where a roof meets a wall. Lead flashing is the most common source of water ingress in Hertfordshire houses, because it's subject to thermal movement (lead expands and contracts significantly with temperature changes) and can crack, lift, or pull away from the wall over time.

The signs of failed lead flashing are damp patches on the chimney breast (inside the house, typically on the wall below the chimney), damp patches around skylights or dormer windows, or damp patches where a lean-to roof meets the main house wall. These damp patches often appear on the ceiling or wall below the flashing, not directly adjacent to it — water travels along the roof structure before finding a way through.

Lead flashing typically lasts 50–80 years if properly installed and maintained. The most common failure mode is the mortar pointing that holds the flashing into the raggle (the groove cut into the brickwork) cracking and falling out, allowing the flashing to lift. Re-pointing the raggle and re-dressing the flashing costs £300–£800 per linear metre. Replacing the flashing entirely costs £500–£1,500 for a typical chimney.

Flat roofs — found on extensions, garages, and some 1960s–1980s houses — have a different set of failure modes from pitched roofs. The most common problems are blistering (where the membrane separates from the substrate, creating bubbles), cracking (where the membrane splits due to thermal movement or age), and ponding (where water collects in low spots because the roof doesn't drain adequately).

Traditional felt flat roofs have a lifespan of 10–15 years and are the most common type found on older extensions in Hertfordshire. When a felt flat roof reaches the end of its life, the options are: re-felting (replacing the felt layers, typically £800–£2,000 for a small extension roof), installing a GRP (fibreglass) overlay (£1,500–£4,000), or installing a full GRP flat roof system (£2,000–£6,000). GRP flat roofs have a 25-year guarantee and require minimal maintenance.

EPDM (ethylene propylene diene monomer) rubber roofing is an increasingly popular alternative to GRP for flat roofs. It's highly durable (50+ year lifespan), flexible (accommodates thermal movement without cracking), and relatively inexpensive (£1,500–£4,000 for a small extension roof). It's also easier to repair than GRP — a patch can be bonded to the existing membrane with adhesive.

Clearing blocked gutters is a task most homeowners can do safely from a ladder, provided the ladder is properly secured and the gutters are accessible from ground level. Replacing a single missing tile is technically possible for a competent DIYer, but working on a pitched roof is dangerous without the right equipment and training — a fall from a roof is frequently fatal. The Health and Safety Executive (HSE) recommends that any work on a pitched roof above 2 metres should be carried out by a professional with appropriate fall protection.

Call a roofer for: any work on a pitched roof, any work involving lead flashing, any flat roof repair or replacement, any ridge tile work, and any situation where you're not certain of the cause of a leak. A roofer will typically charge £200–£400 for a diagnostic inspection, which can be offset against the cost of any repair work. NFRC-registered roofers can be found at nfrc.co.uk.

In Hertfordshire, TCM Building & Maintenance provides roofing maintenance and repair services across Borehamwood, Radlett, Watford, Barnet, and surrounding areas. Our roofing team carries out everything from single tile replacements to full roof replacements, flat roof installations, and lead flashing work.

TCM Building & Maintenance provides roofing maintenance and repair services across Hertfordshire and North London. Our roofing team carries out single tile replacements, lead flashing repairs, ridge tile re-bedding, flat roof repairs and replacements, gutter replacements, and full roof re-tiles. All our roofing work is carried out with appropriate fall protection and is covered by our public liability insurance.

For a client in Radlett whose Victorian detached house had developed a persistent leak around the chimney stack, our roofer identified failed lead flashing on the back gutter (the lead flashing at the rear of the chimney, where it meets the roof slope) as the cause. The original lead had cracked due to thermal movement and the mortar pointing had failed. We replaced the back gutter flashing with new Code 5 lead, re-pointed the raggle, and re-bedded the chimney pot. The repair cost £850 and the leak was resolved immediately.

If you've noticed any of the warning signs described in this guide, read our Roofing Services page for more detail on our approach, or contact us for a free initial assessment.