2mm Aluminium Sloping Coping – 3m Length | 125mm External Leg - Online Metal Store Ltd

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

£84.60
(£101.52 Inc VAT)

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

When the parapet wall is a cavity wall construction or an insulated residential parapet, the 125mm external leg is the right overhang specification. It sits better in proportion against a wider wall, carries water further clear of the wall face, and is frequently the minimum overhang dimension in housebuilder standard drawings and architectural specifications across the South East. The 3m section is the primary run length for any parapet over 3m, giving you the fewest joints, the best use of material, and the cleanest continuous coping line along the straight runs. For a 9m parapet with a cavity wall construction in the 125mm system, three 3m sections give two joints and no waste. Start with the 3m sections, plan the infill positions using 2m sections and 1m sections, and the order practically works itself out.

This is the 2mm aluminium sloping coping in a 3m length with a 125mm external leg. It is the primary run length for the wider-leg sloping coping system from Online Metal Store Ltd, fabricated at the Chelmsford facility in Essex. Available powder coated in any RAL colour, in 29 width sizes from 185mm to 885mm, made to order and non-returnable unless faulty.

100mm or 125mm: Which Leg Size Do You Need?

The full 100mm vs 125mm selection guide, covering wall width proportion, housebuilder specification requirements and water throw-off distance, is on the 125mm 1m length page. In brief:

Use the 100mm External Leg When

The parapet wall is a standard single-skin brick or block construction up to around 200-250mm wide. The project is a domestic rear extension, box dormer or outbuilding in a sheltered residential setting. The site is not exposed, and the overall coping girth falls in the domestic size range. The 100mm external leg 3m section covers this specification.

Use the 125mm External Leg When

The parapet wall is a cavity wall construction, an insulated residential parapet, or any wall wider than around 250mm where a 100mm leg would look narrow against the wall width. The housebuilder or architectural specification sets a minimum 125mm external overhang. The project is a new-build housing development in the South East or Home Counties where cavity wall parapets are the standard construction. The parapet is on a prominent elevation where the visual proportion of the coping matters alongside the weathertight function.

Sizing note: the 125mm system uses a different formula from the 100mm system. The 125mm formula is wall width + 220mm (not + 195mm). For the same parapet wall, the 125mm size is always 25mm wider than the 100mm size. Do not use the 100mm formula here. The size calculation section below has worked examples for the 125mm system.

Product Overview

This 3m section is part of the Online Metal Store Ltd 2mm aluminium sloping coping system with a 125mm external leg, fabricated at the Chelmsford facility. The 125mm external leg overhangs the outside face of the parapet wall by 125mm, carrying the drip point further from the wall face than the 100mm equivalent and giving a wider, more substantial profile at parapet level. The 75mm internal leg returns down the inside face. The built-in slope tilts the top surface toward the external face so rainwater runs off actively over the 125mm drip edge. The 4mm aluminium coping bracket is the correct concealed fixing bracket for this 2mm system, fixed to the wall top before the coping is pressed into place.

This 3m section is compatible with all accessories in the 125mm system: the 2m section and 1m section in the same profile, all four corner types, left and right handed closed stopends, stopend upstands, and the 4mm bracket. Accessories for the 125mm system are different products from the 100mm system and are not interchangeable. Order all corners, stopends and brackets in the 125mm leg size to match the lengths.

Key Benefits

125mm Overhang for Cavity Walls and Prominent Parapets

A 125mm external leg projects 25mm further beyond the wall face than the 100mm equivalent. On a cavity wall parapet where the wall thickness is 150mm or more, that wider projection keeps the drip point in correct proportion against the wall width and carries water further from the rendered or brick face below. On a new-build house on a residential development site where the parapet is visible from the street and forms part of the elevation composition, the 125mm leg gives a coping profile with real presence.

3m Sections for Minimum Joints on Long Runs

Every joint in a coping run is a sealant line. The 3m length minimises joint count compared with shorter sections. On a 12m perimeter parapet, four 3m sections give three joints. Twelve 1m sections give eleven. The fewer joints an installation has, the cleaner it looks and the less dependent it is on every sealant application being perfect. Plan straight runs with 3m sections first, use shorter infill lengths only where the run demands it.

Built-In Slope, Active Drainage From Day One

The slope is formed into the aluminium profile during fabrication. On a 3m section, the full 3000mm run tilts continuously toward the external face, carrying water off the full length of the section rather than relying on a fall across joints. On a cavity wall parapet on a new-build house in the South East, where summer-to-winter temperature variation puts repeated thermal stress on the sealant at joints, reducing joint count through longer sections is a practical maintenance advantage.

Any RAL Colour, Matched Across the System

The powder coat finish is an external grade polyester available in any RAL colour. On a housebuilder development where the coping colour is in the contract specification, ordering the 3m sections, 1m and 2m infill sections, corners, stopends and brackets in the same RAL ensures all components are coated in the same batch at Chelmsford. They arrive colour-matched. There is no colour tolerance issue between components from different batches because everything goes through at the same time.

Made to Order in Chelmsford, Reliable Lead Times

Fabricated at the Online Metal Store Ltd facility in Chelmsford to the width and colour specified at order. Made to order means non-returnable unless faulty. Measure the wall width, apply the 125mm formula (wall width + 220mm), select the correct size, and check it before placing the order. The UK manufacturing base means lead times are short for projects across Essex, the Home Counties, East London and the wider South East.

Technical Specifications

Material: 2mm grade aluminium

Profile: Sloping coping length

Length: 3m (3000mm)

External Leg: 125mm

Internal Leg: 75mm

Width Sizes Available: 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 Note: The "size" refers to the overall WIDTH of the coping profile, not the run length. All sections on this page are 3m long. The size you select must match the overall girth of your parapet wall.

Sizing Formula: Wall width + 220mm = size to order (125mm external leg + 75mm internal leg + 10mm + 10mm returns = 220mm). This is 25mm more than the 100mm system formula of wall width + 195mm.

Finish: Polyester powder coating, external grade

Colour: Any RAL colour to order

Compatible Bracket: 4mm Aluminium Coping Bracket (correct for 2mm coping system)

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

Country of Manufacture: United Kingdom (Chelmsford, Essex)

Calculating the Width Size: The 125mm Formula

The 29 sizes from 185mm to 885mm refer to the WIDTH of the coping profile, not the run length. Every section on this page is 3m long. The formula for the 125mm system is:

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

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

  • Total: wall width + 220mm = the size to order. A 165mm wide wall gives 385mm. A 240mm wall gives 460mm. A 315mm wall gives 535mm.

  • Important: this formula gives results 25mm larger than the 100mm system. A 165mm wall needs the 360mm size on the 100mm system but the 385mm size on the 125mm system. Do not use the wrong formula.

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

  • On site: measure directly across the top of an installed section of this system from external leg tip to internal leg tip. That measurement is the size to order.

How Many 3m Sections Do You Need?

Work out the total linear metres of straight coping run for each face of the parapet. Divide by 3 and round up to get the minimum number of 3m sections for each face, then plan infill separately for any remaining length.

  • 6m face: two 3m sections, one joint, no waste.

  • 9m face: three 3m sections, two joints, no waste.

  • 10m face: three 3m sections plus a 1m section or a 3m section cut to 1m. Use the 1m section to avoid waste on a non-returnable made-to-order product.

  • 7m face: two 3m sections and a 1m section, or a 3m section and a 2m section. Three lengths, two joints in both cases. The 2m section version produces one fewer joint.

  • Multiple faces: calculate each face separately. Corner pieces and stopends are counted per corner and per terminal, not per linear metre.

Use 2m sections for faces between 2m and 5m. Use 1m sections for short faces, final infill pieces, and tight-access positions. Plan with 3m sections first and work down to shorter lengths only where the run layout requires it.

How to Install 2mm 125mm Sloping Coping

Mark the bracket positions along the full parapet run before fixing anything. Fix the 4mm aluminium coping brackets at the correct centres, not exceeding 1000mm, with brackets within 150-200mm of every run terminal, corner junction and stopend position. A 3m section needs a minimum of four brackets: one near each end and two intermediates at approximately 1000mm spacing. Confirm all brackets are flat to the wall top and aligned before pressing any coping.

Press the 3m coping sections onto the brackets from the fixed terminal end of the run. Apply a continuous bead of colour coded sealant in the matching RAL colour to the internal face of each joint before butting the next section up. The sealant bead at the joint is the primary weathertight seal. Keep it continuous and uninterrupted.

Lock the coping to the brackets with colour coded fasteners in the matching RAL colour at the bracket positions. Fit the left and right handed 125mm closed stopends at the run terminals and the appropriate 125mm corner pieces at every change of direction. Apply a neat finishing bead of sealant on all external joint faces.

Where the 3m 125mm Sloping Coping Section Is Used

New-Build Housing Developments with Cavity Wall Parapets

Volume housebuilders across Essex, the Home Counties and the wider South East specifying 125mm sloping coping for cavity wall parapet details on their standard house types will typically order the 3m section as the primary length per plot or per phase. On a development of 30 to 60 units where the same house type repeats, ordering the full system from a single UK manufacturer gives colour consistency across every plot and a traceable specification for the installed coping. The aluminium sloped coping case study shows the sloping coping system installed across a residential development in London, demonstrating the finished result at scale.

Residential Extensions on Larger Properties

Single-storey extensions on detached or larger semi-detached properties often include cavity wall construction at the parapet level, particularly on newer builds where Part L compliance and insulation requirements add thickness to the wall build-up. On these projects, the 125mm leg is the right specification for the parapet width that results, and the 3m section gives the minimum joint count across each straight parapet face.

Two-Storey Extensions and Prominent Parapets

On a two-storey rear or side extension where the parapet is at first-floor ceiling level and visible from adjacent properties and gardens, the 125mm external leg gives a coping profile with a stronger visual presence than the 100mm equivalent. The wider overhang casts a more defined shadow line on the wall below and holds its proportions well against the wider wall construction typical of a two-storey build. The 3m section across the parapet faces at this level keeps joint lines to a minimum on what are often the most scrutinised elevations of the completed project.

Replacement Coping on Existing 125mm Systems

When an existing 125mm sloping coping system has failed or reached the end of its useful life, the replacement must match the original leg dimension. Ordering 100mm sections as a replacement on a 125mm installation produces a visible mismatch in profile width and overhang that is obvious from ground level. The 3m section in the 125mm system is the right primary replacement length, ordered alongside the matching corners, stopends and brackets from the same Chelmsford source.

Frequently Asked Questions

When should I use the 125mm external leg rather than the 100mm?

Use the 125mm when the parapet wall is a cavity wall or insulated construction wider than around 250mm, when the housebuilder or architectural specification calls for a minimum 125mm overhang, when a more substantial coping profile is required on a prominent elevation, or when you are matching the leg dimension of an existing 125mm installation. For standard single-skin domestic extension parapets in sheltered settings, the 100mm system is normally the right choice.

What size do I need for my 125mm system parapet?

Wall width + 220mm = the size to order. That accounts for 125mm external leg, 75mm internal leg and 10mm returns each side (125 + 75 + 10 + 10 = 220). A 165mm wide wall gives 385mm. A 240mm wall gives 460mm. A 315mm wall gives 535mm. This formula gives results 25mm larger than the 100mm system. Do not apply the 100mm formula (wall width + 195mm) to a 125mm installation.

The product shows 29 sizes. Are those 29 different run lengths?

No. Every section on this page is 3m long. The 29 sizes from 185mm to 885mm refer to the WIDTH of the coping profile, which is the overall girth across the top from the external leg tip to the internal leg tip. You select the size that matches your wall width using the formula above. A 165mm wide parapet wall needs the 385mm size, and it arrives as a 3m section that is 385mm wide and 3000mm long.

How many 3m sections do I need?

Divide the total linear metres of each straight parapet face by 3 and round up. A 9m face needs three 3m sections. A 7m face needs two 3m sections plus a 1m section (or one 3m plus one 2m section for a lower joint count). Plan each face separately and add up the total 3m sections across all faces. Do not include the length of corner pieces or stopends in the run calculation.

Can I use 100mm system accessories with these 125mm sections?

No. The 100mm and 125mm system accessories have different profile dimensions and are not interchangeable. A 100mm corner on a 125mm coping run will not be flush at the junction. Order all corners, stopends and upstand stopends in the 125mm leg size to match these sections. The bracket (4mm for 2mm coping) is the same across both leg sizes.

Is this suitable for NHBC new-build projects?

Yes. A 2mm aluminium sloping coping system with 125mm external leg, properly sized to match the parapet wall width, with brackets at correct centres and all joints sealant-bedded, is consistent with NHBC Standards Chapter 7.1 requirements for parapet wall construction on new-build housing. On developments where the house type specification calls for a 125mm external overhang on sloping coping, this product and the full range of 125mm system accessories are the correct specification.

Part of a Complete 2mm Sloping Coping System | 125mm External Leg

This 3m section is the primary run length in the 2mm aluminium sloping coping system with a 125mm external leg. A complete installation needs lengths in the right mix, corner pieces at every change of direction, stopends at every run terminal, 4mm brackets at the correct centres, sealant at every joint, and colour coded fasteners. Order all components from the same Chelmsford manufacturer for matching profiles, consistent colour and a system that goes together correctly on site. The full 2mm sloping coping system with 125mm external leg includes:

For the full sloping coping range across both 100mm and 125mm leg sizes and 2mm and 3mm gauges, visit the Aluminium Sloping Coping collection page. For the 100mm external leg equivalent of this 3m section, see the 2mm sloping coping 3m length with 100mm external leg.

Standards and Compliance

Aluminium sloping coping on flat roof parapets in the UK is specified and installed under BS 6229:2018 - Flat Roofs with Continuously Supported Flexible Waterproof Coverings. The standard covers parapet and edge detailing requirements for flat roofs, including coping specification, joint treatment and fixing requirements. A correctly installed 2mm aluminium sloping coping system with a 125mm external leg, sealant-bedded joints and brackets at the correct centres is consistent with the weathertight parapet detailing requirements of this standard.

The external grade polyester powder coat applied to all components in this range meets the requirements of BS EN 12206-1 - Organic Coatings on Aluminium and Aluminium Alloys. The same coating specification applies to every component ordered together, ensuring consistent colour and durability across 3m sections, infill lengths, corners and stopends.

For NHBC-registered new-build projects, Chapter 7.1 of the NHBC Standards covers parapet wall and flat roof construction. A 2mm aluminium sloping coping system with 125mm external leg, correctly sized and installed, is consistent with these requirements on new-build completions where the wider overhang is the specified configuration.

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Custom Fabricated Item

This is a custom-fabricated item made to your selected size and finish. Please double-check measurements before ordering. This product is non-returnable unless faulty, as explained in our Refund & Return Policy

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