3mm Aluminium Flat Coping – 90° Corner | 75mm External Leg
3mm Aluminium Flat Coping – 90° Corner | 75mm External Leg
There are jobs where 2mm aluminium flat coping is exactly right. A domestic rear extension in a sheltered suburban setting with a modest parapet wall width is a typical example. But the moment you move onto a commercial flat roof, a taller building, an exposed site on the Essex coast or the Thames Estuary, or a parapet wall that is wider and therefore puts more leverage on the corner piece, the specification changes. A 3mm gauge corner is not just marginally thicker than a 2mm. It is stiffer, it resists wind uplift more effectively, and it is the gauge that most commercial specifiers and NHBC-registered builders reach for on new-build projects where the coping is expected to perform for decades without remedial work.
This 3mm aluminium flat coping 90 degree corner is the right-angle component for the 3mm flat coping system with a 75mm external leg. It covers right-angle parapet corners with the same clean, pre-formed profile as the 2mm version but with the added rigidity and durability that heavier-specification projects require. Manufactured in Chelmsford, Essex, and available powder coated in any RAL colour, it is the commercial-grade corner for flat roof parapets that need to last.
Product Overview
This corner is one component in the Online Metal Store Ltd 3mm aluminium flat coping range with a 75mm external leg. It handles right-angle turns in parapet walls where two flat coping runs meet at 90 degrees, the most common corner on rectangular flat-roof commercial buildings, extensions, and boundary wall structures. The 75mm external leg provides the overhang and drip edge that carries rainwater away from the wall face, and the internal leg matches the 3mm flat coping profile so the junction between the corner and the straight runs is flush and weathertight throughout. The matching 3mm flat coping lengths are available in 1m, 2m and 3m sections for the straight parapet runs, and the 3mm flat coping 135 degree corner covers obtuse-angle junctions in the same gauge and leg size.
The 3mm gauge is the standard specification for commercial and exposed-site flat roof copings in the UK. It provides greater resistance to wind uplift forces, better rigidity across wider wall widths, and a longer fatigue life under the repeated thermal expansion and contraction cycles that a fully exposed aluminium coping experiences over a British building lifetime. The powder coat finish is an external grade polyester applied to the same specification as the 2mm flat coping 90 degree corner, and it is available in any RAL colour to match the straight lengths, stopends and brackets in your order. For an overview of the full 3mm aluminium flat coping range, the aluminium flat copings collection page covers all gauges and leg sizes.
Key Benefits
Greater Rigidity for Commercial and Exposed-Site Specification
The extra millimetre of gauge makes a meaningful difference to the stiffness of the corner profile. On a domestic extension with a short parapet run and a sheltered aspect, 2mm is sufficient. On a commercial flat roof on a building of any real height, on a site exposed to prevailing south-westerly winds across open ground, or on a coastal location in Essex, Kent or Suffolk where salt-laden air and higher wind speeds are the norm, 3mm provides the rigidity and wind uplift resistance that the project demands. Where a structural engineer or specifier has called for 3mm on the project, this is the correct component.
Consistent Profile Across the Full 3mm System
The corner is pressed to the same profile as the 3mm flat coping lengths running either side of it. There is no step, no mismatch and no visible gauge transition at the junction. On a commercial parapet where the coping is visible from ground level or from adjacent buildings, profile consistency matters as much as colour consistency. Ordering the corner alongside the straight lengths, stopends and brackets ensures that everything is fabricated to the same specification and finished in the same batch.
Powder Coated in Any RAL Colour
Commercial projects almost always have a specified coping colour, whether that is anthracite grey to match the window frames on a new office building, signal white on a healthcare facility, or a project-specific RAL that the architect has called up in the specification. This corner is available in any RAL colour, with no minimum order quantity on standard colours. When the corner, lengths, stopends and brackets are ordered together, all components go through the same powder coating batch at the Chelmsford facility and arrive colour-matched to the same standard.
Corrosion Resistance on Demanding Sites
Aluminium is the material of choice for parapet coping on buildings where long service life and low maintenance are non-negotiable. It does not rust. It forms a natural oxide layer that protects the base metal without any additional treatment, and the external grade powder coat extends that protection across the full surface of the profile. For coastal sites, urban environments with higher pollution levels, or buildings where accessing the parapet for maintenance is difficult or expensive, a 3mm aluminium flat coping system is a sound long-term investment.
UK Manufactured for Fast Programme Delivery
This corner is made at the Online Metal Store Ltd facility in Chelmsford, Essex. For commercial programmes in the South East, the Home Counties, or anywhere across the UK, manufacturing from a UK base means shorter lead times than sourcing from a European or overseas supplier. On a construction programme where the watertight stage is on the critical path, a UK-manufactured coping system with fast turnaround removes a potential delay from the schedule.
Technical Specifications
Material: 3mm 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: 3mm Aluminium Flat Coping range | 75mm External Leg
Recommended Bracket: 5mm Aluminium Coping Bracket (use 5mm bracket with 3mm coping for correct specification)
Country of Manufacture: United Kingdom (Chelmsford, Essex)
2mm or 3mm: Choosing the Right Gauge for Your Project
Both gauges use the same 75mm external leg profile and the same powder coat finish. The decision is about specification, not appearance. Here is a practical guide:
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Choose 2mm for: domestic flat roof extensions, box dormers, flat-roofed garages and outbuildings in sheltered suburban or rural settings, residential projects where the parapet is low and the wall width is modest, and projects where budget is a primary constraint and the site exposure is low.
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Choose 3mm for: commercial and light industrial flat roofs, new-build housing developments where NHBC standards apply, taller buildings and higher parapets where wind uplift forces are greater, exposed sites including coastal locations, hilltop positions, and open-aspect sites in Essex, Kent, Suffolk and across the South East, and any project where the structural engineer or specifier has called up 3mm in the specification.
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Mixed-gauge projects: if some sections of a parapet require 3mm for structural reasons while others do not, it is generally cleaner to specify 3mm throughout and keep the system consistent. Mixing gauges on the same parapet run creates profile transitions at the joints that are difficult to detail neatly.
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Corner angles: this product covers right-angle 90 degree corners. If any part of your parapet turns at an obtuse angle wider than 90 degrees, the matching 3mm flat coping 135 degree corner is available in the same range for that junction.
How to Fit a 3mm Flat Coping Corner
Plan the bracket positions for both legs of the corner before fixing. Work out the straight coping runs on each side and confirm that the 5mm aluminium coping brackets are positioned at the correct centres for the 3mm system. The brackets immediately adjacent to the corner should give the corner wings full bearing without any unsupported overhang at the junction. At 3mm gauge, the corner piece is heavier than the 2mm equivalent, so handling on site is straightforward but the bracket positions need to be accurate.
Set the corner piece in position and dry-check the alignment with the straight 3mm flat coping lengths running either side before committing to any permanent fixing. The profiles must sit flush at the junction between the corner wings and the straight runs. Once the position is confirmed, apply colour coded sealant along the internal face of both joints before pressing the straight coping lengths home. On a commercial project with a long parapet run, the sealant bead at each corner junction is particularly important because it is the only thing preventing water from tracking back under the coping at a joint. Do not skip or reduce the sealant application.
Fix the straight lengths to the brackets using colour coded fasteners in the matching RAL colour. On a commercial project with a metal substrate or structural steel curb, use the metal fasteners rather than timber fixings. Work along both legs from the corner outward, checking alignment as you go. Finish with a neat sealant bead on the external face of each corner joint.
Where the 3mm Flat Coping 90 Degree Corner Is Used
Commercial Flat Roof Parapets
Commercial buildings are the primary market for 3mm aluminium flat coping. Retail units, office buildings, light industrial units, distribution centres and mixed-use developments across Essex, East London and the wider South East commonly specify 3mm for the parapet coping system. The corner pieces are required at every right-angle turn in the perimeter, and on a commercial project the specifier will typically call for all system components, corner pieces, lengths, stopends and coping brackets, to be ordered from the same manufacturer to ensure colour and profile consistency. The aluminium coping case study demonstrates this system in use on a live UK commercial project.
New-Build Housing Developments
NHBC-registered housebuilders on new-build developments across the Home Counties, Essex and the South East frequently specify 3mm aluminium coping for parapet details on flat-roof elements. Whether that is a flat-roofed garage block, a covered walkway, a communal roof terrace or a parapet on a semi-detached house, the 3mm specification is common where the NHBC warranty position requires a heavier gauge. Ordering the corner pieces alongside the 3mm flat coping lengths and stopends from a single UK supplier simplifies the supply chain on a volume development.
Exposed and Coastal Sites
Parapet copings on exposed sites take more punishment than almost any other building element. Wind-driven rain at pressure, frost cycles through winter, and the salt-laden air that reaches sites within a few kilometres of the Essex and Kent coasts all put demands on the coping material and its fixings. The 3mm gauge provides greater resistance to the repeated loading from wind pressure and uplift that an exposed parapet corner experiences over its service life. For sites in Southend-on-Sea, Clacton, Mersea Island, or anywhere on the Thames Estuary shoreline, the 3mm specification is the right one.
Schools, Care Homes and Public Buildings
Public buildings including schools, care homes, GP surgeries and community facilities almost always carry a commercial coping specification. The asset will be maintained by a facilities management team rather than an owner-occupier, and the expectation is that the coping system will require no intervention for at least 25 years. Specifying 3mm coping on these buildings, and ordering the full system from aluminium flat copings through to the colour coded sealant from a single UK manufacturer, gives the client and the contractor a system with a traceable specification and a clear maintenance position.
Frequently Asked Questions
When should I use 3mm aluminium flat coping instead of 2mm?
Use 3mm when the project is commercial rather than domestic, when the site is exposed to higher wind loads, when the parapet wall is wide or tall, when an NHBC or structural specification calls for 3mm, or when the building is in a coastal or high-exposure environment. For straightforward domestic rear extensions in sheltered locations, 2mm is usually the right choice. For anything else, 3mm is the safer and more durable specification.
Is the 3mm corner compatible with 2mm flat coping lengths?
No. The 3mm corner is designed to work with 3mm flat coping lengths in the 75mm external leg range. While the overall profile shape is the same, the wall thickness is different, which means the junction between a 3mm corner and a 2mm straight length will not be flush. Always match the corner gauge to the straight lengths you are using. If you are using 3mm lengths, use this 3mm corner. If you are using 2mm lengths, use the 2mm 90 degree corner from the same range.
Do I need a different bracket for 3mm coping?
Yes. For 3mm aluminium flat coping, the 5mm aluminium coping bracket is the correct specification. The 5mm bracket is heavier and provides greater fixing resistance, which is appropriate for the heavier gauge coping and the more demanding sites where 3mm is typically used. Using the correct bracket also ensures the system meets wind uplift requirements on exposed sites. Do not use the 4mm bracket with 3mm coping on commercial or exposed-site projects.
Can this corner be ordered in any RAL colour?
Yes. Like all components in the 3mm flat coping range, this corner is available powder coated in any RAL colour. Specify the RAL number at the time of order and the corner will be finished in the same colour as the straight lengths, stopends and brackets in the order. There are no minimum order quantities for standard RAL colours. If your project requires a BS colour or a bespoke finish, contact Online Metal Store Ltd to discuss the specification.
What is the difference between the 3mm 90 degree and 135 degree corners?
Both are 3mm aluminium flat coping corners in the 75mm external leg range, but they cover different angles. The 90 degree corner is for right-angle parapet junctions, which is the standard corner on rectangular buildings. The 135 degree corner is for obtuse-angle junctions, wider than a right angle, which occurs on buildings with L-shaped plan forms, angled boundary walls, or irregular plot configurations. Many commercial projects need both corner types on the same parapet. Order both from the same range and they will be finished in a matching colour and profile.
Part of a Complete 3mm Flat Coping System
This corner is one component in the complete 3mm aluminium flat coping system with a 75mm external leg. Ordering all components from Online Metal Store Ltd ensures matching profiles, consistent powder coat colour across the full perimeter, and a single UK-manufactured system with a clear specification. The full 3mm flat coping system with 75mm external leg includes:
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3mm Aluminium Flat Coping 90 Degree Corner | 75mm External Leg (this product)
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3mm Aluminium Flat Coping 135 Degree Corner | 75mm External Leg
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3mm Aluminium Flat Coping - Closed Stopend | 75mm External Leg
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3mm Aluminium Flat Coping - Stopend Upstand | 75mm External Leg
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3mm Aluminium Flat Coping - 90 Degree T-Junction | 75mm External Leg
For the full range overview, visit the Aluminium Flat Copings collection page. If you are working on a domestic project where 2mm is the appropriate gauge, the 2mm flat coping 90 degree corner is the equivalent component at the lighter specification.
Standards and Compliance
Aluminium parapet coping on flat roof constructions in the UK is specified and detailed in accordance with BS 6229:2018 - Flat Roofs with Continuously Supported Flexible Waterproof Coverings. This standard covers edge and parapet detailing requirements for flat roofs and provides the technical basis for specifying coping systems on commercial and residential projects. The 3mm gauge is consistent with the heavier-specification requirements for commercial and exposed-site applications referenced within the standard.
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 defines the performance requirements for external-grade powder organic coatings on aluminium. On a commercial project where the coping specification forms part of a warranty or long-term maintenance commitment, the coating standard is as important as the substrate gauge.
For new build projects registered with NHBC, Chapter 7.1 of the NHBC Standards covers flat roof and parapet wall construction. The 3mm aluminium flat coping system is consistent with NHBC parapet detailing requirements and supports the warranty position on new build completions where heavier gauge coping is specified.