What the westerly does to your roof, year after year

A roof almost never fails all at once. It fails in stages, and every stage is visible to anyone who goes up to look.

The trouble is that nobody goes up. People look at a roof from the garden, which reveals a missing tile and virtually nothing else.

I. How the westerly works

Around the Bay the prevailing wind comes from west to south-west. In winter it blows very regularly at 30 to 60 km/h, with around ten annual episodes gusting above 80 km/h and, every few winters, a notable storm.

What that wind does to a roof is not what people imagine. It does not push on the tiles: it creates suction above the covering, particularly at verges and hips, which lifts elements upwards.

A tile is held by its weight and its interlock. At the verge, the eaves and the ridge, that restraint is weakest and the suction strongest. So that is always where it starts.

The movement is tiny — a few millimetres — but it repeats thousands of times a winter. Bedding mortar cracks, clips work, tiles lose their seating. When failure comes it looks sudden. It had been in preparation for five years.

II. The six inspection points

1. Verge tiles, west elevation. The starting point in eight cases out of ten. Check the bedding, the mechanical fixings, and any movement.

2. The ridge. A mortar-bedded ridge ages badly in a windy, humid climate. A dry ridge, ventilated on a ridge closure, is now the reference solution when renewing. Look for cracks in the mortar and torn closures.

3. Flashings and abutments. Junctions between the covering and any projection — chimney stack, ventilation outlet, rooflight — concentrate water ingress. A loose flashing admits water along an entire wall.

4. Gutters and outlets. Pine needles block them within a season. A full gutter overflows backwards, between covering and wall: the most insidious form of ingress, because it is visible neither from the garden nor from inside for months.

5. Metalwork. Valleys, verges, eaves trims. Zinc and aluminium perform well in salt air; steel fixings do not. Rust spots mark the deadline.

6. Flat roofs. Common on the contemporary villas at Pyla and the Cap. The critical point is the perimeter waterproofing upstand, and outlets whose gratings clog. A flat roof with a blocked outlet loads a slab that was never designed for it.

III. The chronology of untreated ingress

It is worth understanding why a small water entry becomes a large project. The mechanism is always the same.

A displaced tile lets water through in driving rain. Where a sarking membrane exists, it carries the water to the eaves: nothing shows. That is the favourable case.

Without a membrane, or where it has perforated with age, water reaches the insulation. Mineral wool compacts, loses performance and no longer dries. Over several winters purlins and rafters stay damp and wood-decaying fungi establish themselves.

The interior signal — a stain on a ceiling — appears months, sometimes years, after the process began. When an owner calls us about "a small mark in the back bedroom", we know we are going to open up and find considerably worse.

IV. What it costs, before and after

The orders of magnitude below apply to a typical villa on the Bay, subject to access and the type of covering.

The gap between the first and last lines turns on two visits a year. It is the simplest trade-off in the whole of house maintenance, and the one most often deferred — because a roof that is not leaking asks for no attention.

V. What to do after a wind event

The instinct of absent owners is to wait for the next stay. Two months later, a displaced tile has admitted eight weeks of winter rain.

The right protocol after an episode above 80 km/h:

1. Have the roof inspected from ground level with binoculars or a drone, on all four elevations.
2. Check the ground for fragments of tile or mortar — the best indicator of a fault above.
3. Inspect the roof space, if accessible, in daylight: any daylight visible from inside is a water entry.
4. Get a roofer out within fifteen days if in doubt, before the queue forms.

That last point deserves emphasis. After a notable storm, roofers around the Bay are booked out for four to six weeks. Owners who arrange an inspection within two days go first. The others wait, and water comes in meanwhile.