2mm Aluminium Flat Coping 135° Corner | 75mm External Leg
2mm Aluminium Flat Coping 135° Corner | 75mm External Leg
Most parapet walls are not square. If you have worked on any volume of residential or commercial flat roofing in the South East, you already know this. L-shaped extensions, bay projections, angled boundary walls, and awkward plot configurations mean that 90 degree corners are only half the story. When that wall turns at 135 degrees and you have no corner piece to match the coping run, you end up with an exposed joint that the weather will find in short order. Water tracking back under the coping at a badly finished corner is one of the most common causes of damp ingress into the flat roof build-up, and it is entirely avoidable.
This 2mm aluminium flat coping 135 degree corner is the purpose-made solution. It forms a neat, weathertight junction wherever your parapet wall changes direction at an obtuse angle, and it matches directly into the 2mm flat coping lengths running either side of it. Manufactured here in Chelmsford, Essex, and available powder coated in any RAL colour to match your project spec exactly, it removes the guesswork from corner detailing and keeps the whole system tight from day one.
Product Overview
This corner piece is part of the Online Metal Store Ltd 2mm aluminium flat coping range. It is designed for parapet walls where the wall direction changes at a 135 degree angle, which is the angle you get when two walls meet at an obtuse junction rather than a straight right angle. The 75mm external leg sits over the outside face of the wall, providing the overhang and drip detail that keeps water clear of the substrate below. The internal leg matches the profile of the standard flat coping lengths so that the transition from straight run to corner is flush, tight and consistent. You can order the matching 2mm aluminium flat coping lengths in 1m, 2m and 3m sizes as part of the same system, and the 90 degree corner is also available where walls meet at a right angle.
The material is 2mm grade aluminium, which gives enough rigidity across the corner profile without adding unnecessary weight. All products in this range are powder coated using an external grade polyester powder coating process. The finish bonds directly to the aluminium surface and is available in any RAL colour, so whether the spec calls for anthracite grey, white, or a project-specific colour, the corner piece will match the rest of the system. If you need a heavier gauge, the 3mm aluminium flat coping 135 degree corner is also available from the same range.
Key Benefits
Purpose-Made for 135 Degree Junctions
Cutting and mitreing a standard coping run at a corner is never ideal. Even done carefully, a mitred joint has a seam running straight through the most vulnerable part of the detail. A purpose-made 135 degree corner is formed as a single pressed piece with no mid-corner joint in the aluminium itself. That means there is no seam at the point where two wall faces meet, which is exactly where the wind-driven rain wants to find a gap. The corner piece integrates cleanly with the flat coping runs either side of it, giving you a continuous weathertight profile across the change of direction.
Powder Coated in Any RAL Colour
The finish on this corner is an external grade polyester powder coat applied in Chelmsford to the same specification as every other component in the flat coping range. You can order it in any RAL colour to match the coping lengths, stopends and brackets on your project. That matters on visible parapets where colour consistency across every component is part of the specification. There are no minimum order quantities for standard RAL colours, and the colour you specify will be applied to all components in your order so that the system looks uniform on site.
Corrosion Resistance and Long Service Life
Aluminium forms a natural oxide layer that protects the base metal from corrosion. Combined with an external grade powder coat finish, this corner piece is built to perform in the UK climate without the maintenance that lead or zinc alternatives require. Coastal sites in Essex, Kent and East Anglia, where salt-laden air accelerates corrosion in ferrous metals, are well within the operational envelope for aluminium. A properly installed aluminium coping system has a service life well in excess of 25 years with no routine maintenance beyond an occasional clean.
Lightweight and Easy to Handle on Site
At 2mm gauge, this corner piece is light enough to handle and position without assistance, which matters when you are working at parapet height on a flat roof. There is no specialist tooling needed to fit it. The corner integrates with the standard coping bracket and clip system so that installation follows the same sequence as the straight lengths either side of it.
UK Manufactured with Fast Delivery
This corner is manufactured at the Online Metal Store Ltd facility in Chelmsford, Essex. Lead times are short because the products are made and held in the UK, not shipped from overseas. For construction programmes in the South East, the Home Counties, or anywhere across the UK, that means you are not waiting weeks for a corner piece to complete a coping order.
Technical Specifications
Material: 2mm grade aluminium
Profile: Flat coping
Corner Angle: 135 degrees (obtuse, for walls meeting at a wider-than-right-angle 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 products for full fixing specification
Choosing the Right Corner: 90 Degree or 135 Degree?
Not every corner on a parapet wall is a right angle. Here is a quick guide to which corner piece you need:
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90 degree corner: use this where two walls meet at a right angle. Standard on most rectangular flat roof extensions, box dormers, and simple residential flat roof builds. Use the matching aluminium flat coping 90 degree corner for this junction.
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135 degree corner: use this where two walls meet at an obtuse angle, wider than 90 degrees. Common on L-shaped extensions, bay projections, commercial units with angled plan forms, and boundary walls that follow the line of a plot rather than a straight property edge.
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If you are unsure about your angle: a digital angle finder or a site measurement against a protractor will confirm it quickly. The 135 degree piece is the most common obtuse coping corner on UK flat roof projects, but if your angle differs, get in touch with Online Metal Store Ltd to discuss bespoke corner options.
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Matching gauge: always match the corner gauge to the lengths you are using. This product is 2mm and works with all 2mm flat coping lengths in the 75mm external leg range. If you are using 3mm lengths, use the 3mm version instead.
How to Fit a 135 Degree Flat Coping Corner
Before you start, make sure you have all components for the run. The corner piece sits at the junction between two straight coping lengths and both runs should be cut and dry-fitted first so that you know the corner is in the right position. Fix the aluminium coping brackets to the wall at the standard centres, working out from the corner in both directions. The bracket positions at either side of the corner should give the corner piece full bearing without overhanging unsupported.
Once the brackets are positioned, set the corner piece in place and check the alignment with the straight runs either side. The flat coping lengths should butt up tight to the corner wings with no visible gap. Apply colour coded sealant at the junction between the corner wings and the straight coping lengths. Run a continuous bead along the internal face of the joint before pressing the straight lengths home. This sealant joint is the primary defence against water tracking back through the butt joint, and skipping it is false economy on any exposed parapet.
Fix the straight lengths to the brackets using colour coded fasteners in the matching RAL colour so that fixings do not stand out against the powder coat finish. Work along both legs of the corner in sequence, checking alignment as you go. Once the straight runs are fixed, the corner piece is captured between them and held in position. Apply a neat finishing bead of sealant to the external face of the joints on the corner wings for a clean and fully weathertight detail.
Where the 135 Degree Flat Coping Corner Is Used
L-Shaped Residential Flat Roof Extensions
The single most common use for a 135 degree coping corner in domestic work is on L-shaped rear extensions. When a flat roof extension wraps around the back of a semi-detached or terraced house, the parapet wall typically forms an internal and external L-shape, with at least one junction that is not a right angle. The 135 degree corner allows the flat coping system to follow that change of direction cleanly without fabricated mitres or exposed cut edges. From Chelmsford to Brentwood, Southend to Colchester, this scenario comes up on almost every domestic extension project involving a parapet.
Commercial Flat Roof Parapets with Angled Plan Forms
Commercial buildings, particularly retail units, light industrial units, and mixed-use developments across Essex and the wider South East, are rarely perfectly rectangular in plan. Where a parapet wall follows the line of a plot boundary or responds to an irregular site shape, the coping run will include obtuse corners. The 135 degree corner piece handles this transition as part of a continuous aluminium coping system, giving the specifier a consistent profile, finish and colour across the whole perimeter.
Boundary Walls and Garden Parapets
Aluminium flat coping is not limited to roof parapets. On low boundary walls, screen walls, and raised planting beds associated with commercial or residential landscaping projects, the same 2mm flat coping system provides a neat, low-maintenance cap. Where boundary walls follow a plot line that turns at an obtuse angle, the 135 degree corner is the right component. It works alongside the closed stopend and stopend upstand components to terminate the run cleanly at both ends of the wall.
New Build Housing Developments
Housebuilders working to NHBC standards on new build developments across the East of England and the Home Counties will be familiar with the requirement for properly detailed parapet copings. On housing schemes with varied plot orientations and angled plot boundaries, coping corners are required in both 90 and 135 degree versions. Ordering both corner types from the same supplier ensures colour and profile consistency across the whole development, and the fast turnaround from Chelmsford means the coping components arrive on programme without holding up the watertight stage.
Frequently Asked Questions
What does a 135 degree coping corner actually do?
It bridges the junction between two flat coping lengths where a parapet wall changes direction at an obtuse angle. Instead of cutting and mitreing two lengths together at the corner, which leaves a seam at the most exposed point, the 135 degree corner piece is a single pre-formed component that covers the change of direction with no mid-corner joint in the aluminium. It clips or fixes between the two straight runs and is sealed into place to give a continuous, weathertight coping profile across the corner.
How do I know if I need a 135 degree or a 90 degree corner?
Measure the internal angle of the wall corner. A 90 degree corner is a right angle. A 135 degree corner is wider than a right angle, which is what you get when two walls meet at an obtuse junction. The most reliable way to confirm the angle on site is with a digital angle finder or a simple site measurement. If your walls meet at 135 degrees, use this product. If they meet at 90 degrees, you need the matching 90 degree corner from the same range.
Does this corner come powder coated to match my coping lengths?
Yes. All components in the 2mm flat coping range, including this corner piece, are available powder coated in any RAL colour. When you order the corner alongside the coping lengths and other accessories, specify the RAL colour at the time of order and all components will be coated in the same colour in the same batch. That gives you full colour consistency across the system without having to match colours from different suppliers or different batches.
How many coping corners do I need?
One corner piece per change of direction in the parapet. If your parapet wall has two 135 degree changes of direction, you need two corners. Count the number of obtuse angle turns on your parapet plan, then check whether each is an internal or external turn. This product is for external corners (where the wall turns away from you as you look down from the roof). Check the full range for the internal 135 degree version if you also have internal obtuse corners on the same project.
Is this product the same as the 3mm version?
The profile and angle are the same, but the gauge is different. This product is 2mm aluminium, which is the standard gauge for most domestic and light commercial flat roof parapet copings. The 3mm version is heavier and suited to exposed sites, larger wall widths, or commercial projects where the specification calls for a heavier gauge. Both use the same 75mm external leg and the same bracket system, so if you are mixing gauges on a project, the fixing centres and installation method are consistent.
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 a single point of contact for the whole system. 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
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2mm Aluminium Flat Coping 135 Degree Corner | 75mm External Leg (this product)
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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 an overview of the full aluminium flat coping range, visit the Aluminium Flat Copings collection page. If you are working with a wider wall or a more demanding specification, the 3mm flat coping 135 degree corner is also available in the same profile.
Standards and Compliance
Aluminium parapet coping systems used on flat roof constructions in the UK are covered by BS 6229:2018 - Flat Roofs with Continuously Supported Flexible Waterproof Coverings, which sets out the requirements for edge and parapet detailing. A properly specified and installed aluminium coping at the parapet head protects the edge of the waterproof layer and prevents water from standing against the upstand construction.
The powder coat finish on all Online Metal Store Ltd aluminium coping products is applied in accordance with BS EN 12206-1 - Organic Coatings on Aluminium and Aluminium Alloys, which specifies the performance requirements for powder organic coatings on aluminium used in external applications. Getting the coating specification right on a coping system protects both the building and the finish over the full service life of the product.
For new build projects, NHBC Standards Chapter 7.1 covers the requirements for flat roof and parapet construction on homes registered with NHBC, and a correctly detailed aluminium coping system is consistent with those requirements.