Question answered
What is a verge undercloak?
The short answer
A verge undercloak is the board or strip laid beneath the end tiles at a gable. It supports the tiles and the mortar or dry-verge parts above, and keeps that side level. Many are fibre-cement, and boards on a building from before 2000 may contain asbestos, so they should be identified before anyone cuts, drills or breaks them.
The undercloak is a hidden strip under the tiles at the side of a gable roof. It props up the last tiles, and on older houses it may be a fibre-cement board that needs careful handling.
What the undercloak does along a gable
On a gabled house the roof stops over the wall, with no gutter, and that sloping side is called the verge. The last tiles there overhang the brickwork slightly, so rain drips clear of the wall instead of running down it.
Those overhanging tiles need something underneath. The undercloak is a narrow strip, fixed to the ends of the battens, that the tile edge rests on and that the verge mortar or dry verge cap bonds to. It sets the line of the edge and fills the gap between tile and wall head.
You rarely see it from the ground, though a pale grey strip along the underside of the verge is sometimes visible. When it fails, the end tiles tilt or the pointing falls away in pieces, which is often the first thing a homeowner notices.
Fibre-cement, and other materials
The most familiar undercloak is a flat fibre-cement board, cut to a strip and nailed or screwed to the battens. It is stiff, does not rot and takes mortar well, which is why it became so widely used.
Other materials exist. Some roofs use plain tiles or slate strips as an undercloak, laid as a course under the verge tiles. Newer dry verge systems often include a purpose-made plastic or composite strip that is designed to work with the cap and clips supplied alongside it.
Up on the ridge the matching parts are ridge tiles, but at the verge, the choice of undercloak affects how the cap fits and how well that side holds in wind, so the replacement should suit the system above it.
Whatever the material, an undercloak is judged by how firmly it is held. A strip with loose nails or a split along its length will not give the edge tiles a stable base, however good the cap above it.
Older boards and asbestos
Fibre-cement boards fitted before the late 1990s may be asbestos cement. HSE advice is direct: treat asbestos as present wherever a property was put up, or last refurbished, before 2000. HSE adds that an asbestos insulating board can look much the same as a non-asbestos one.
That means an old undercloak should be treated with caution until it is identified. Do not drill, saw, sand, scrub or break it, and do not pressure-wash it. Disturbing the surface releases fibres, which are the hazard. The strip sits in the shadow of the overhang, so weathering and moss are common on it, and that is no reason to scrub it clean.
An intact board that is simply sitting there is not a danger in itself. The risk comes when it is cut or damaged. If you are unsure, photograph the underside of the verge and record roughly when the house was built, and we will set out the next step before any work starts.
If the board has to be replaced
On HSE's reading, taking out asbestos cement is non-licensed work when the board comes away carefully and intact, and weathered material that has not been badly damaged is included. If it is badly damaged or crumbles, HSE treats the job as notifiable non-licensed work, with notice due before it begins.
HSE waste guidance asks for double wrapping, labels and a separate container, so asbestos is not mixed into general rubbish. For a household job the removing contractor consigns it, and fills in the consignment note in the waste producer's place.
A sample can be tested before work to confirm what the board is, which saves guesswork and tells everyone how to proceed. Any lifted or damaged undercloak is a reason to stop and ask rather than carry on with a bar and a hammer. Whoever does the job, ask how the board will be removed and where it will go before the work is agreed.
What a sound verge looks like afterwards
A good verge has a firm, level undercloak, tiles bedded or fixed along it, and a finish that sheds water cleanly. Where a system is dry fixed, the caps clip on over the end tiles, and the work follows the maker's instructions and BS 8612 practice.
Leaks at a gable often turn out to be a problem with this side. Read our page on whether a ridge can leak for the top of the roof, and ridge mortar mix for the bedding often used along the verge as well.
The survey gives you photographs of that side of your own house, and a written quote follows at one total price. If the repair involves a dry system, dry ridge cost sets out what moves the price. All of this work is gathered under ridge tile repairs.
Old undercloak boards: two questions
Can I drill or screw into an old fibre-cement undercloak?
Not until you know what it is. If the building dates from before 2000, assume the board may contain asbestos, and leave it undisturbed. Drilling creates dust, which is exactly what should be avoided. A roofer can arrange identification first.
What happens to the old board once it is taken off?
If it is asbestos, it is double-wrapped, labelled and kept apart from general rubbish, then consigned under a note the contractor signs as the waste’s producer. It does not go in an ordinary skip. If it is not asbestos, it is cleared with the other site waste.
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