2mm Aluminium Sloping Coping – 135° Internal Corner | 100mm External Leg

Angled parapet returns are easy to underestimate until water starts sitting in the wrong place. On a flat roof, terrace wall or low boundary detail, a poor internal corner can leave gaps, visible misalignment and weak points where driving rain, frost cycles and wind-driven moisture can get behind the coping run.

That is why a made to order 135 degree internal coping corner matters. Whether the job is a domestic extension in Chelmsford, a terrace refurbishment in Brentwood, a school roof in Colchester or a small commercial unit near East London, the corner needs to match the slope, the width and the finish of the rest of the system.

Product Overview

The 2mm Aluminium Sloping Coping 135° Internal Corner is a pre-formed aluminium corner section used where two sloping coping runs meet at an inward 135 degree angle. It is designed for parapet walls, flat roof edges and architectural wall capping where a clean angled return is needed without trying to cut and join straight lengths on site.

This product is made from 2 mm aluminium with a 100 mm external leg and is available in widths from 185 mm to 885 mm. It is manufactured in Chelmsford, Essex, and supplied powder coated in the RAL colour selected for the project. For the full run, it should be planned alongside matching aluminium sloping coping, suitable fixings and weathering accessories.

Online Metal Store Ltd supplies this corner as part of a wider roof edge and parapet system, so the angle, finish and related components can be kept consistent. Where the same project also needs straight wall capping, trims or roof edge detailing, use the main aluminium copings range and trims, flashings and angles collection to keep everything aligned.

Key Benefits

Cleaner finish on angled internal returns

A 135 degree internal return is difficult to finish neatly with cut straight lengths. A pre-formed corner gives the coping run a cleaner visual line and reduces the risk of messy mitres, uneven laps or exposed edges. It is useful on angled parapet layouts, roof terraces and modern extensions where the finish is clearly visible from the ground or nearby windows.

Built for UK weather and roof edge exposure

Aluminium is well suited to damp UK conditions because it resists corrosion and performs well through rain, frost, sun exposure and coastal air. The sloped profile helps shed water away from the wall head, which helps reduce staining, ponding and freeze related damage around vulnerable parapet junctions.

Powder coated in any RAL colour

The corner can be powder coated to the selected RAL colour so it matches the straight coping, nearby fascia, window frames, rainwater goods or cladding. That is important on visible projects in places such as Billericay, Southend, Kent and the Home Counties, where colour consistency often matters as much as weather protection.

2 mm aluminium balances strength and handling

The 2 mm thickness gives the corner a strong, stable feel without making it awkward to move, position or fit on site. Roofers and builders can handle it more easily than heavier traditional materials, which helps when working at height or when manoeuvring around awkward parapet returns.

Made to order for a better system match

The product is offered in a wide size range from 185 mm to 885 mm, so the corner can be selected to match the wall width and coping profile rather than forcing the installer to adapt a standard size. The correct width helps maintain the overhang, slope and visual balance across the whole run.

UK manufactured with fast delivery support

Manufacturing in Chelmsford, Essex gives UK contractors a more practical route than waiting for a generic imported part. For time-sensitive roofing work, housing developments, care homes, schools and domestic projects, local support helps reduce delays when colour, size or site requirements need checking.

Useful for complete parapet detailing

This corner works best when treated as part of a complete coping detail, not a standalone trim. Pairing it with matching straight sections, colour coded sealant, and suitable colour coded metal fasteners helps the finished junction look more consistent and perform more reliably.

Technical Specifications

Product Name: 2mm Aluminium Sloping Coping 135° Internal Corner | 100mm External Leg

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

Angle: 135 degree internal corner

Material: Aluminium

Thickness: 2 mm

External Leg: 100 mm

Profile: Sloping coping corner

Finish: Powder coated finish

Colour Options: Any RAL colour selected at order stage

Available Widths: 185 mm, 210 mm, 235 mm, 260 mm, 285 mm, 310 mm, 335 mm, 360 mm, 385 mm, 410 mm, 435 mm, 460 mm, 485 mm, 510 mm, 535 mm, 560 mm, 585 mm, 610 mm, 635 mm, 660 mm, 685 mm, 710 mm, 735 mm, 760 mm, 785 mm, 810 mm, 835 mm, 860 mm, 885 mm

Price Shown on Current Page: From £57.60 ex VAT, £69.12 inc VAT

Manufacturing Location: Chelmsford, Essex, United Kingdom

Ordering Note: Custom fabricated item made to the selected size and finish. Measurements should be checked before ordering.

Best Used With: Matching sloping coping lengths, sealant, colour matched fasteners, roof edge trims and related parapet accessories

Choosing the Right Size / Width / Thickness

The width should be selected from the actual wall or parapet build-up, allowing for the profile, overhang and project detail. Do not choose the closest size by eye, because small measurement errors can show clearly at internal corners.

·         Use the narrower 185 mm to 285 mm sizes for slim garden walls, small parapet returns, porch roofs and compact domestic extensions where the wall build-up is modest.

·         Use the mid-range 310 mm to 510 mm sizes for common UK extension parapets, terrace walls, Edwardian semis, Victorian terrace refurbishments and low-rise residential roof edges.

·         Use the 535 mm to 710 mm sizes where the wall build-up includes insulation, cavity zones, wider masonry or a deeper roof edge detail.

·         Use the larger 735 mm to 885 mm sizes for commercial builds, larger housing developments, schools, care homes and broader parapet constructions where a standard narrow part will not cover the build-up.

·         Use the same width across the straight coping and corner pieces unless a detailed drawing shows a deliberate transition.

·         Keep the 2 mm thickness in mind when coordinating corners with other aluminium coping components, because inconsistent material thickness can affect the finished line.

How to Install / How to Fit

Start by checking the wall width, the angle of the internal return and the direction of the slope before ordering. The straight coping run and the corner must be set out together, especially on angled parapets where one small error can throw the joint line out across the rest of the roof edge.

Dry position the corner before fixing. Check that the 100 mm external leg sits correctly, the slope directs water away from the vulnerable wall head, and the adjacent coping lengths line up without forcing the metal. For related roof edge weathering, the aluminium roof flashing product may also be relevant where a roof covering or vertical upstand needs extra protection.

Fix the system using the correct substrate-specific fasteners. For timber substrates, use colour coded timber fasteners. For metal substrates, use colour coded metal fasteners. Colour matched fixings help keep the finished corner looking tidy, especially on darker RAL colours such as anthracite grey or black.

Seal the correct joints and laps according to the project detail. Use colour coded sealant where sealing is required so the visible finish stays coordinated with the powder coated corner. Avoid overfilling the joint, because messy sealant lines can make a premium coping detail look rushed.

Once fitted, check the corner from above and from the main viewing angle at ground level. A good installation should look continuous, shed water cleanly and avoid visible gaps at the internal return. On larger projects, keep one approved sample or drawing on site so each corner is fitted consistently.

Where This 135° Internal Coping Corner Is Used

Angled parapet walls on flat roof extensions

Many domestic extensions in Chelmsford, Brentwood and Basildon include angled roof lines where a standard 90 degree corner is not suitable. This 135 degree internal corner helps the coping follow the wall layout properly while keeping the finished roof edge neat and weather protected.

Roof terraces with inward returns

On roof terraces, the coping is often visible from close range. A pre-formed internal angle gives a cleaner finish than a site cut mitre and can be planned alongside matching aluminium flat copings or sloped sections depending on the roof edge design.

Commercial and residential parapet refurbishment

Refurbishment work often exposes old lead, cracked mortar, stained concrete or poorly joined capping pieces. Replacing those details with a made to order aluminium corner gives builders and roofing contractors a more consistent finish on offices, small retail units, apartment blocks and local authority buildings.

New-build housing and developer projects

For housing developments and new-build schemes, repeatable detailing matters. A pre-formed 135 degree corner helps maintain a consistent line across multiple plots, especially where parapets, balconies or roof terraces share the same specification and RAL colour.

Projects where appearance matters from the street

On modern homes, schools, care homes and commercial frontages, coping is not just a protective component. It is part of the visible architectural finish. For project proof and inspiration, the aluminium coping case study can help show how a coordinated aluminium system supports a cleaner finished look.

Frequently Asked Questions

What is a 135 degree internal coping corner?

A 135 degree internal coping corner is a pre-formed metal corner used where two coping runs meet at an inward angled return. It is designed to continue the sloped coping profile around the parapet without relying on rough site cutting or a poorly aligned mitre.

Do I need an internal corner or an external corner?

You need an internal corner when the wall turns inward and creates an inside angle. You need an external corner when the wall turns outward around an outside edge. If the drawing shows a 135 degree inward return, this product is the correct style. If the angle projects outward, use the external version instead.

Can this corner be made to match my straight coping lengths?

Yes. The corner is available in the same width range shown on the product page and can be powder coated to the selected RAL colour. The best result comes from ordering the straight coping and corner pieces together so the finish, profile and measurements are coordinated.

Is aluminium better than lead for this type of corner?

Aluminium is often a better choice for modern parapet coping because it is lighter, corrosion resistant and easier to colour match. Lead can still have a role on listed buildings or conservation work where a traditional material is requested by the project team or conservation officer.

How many 135 degree internal corners do I need?

Count each inward 135 degree angled return on the parapet or roof edge layout. A simple straight run may not need any, while an angled terrace or irregular extension may need several. Always check the roof plan before ordering, because internal and external corners are not interchangeable.

Does the sloped profile help with water drainage?

Yes. The sloped profile helps rainwater run away from the wall head rather than sitting on the surface. Good drainage is important in UK weather because repeated wetting, frost cycles and trapped moisture can stain masonry and shorten the service life of surrounding details.

Comparison Section

Aluminium 135 degree internal corner

An aluminium pre-formed corner is the strongest option when the priority is a neat, durable and colour matched finish. It suits modern flat roofs, parapet walls, roof terraces, commercial units and domestic extensions where the coping needs to look clean and perform well in exposed weather.

Site cut straight coping lengths

Cutting straight lengths on site can work for temporary or low visibility details, but it is easier to end up with uneven joints, rough exposed cuts and sealant-heavy corners. On a visible parapet return, a purpose-made corner is usually the better long-term option.

Lead or mortar capping

Lead and mortar capping still appear on older UK buildings and conservation-led repairs. They can be suitable where the building style, listing status or planning requirement calls for a traditional detail. For most modern projects, powder coated aluminium gives a sharper finish, lower handling weight and better colour control.

For a complete roof edge package, use this component with the wider aluminium copings range and the relevant roof accessories needed for the build-up.

Part of a Complete System

This product should be positioned as a system component rather than a one-off accessory. A complete order helps the colour, profile and site fit stay consistent.

·         Matching straight sloping coping lengths for the main parapet runs.

·         The 135 degree external coping corner for outward angled returns.

·         The 90 degree internal coping corner for standard inside turns.

·         Colour coded sealant for neat joint sealing where specified.

·         Colour coded timber fasteners for timber substrates.

·         Colour coded metal fasteners for metal substrates.

·         Aluminium roof flashing where the roof covering or upstand detail needs extra weathering support.

·         Trims, flashings and angles for adjacent finishing work around the roof edge.

When a contractor orders the full system from one supplier, the finish and profile are easier to coordinate. That reduces the chance of mismatched colours, awkward corner changes and last-minute site fixes.

Standards and Compliance

For flat roof and parapet work, detailing should be planned with the roof design, waterproofing layer and site conditions in mind. BS 6229:2025 is the current British Standard code of practice for flat roofs with continuously supported flexible waterproof coverings. It is relevant because coping details sit at the roof edge, where poor design can affect the wider roof build-up.

For architectural aluminium coatings, BS EN 12206-1:2021 gives the relevant reference point for powder coatings prepared from thermosetting coating powder on aluminium and aluminium alloys. It supports a more credible explanation of the powder coated finish than vague claims about long life.

On new-build housing or warranty-backed projects, the project team should also consider NHBC Standards where relevant. Getting this right protects the warranty, the building and the people inside it.