2mm Aluminium Sloping Coping – 90° Internal Corner | 125mm External Leg

Internal parapet corners are one of the first places water finds a weakness. If two coping runs meet without a properly formed corner, you can end up with opened joints, stained masonry, damp marks below the wall head and a finish that looks patched rather than planned.

That matters on real UK jobs, from domestic extensions in Chelmsford and Brentwood to commercial roof edges in Basildon, Colchester and East London. A 90 degree internal corner gives the inside angle a clean, purpose-made junction so the coping run looks right and has a better chance of standing up to driving rain, frost cycles and daily weather movement.

Product Overview

This 2mm aluminium sloping coping internal corner is made for 90 degree inward parapet junctions where two coping lengths meet at an inside angle. It gives the corner a formed section rather than relying on two cut pieces, which helps the detail look sharper and keeps the joint easier to seal.

It is designed to sit within an aluminium sloping coping system and is suited to roof edges, parapet walls and wall heads where rainwater needs to shed away from the protected surface. Online Metal Store Ltd supplies this product from Chelmsford, Essex, with size options to match the selected coping width and a 125mm external leg for deeper wall coverage.

For a complete installation, the corner should be ordered with the right coping lengths, colour coded sealant and suitable colour coded metal fasteners. Keeping the system together from one supplier helps the colour, finish and profile work as one clean roof edge detail.

Key Benefits

Formed corner detail for inward parapet angles

A factory-formed 90 degree internal corner gives the inside junction a cleaner result than a rushed site cut. The corner keeps the coping profile consistent through the angle, which is helpful on visible parapets, roof terraces, schools, care homes and commercial units where the roofline is part of the finished appearance.

Built for UK rain, frost and damp conditions

The 2mm aluminium construction gives the corner strength without the heavy handling that comes with some traditional materials. Aluminium does not rust like ferrous metal, so it is well suited to UK roofs exposed to damp air, wind-driven rain, winter frost and long periods of moisture around the wall head.

Powder coated in any RAL colour

The product can be powder coated to suit the selected RAL colour, which helps the corner match the coping lengths, facade trims and other architectural metalwork. That is useful on projects where colour continuity matters, such as anthracite grey extensions, aluminium window details or modern commercial elevations.

Lightweight and easier to handle on site

A lightweight aluminium corner is easier to move, align and position than heavier alternatives. That helps roofers and builders work more cleanly around a parapet corner, especially on domestic extensions, tight access roofs and multi-unit projects where every fitting needs to sit correctly before sealing.

Made to support a watertight coping system

The corner is not just a neat finishing item. It helps create a controlled junction where two coping runs meet. When the width, fixings and sealant are selected correctly, the system can manage rainwater more reliably than a corner made from mismatched site materials.

UK manufactured with fast delivery support

Manufacturing support from Chelmsford, Essex gives UK buyers a more practical route than waiting on awkward imported parts. It suits contractors, builders and homeowners who need a matching corner section without losing time on project sequencing.

Technical Specifications

Product name: 2mm Aluminium Sloping Coping, 90 degree Internal Corner with 125mm External Leg

Material: Architectural grade aluminium

Thickness: 2mm

Corner type: 90 degree internal corner for inward parapet junctions

External leg: 125mm external leg, as stated on the product page

Size options: 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 in a selected RAL colour

Base price shown on page: £59.04 ex VAT

Price including VAT shown on page: £70.85 inc VAT

Application: Sloping coping systems for parapet walls, roof edges and wall heads

Manufacturing location: Chelmsford, Essex, United Kingdom

Order note: Custom fabricated item. Measurements and finish should be checked before ordering.

Choosing the Right Size / Width / Thickness

The right size is based on the finished wall width, the coping profile and the amount of coverage needed over the wall face. The corner should match the coping lengths in the same run so the profile, leg depth and colour line continue around the inward angle.

·         Use narrower sizes such as 185mm to 285mm for smaller parapet walls, garage roofs and compact domestic extensions where the wall build-up is modest.

·         Use mid-range sizes such as 310mm to 510mm for common flat roof details, Victorian terrace rear extensions and Edwardian semi renovations where the wall head needs stronger coverage.

·         Use wider sizes such as 535mm to 885mm for commercial builds, housing developments, schools, care homes and deeper parapet constructions.

·         Keep the corner size the same as the coping lengths on both sides of the junction unless the roof detail has been designed with a change in wall width.

·         Check membrane upstand, insulation, render, cladding and wall finish before ordering, because these details can change the finished width needed on site.

How to Install / How to Fit

Start by checking the finished wall width and confirming that the internal corner size matches the coping runs on both sides. Dry fit the corner before applying sealant so you can check the angle, overhang, alignment and fall.

Set out the adjoining coping lengths and leave the correct joint allowance. Use the chosen colour coded sealant at sealed joints and follow the project specification for laps, joints and weathering. Sealant should support the system detail, not hide poor measurement or an unsupported corner.

Fix the corner using appropriate project fixings. For timber substrates, use colour coded timber fasteners. For metal substrates, use colour coded metal fasteners. Keep fixings consistent with the coping system so the finish looks planned rather than pieced together.

Once the internal corner is secure, continue the run with matching coping lengths and check the surrounding roof edge details. Where adjoining flashings are needed, use compatible trims, flashings and angles rather than mixing unrelated profiles on the same detail.

Where Aluminium Coping Internal Corner 125mm Is Used

Flat roof parapets on domestic extensions

Rear extensions in Chelmsford, Billericay and Brentwood often include parapet walls around flat roof areas. A 90 degree internal corner helps finish the inside return neatly where two walls meet, especially when the coping is visible from gardens, upper windows or neighbouring properties.

Commercial roof edge junctions

Commercial units in Basildon, Southend and East London often need durable roof edge detailing that can handle weather exposure and still look clean from ground level. A formed internal corner gives contractors a consistent way to close the inward junction without rough cutting on site.

Housing developments and repeat-build projects

On housing developments across Essex, Kent and the South East, repeatable details help reduce mistakes. Ordering matching internal corners with the coping lengths keeps the finish consistent across plots and helps the site team avoid mismatched corner solutions.

Roof terraces and visible parapet returns

Roof terraces need tidy metalwork because people see the parapet from close range. The internal corner gives the junction a purposeful finish, which matters when the coping sits alongside balustrades, paving, render or aluminium facade features.

Refurbishment projects with tired wall heads

Older parapets on Victorian terraces, Edwardian semis and small commercial buildings often have failed mortar, stained render or awkward lead details. A new aluminium system, supported by the right aluminium roof flashing, can improve the finished edge while helping the wall head shed water more cleanly.

Frequently Asked Questions

What is a 90 degree internal coping corner?

A 90 degree internal coping corner is a formed aluminium section used where two coping runs meet at an inward parapet angle. It helps create a neater and more controlled junction than cutting two separate lengths together on site.

How do I choose the correct width?

Choose the width that matches the coping lengths on the same parapet run. Measure the finished wall width after membranes, insulation, render or cladding have been allowed for, then select the closest suitable product size from the available options.

Do I still need sealant with a formed internal corner?

Yes, a formed corner still needs correct sealing at the joints. The corner gives the shape and profile, while the sealant helps weatherproof the connection between adjoining coping sections.

Is aluminium better than lead for this corner detail?

Aluminium is often better for modern parapet coping because it is lightweight, corrosion resistant and can be powder coated in a RAL colour. Lead can still have a role on listed buildings or conservation work where the design or officer requires a traditional material.

Can I cut straight coping lengths instead of buying a corner?

You can cut straight lengths on some basic jobs, but a factory-formed corner gives a cleaner, more consistent detail. It is usually the better option when the roof edge is visible or when you want the coping system to look professionally finished.

How many internal corners do I need?

You need one internal corner for each inward 90 degree angle in the coping run. Count every inside parapet junction on the roof plan, then order the matching width and colour for each corner.

Comparison Section

Aluminium formed internal corner

A formed aluminium internal corner is the best fit for a clean modern coping system. It gives a consistent profile, can be powder coated to match the rest of the roof edge and works well on domestic, commercial and new-build parapet details.

Site-cut coping lengths

Site-cut lengths can work on simple or hidden areas, but they rely heavily on measurement, cutting quality and sealing. On visible parapet corners, the finish can look less precise, especially if the cut is rushed or the wall angle is not perfectly square.

Lead corner detailing

Lead is still used on some traditional buildings and may be required on listed or conservation-led work. For most modern aluminium coping systems, a matching powder coated aluminium corner is easier to coordinate with the full roofline design.

For broader system selection, review the full aluminium copings range so straight lengths, corners, stopends, fixings and sealant can be ordered around the same project detail.

Part of a Complete System

This product should be positioned as one component in a complete parapet coping system, not as an isolated accessory. A complete order helps the profile, colour, leg depth and fixing approach stay consistent across the roof edge.

·         aluminium sloping coping: Use with matching sloping coping lengths for the main parapet runs.

·         aluminium flat copings: Link where the buyer is comparing flat and sloped coping profiles.

·         colour coded sealant: Use for sealing joints around corners, lengths and stopends.

·         colour coded timber fasteners: Use where the coping is fixed into timber substrate details.

·         colour coded metal fasteners: Use where the coping is fixed into suitable metal substrate details.

·         trims, flashings and angles: Use when the surrounding roof edge detail needs compatible trim or flashing products.

·         roof accessories: Use as the wider range link for related fitting products.

Standards and Compliance

Flat roof edge details should be designed and installed with the wider roof build-up in mind. BS 6229:2025 is the current British Standard code of practice for flat roofs with continuously supported flexible waterproof coverings, so it is a useful reference where parapet detailing forms part of the flat roof design.

For the coating finish, BS EN 12206-1:2021 covers powder coatings on aluminium and aluminium alloys for architectural purposes. Getting the corner, coating, sealant and fixing detail right protects the warranty, the building and the people inside it.