Why Do Ridge Tiles Come Loose?

The mortar bed

Most ridges are bedded in mortar laid along the apex of the roof, with the tiles pressed into it. That bed is the only thing holding the tiles on an older roof. Mortar is strong in compression but brittle, and the roof it sits on is not static. Timber swells and shrinks, the house settles, and the whole ridge flexes in strong wind. The bed cracks, water gets into the cracks, and the damage spreads.

Frost and water

Water in a crack freezes in winter and expands, forcing the crack wider. Each cycle of freeze and thaw removes a little more of the bed. By the time the pointing starts to fall out, the mortar behind it may be hollow or sandy. Moss and lichen along the joints hold water against the mortar and speed the process. Our answer on how long ridge mortar lasts covers this in more detail.

Wind

The ridge is the highest line of the roof and the first thing the wind hits. A gust creates uplift as it passes over the apex, and a ridge tile with a weak bed or no mechanical fix can be lifted or rocked. Each movement works the bed looser. The tiles at the gable ends take the worst, because they are exposed on two sides. A ridge that has lasted for years can fail in a single storm if the bed was already weak.

No mechanical fixing

Old ridges depended on the mortar alone. Under BS 5534:2014 the ridge line should be held by clips, screws or straps as well as the bed, so that a cracked bed does not release the tile. A roof that was bedded before this was standard has nothing but the bond holding it, and when the bond fails, the tile moves. The standard is explained in our guide to BS 5534 and BS 8612 fixing.

Poor workmanship and materials

A mix that is too strong cracks away from softer tiles, and one that is too weak crumbles. Mortar laid on dirty or wet tiles does not bond. Tiles pressed into a bed that is too thin leave voids, and a bed laid in freezing weather can be spoiled before it sets. A repair that only repoints the joints, leaving the old crumbled bed in place, looks tidy but fails again quickly. Colour-matched mortar also hides the true condition from the ground, so a neat-looking ridge is no proof that the bed beneath it is sound, and only a close inspection will tell.

Structural movement

If the ridge timber has dropped, rotted or been disturbed by roof alterations, the line of the ridge dips, and the tiles sit unevenly on it. Loft conversions, chimney work and heavy snow can all move the apex. A ridge that is out of line often has an underlying structural cause, which has to be looked at before new tiles are fixed to it.

Roof ventilation and trapped moisture

Damp air in the loft can add to the problem. Where condensation collects under the ridge, the timber stays wet, the underside of the bed absorbs moisture and the mortar softens from below. Blocked eaves vents, bathroom fans that discharge into the roof space and a lack of air movement at the ridge all raise the moisture level. Fixing the ventilation does not repair a failed bed, but it stops the next one failing early. Our guide to ridge ventilation and condensation covers it.

Birds and insects are a smaller cause. Starlings and sparrows nest in gaps at ridge ends, pull at loose mortar and widen the openings. Protected species such as nesting birds and bats may mean work has to be timed, so we check before we lift anything.

Signs and what to do

Look from the ground for tiles out of line, gaps between tiles, mortar on the path, and moss along the ridge. Our page on the signs your ridge tiles are failing lists them. If a tile has already dropped, see what to do when a ridge tile has fallen off.

The lasting fix

We lift the loose tiles, clear the crumbled bed, check the ridge timber and relay the tiles on fresh mortar with mechanical fixings, or move to a dry ridge where the roof suits it. The survey includes photos so you can see the cause. The fixed written quote lists the work, and our ridge tile repairs page shows the rest of what we do.