3mm Aluminium Flat Coping - 135° Corner | 75mm External Leg
3mm Aluminium Flat Coping - 135° Corner | 75mm External Leg
Angled parapet corners are one of those details that look simple until water starts finding the joint. On a wide commercial wall in Chelmsford, Brentwood or East London, a site-cut mitre can leave the most exposed point of the coping system relying on a thin sealant line. Once driving rain, frost cycles and wind lift get involved, that small weak point can turn into damp staining, failed decoration and expensive remedial work.
This 3mm aluminium flat coping 135 corner gives you a proper factory-formed fitting for obtuse external turns. It is built for wider parapets where the 3mm system is the right specification, with a 75mm external leg to keep the roofline neat while still throwing rainwater clear of the wall face.
Product Overview
The 3mm aluminium flat coping 135 corner from Online Metal Store Ltd is designed to connect two straight coping runs where a parapet turns at an obtuse 135 degree angle. It forms part of the aluminium flat copings range and is manufactured in Chelmsford, Essex for UK commercial, residential and refurbishment projects.
This product suits the same wide-wall system as the 3mm aluminium flat coping 3m length. The 3mm gauge gives extra stiffness for larger widths from 510mm to 1060mm, while the 75mm external leg keeps the exposed face compact, clean and consistent across the full parapet line.
Use this fitting where the wall changes direction wider than a right angle. For standard rectangular corners, specify the 3mm flat coping 90 degree corner instead. For run terminals, pair the system with matching stopends, fixings and sealant so the whole edge detail works as one complete system.
Key Benefits
Factory-Formed 135 Degree Corner for Cleaner Detailing
A factory-formed 135 degree fitting removes the need to cut and join two coping lengths on site across the most vulnerable part of the turn. The result is a cleaner corner, better alignment and fewer opportunities for water to creep into the parapet core. On visible commercial rooflines, that also means a sharper, more professional finish from ground level.
3mm Aluminium for Wider Parapet Walls
The 3mm aluminium gauge is useful where wider wall sizes demand extra rigidity. This product is offered from 510mm through to 1060mm overall width, which places it firmly in the commercial and wide parapet category. It is easier to handle than stone or concrete, but strong enough for exposed roof edge work when installed with the correct bracket system.
75mm External Leg for a Compact Modern Roofline
The 75mm external leg gives the corner a slim architectural face while still covering the outer wall edge and drip detail. That matters on modern buildings where the coping should protect the wall without creating a bulky cap. It works well on contemporary offices, apartment blocks, retail units, schools and larger domestic extensions where clean lines are part of the specification.
Powder Coated in Any RAL Colour
The corner can be powder coated in any RAL colour to match the straight coping lengths, stopends, brackets and surrounding facade details. For projects using anthracite grey, black, white or a specific architect-specified colour, ordering every component together helps keep the colour consistent across the full run.
Better Suited to UK Weather Than Site-Cut Joints
UK parapets deal with driving rain, damp winters, summer expansion and repeat freeze thaw cycles. A purpose-made aluminium corner gives the joint a more controlled starting point than site cutting, especially when used with the correct bracket spacing and sealant. The detail stays neater and the wall below has better protection against water tracking.
Manufactured in Chelmsford with Fast UK Supply
The product is made to order in Chelmsford, Essex, which supports faster communication and shorter UK supply chains compared with imported systems. For builders and contractors working across Basildon, Braintree, Colchester, Southend, Kent, East London and the wider Home Counties, that gives a practical ordering route for project-specific sizes and colours.
Technical Specifications
Product Name: 3mm Aluminium Flat Coping - 135° Corner | 75mm External Leg
Material: 3mm architectural-grade aluminium
Profile: Flat coping corner
Corner Angle: 135 degree external corner for obtuse parapet turns
External Leg: 75mm
Size Options: 510mm, 535mm, 560mm, 585mm, 610mm, 635mm, 660mm, 685mm, 710mm, 735mm, 760mm, 785mm, 810mm, 835mm, 860mm, 885mm, 910mm, 935mm, 960mm, 985mm, 1010mm, 1035mm, 1060mm
Finish: Polyester powder coated finish
Colour: Any RAL colour to order
Price Shown on Page: From £97.20 ex VAT and £116.64 inc VAT
Compatible System: 3mm aluminium flat coping system with 75mm external leg
Fixing Method: Concealed bracket system, bracket specification to match 3mm flat coping
Manufacturing Location: Chelmsford, Essex, United Kingdom
Ordering Note: Custom fabricated to the selected size and finish, so measurements should be checked before ordering
Choosing the Right Size / Width / Thickness
The size selector refers to the overall coping width, not the corner length around the parapet. Measure the finished wall width at the top of the parapet, including any build-up, insulation, render or plywood carrier that the coping must cover.
· Use the 3mm system where the selected overall width is 510mm or above, or where the specification calls for extra rigidity on a wide or exposed parapet.
· Choose the 75mm external leg where you want a compact face detail on both sides of the wall, rather than a deeper downstand.
· For commercial units, schools, care homes and apartment blocks, keep all straight lengths, corners, stopends and T-junctions in the same 3mm system.
· If a wall turns at 90 degrees, use the matching right-angle corner instead of this 135 degree fitting.
· If the measured width falls between two listed sizes, move up to the next available size so the coping is not too tight over the wall build-up.
How to Install / How to Fit
Set out the parapet run before fixing the corner. Mark the position of each straight length, the 135 degree turn and the adjoining joints. Use the correct 3mm coping brackets for the system and keep bracket centres tight around the corner so the fitting is fully supported at the angle.
Dry fit the corner before sealing. Check that the external leg sits square to both wall faces and that the adjoining 3mm flat coping lengths line through without forcing the profile. Allow a controlled expansion gap at each adjoining joint rather than pushing the metal tight.
Apply colour coded sealant to the joint faces and keep the bead continuous. The sealant should work with the bracket system and the factory-formed corner, not as a substitute for either. Use matching colour coded metal fasteners where the fixing detail calls for exposed or secured components.
Once fitted, check the corner line from both roof level and ground level. Make sure the coping sits flat, the drip return clears the wall face, and any adjoining closed stopend or stopend upstand is sealed into the same system.
Where 3mm Aluminium Flat Coping 135 Corners Are Used
Commercial Parapets with Angled Facades
Many commercial buildings do not follow a simple rectangular footprint. Office entrances, retail frontages and mixed-use developments often include angled elevations where the parapet turns wider than 90 degrees. This corner keeps the coping run continuous through that change of direction.
Wide Flat Roof Extensions and Contemporary Homes
Larger domestic projects in Chelmsford, Brentwood and the South East often use wide insulated parapets to create a modern flat roof edge. Where the wall layout includes an obtuse corner, this fitting gives a neater result than trying to cut two straight lengths on site.
Schools, Care Homes and Public Sector Buildings
Public sector and care sector buildings need predictable details that can be repeated across several roof areas. A 3mm corner helps create a consistent specification where wide parapets, colour matching and long-term durability matter.
Commercial Refurbishment Projects
When old coping is being replaced on a commercial roof, matching the gauge and profile is important. If the existing system or new design calls for 3mm flat coping, the corners, T-junctions and stopends should all match so the finished edge is uniform.
Exposed Rooflines Near Coastal or Open Sites
Buildings around Southend, Kent and exposed parts of the South East face wind-driven rain and salt-laden air. Aluminium with a suitable powder coated finish gives a durable solution, while the 3mm gauge supports better rigidity on wider wall caps.
Frequently Asked Questions
What is a 3mm aluminium flat coping 135 corner used for? It is used where a flat parapet wall changes direction at a 135 degree external angle. The corner joins two straight coping runs while keeping the roof edge protected, aligned and colour matched.
Do I need this corner or a 90 degree version? Use this 135 degree corner when the wall turns at an obtuse angle, wider than a right angle. Use the 90 degree corner where two wall faces meet squarely, such as on a standard rectangular flat roof.
Can I use this with 2mm flat coping lengths? No. This is a 3mm fitting and should be used with the matching 3mm flat coping system. Mixing 2mm and 3mm components can create profile mismatch, uneven joints and a poor finished line.
How do I choose the correct size? Measure the finished parapet width at the top of the wall, including the full build-up. Then choose the closest suitable overall coping size from 510mm to 1060mm, moving up if your measurement falls between sizes.
Does the 75mm external leg suit commercial buildings? Yes, the 75mm leg is suitable where a slimmer external face is preferred. For wider commercial parapets, the key factor is not just leg depth, but using the correct 3mm gauge, bracket support, joint seal and full system match.
Is sealant still required with a factory-formed corner? Yes. The factory-formed corner improves the shape and alignment, but the joints where it meets straight lengths still need proper sealing. Use compatible colour coded sealant and follow the installation detail for expansion gaps and waterproofing.
Comparison Section
3mm Aluminium Flat Coping Corner
This is the right option for wide parapet walls, commercial specifications and exposed projects where extra stiffness is needed. It keeps the profile lightweight compared with stone, but gives more rigidity than a thinner domestic-grade metal coping component.
2mm Aluminium Flat Coping Corner
A 2mm corner can be suitable for narrower domestic parapets and smaller roof edge details. It should not be mixed into a 3mm system because the profile and stiffness will not match. Choose the same gauge across the whole coping run.
Stone, Concrete or Lead Corners
Stone and concrete still have a role on heritage or traditional projects, especially where the planning context expects that appearance. Lead can still be required on listed buildings, but it needs skilled detailing. For most modern commercial parapets, powder coated aluminium gives a lighter, cleaner and easier-to-match system.
For the wider range of lengths, corners and stopends, browse the aluminium copings collection or the focused aluminium flat copings page.
Part of a Complete System
This product should be ordered as part of a matched 3mm flat coping system rather than treated as a stand-alone item. That protects the visual finish, the colour consistency and the installation quality.
· 3mm flat coping 90 degree corner
· 3mm flat coping 135 degree corner
· 3mm flat coping closed stopend
· 3mm flat coping stopend upstand
· colour coded timber fasteners
· colour coded metal fasteners
Standards and Compliance
Flat roof parapet details should be considered alongside BS 6229:2025, which covers flat roofs with continuously supported flexible waterproof coverings. Correct coping, edge protection and joint detailing all contribute to the wider weatherproofing strategy.
The powder coated aluminium finish should be specified with reference to BS EN 12206-1:2021 for coating aluminium and aluminium alloys for architectural purposes using thermosetting coating powder.
For NHBC-registered new-build projects, the coping detail should also be checked against the project specification, warranty provider guidance and any architect or structural engineer requirements. Getting this right protects the warranty, the building and the people inside it.