"Dry verge" is one of those terms that gets used a lot in quotes and surveys without much explanation, so it's worth breaking down plainly: what it is, why it's an improvement over the traditional approach, and when it's actually worth doing.
The traditional approach, and why it fails
Traditionally, the tiles along a roof's verge (the sloped edge) and ridge (the top) are bedded in place with mortar. Mortar is rigid, but roofs move slightly with temperature changes and settle over decades — and rigid mortar doesn't cope well with that. Over time it cracks, and once it cracks, water gets in behind it, freezes in winter, and accelerates the cracking further. Eventually tiles along the edge become loose, which is a real problem in high wind.
What a dry verge or dry ridge system does differently
A dry system replaces the mortar with mechanically fixed plastic or GRP units that hold the tiles in place without relying on a rigid bond. Because it's a fixing rather than a bond, it flexes with the roof rather than cracking, which means significantly less ongoing maintenance — no re-pointing every few years, no loose tiles after a storm. Many dry ridge systems also include built-in ventilation, which is a useful bonus if your roof space needs better airflow anyway.
When it's worth doing
If you're already having a full roof replacement, it's worth doing at the same time — the labour overlap makes it cost-effective. It's also worth considering on its own if your existing mortar verge or ridge keeps cracking and needing repointed, since at that point you're paying for the same fix repeatedly rather than solving the underlying issue once. See our dry verge & dry ridge service for more detail.