Look at the gable end of a house with a mortar verge and you can often read its history in the cracks. A line of pointing has dropped away, a dark gap shows under the edge tile, and moss grows where water has stood. The verge is the part of the roof where wind and water attack from two sides at once, and for generations it was held together by little more than a strip of mortar. A dry verge replaces that mortar with a system of mechanical fixings, clips and trims. It is now a common choice, and a good one when it is fitted properly and matched to the tiles. This page explains how the systems work and where they go wrong.
The verge, and why it needed a rethink
The verge is the sloping edge of the roof at a gable. The outer tiles overhang the wall slightly and are bedded in mortar on a course of undercloak, which is a strip of board that supports the tile edge and directs water back onto the roof. The mortar both holds the tiles and closes the gap against the wind. Because it is exposed on two faces and has to resist suction at the roof edge, it fails earlier than almost any other part of a tiled roof. Our page on what a roof verge is explains the parts, and the guide to verge repairs sets out the repair options.
The tiling code, BS 5534:2014, expects verge components to be held on mechanically. Mortar is not relied on alone. A second standard, BS 8612:2018, sets performance requirements for dry-fix systems. Together they explain why dry verge has become routine. The wider rule for ridge, hip and verge together is set out in our guide to BS 5534 and BS 8612.
How a dry verge works
A dry verge system has three jobs: to hold the edge tiles down, to protect the gap between the tile and the wall, and to close the end of the roof against wind and water without wet mortar. It does so with a set of parts.
- Undercloak. A strip of board under the edge tiles. It supports them and shields the wall top.
- Verge trim or cap. A moulded piece that sits along the edge, covers the end of the tiles and finishes the line. Often it is made of polymer or fibre-reinforced material, shaped to suit a particular tile.
- Cleats or clips. Metal or polymer fittings that grip the tiles and tie them to the batten.
- Fixings. Screws or nails into the batten or the roof timber, usually stainless steel or another corrosion-resistant metal.
- Seals and end pieces. Flexible strips and end caps to close the joints at the eaves and ridge.
There is no wet mortar anywhere in the system, so there is nothing to shrink, crack or wash out. Movement in the roof is taken by the flexible parts.
The main types
Dry verge systems come in a few forms, and your tile decides which suits.
Tile-specific verge systems. Many tile manufacturers make verge units that match their own profile. These are the most reliable, because the lock, the thickness and the colour match. They tend to be used with concrete interlocking tiles.
Universal verge cap systems. Generic caps and trims designed to fit several profiles, with adjustable clips. These are cheaper and more flexible and are often used when the tile is old or unusual. They need careful fitting to avoid gaps and rattle.
Verge systems for plain tiles. Plain tile roofs need a different approach, because the tile is small and the verge is made up of tile-and-a-half and special pieces. Dry systems for plain tile exist, but many plain tile verges are better served by a mortar verge that is also mechanically fixed. Our guide to plain and interlocking tiles explains the difference between the formats.
Combined verge and undercloak units. Some manufacturers supply a pre-formed unit that includes an integral undercloak. They speed fitting and reduce the number of joints.
How a dry verge is fitted
The steps are straightforward, and each matters.
- Strip the old verge. The mortar and the outer tiles are removed back to sound material, and the edge is cleaned.
- Check and repair the edge. The barge board, edge battens and undercloak are inspected. Rotten timber is cut out and replaced. Broken undercloak is renewed.
- Fit the undercloak. A fresh strip of undercloak is fixed along the edge, level and projecting the right distance beyond the wall.
- Fix the batten and cleats. Edge battens are fixed, and cleats or clips are attached at the specified spacing.
- Lay the tiles. The verge tiles are laid and clipped, cut to size where needed, with the specified overhang.
- Fit the trim. The verge cap or trim is clipped or screwed on, with joints lapped and sealed.
- Finish the ends. The foot and the top are closed with end pieces and the junction with the ridge is sealed.
On a typical gable, the work takes a fraction of the time of a mortar verge, because there is no curing to wait for. Our pages on fitting dry verge to an existing roof and whether you need approval for dry verge cover the practical questions that follow.
Advantages
The case for dry verge rests on a few real strengths. It is mechanically fixed, so it resists wind lift in the way the standard expects. It does not crack, because there is no mortar to shrink, so it needs far less upkeep. It can be fitted in cold or damp conditions, when mortar would not cure. It is quick, which cuts scaffold time. And on an exposed roof, it stays put when mortar would go.
It also tidies the look of the edge. A mortar verge ages unevenly, with cracks, stains and moss. A dry verge keeps a consistent line, though the look differs from mortar and some owners prefer the traditional one. Where the house is listed or sits within a protected area, the council's conservation officer should hear about the change first.
Why the undercloak matters so much
Undercloak is the least visible part of a verge and often the cause of its leaks. It is a narrow strip, commonly fibre cement, slate or a plastic or timber section, fixed to the top of the gable wall so that the edge tiles rest on it and overhang the wall face. Water that runs under the verge tiles lands on the undercloak and is carried back onto the roof rather than into the wall. If it has cracked, rotted or been left out, the water goes into the masonry or the edge batten instead.
Fitting a dry verge over bad undercloak just hides the fault. A good fitter lifts the old verge, looks at what is underneath and renews the undercloak if it is damaged. We photograph that stage so you see what was there. It is one of the details that separates a verge that lasts from one that fails again in a few winters.
The ends of the verge: eaves and ridge
A verge is a line with two ends, and the ends are where it is most likely to fail. At the bottom, where the verge meets the eaves, the edge tile has to be finished neatly and the gutter or fascia must not be allowed to catch the wind. At the top, the verge meets the ridge, and the end piece must close the gap between the verge trim and the ridge tiles. A dry system has special pieces for each, and they must be matched. If the verge was fitted dry but the ridge is still mortar, the junction needs particular care so the two systems do not fight each other. That is another reason to review the ridge, the hips and the verges as a set.
Checking a dry verge after a storm
A dry verge needs little attention, and a quick check after a gale is enough. From the ground, look along each edge for caps that have shifted, trim that has lifted at the end, a visible gap between trim and tile, or a missing end cap. Listen for rattling in the wind. If you see something, photograph it and call for a survey rather than climbing up. A loose cap can be refixed in minutes, and a missing one lets wind and rain under the edge tiles.
Problems and how to avoid them
Dry verge is not trouble-free, and most of its faults come from the fitting, not the idea.
| Problem | Usual cause | Remedy |
|---|---|---|
| Caps working loose or falling off | Wrong fixings, clips not engaged, no edge batten | Refix with correct clips and fixings |
| Rattling in the wind | Loose fit, poor tile match, thin trim | Re-seat the trim, add seals |
| Gaps at joints | Cut tiles not matched, no end pieces | Re-fit with correct pieces and seals |
| Colour mismatch | Generic trim on an aged roof | Choose a closer colour or a coated trim |
| Leaks at the edge | Missing or broken undercloak | Renew the undercloak |
Our short answers on why dry verge caps fall off and whether dry verges rattle look at the two commonest faults in detail. The cause in both cases is nearly always the same: a system chosen to suit a price, not a profile, or fitted without the correct clips.
Choosing a system
Before you accept a quote, ask the roofer four things. What system is it, and is it made for my tile profile? What are the fixings made of? What happens at the undercloak? And what does the manufacturer say about the fitting? A system with a clear installation guide, matched to the tile, is more likely to last.
Think about the tile you have. A common interlocking concrete tile is well served by a purpose-made system. An old or unusual tile may need a universal cap, with extra care. A plain tile roof needs a considered answer, and sometimes the right answer is a mortar verge with mechanical fixing. Our guide to dry verge installation cost explains what moves the price.
Verges in the wider roof
The verge is one of three edges that benefit from dry-fix treatment. The ridge runs along the top and the hips run diagonally down hipped roofs. The same logic applies to all three, and a roof that is being re-edged is often best done in one go. Our guides to hip tiles and dry hip systems and dry ridge against mortar deal with the others.
What we do on a verge survey
We examine the verge from the roof and the scaffold line, check the undercloak and edge timbers, and photograph the failures on your gable. We tell you whether a mortar repair, with mechanical fixing, would do the job or whether a dry system is the better choice, and we name the system and the tile it suits. The fixed quote is written and detailed, and a decade-long written guarantee backs the workmanship. We take away the old mortar and waste and leave the site clear. The rest of our edge-of-roof work sits under ridge tile repairs in Basingstoke.
