Aluminium Roof Edge Drip Trim – 90° External Corner

External corners are the most visible part of any drip trim installation. They are the first thing you see from the ground, the detail that catches your eye from across the street, and the point where a neat job announces itself or a rough one gives the game away. Get the corner right and the whole roofline looks sharp. Get it wrong and no amount of straight trim either side will save it.

Our pre-formed aluminium drip trim external corner is factory-made to an exact 90-degree angle, profile-matched to our drip trim system, and available in 14 sizes from 75mm to 400mm. Whether you are finishing a flat roof on a new build in Chelmsford, a garden office in Colchester, or a commercial extension in Basildon, this corner gives you the clean, precise outward turn that the job demands.

Product Overview

This external corner is a pre-formed 90-degree aluminium corner piece designed to connect two lengths of our aluminium roof edge drip trim where the roof edge turns outward. It matches the exact profile of the drip trim, creating a seamless junction with no on-site mitre cutting required.

We stock the corner in 14 sizes, from 75mm right up to 400mm, covering every drip trim in our system. Each corner can be ordered in mill finish or powder coated to any RAL colour. Because external corners are the most visible component in the trim run, powder coating is especially important here. A colour-matched corner maintains the clean, continuous appearance of the roofline from every viewing angle.

Online Metal Store Ltd manufactures these corners at our factory in Chelmsford, Essex, on the same production line as the drip trim, internal corners and internal joiners. That guarantees a precise profile match across every component in the system.

Key Benefits

The most visible corner on the roofline

External corners project outward and are typically the first detail a viewer notices from ground level. A factory-formed corner with clean edges and a precise 90-degree angle gives the roofline a crisp, architectural quality that is impossible to replicate with an on-site mitre. On front-facing elevations, this is the detail that defines whether the job looks professional or not.

Factory-formed for a precise angle

Cutting a clean external mitre on site is even harder than an internal one, because any gap or rough edge is fully exposed and visible from below. A factory-formed corner eliminates that risk. The angle is exact, the profile matches the trim perfectly, and the edges are clean and straight. No filing, no adjusting, no hoping it looks alright from the ground.

Watertight outward turn

External corners are exposed to wind-driven rain on two faces simultaneously. If the corner detail is not properly sealed, water can be driven behind the trim at the most exposed point on the whole perimeter. A pre-formed corner with sealant at the joints provides a reliable defence against water ingress at this vulnerable detail.

14 sizes from 75mm to 400mm

We stock the external corner in every size that matches our drip trim range: 75mm, 100mm, 125mm, 150mm, 175mm, 200mm, 225mm, 250mm, 275mm, 300mm, 325mm, 350mm, 375mm and 400mm. Whatever drip trim size is on the specification, the matching external corner is available from stock.

Powder coating in any RAL colour

Because the external corner is the most visible component in the system, powder coating is more important here than on any other drip trim accessory. A mill finish corner next to powder coated straight trims would stand out immediately. We coat the corner to the same RAL colour as the rest of the system for a seamless finish.

Made in Chelmsford, shipped across the UK

We manufacture these corners at our facility on Southend Road in Chelmsford, Essex. They come off the same production line as the trim, joiners and internal corners, so every profile matches. Orders are dispatched quickly across the country.

Technical Specifications

Material: High-grade aluminium

Type: Pre-formed 90-degree external corner for aluminium drip trim

Available Sizes: 75mm, 100mm, 125mm, 150mm, 175mm, 200mm, 225mm, 250mm, 275mm, 300mm, 325mm, 350mm, 375mm, 400mm

Finish Options: Mill finish as standard, or polyester powder coated (PPC) to any RAL colour

Compatible With: Online Metal Store Ltd aluminium roof edge drip trim system

Manufactured In: Chelmsford, Essex, United Kingdom

Custom Fabrication: Yes. Powder coated to order. Non-returnable unless faulty.

How to Fit a Drip Trim External Corner

Fitting is straightforward, but the external corner is the most visible part of the installation, so neatness counts. Here is the process:

Position the pre-formed external corner at the outward angle of the roof edge. Fix it to the timber substrate using screws or appropriate fasteners, ensuring it sits flush, level and plumb. Apply a bead of sealant along the inside edge of both return legs where they will meet the incoming straight trim lengths. Our colour coded sealant is ideal for this step, especially on powder coated corners.

Slide an internal joiner into each leg of the corner to bridge the connection to the incoming straight trim lengths. Push the trim lengths onto the joiners, butt them up to the corner and fix them down. The joiner keeps everything aligned and the sealant provides the waterproof seal. Take a moment to step back and check the corner from ground level before moving on. It should read as a single, continuous piece.

Where Drip Trim External Corners Are Used

Every rectangular flat roof

This is the fundamental application. A simple rectangular flat roof has four external corners where the drip trim changes direction outward. Whether it is a kitchen extension in Brentwood, a garage roof in Billericay or a new build in Witham, every rectangular flat roof needs four external corners. It is the single most common drip trim accessory on any domestic job.

Complex roof shapes and setbacks

On L-shaped, T-shaped or stepped building footprints, the flat roof perimeter has a mix of external and internal corners. Each outward turn needs an external corner. On a complex commercial building, that might be six, eight or more external corners on a single roof. Pre-formed corners keep the whole perimeter consistent.

Garden rooms, offices and outbuildings

The garden room and home office market drives a lot of demand for drip trim external corners. Most of these structures are rectangular, so four external corners per roof is standard. On a building that is highly visible from the house and garden, the quality of the corner detail is immediately noticeable. A clean, pre-formed corner makes all the difference.

Commercial flat roofs and shopfronts

On commercial buildings, the drip trim perimeter is often visible from the street or car park. External corners on front-facing elevations need to look sharp. On these jobs, ordering the full drip trim system from a single supplier keeps every component consistent. Our complete system includes the drip trim in 3 metre lengths, external corners (this product), internal corners and internal joiners.

Refurbishment and re-roofing

When a flat roof is being re-covered, the old perimeter trims are usually replaced. New pre-formed external corners ensure the replacement system goes in neatly. On the same job, you may also need an aluminium termination bar at the upstands and aluminium roof flashing where the roof meets the wall.

Frequently Asked Questions

What is a drip trim external corner used for?

A drip trim external corner is a pre-formed 90-degree aluminium corner piece that connects two lengths of drip trim where the roof edge turns outward. It provides a precise, watertight outward turn without the need for on-site mitre cutting. External corners are needed at every outward angle on a flat roof perimeter. A simple rectangular flat roof has four external corners.

What is the difference between an internal and external drip trim corner?

An internal corner is used where the roof edge turns inward, such as where an L-shaped extension creates an inward angle. An external corner is used where the roof edge turns outward, which is the standard corner on every rectangular flat roof. A rectangular roof needs four external corners. An L-shaped roof typically needs four external corners and two internal corners. Both are available from Online Metal Store Ltd in the same size range and finish options.

How do you fit a drip trim external corner?

Fix the pre-formed corner to the timber substrate at the external angle. Apply sealant along the inside of each leg. Slide an internal joiner into each leg to bridge the connection to the incoming straight trim lengths. Push the trim lengths onto the joiners, butt them against the corner and fix them down. Check the corner from ground level to ensure it reads as a clean, continuous line.

What size drip trim external corner do I need?

The corner size must match the drip trim size. If you are using a 150mm drip trim, order the 150mm external corner. We stock corners in 14 sizes from 75mm to 400mm. Measure the visible front face of the installed or specified trim and order the corresponding corner.

Can drip trim external corners be powder coated?

Yes, and we strongly recommend it. The external corner is the most visible component in the drip trim system, so a colour mismatch here is especially noticeable. We offer powder coating in any RAL colour to match the rest of the trim run. Select your colour when you order.

Part of a Complete Drip Trim System

This external corner is one component in a complete aluminium drip trim system manufactured by Online Metal Store Ltd. The full system includes the drip trim in 3 metre lengths, internal joiners for splicing straight runs, 90-degree internal corners for inward turns, and external corners (this product) for outward turns. Ordering all components together from the same manufacturer guarantees a precise profile match across every piece.

The entire system is available in 14 sizes from 75mm to 400mm and can be powder coated to any RAL colour across all components. Whether you are specifying for a simple domestic extension or a complex commercial flat roof, the complete system is available from stock with fast UK-wide delivery from our Chelmsford factory.

Standards and Compliance

Our aluminium drip trim system, including this external corner, is manufactured from high-grade aluminium and powder coated with external-grade polyester paint for long-lasting durability. The system is suitable for use on flat roofs in accordance with BS 6229:2018 (flat roofs with continuously supported flexible waterproof coverings) and is compatible with EPDM, single ply, felt and liquid-applied membrane systems.