Roof Flashings and Cowls
Roof flashings for sealing duct and pipe penetrations through the roof — the finishing touch that makes a vertical duct run weathertight. We stock the Master Flash range of flexible conical flashings in ten overlapping size ranges covering pipe diameters from 6mm right up to 724mm, in standard and high-temperature versions.
How Master Flash flashings work
A Master Flash is a flexible cone on a shaped metal-edged base. Trim the cone to match your duct diameter, slide it down over the duct, dress the base to the roof profile — it forms to corrugated and profiled sheets as well as flat roofs — and seal and fix the perimeter. The result is a durable, watertight seal that accommodates the movement and vibration a duct stack sees in service, without fabricated soakers or wet trades.
Standard or high temperature?
The standard Master Flash roof flashing handles general ventilation and extract ducts. Where the duct or flue runs hot — kitchen extract stacks, process exhaust, flue pipes — specify the high-temperature Master Flash, available in the same ten size ranges.
Choosing a size is simple: the ranges overlap deliberately, so pick the flashing that puts your duct diameter comfortably within its span rather than at either extreme — the cone then grips snugly after trimming. Top the stack with a weather hat or jet cowl to complete the termination, and support the stack with matching bracketry so no load rests on the flashing itself. Stocked items despatch next day when ordered by 3pm, with free UK mainland delivery on orders over £400 ex VAT.
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Master Flash Fixing Kits
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Master Flash Multi-Flash Roof Flashing
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Master Flash Residential Roof Flashing
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Master Flash Retrofit Roof Flashing
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Master Flash Roof Flashing
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Master Flash Roof Flashing – High Temperature
Roof Duct Terminations
Wherever a duct passes through a roof, it requires a weatherproof termination to prevent rainwater entering the ductwork and the building. The choice of termination depends on the roof type, duct size, and whether the duct is for supply (intake) or extract (exhaust).
Flat Roof Products
Flat roof curbs provide a raised, weatherproof collar around the duct penetration, incorporating a flashing flange that is dressed into the roof membrane. Mushroom cowls sit on top of the curb to protect against rain while allowing air to exit or enter around the perimeter.
Pitched Roof Products
Pitched roof flashings are angled to match common roof pitches (typically 15°, 30°, and 45°). The lead or aluminium flashing plate sits under the roof tiles, with the duct passing through the centre. A weather collar or cowl on top completes the weatherproofing.
Cowls and Caps
- Mushroom cowls — Wide cap that deflects rain, suitable for extract and low-velocity intake
- Chinese hat cowls — Conical cap on a stand-off, commonly used on flue and extract terminations
- Rain caps — Simple disc cap to prevent direct rainfall entry
Why Choose Alpha Air?
We stock standard sizes of flashings and cowls for immediate dispatch, with bespoke sizes available to order. Contact our team for advice on the right termination for your roof type and application.
Frequently Asked Questions
What angle roof flashing do I need?
Measure the pitch angle of your roof. Most UK pitched roofs are between 15° and 45°. We stock flashings in standard angles to suit common roof pitches. If your roof has a non-standard pitch, we can manufacture a custom flashing to order.
Do I need a cowl on top of a roof flashing?
For extract (exhaust) ducts, a cowl is recommended to prevent rain and debris entering the ductwork. For intake (supply) ducts, a cowl with insect mesh is essential to keep out rain, leaves, birds, and insects. The specific cowl type depends on whether the duct is for supply or extract.