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

This is the 90° external corner piece for the 2mm aluminium sloping coping system with a 125mm external leg. It sits at every right-angle outside corner of the parapet, carrying the same wider 125mm overhang and built-in slope as the straight sections in the same system. Without it, the straight 1m, 2m and 3m lengths have nowhere to terminate cleanly at a building corner. One corner piece is required per right-angle external corner on the parapet plan.

Available in the same 29 width sizes as the straight lengths, powder coated in any RAL colour, and fabricated to order at the Online Metal Store Ltd facility in Chelmsford. This corner is specific to the 125mm external leg system and is not interchangeable with the 100mm external leg corner. If you are not certain whether you need the 100mm or 125mm version, the guide below will help you decide.

100mm or 125mm Corner: Which System Are You Using?

This is the most important check before ordering. The 100mm and 125mm sloping coping corners have different profile dimensions and are not interchangeable. Fitting a 100mm corner on a 125mm coping run produces a visible mismatch in overhang depth and profile width at the junction. You need to match the corner leg size to the leg size of your straight coping lengths.

If Your Straight Coping Lengths Have a 100mm External Leg

You need the 90° external corner for the 100mm system. That corner uses the wall width + 195mm sizing formula. The system accessories for the 100mm and 125mm ranges are different products.

If Your Straight Coping Lengths Have a 125mm External Leg (This Product)

You need this corner. It uses the wall width + 220mm sizing formula, which is 25mm wider than the 100mm system for the same parapet wall. Your straight lengths, corners, stopends and upstand stopends must all be the 125mm version to maintain a consistent profile throughout the installation.

Not Sure Which Leg Size You Need?

The full 100mm vs 125mm selection guide is on the 125mm 1m coping length page. In brief: the 125mm external leg is the correct specification for cavity wall parapets, wider wall constructions, NHBC new-build housing where the house type calls for a 125mm overhang, and projects where a more substantial visual profile is preferred.

External Corner or Internal Corner?

External Corner (This Product)

An external corner sits at an outside angle of the building where the parapet projects outward and the coping wraps around the corner of the structure. Standing looking at the building from the outside, the corner sticks toward you. On a rectangular rear extension, all four parapet corners are external corners.

Internal Corner

An internal corner sits at a re-entrant angle in the parapet plan, where the coping turns inward. These appear on L-shaped building plans, buildings with recessed bays, and any plan form that creates an inside angle in the parapet. If the corner angles away from you when you stand looking at the building, it is an internal corner. The 90° internal corner for the 125mm system is available from the same range.

Key Benefits

• Flush 125mm profile at the corner: the wider 125mm overhang carries around the external corner without reduction or step. The corner maintains the same profile width as the straight sections on both legs of the junction.

• Built-in slope resolves through the turn: the slope in the profile is carried correctly through the 90° turn, ensuring active surface drainage at the corner position rather than water sitting at the junction.

• 29 sizes matching the straight lengths: same 185mm to 885mm size range. Order the same size as your straight run sections.

• Watertight corner junction: a factory-formed corner profile seals correctly with a sealant bead on each leg. Far more reliable than a site-mitred corner between two straight sections.

• Any RAL colour, batch-matched: order the corner in the same RAL as all other system components for consistent colour from the same Chelmsford coating batch.

• 4mm bracket compatible: uses the same concealed bracket system as the straight lengths in the 2mm system.

Technical Specifications

Material: 2mm grade aluminium

Profile: Sloping coping corner

Corner Angle: 90 degrees external

External Leg: 125mm

Internal Leg: 75mm

Width Sizes: 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 (29 sizes in 25mm increments)

Size Rule: Order the same size as your 125mm straight coping lengths

Sizing Formula: Wall width + 220mm = size to order (125mm external leg + 75mm internal leg + 10mm + 10mm returns = 220mm)

Formula Note: This is 25mm wider than the 100mm system formula (wall width + 195mm). Apply the correct formula for the system you are using.

Finish: Polyester powder coating, external grade

Colour: Any RAL colour to order

Compatible Bracket: 4mm Aluminium Coping Bracket

Compatible System: 2mm Aluminium Sloping Coping | 125mm External Leg

Not Compatible With: 100mm external leg system -- profiles are different dimensions

Fabrication: Made to order -- non-returnable unless faulty

Country of Origin: United Kingdom (Chelmsford, Essex)

Getting the Size Right: The 125mm Formula

The 29 sizes refer to the overall WIDTH of the coping profile at the corner, from external leg tip to internal leg tip. Order the same size as your straight coping lengths. The formula for the 125mm system is wall width + 220mm. This is 25mm more than the 100mm system formula. A buyer who applies the 100mm formula (wall width + 195mm) to a 125mm installation will order a corner 25mm too narrow on a non-returnable product. A full worked guide is on the 125mm sloping coping 1m length page, but in brief:

• Measure the parapet wall width at the top from outside face to inside face.

• Add 125mm (external leg) + 75mm (internal leg) + 10mm + 10mm (returns) = 220mm.

• Wall width + 220mm = the size to order for all 125mm system components, including this corner.

• A 165mm wide wall gives 385mm. A 240mm wall gives 460mm. A 315mm wall gives 535mm.

• If the result falls between two available sizes, select the next size up.

Critical: do not use the 100mm system formula (wall width + 195mm) here. The 125mm corner on a 165mm wall is 385mm, not 360mm.

Installation

Fix the 4mm aluminium coping brackets along the run as normal. Position a bracket within 150-200mm of the corner piece on each leg of the adjacent straight sections. The corner piece itself does not typically require a separate bracket beneath it: the two brackets on the adjacent straight sections provide sufficient support at the corner position.

Press the corner piece into position and butt the straight 125mm sections up to it from each leg. Apply a continuous bead of colour coded sealant in the matching RAL to the internal face of both joints where the straight sections meet the corner piece. Both legs of a 90° corner are exposed to weather and both joints must be fully sealed.

Lock the adjacent coping sections to their brackets using colour coded fasteners in the matching RAL. Apply a neat finishing bead of sealant on both external joint faces at the corner. On a new-build development where the coping is installed in volume, working systematically corner by corner and sealing as you go keeps the installation consistent.

Where This Corner Piece Is Used

New-Build Housing Developments with Cavity Wall Parapets

On NHBC-registered residential developments specifying the 125mm sloping coping system for cavity wall parapets, this corner piece appears at every right-angle parapet corner across the development. For housebuilders ordering the full system per plot or per phase, including the 1m infill sections, 2m sections, 3m primary lengths and all accessories from the same Chelmsford manufacturer, the corner pieces arrive colour-matched and dimensionally consistent with every other component in the order.

Two-Storey Extensions and Prominent Parapets

On two-storey rear and side extensions where the 125mm leg has been chosen for its wider profile and greater visual presence at height, the corner pieces carry that specification correctly through every angle in the parapet plan. A corner cut from a straight section, or a 100mm corner substituted in a 125mm run, is visible at the building corner and undermines the specification.

Replacement Coping on Existing 125mm Installations

When replacing failed corners on an existing 125mm sloping coping installation, the replacement must be the 125mm version. Order the corner in the correct width size using the wall width + 220mm formula and in the closest RAL to the existing system. For a full replacement where multiple components are being renewed, order the corners alongside the straight lengths, stopends and brackets in the same batch for colour consistency.

Why a Factory-Formed Corner Matters

The corner is the most weather-exposed position on any parapet coping run. It faces the full force of two wall elevations simultaneously, and water driven from any angle meets the corner junction first. A mitred joint between two straight 125mm sections at a corner is difficult to execute cleanly in the field and relies on site workmanship for its weathertightness at the one position where workmanship matters most.

A factory-pressed corner profile, formed to the correct 125mm leg dimensions with the slope resolved accurately through the 90° turn, removes that dependency. The joint is sealed with colour coded sealant on both legs in the same way as every other joint in the run, and the dimensional consistency between the corner and the adjacent straight sections is guaranteed by manufacture rather than by cutting.

Why Choose Online Metal Store Ltd

Every component in the 2mm sloping coping 125mm system is manufactured at our Chelmsford facility. Corner pieces are fabricated to the same dimensional specification as the straight lengths, stopends and brackets in the same system, and finished in the same external grade polyester powder coat process. When you order the full system together in the same RAL, everything is coated in the same batch and arrives on site colour-matched. Contact our team at sales@onlinemetalstore.co.uk or on +44 7907 239290 to discuss your corner count, confirm your sizing, or get a quote for the full system.

Complete Your 2mm Sloping Coping 125mm System

All components for a complete 125mm sloping coping installation:

• 2mm Sloping Coping – 1m Length | 125mm External Leg

• 2mm Sloping Coping – 2m Length | 125mm External Leg

• 2mm Sloping Coping – 3m Length | 125mm External Leg

• 2mm Sloping Coping – 90° External Corner | 125mm External Leg (this product)

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

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

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

• 2mm Sloped Coping – Left Handed Closed Stopend | 125mm External Leg

• 2mm Sloped Coping – Right Handed Closed Stopend | 125mm External Leg

• 2mm Sloped Coping – Right Handed Stopend Upstand | 125mm External Leg

• 4mm Aluminium Coping Bracket

• Colour Coded Sealant 300ml

• Colour Coded Fasteners (Timber)

If you are using the 100mm external leg system instead, the correct corner is the 90° external corner for the 100mm system. For the full sloping coping range across all leg sizes and gauges, visit the Aluminium Sloping Coping collection page. To see the 125mm system in use on a residential development, view the aluminium sloped coping case study.

Frequently Asked Questions

How is this corner different from the 100mm external leg version?

The 125mm corner has a wider external leg than the 100mm version, matching the wider straight lengths in the 125mm system. The sizing formula is also different: wall width + 220mm for the 125mm system versus wall width + 195mm for the 100mm system. The two corners are not interchangeable. If your straight coping lengths are the 100mm version, you need the 90° external corner for the 100mm system.

What size corner do I order for the 125mm system?

Wall width + 220mm = the size to order. This is the same formula as for the straight lengths in the 125mm system. If you have already worked out the size for your straight sections, that is the size for the corner pieces too. A 165mm wide parapet wall needs the 385mm size throughout the 125mm system, including the corners.

How many corner pieces do I need?

One per right-angle external corner on the parapet plan. On a rectangular parapet, that is four pieces. On an L-shaped plan, count each external corner separately and note any internal corners (which need the internal corner product). On a new-build development, count per house type and multiply by the number of units per phase.

Can I sealant just one leg of the corner to save time?

No. Both legs of a 90° external corner must be sealed. The corner faces weather from both wall elevations and both joint lines are part of the weathertight seal between the corner piece and the adjacent straight sections. A single sealed leg leaves the other joint open to driven rain at the most exposed position on the parapet run.

Does the 125mm corner use the same bracket as the 100mm corner?

Yes. Both the 100mm and 125mm sloping coping systems use the 4mm aluminium coping bracket. The bracket is the same across the 2mm sloping coping system regardless of leg size. The dimensional difference between the 100mm and 125mm systems is in the profile accessories (lengths, corners, stopends) only.

What is the difference between an external and internal corner?

An external corner sits at an outside angle of the parapet where the wall projects toward you. An internal corner sits at a re-entrant angle where the parapet turns inward. On most rectangular buildings, all parapet corners are external. Internal corners appear on buildings with complex plan forms, L-shapes or recessed bays. The 90° internal corner for the 125mm system is available from the same range.

Ready to Order?

Select the size matching your straight 125mm coping lengths from the dropdown above, choose your RAL colour, and add to basket. If you need to confirm your corner count, check whether you need external or internal corners at specific positions, or get a quote for the full 125mm system, contact us at sales@onlinemetalstore.co.uk or call +44 7907 239290, Monday to Saturday 6:30am to 4:30pm.

Custom Fabricated Item: Made to order at our Chelmsford facility. Please check your measurements carefully before ordering. Non-returnable unless faulty. See our Refund and Returns Policy for full details.