3mm Aluminium Sloping Coping – 90° External Corner | 100mm External Leg

The 90° external corner piece for the commercial 3mm sloping coping system. It sits at every right-angle outside corner of the parapet, carrying the same 100mm external leg and built-in slope as the 3m lengths, 2m sections and 1m pieces in the same 3mm system. Without it, the straight sections have no clean way to turn the corner of a commercial parapet. One corner piece is required per right-angle external corner on the parapet plan.

Available in the same 23 commercial width sizes as the straight lengths, from 510mm to 1060mm, 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 3mm sloping coping system and is not compatible with the 2mm system. The 2mm version of this corner is the 90° external corner for the 2mm 100mm system.

2mm or 3mm Corner: Are You on the Right Page?

The 2mm and 3mm sloping coping systems use different corner profiles with different wall thicknesses. They are not interchangeable. Fitting a 2mm corner on a 3mm run, or vice versa, produces a mismatch at the junction and does not seat correctly. You need the corner that matches the gauge of your straight coping lengths.

Use the 2mm Corner When

Your straight coping lengths are 2mm gauge. The 2mm system covers domestic and light commercial parapets with coping girths from 185mm to 885mm. The 2mm sloping coping 90° external corner for the 100mm system is the correct component for those installations.

Use This 3mm Corner When

Your straight coping lengths are 3mm gauge. The 3mm system covers commercial parapets in the 510mm to 1060mm size range, NHBC new-build housing with heavier specifications, exposed and coastal sites, and elevated buildings where wind uplift forces require the heavier gauge. Every component in a 3mm installation must be 3mm gauge throughout: lengths, corners, stopends and the 5mm coping bracket. Do not substitute 2mm accessories.

External Corner or Internal Corner?

External Corner (This Product)

Sits at an outside angle of the parapet, where the building wall projects outward and the coping wraps around the corner of the structure. Standing and looking at the building from the outside, the corner sticks toward you. On most commercial buildings with a rectangular or near-rectangular plan, all perimeter parapet corners are external corners.

Internal Corner

Sits at a re-entrant angle in the parapet plan, where the coping profile turns inward. These appear on buildings with complex plan forms, stepped parapets, projecting structural elements, and L-shaped or U-shaped layouts. If the parapet corner angles away from you as you look at the building, it is an internal corner. The 3mm 90° internal corner is available from the same range.

Key Benefits

• 3mm gauge throughout: matches the 3mm straight lengths in rigidity and commercial specification. A 2mm corner in a 3mm run is under-specified and dimensionally mismatched.

• Flush profile at the corner: the 100mm overhang and slope carry around the 90° turn without reduction. The profile width at the corner matches the adjacent straight sections exactly.

• Built-in slope resolves at the corner: surface drainage continues through the corner piece in both directions, preventing water from sitting at the junction.

• 23 commercial sizes matching the lengths: same 510mm to 1060mm range. Order the same size as your 3mm straight sections.

• Factory-formed watertight junction: more reliable than a site-mitred corner. The profile is dimensionally consistent and seals correctly with a sealant bead on each leg.

• Any RAL colour, batch-matched: order in the same RAL as all other 3mm system components for colour-consistent arrival from the same Chelmsford coating run.

Technical Specifications

Material: 3mm grade aluminium

Profile: Sloping coping corner

Corner Angle: 90 degrees external

External Leg: 100mm

Internal Leg: 75mm

Width Sizes: 510mm, 535mm, 560mm, 585mm, 610mm, 635mm, 660mm, 685mm, 710mm, 735mm, 760mm, 785mm, 810mm, 835mm, 860mm, 885mm, 910mm, 935mm, 960mm, 985mm, 1010mm, 1035mm, 1060mm (23 sizes in 25mm increments)

Size Rule: Order the same size as your 3mm straight coping lengths

Sizing Formula: Wall width + 195mm = size to order (100mm external leg + 75mm internal leg + 10mm + 10mm returns = 195mm)

Wall Width Range: Approximately 315mm to 865mm

Finish: Polyester powder coating, external grade

Colour: Any RAL colour to order

Compatible Bracket: 5mm Aluminium Coping Bracket (required for all 3mm coping)

Compatible System: 3mm Aluminium Sloping Coping | 100mm External Leg only

Not Compatible With: 2mm sloping coping system -- different gauge and profile dimensions

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

Country of Origin: United Kingdom (Chelmsford, Essex)

Getting the Size Right

The 23 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 3mm coping lengths. The formula is wall width + 195mm, the same as for the straight lengths in this system.

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

• Add 100mm (external leg) + 75mm (internal leg) + 10mm + 10mm (returns) = 195mm.

• Wall width + 195mm = the size to order. A 315mm wide commercial parapet gives 510mm. A 415mm wall gives 610mm. A 540mm wall gives 735mm.

• If the result falls below 510mm, the parapet is likely in the domestic 2mm system range.

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

How Many Corner Pieces Do You Need?

Count the right-angle external corners on the parapet plan. One corner piece per corner. On a rectangular commercial perimeter, that is four pieces. On a more complex plan form, count each external corner separately and note any internal corners, which need the internal corner product.

• Simple rectangular commercial parapet: 4 external corners.

• Building with a projecting element (e.g. stair enclosure): additional external corners at each angle of the projection.

• Stepped parapet: count each external step angle separately.

• Any obtuse angle (not 90 degrees): use the 135 degree corner, not this product.

• Re-entrant angles: use the 3mm 90° internal corner.

Installation

Fix the 5mm aluminium coping brackets along the run in the normal way. Position a bracket within 150-200mm of the corner piece on each leg of the adjacent straight sections. The corner piece does not require a separate bracket beneath it: the brackets on the adjacent lengths provide the support at the corner position.

Press the corner piece into position at the junction. Butt the straight sections up to it from each leg and apply a continuous bead of colour coded sealant in the matching RAL to the internal face of both joints. Both legs of the corner must be sealed: the corner faces weather on two elevations simultaneously and both joints are part of the weathertight line.

Lock the adjacent straight sections to their brackets using colour coded metal fasteners in the matching RAL. Apply a finishing sealant bead on both external joint faces at the corner. On a commercial development with multiple plots or a long perimeter run, work corner by corner systematically and complete the sealant at each one before moving on.

Where This Corner Piece Is Used

Commercial Flat Roof Parapets

The primary application. On a commercial office, retail unit, or mixed-use building with a perimeter flat roof parapet, this corner appears at every right-angle turn in the parapet plan. It is ordered as part of the full 3mm sloping coping system alongside the 3m primary lengths, 2m sections, 1m infill pieces, stopends and brackets. The aluminium coping case study shows a completed commercial coping installation on a live UK project.

NHBC New-Build Housing Developments

On NHBC-registered residential developments where the house type specification calls for 3mm sloping coping, this corner piece appears at every right-angle parapet corner on each unit. Housebuilders ordering the full system per phase, including lengths, corners, closed stopends and 5mm brackets, get colour-matched, dimensionally consistent components from the same Chelmsford manufacturing run. The aluminium sloped coping case study demonstrates the system at residential development scale.

Exposed and Coastal Sites

On buildings near the Essex or Kent coast, or on elevated exposed sites where 3mm has been specified for wind loading reasons, the corner piece maintains that specification at every right-angle turn. The corner faces the full force of two wall elevations simultaneously, making a factory-formed 3mm gauge piece the correct choice at this position.

Why a Factory Corner Matters on a Commercial Parapet

The corner is the weakest point in any coping run. Two wall faces meet at the corner junction and water driven from any direction finds the joint first. A site-mitred corner between two straight 3mm sections relies on accurate cutting and field application of sealant at the most critical position on the parapet. A factory-formed corner profile removes that dependency: the profile is pressed to the correct 100mm leg dimensions with the slope resolved accurately through the 90° turn, and the joint is sealed in the same way as every other joint in the run.

On a commercial project with a 30-year expected service life, the corner junction is the position most likely to show early failure if the detail is not correct from installation day. Getting a factory-formed corner piece of the correct gauge is the straightforward way to take that risk off the table.

Why Choose Online Metal Store Ltd

All 3mm sloping coping components are manufactured at our Chelmsford facility, including the corner pieces. They are fabricated to the same dimensional specification as the straight lengths and finished in the same external grade polyester powder coat process. Ordering corners alongside lengths, stopends and brackets in the same RAL at the same time means every component is coated in the same batch and arrives on site colour-matched. Contact our team at sales@onlinemetalstore.co.uk or call +44 7907 239290, Monday to Saturday 6:30am to 4:30pm, to confirm your corner count, check your sizing, or quote for the complete 3mm system.

Complete Your 3mm Sloping Coping 100mm System

• 3mm Sloping Coping – 1m Length | 100mm External Leg

• 3mm Sloping Coping – 2m Length | 100mm External Leg

• 3mm Sloping Coping – 3m Length | 100mm External Leg

• 3mm Sloping Coping – 90° External Corner | 100mm External Leg (this product)

• 3mm Sloping Coping – 90° Internal Corner | 100mm External Leg

• 3mm Sloping Coping – 135° External Corner | 100mm External Leg

• 3mm Sloping Coping – 135° Internal Corner | 100mm External Leg

• 3mm Sloped Coping – Left Handed Closed Stopend | 100mm External Leg

• 3mm Sloped Coping – Right Handed Closed Stopend | 100mm External Leg

• 5mm Aluminium Coping Bracket

• Colour Coded Sealant 300ml

• Colour Coded Metal Fasteners

If you are using the 2mm sloping coping system, the correct corner is the 2mm 90° external corner for the 100mm system. For the full sloping coping range across both gauges and all leg sizes, visit the Aluminium Sloping Coping collection page and the Aluminium Copings overview.

Frequently Asked Questions

Can I use this 3mm corner with 2mm coping lengths?

No. The 2mm and 3mm sloping coping profiles have different wall thicknesses. A 3mm corner on a 2mm installation does not produce a flush junction. All components on a 3mm installation must be 3mm gauge. Equally, a 2mm corner on a 3mm installation is under-specified for the conditions that required 3mm in the first place. For the 2mm system, use the 2mm 90° external corner.

What size 3mm corner do I order?

The same size as your straight 3mm coping lengths: wall width + 195mm. A 315mm wide commercial parapet gives 510mm, the smallest available size. A 415mm wall gives 610mm. A 540mm wall gives 735mm. The 23 sizes are coping widths, not run lengths. If you have already worked out the size for your straight sections, order the same size for the corners.

What bracket do I use with the 3mm corner?

The 5mm aluminium coping bracket is the correct bracket for all 3mm sloping coping components, including corner pieces. Do not use the 4mm bracket, which is for 2mm coping only. Position brackets within 150-200mm of the corner piece on each leg of the adjacent straight sections.

How many corner pieces does a standard commercial parapet need?

One per right-angle external corner on the parapet plan. A standard rectangular commercial parapet has four corners and needs four pieces. On buildings with projecting elements, stepped parapets or complex plan forms, count each external corner separately. Re-entrant angles and obtuse angles need different products.

Do I need to seal both legs of the corner?

Yes. Apply colour coded sealant to the internal face of both joints where the straight sections butt up to the corner piece. The corner faces weather from both wall elevations and both joint lines are weathertight seals. Sealing only one leg leaves the other open to driven rain at the most exposed position on the parapet.

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 outward. An internal corner sits at a re-entrant angle, where the parapet turns inward. Most standard commercial buildings have only external corners at the perimeter parapet. Internal corners appear on buildings with complex plan forms. The 3mm 90° internal corner is available from the same 3mm sloping coping range.

Ready to Order?

Select the size matching your straight 3mm coping lengths from the dropdown above, choose your RAL colour, and add to basket. To confirm your corner count, discuss the full 3mm system specification, or get a quote for lengths, corners, stopends and brackets together, contact our team 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.