2mm Aluminium Sloping Coping – 135° External Corner | 125mm External Leg
2mm Aluminium Sloping Coping – 135° External Corner | 125mm External Leg
External angled parapet corners are easy to underestimate until water starts finding the weakest joint. A poorly cut corner can leave exposed edges, uneven sealant lines, staining on the wall face and a roofline that looks improvised instead of professionally finished.
That matters on UK buildings where coping has to deal with driving rain, frost cycles, coastal winds and regular temperature movement. Whether the job is a modern extension in Chelmsford, a commercial unit in Basildon, a housing development near Colchester or an angled roof terrace in East London, the outside corner needs to look clean and protect the wall head properly.
Product Overview
This 2mm aluminium sloping coping external corner is made for 135 degree outward parapet junctions where two coping runs meet around an angled outside corner. It gives the detail a formed, purpose-made piece instead of relying on two site-cut lengths meeting at a vulnerable point.
It is designed to work as part of an aluminium sloping coping system, with a 125mm external leg for deeper face coverage on medium to larger wall heads. Online Metal Store Ltd supplies this product from Chelmsford, Essex, with size options from 185mm to 885mm and powder coating in any RAL colour to match the wider roofline package.
For a complete run, this corner can be specified alongside matching aluminium copings, stopends, sealant and colour matched fixings. That keeps the profile, finish and installation detail consistent across the full parapet rather than mixing parts from different systems.
Key Benefits
Purpose-Made for 135 Degree External Corners
A factory formed 135 degree external corner gives an angled parapet return a cleaner and more reliable junction than a rushed site cut. It helps the installer create a neat corner line, reduce exposed edges and avoid the patched appearance that can happen when straight lengths are forced to do a specialist corner job.
Better Protection in UK Weather
The sloped profile helps move water away from the wall head, while the aluminium construction resists corrosion in damp, exposed and changeable conditions. That is especially useful on flat roof edges, garden walls and commercial parapets where rain can sit around corners if the detail is not planned properly.
125mm External Leg for Deeper Coverage
The 125mm external leg gives more visible face coverage than shorter-leg options, which can be helpful on thicker parapet walls or projects where the designer wants a stronger roofline detail. It also helps the corner feel balanced when used with matching coping lengths across wider wall heads.
Powder Coated in Any RAL Colour
The corner can be powder coated in any RAL colour, so the finish can match windows, fascias, cladding, rainwater goods or existing project specifications. This is useful on residential work where the client wants a neat finish and on commercial buildings where colour consistency matters across the elevation.
Lightweight and Easier to Handle on Site
Aluminium gives good strength without the weight of heavier materials. That makes the corner easier to handle, position and fit at roof level, especially when access is limited or the installer is working around parapets, terraces, scaffolding or finished facade surfaces.
UK Manufactured with Fast Delivery
The product is manufactured in Chelmsford, Essex, which supports better control over sizing, finish and lead times. For roofers, contractors and builders working across Essex, Kent, London, the South East and wider UK, that helps reduce delays when a coping run needs matching corners to complete the job properly.
Technical Specifications
Product type: Aluminium sloping coping 135 degree external corner
Material: Aluminium
Thickness: 2mm
Corner angle: 135 degree external corner
External leg: 125mm
Available widths: 185mm, 210mm, 235mm, 260mm, 285mm, 310mm, 335mm, 360mm, 385mm, 410mm, 435mm, 460mm, 485mm, 510mm, 535mm, 560mm, 585mm, 610mm, 635mm, 660mm, 685mm, 710mm, 735mm, 760mm, 785mm, 810mm, 835mm, 860mm and 885mm
Finish: Powder coated in selected RAL colour
Price shown on live page: From £59.04 ex VAT, £70.85 inc VAT
Manufacturing location: Chelmsford, Essex, United Kingdom
Best suited for: Angled external parapet corners, roof edge returns, wall heads and coping systems that need a formed 135 degree outside corner
Return status: Custom fabricated item, non-returnable unless faulty
Choosing the Right Size / Width / Thickness
The width should be selected to suit the full wall build-up, not just the visible brick or block measurement. Allow for the wall width, waterproofing build-up, insulation line where relevant, finish tolerances and the way the coping needs to sit over the top of the wall.
· Use narrower widths, such as 185mm to 285mm, for slim parapet walls, small boundary walls and compact domestic extensions where the wall build-up is modest.
· Use mid-range widths, such as 310mm to 510mm, for many residential parapets, garage roof edges, Edwardian semis, Victorian terraces and standard flat roof extensions.
· Use wider options, such as 535mm to 885mm, for thicker wall heads, commercial units, schools, care homes and projects with insulation, render or cladding build-up around the parapet.
· Choose this 125mm external leg when the outside face needs deeper coverage, stronger visual definition or better alignment with deeper matching coping lengths.
· Check the angle before ordering. A 135 degree external corner is for an outward angled return, not a square 90 degree corner or an inward corner.
How to Install / How to Fit
Start by checking the parapet is sound, clean, level and ready to receive the coping system. The waterproofing should be turned and detailed correctly before the metalwork is installed, because the coping is there to protect and finish the wall head rather than hide a poor substrate.
Dry-fit the 135 degree external corner first, then offer up the adjoining coping lengths so the joint line, overhang and slope direction are correct. If the system needs sealing at the junction, use colour coded sealant to help keep the finish neat and matched to the selected RAL colour.
Fixing should follow the project detail and the selected substrate. Use suitable colour coded timber fasteners or colour coded metal fasteners where visible fixings are part of the installation approach, making sure fixings are set out cleanly and do not compromise waterproofing beneath.
Where the corner meets flashings, trims or other roof edge items, coordinate it with the wider trims, flashings and angles package. On exposed buildings in places such as Southend, Kent or East London, take extra care with sealant continuity and water shedding direction around the external return.
Where Aluminium Coping External Corner 125mm Is Used
Angled Parapet Walls on Flat Roofs
This corner is used where a flat roof parapet turns through a 135 degree external angle. It helps the aluminium copings run continue around the outside return without leaving a weak corner detail exposed to rain.
Modern Domestic Extensions
On extensions in Chelmsford, Billericay, Brentwood and the Home Counties, angled parapets are often used to suit plot shape, glazed openings or planning constraints. A formed external corner keeps the roofline tidy and avoids a rough join where the design is meant to look clean and modern.
Commercial Units and Retail Buildings
Commercial roof edges often have longer coping runs, exposed elevations and more visible corner details. A 135 degree external corner gives the outside return a professional finish, especially where customers, tenants or maintenance teams will see the parapet from ground level.
Rendered Walls and Clad Facades
Rendered elevations, cladding panels and facade upgrades need neat metal edges to avoid staining and awkward junctions. This corner can work alongside aluminium roof flashing where the wall head and roof edge details need to be coordinated.
Higher Specification Roofline Packages
For projects where appearance matters, such as offices, schools, care homes and architect-led homes, the corner helps the coping system look like one planned package. The coping case study can also support trust by showing how aluminium coping details are used on real UK projects.
Frequently Asked Questions
What is a 135 degree external aluminium coping corner?
A 135 degree external aluminium coping corner is a pre-formed corner piece used where two coping runs meet around an angled outside parapet return. It helps protect the wall head, keeps the roofline clean and reduces the need to cut and form a difficult angled joint on site.
Do I need an external corner or an internal corner?
You need an external corner when the coping turns around an outside angle of the building or wall. You need an internal corner when the coping turns into an inside angle. If you are standing outside the wall and the corner projects outwards, this product is usually the correct style.
How do I choose the correct width?
Measure the full wall build-up, including the wall, finishes and any waterproofing or insulation allowances. The corner should match the width of the coping lengths used on the same run, so the overhang, slope and joint detail stay consistent around the parapet.
Can this coping corner be powder coated to match the rest of the roofline?
Yes, this product is available with powder coating in a selected RAL colour. That means it can be matched with coping lengths, stopends, fascias, windows, doors, cladding or rainwater goods for a cleaner architectural finish.
Is it better to use a formed corner instead of cutting two coping lengths?
A formed corner is usually better for a neat, repeatable and more controlled finish. Cutting two straight lengths on site can work in some situations, but it often creates more risk around exposed edges, uneven joints and sealant lines, especially on visible or weather-exposed parapets.
Does the corner still need sealant?
Most coping systems still need careful sealing at joints and interfaces. A formed corner improves the shape and finish of the junction, but the installer should still follow the correct fixing and sealing detail, using compatible sealant and allowing for movement where needed.
Comparison Section
Aluminium 135 Degree External Corner
The aluminium external corner is the best choice when the project needs a clean, lightweight and corrosion-resistant finish around an angled outside parapet return. It suits modern residential and commercial buildings where the coping system must look precise and perform in wet UK conditions.
Site-Cut Coping Lengths
Cutting straight coping lengths on site can sometimes be used on low-visibility or budget-led work, but it relies heavily on installer skill and creates more room for small gaps or uneven joints. It can also make powder coated edges harder to protect if cuts are exposed or poorly finished.
Lead or Traditional Metal Detailing
Lead and other traditional materials still have a place on listed buildings, heritage properties and projects where conservation officers require a specific appearance. For most modern parapet and flat roof edge work, powder coated aluminium gives a cleaner look, lower weight and strong colour matching options.
For a full roof edge package, link this product back to the aluminium copings collection so buyers can choose straight lengths, corners, stopends and matching accessories together.
Part of a Complete System
This product should be treated as part of a complete coping system rather than a standalone detail. Ordering the full system together helps improve colour consistency, profile alignment and installation planning.
Standards and Compliance
Flat roof parapet detailing should be considered in the context of BS 6229:2025, which covers the design, construction, care and maintenance of flat roofs with continuously supported flexible waterproof coverings. Getting the parapet and coping interface right helps protect the roof, the wall below and the people inside the building.
For powder coated architectural aluminium, BS EN 12206-1:2021 is the relevant coating standard to reference for aluminium and aluminium alloys prepared with thermosetting coating powder. On new-build projects, check the current NHBC Standards and project specification so the coping detail supports warranty expectations rather than becoming a weak point.