2mm Aluminium Flat Coping – 90° Corner | 75mm External Leg
2mm Aluminium Flat Coping – 90° Corner | 75mm External Leg
Every flat roof with a parapet wall has at least four corners. On a standard rectangular extension, dormer, or flat-roofed outbuilding, those corners are right angles, and if you are running aluminium flat coping along the top of the parapet, you need a proper corner piece at each turn. A mitre cut on two lengths of coping can be done, but the joint sits right at the most exposed point of the detail. Wind-driven rain does not need a large gap to get in under a parapet coping, and a poorly finished corner is one of the most reliable sources of water ingress into the flat roof edge build-up. Remedial work on a failed corner detail is time-consuming and disruptive, particularly once the interior finishes are in.
This 2mm aluminium flat coping 90 degree corner eliminates that risk. It is a purpose-made component that covers the right-angle turn in the parapet as a single pre-formed piece, with no mid-corner seam in the aluminium itself. It integrates directly with the 2mm flat coping lengths running either side of it and is available powder coated in any RAL colour to match the rest of the system. Manufactured in Chelmsford, Essex and supplied with fast UK delivery, it is the straightforward fix for the most common corner on any flat roof parapet project.
Product Overview
The 90 degree corner is part of the Online Metal Store Ltd 2mm aluminium flat coping range with a 75mm external leg. It is designed for parapet walls where two faces meet at a right angle, which is the standard junction on rectangular flat roof extensions, box dormers, flat-roofed garages and most commercial flat roof perimeters. The 75mm external leg sits over the outside face of the wall, providing the overhang and drip detail that keeps rainwater well clear of the wall below. The internal leg matches the flat coping profile so the transition from the corner into the straight runs is flush and consistent throughout. You can see the matching 2mm flat coping lengths in 1m, 2m and 3m for the straight sections of the parapet, and if any part of your parapet turns at an obtuse angle wider than 90 degrees, the 135 degree corner is also available in the same range.
The material is 2mm grade aluminium, which provides the right balance of rigidity and weight for a flat coping corner at this leg depth. All components in this range are powder coated with an external grade polyester finish that is available in any RAL colour. Whether the project calls for anthracite grey, signal white, or a colour-matched specification, the corner will be finished to the same shade as the lengths, stopends and brackets ordered alongside it. For projects where a heavier gauge is specified, the 3mm aluminium flat coping 135 degree corner is available in the same profile, and the full aluminium flat copings range covers both 2mm and 3mm options across the complete system.
Key Benefits
No Mid-Corner Seam in the Aluminium
The single biggest advantage of a purpose-made 90 degree corner over a field-fabricated mitre is that there is no seam in the aluminium at the change of direction. The corner piece is pressed as a single component. The only joints in the installed system are where the straight coping lengths butt up to the corner wings, and those joints are sealed and captured by the lengths themselves. At the most exposed point of a parapet, the corner, there is no opportunity for water to track back through a fabricated seam.
Exact Colour Match Across the Full System
Ordering the corner alongside the coping lengths, stopends and brackets means all components go through the same powder coating batch at the Chelmsford facility. The RAL colour you specify is applied consistently across every part of the order. That matters on visible parapets where a mismatched corner in a slightly different shade of grey stands out immediately. There are no minimum order quantities for standard RAL colours, and the full range of RAL options is available on this corner as on all other components in the range.
Corrosion-Resistant for the UK Climate
Aluminium is the right choice for exposed parapet copings in the UK. It does not rust, it forms a natural oxide layer that protects the base metal, and the external grade powder coat further extends the service life well beyond what you would expect from UPVC or painted steel alternatives. On coastal sites in Essex, Suffolk, Kent and the South East, where salt-laden air and higher humidity accelerate corrosion in ferrous metals, aluminium is the low-maintenance, long-life option. A properly installed aluminium coping system is expected to perform for 25 years or more without routine maintenance.
Lightweight and Quick to Handle on Site
At 2mm gauge with a 75mm leg, this corner piece is light enough to position and align without assistance. There is no specialist tooling required to fit it. It works with the standard aluminium coping bracket system, and installation follows the same sequence as the straight lengths on either side. For roofers working at parapet height on domestic extensions, the ease of handling matters as much as the product quality.
UK Manufactured with Short Lead Times
This corner is made at the Online Metal Store Ltd factory in Chelmsford, Essex. Products are manufactured and held in the UK, which keeps lead times short for construction programmes across the South East and the wider UK. If you are ordering a full flat coping system for a tight programme, the components are coming from a UK manufacturer with fast turnaround, not from a European or overseas supplier with extended shipping times.
Technical Specifications
Material: 2mm grade aluminium
Profile: Flat coping
Corner Angle: 90 degrees (right angle, for walls meeting at a standard perpendicular junction)
External Leg: 75mm
Finish: Polyester powder coating, external grade
Colour: Any RAL colour to order
Compatible System: 2mm Aluminium Flat Coping range | 75mm External Leg
Country of Manufacture: United Kingdom (Chelmsford, Essex)
Fixing Method: Coping bracket system - see bracket product for full fixing specification
90 Degree or 135 Degree: Which Corner Do You Need?
The two most common coping corner angles are 90 degrees and 135 degrees. Here is how to decide which you need:
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90 degree corner (this product): use this wherever two parapet wall faces meet at a right angle. This is the standard corner on rectangular flat roof extensions, box dormers, flat-roofed outbuildings, garages and most straightforward commercial flat roof perimeters. If your walls are square in plan, every corner is a 90 degree corner.
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135 degree corner: use this wherever two parapet wall faces meet at an obtuse angle wider than a right angle. This is needed on L-shaped extensions, angled bay projections, commercial units with irregular plan forms, and boundary walls that follow a plot line rather than a straight rectangular edge. The matching 135 degree corner is available in the same 2mm flat coping range.
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Mixed parapets: many flat roofs have both right-angle and obtuse-angle corners. An L-shaped extension, for example, typically has 90 degree corners at the outer right-angle corners and a 135 degree corner at the inner re-entrant turn. Order both corner types from the same range to ensure colour and profile consistency across the full perimeter.
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Confirming your angle on site: if you are unsure whether a corner is 90 or 135 degrees, a digital angle finder will confirm it in under a minute. Do not assume - a 135 degree corner installed in a 90 degree opening will not seat correctly.
How to Fit a 90 Degree Flat Coping Corner
Plan the coping run for both legs meeting at the corner before fixing anything. Dry-fit the straight lengths on both sides and work out the bracket positions so that the corner piece will have full bearing from brackets on either leg. Fix the aluminium coping brackets at the standard centres, working away from the corner in both directions. The brackets immediately adjacent to the corner should be positioned so that the corner wings can seat fully without overhanging unsupported at the junction.
Set the corner piece in place and check the alignment with the straight runs on both legs before committing to the fix. The flat coping profile on the corner wings should line up flush with the profile of the lengths. Once the position is confirmed, apply colour coded sealant in the matching RAL colour along the internal face of the joint between the corner wings and the straight lengths. Run a continuous bead before pressing the straight lengths home. This internal sealant bead is the primary weathertight seal at the joint and is not optional on an exposed parapet.
Fix the straight coping lengths to the brackets using colour coded fasteners in the matching RAL to keep the fixing heads flush with the surface colour. Work along both legs from the corner outward, checking alignment as you go. Once the straight lengths are fixed either side, the corner piece is captured between them. Finish with a neat bead of sealant on the external face of the corner joints for a clean, fully weathertight detail.
Where the 90 Degree Flat Coping Corner Is Used
Domestic Flat Roof Extensions
The single most common application for a 90 degree flat coping corner is on domestic rear extensions across the UK. From Victorian terraces in East London to Edwardian semis in Brentwood and new-build homes in Chelmsford, the rear single-storey flat roof extension with a parapet is one of the most common roofing projects a roofer or builder will encounter. A rectangular extension with a parapet has four right-angle corners, and each one needs a proper corner piece. The 2mm flat coping system covers the full perimeter of a standard extension from a single supplier: lengths, corners, stopends and brackets, all in the same colour.
Box Dormers
Box dormers on residential properties have a flat roof parapet across the front face and typically two 90 degree corners where the front parapet meets the side cheeks of the dormer. These are exposed, prominent details that are highly visible from street level, particularly on terraced houses in the South East where dormer extensions are common. A well-fitted 90 degree corner in a powder-coated colour that matches the dormer cladding or the window frame specification gives a clean, finished look that a bodged mitre cut never achieves.
Flat-Roofed Garages and Outbuildings
Garages, garden offices, stores and outbuildings with flat roofs account for a significant proportion of flat coping orders from domestic buyers. These structures are almost always rectangular, which means every corner is a right angle. For homeowners in Basildon, Colchester, Braintree and across Essex ordering a coping system for a new garage or replacement coping on an existing outbuilding, having the corner pieces available as part of the same product range simplifies the order. The closed stopend finishes the ends of each run cleanly, and the full system ships from Chelmsford.
Commercial Flat Roof Parapets
Commercial buildings with flat roof parapets, including retail units, light industrial units, office buildings and care homes, typically have rectangular or near-rectangular plan forms with predominantly 90 degree corners. On these projects, colour and profile consistency across the full perimeter coping system is part of the specification, and ordering all components including corners, lengths, stopends and coping brackets from a single UK supplier keeps the supply chain simple and ensures everything arrives in the same colour from the same batch. The aluminium coping case study shows this system in use on a live UK project.
Frequently Asked Questions
What does a 90 degree flat coping corner actually do?
It provides a purpose-made, weathertight junction at right-angle corners of a parapet wall, where two flat coping lengths would otherwise need to be cut and mitreed together. Instead of a fabricated mitre with a seam at the most exposed point of the parapet, the corner piece is a single pre-formed component that covers the change of direction cleanly. It integrates with the straight coping runs on either side and is sealed into place to give a continuous, weathertight coping profile around the corner.
How do I know whether to order a 90 degree or 135 degree corner?
Measure the internal angle of the corner on your parapet wall. A 90 degree angle is a right angle, which is what you get on a standard rectangular building. A 135 degree angle is wider than a right angle, which occurs where walls meet at an obtuse junction on L-shaped plans, angled boundary walls, or buildings with non-rectangular plan forms. This product is for 90 degree right-angle corners. If any corners on your parapet are at a wider obtuse angle, you will also need the 135 degree version from the same range.
How many 90 degree corners do I need?
Count the number of right-angle turns on your parapet plan. A standard rectangular flat roof extension has four corners, which means four 90 degree corner pieces. An L-shaped extension has more turns, but some of those will be 135 degree obtuse corners rather than right-angle corners. Sketch your parapet plan, identify each corner angle, and order the appropriate corner type for each. If you are unsure how many corners to order, the team at Online Metal Store Ltd can help you work through the plan.
Does this corner need to be the same thickness as my coping lengths?
Yes. This corner is 2mm aluminium and works with the 2mm flat coping lengths in the 75mm external leg range. If you are using 2mm lengths, use this 2mm corner. Mixing gauges on the same system is not recommended because the profile dimensions will not match exactly at the junction between the corner and the straight length. If your project calls for 3mm coping, use the 3mm corner piece from the same range instead.
Can I get this corner in any colour?
Yes. Like all components in the 2mm flat coping range, this corner is available powder coated in any RAL colour. Specify the RAL number at the time of order and it will be coated in the same colour as the coping lengths, stopends and brackets in your order. There are no minimum quantities for standard RAL colours. If you need a BS colour or a bespoke finish, contact Online Metal Store Ltd directly to discuss the specification.
Part of a Complete Flat Coping System
This corner piece is one component in a complete aluminium flat coping system with a 75mm external leg. Ordering all components from the same source means matching profiles, consistent powder coat colour, and everything arriving in the same delivery. The full 2mm flat coping system with 75mm external leg includes:
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2mm Aluminium Flat Coping 90 Degree Corner | 75mm External Leg (this product)
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2mm Aluminium Flat Coping 135 Degree Corner | 75mm External Leg
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2mm Aluminium Flat Coping - Closed Stopend | 75mm External Leg
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2mm Aluminium Flat Coping - Stopend Upstand | 75mm External Leg
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2mm Aluminium Flat Coping - 90 Degree T-Junction | 75mm External Leg
For the full range overview, visit the Aluminium Flat Copings collection page. If you need the 3mm gauge for a more demanding specification, the 3mm flat coping 90 degree corner is also available in the same profile. For projects that include both right-angle and obtuse corners, see the 2mm flat coping 135 degree corner for the obtuse angle version.
Standards and Compliance
Aluminium parapet coping used on flat roof constructions is covered by BS 6229:2018 - Flat Roofs with Continuously Supported Flexible Waterproof Coverings, which sets out the requirements for edge and parapet detailing on flat roofs in the UK. A correctly specified coping at the parapet head is part of the waterproofing strategy for the flat roof as a whole, not just a finishing detail.
The powder coat finish on all Online Metal Store Ltd aluminium coping products meets the requirements of BS EN 12206-1 - Organic Coatings on Aluminium and Aluminium Alloys, the standard that governs the performance of powder organic coatings on aluminium used in external architectural applications. Getting the coating right on a coping system that sits fully exposed to the UK climate is as important as getting the profile right.
For new build projects registered with NHBC, Chapter 7.1 of the NHBC Standards covers flat roof and parapet wall construction requirements. A properly detailed aluminium flat coping system is consistent with those requirements and supports the warranty position on new build completions.