The short answer
Dry verge caps fall off when whatever holds them has failed. The usual causes are screws that were too short or stripped their holes, clips that never seated properly, a fixing strip fixed to weak timber, plastic that has become brittle in sun and frost, or wind lifting a gable that was fitted with too few fixings. A cap that has fallen is a sign that its neighbours are probably loose as well, so the whole run needs checking, not just the missing piece.
How the caps are meant to stay on
A dry verge replaces the mortar at the edge of a gable with a run of cap pieces. A fixing strip, usually a batten or a plastic profile, is screwed along the edge of the roof, and the caps are clipped or screwed to it, with each piece overlapping the next. When all that holds, the verge is quiet and weathertight. Our guide to dry verge systems describes the common types.
Cause one: fixings that are too weak
The most frequent fault is in the fixing. A screw that is too short only bites into the thin edge of the board, and one driven too hard strips the hole it sits in. Over time, wind pulls on the cap, the screw works loose and the cap lifts. If the fixing strip itself is nailed to a rotten bargeboard or a damp rafter end, it moves with the timber. In each case the cap is held by very little, and it lets go in the first strong gust.
Cause two: ageing material
Many dry verge caps are plastic or a composite. Sun, frost and ultraviolet light make cheaper plastics brittle over the years, and a brittle cap can crack around its fixing and snap off. Heat makes the material expand, which can push a poorly fitted cap out of its clip along a long run. Cap pieces that have faded or warped tell you the material has little service left in it.
Cause three: wind
The gable is the most exposed part of the roof. Wind hits the wall, rushes up and over the edge, and tries to lift anything that is not held down firmly. A verge on an open site near Basingstoke, with nothing nearby to shelter it, gets this more than one in a terrace. A system fitted with too few fixings, or without the extra fixings the maker asks for in exposed places, can lose caps in a storm even if it looked sound.
Cause four: the edge underneath
Sometimes the caps are blameless. The undercloak, the thin board or row of tiles under the last course, can sag, rot or be cut too short, and then the fixing strip has nothing firm to sit on. A cap pinned to a wobbling strip works loose however well it is screwed. The same happens when the bargeboard behind a gable has gone soft from years of damp. Replacing the caps without dealing with the base only buys a season or two, which is why we look under the verge, not just at it.
Poor spacing is another hidden cause. If the fixings were set too far apart, long stretches of cap carry the wind load on a couple of screws. Adding fixings at the right centres often cures a verge that seems to shed a piece every winter.
Why it matters
A missing cap leaves the edge of the tiles and the undercloak (the board or tile strip that supports them) open to rain. Water can reach the rafter ends, the bargeboard and the wall top, and in time it causes damp or rot. A cap that has dropped can also land on a path or a car. Pick up any pieces if it is safe, keep them, and take photographs from the ground. Our answer on whether dry verges rattle describes the early warning signs.
How we put it right
We check every fixing along the verge from a safe working platform. We replace stripped screws with longer ones that reach sound timber, reseat clips, swap any cracked or warped caps and replace a rotten fixing strip or board before the caps go back. If the whole system was fitted without enough fixings, we refit it to the maker's pattern and use extra fixings at the exposed end. The survey photos show you each fault, and the fixed written quote lists what is replaced. See also our guide to verge repairs.
Repair or replace the verge?
If only one or two caps have failed and the rest are sound, a repair is enough. If most are brittle or loose, a new set is more sensible, and for some gables a return to a bedded verge with mechanical fixings is better. We tell you which fits your roof. Start from our ridge, verge and dry-fix page for the full range.
Every roof is different. A free survey with photos settles it for yours.
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