2mm Aluminium Sloping Coping – 135° Internal Corner | 125mm External Leg

Angled parapet corners are often where a coping run starts to look weak. A straight length might sit cleanly across the wall, but once the roofline turns through a wider internal angle, site cuts and rushed joints can leave small gaps for driving rain, frost and dirt to work into the building.

For roofers and builders working on extensions in Chelmsford, commercial units in Basildon, school buildings around Colchester or refurbishment work across East London, that corner detail matters. A proper 135 degree internal coping corner gives the parapet a neater line, better water control and a more professional finish than trying to force a standard length into an awkward angle.

Product Overview

This 2mm aluminium sloping coping corner is a pre formed 135 degree internal angle made for parapet wall runs with a 125mm external leg. It is used where two sloping coping sections meet on an inward angled corner, helping the system continue around the roof edge without leaving a weak joint or a messy site-made cut.

Online Metal Store Ltd supplies this component as part of the aluminium sloping coping range, with width options from 185mm to 885mm and a powder coated finish available in any selected RAL colour. It suits roofers, builders, architects and homeowners who want a clean coping line on flat roof extensions, terraces, parapet walls and commercial roof edges.

Manufactured for UK building conditions and supplied from Chelmsford, Essex, the corner works best when ordered with the aluminium copings collection, matching stopends, fixings and colour coded sealant. Buying the system together helps the colour, profile and installation detail stay consistent across the full run.

Key Benefits

A Clean Solution for 135 Degree Internal Angles

A 135 degree internal corner is not a standard square turn. It usually appears on angled parapet layouts, bay-style roof edges, roof terraces and bespoke commercial details. A pre formed aluminium corner gives the installer a shaped component made for that angle, so the coping line turns neatly without relying on awkward on-site trimming.

Built for UK Weather and Corrosion Resistance

Aluminium is a sensible choice for roof edge details in the UK because it resists corrosion, handles damp conditions well and does not carry the weight issues of heavier materials. On exposed parapets in Southend, Kent, Essex or the Home Counties, that matters when the product has to deal with driving rain, frost cycles, coastal winds and regular temperature movement.

Powder Coated in Any RAL Colour

The corner can be powder coated to match the main coping run, surrounding fascia, window surrounds or other architectural metalwork. That colour consistency is useful on new-build homes, care homes, schools and commercial units where the roof edge is part of the visible building design rather than a hidden detail.

Lightweight and Easier to Handle on Site

At 2mm thick, the aluminium gives a practical balance between rigidity and workability. It can be handled more easily than many heavier roof edge materials, which is helpful when installers are working at height, carrying sections along scaffold or fitting components on a roof terrace with limited access.

UK Manufactured with Fast Delivery Support

The product is supplied by Online Metal Store Ltd from Chelmsford, Essex, with UK projects in mind. For contractors ordering for live works in Brentwood, Braintree, Billericay, Central London or the South East, having a matching corner available as part of the system helps reduce delays caused by missing details.

Helps the Coping System Stay Watertight

The sloping profile helps guide water away from the parapet, while the pre formed corner reduces the number of weak site joints at the most exposed part of the run. Used with correct sealant, fixings and matching lengths, it supports a more dependable roof edge finish.

Technical Specifications

Product Name: 2mm Aluminium Sloping Coping 135 Degree Internal Corner with 125mm External Leg

Product Type: Pre formed internal corner for sloping aluminium coping systems

Angle: 135 degree internal corner

Material: Aluminium

Thickness: 2mm

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, 885mm

Finish: Powder coated aluminium finish

Colour Options: Any RAL colour selected at order stage

Listed Price: From £59.04 ex VAT, shown as £70.85 inc VAT on the current page

Primary Use: Creating a neat inward angled transition on sloping parapet coping runs

Recommended Accessories: Matching coping lengths, colour coded sealant, appropriate fasteners, stopends and other corner pieces

Supplier: Online Metal Store Ltd, Highlands Farm, Southend Road, Chelmsford, CM3 8EB

Choosing the Right Size / Width / Thickness

The correct width depends on the finished wall build-up, not just the blockwork size. Always measure the full parapet width after render, insulation, membrane upstands or capping boards have been allowed for.

·         Use narrower options such as 185mm to 285mm for slim parapets, small domestic extensions and garage roof edges where the wall build-up is compact.

·         Use mid-range widths such as 310mm to 535mm for many modern extensions, Victorian terrace rear additions and standard flat roof parapet details.

·         Use wider sizes such as 560mm to 885mm for commercial buildings, roof terraces, insulated upstands and larger parapet walls where the finish needs broader coverage.

·         Choose the 125mm external leg version where the external face requires deeper coverage than the 100mm version, especially on taller upstands or thicker external finishes.

·         For non standard angles, check the roof plan carefully before ordering so the internal and external corner components match the actual parapet direction.

How to Install / How to Fit

Start by checking that the parapet is level, clean and ready to receive the coping system. The waterproofing should be correctly dressed up the wall, and any uneven surfaces should be dealt with before the corner is offered into place. A good corner will not hide a badly prepared substrate.

Dry fit the 135 degree internal corner with the adjacent coping lengths before applying sealant. This helps confirm the angle, width, external leg position and fall direction. If the run also needs a 135 degree external corner with 125mm leg or a 90 degree internal corner with 125mm leg, set out those components at the same stage so the full roof edge line remains consistent.

Apply colour coded sealant at the joint positions, then fit the corner into the coping run using the fixing method specified for the system. Use colour coded timber fasteners or colour coded metal fasteners where exposed or project-specific fixings are required, making sure the substrate is suitable for the fastener type.

Finish by checking that the internal angle drains correctly and that no open gap remains at the joint. Wipe away excess sealant cleanly, confirm the powder coated surface has not been scratched during fitting, and inspect the corner after the first heavy rainfall where possible.

Where 135 Degree Internal Aluminium Coping Corners Are Used

Angled Flat Roof Extensions

Many domestic extensions do not follow a simple square plan. On angled rear additions in Chelmsford, Brentwood or East London, a 135 degree internal corner lets the coping follow the roof edge neatly while keeping the parapet protected from water ingress.

Roof Terraces and Balcony Upstands

Roof terraces often include angled returns around seating areas, privacy screens or access points. A matching internal coping corner helps the edge detail look intentional rather than patched together, which matters on high-value residential projects and premium outdoor spaces.

Commercial Parapet Runs

Commercial units, care homes, offices and schools often have long rooflines with non standard corners. Using a pre formed angle from the same aluminium copings collection helps contractors keep the roof edge consistent from straight lengths through to corners and stopends.

Refurbishment Work on Older Buildings

Older parapets in towns such as Colchester, Braintree and Southend can have awkward geometry after years of alteration. A made-to-size aluminium corner gives the refurbishment team a cleaner route than relying on cut-and-seal details that can fail early.

Full Coping System Orders

This part is best specified with matching lengths, left handed coping stopend, right handed coping stopend, colour coded sealant and suitable roof accessories. That approach keeps the finish consistent and reduces missing parts on site.

Frequently Asked Questions

What is a 135 degree internal coping corner? A 135 degree internal coping corner is a pre formed angled component used where two coping runs meet on an inward corner that is wider than a normal 90 degree return. It helps the parapet coping follow the building shape while keeping the roof edge neat and better protected.

Do I need a pre formed corner or can I cut the coping on site? A pre formed corner is usually the better choice for a visible or exposed coping run because it reduces the risk of poor alignment, open joints and uneven sealant lines. Site cutting still has a place for small adjustments, but it should not replace a proper corner component where the angle is known.

How do I know if I need the 125mm external leg version? Choose the 125mm external leg version when the outside face of the parapet needs deeper coverage. That can be the case on thicker wall finishes, insulated upstands, rendered parapets or commercial roof edges where a 100mm leg may not provide the visual or weathering coverage required.

Can the corner be colour matched to the straight coping lengths? Yes, the product is supplied with a powder coated finish in the selected RAL colour. For the best result, order the corner and straight lengths together so the colour, profile and finish are planned as one complete system.

What size should I order for my wall? Measure the finished parapet width after all coatings, membranes, insulation and wall finishes are included. Choose the listed size that suits the finished build-up, and avoid ordering from unfinished blockwork measurements alone because that can leave the coping too tight.

Should I use sealant with this corner? Yes, sealant is part of the roof edge detailing. The corner should be fitted with the correct jointing method and colour coded sealant so the transition between the corner and straight coping lengths is clean, protected and visually consistent.

Comparison Section

Pre Formed Aluminium 135 Degree Internal Corner

This is the strongest choice when the angle is known and the finish will be visible. It gives the installer a shaped component that follows the parapet line, keeps the powder coated finish consistent and reduces the number of weak site-made joints.

Site-Mitred Aluminium Coping

A site mitre can be useful for minor adjustments or unusual details, but it depends heavily on installer skill, clean cutting and careful sealing. On prominent parapet lines, it can look less tidy than a pre formed corner and may create more opportunity for gaps or poor sealant work.

Lead or Plastic Corner Detailing

Lead can still be suitable on some listed buildings or conservation projects where the appearance has to match existing traditional details. Plastic can suit low-cost temporary work, but it rarely gives the same crisp architectural finish as powder coated aluminium on modern UK parapets.

For most modern flat roof edges, the best route is to specify the corner as part of the full aluminium copings collection so the straight sections, corners, stopends, fixings and sealant all work together.

Part of a Complete System

This corner should not be treated as a loose one-off item. It is part of a complete coping system, so the order should include the straight aluminium sloping coping range, matching 135 degree external corner with 125mm leg, 90 degree internal corner with 125mm leg, left handed coping stopend, right handed coping stopend, colour coded sealant and appropriate fixings.

For projects where the roof edge ties into trims, flashings and angles, it is worth checking the surrounding details at the same time. A full-system order from one supplier reduces the risk of mismatched colours, incompatible profiles and return visits caused by missing small parts.

·         Main sloping coping lengths for the straight parapet runs.

·         Matching internal and external corners for non standard roof layouts.

·         Left and right handed stopends for closing exposed ends cleanly.

·         Colour matched sealant for visible joints and weathering details.

·         Timber or metal fasteners selected around the substrate on site.

·         Roof accessories and flashings for nearby edge or waterproofing details.

Standards and Compliance

For flat roof projects, the surrounding roof design and detailing should be considered alongside BS 6229:2025, which covers flat roofs with continuously supported flexible waterproof coverings. A coping corner is only one component, but poor parapet detailing can still affect water management, workmanship and long-term roof performance.

For the powder coated aluminium finish, BS EN 12206-1:2021 is the relevant reference for coatings prepared from thermosetting coating powder on aluminium and aluminium alloys for architectural purposes. Where the project is a new-build home, school, care home or warranty-led development, the roof edge detail should also be checked against the project specification and NHBC Standards where applicable.

Getting the corner, coping length, sealant and fixing detail right protects the warranty, the building fabric and the people inside it. It also gives the installer a cleaner detail that is easier to sign off at handover.