Repair or replace an ageing roof?

Every roof reaches a point where repairs stop being good value. The difficulty is knowing when that point has arrived. Replace a roof too early and you spend money you did not need to. Keep patching too long and each repair buys less time, while water quietly damages the timbers underneath.

This guide explains the signs a roofer looks for on slate, concrete tile and felted roofs, when a partial re-roof can make sense and how Building Regulations apply when a roof is replaced.

Is the problem local or general?

The most useful starting point is to ask whether the problem is local or general. A few slates lifted in a storm, a cracked ridge tile or a failed flashing are local problems. They can usually be repaired, and the rest of the roof carries on doing its job.

General problems affect the whole covering or the materials holding it in place. Corroded nails across an entire slope, slates flaking everywhere, tiles that have turned porous or felt that has rotted along the eaves are all general. Repairs here tend to fix one spot while the next one starts to fail.

Signs of age on a natural slate roof

Good natural slate can last a very long time. On many older roofs, it is the fixings and timbers that give up first.

Nail fatigue

Slates are held by nails driven into timber battens. On older roofs those nails were often iron, which corrodes over time. When nails rust through, slates slide down the roof or drop out altogether. This is often called nail fatigue or nail sickness.

One or two slipped slates are normal maintenance. Signs that it is happening across the whole roof include:

• Slipped slates appearing in different places after each windy spell.
• Lots of metal strips (tingles) or clips holding slates in place from earlier repairs.
• Slates turning up in the gutter or on the ground when there has been no real storm.

Delamination

Some slates begin to split into layers as they age. The surface flakes, the edges crumble and the slate can feel soft or powdery. Once delamination is widespread those slates cannot be reused, which affects how much of the existing covering a re-roof can salvage.

Battens and torching

Many older slate roofs have no underlay at all, or rely on lime mortar (torching) applied to the underside of the slates between the battens. From the loft, a roofer will check for decayed or broken battens, torching that has crumbled away and damp staining on the rafters.

Signs of age on a concrete tile roof

Concrete tiles became a common choice in the second half of the twentieth century, and many older houses were re-roofed with them. They wear differently from slate:

• Surface erosion: the tiles lose their smooth finish and colour, turn rough and start to hold water and moss.
• Porosity: worn tiles soak up more water, which makes them heavier and more prone to frost damage.
• Cracked or broken tiles scattered across the roof rather than grouped in one area.
• Ridge and hip trouble: mortar bedding that has cracked or washed out, leaving ridge tiles loose.

Heavy moss on its own does not mean the roof needs replacing, but it can block gutters and hold moisture against the tiles.

Checking the felt and timbers

On pitched roofs that do have an underlay, the condition of the felt often settles the question. Older bitumen felt can turn brittle and tear, particularly at the eaves, where it is exposed to sunlight and weather. When the felt rots at the bottom edge, water running down it can drip behind the gutter onto the fascia and into the wall.

In the loft, look for sagging felt, tears, daylight and damp patches on the rafters. A roofer will also judge whether the structure itself is sound. A sagging ridge line or a dip in the middle of a slope can mean the timbers need attention, which is normally dealt with as part of a larger job.

Partial re-roof or full replacement?

A full replacement is not the only option for a struggling roof. On many terraced and semi-detached houses, one slope faces the worst of the weather and fails well before the other. Re-roofing a single elevation can be a sensible middle ground.

Things to weigh up include:

• Matching the look: on a slate roof, sound slates salvaged from one slope can be used to make up the front, with new or reclaimed slates on the rear, where appearance matters less.
• Scaffolding: if scaffolding is going up anyway, it can be worth tackling the chimney, lead flashings, fascias or gutters at the same time.
• What stays behind: a partial re-roof only makes sense if the part you keep has plenty of life left in it.
• Flat roof sections: a tired flat roof on a rear offshoot can often be replaced on its own in felt, EPDM or GRP without touching the main roof.

Building Regulations when re-roofing

Small repairs do not normally need Building Regulations approval. Re-roofing is different. The government's Planning Portal says that in most situations replacing a roof covering will need approval.

A few points are worth knowing before you commit:

• Insulation: a roof counts as a thermal element. When more than half of a roof surface is renovated, the insulation will usually need upgrading where that is technically and practically feasible.
• Weight: if the new covering is significantly heavier or lighter than the old one, such as a change between slate and concrete tiles, the structure may need checking and possibly strengthening.
• Ventilation and fire: changes to a roof can affect condensation risk and fire performance, so these are considered too.
• Sign-off: ask your roofer how compliance will be handled, whether through the council's building control service or a registered competent person scheme, and make sure you receive the paperwork at the end.

If your house is listed or in a conservation area, changing the roof material may also need planning permission or listed building consent. Check with the council's planning team before settling on materials.

Getting an honest assessment

The right answer depends on the condition of your roof, not its age alone. Ask any roofer to explain what they found, show you photos and set out the options side by side: repair now, partial re-roof or full replacement. Newcastle Roofs provides free, no-obligation quotes for both repairs and new roofs, and can talk you through each option so you can choose what suits your property and your plans for it.