3mm Aluminium Flat Coping – 3m Length | 75mm External Leg

This is the primary run length in the 3mm aluminium flat coping range. Supplied in 3-metre sections with a 75mm external leg on each side, it covers long commercial parapet runs with the minimum number of joints and the rigidity that commercial and exposed-site specifications require. Available in 23 width sizes from 510mm to 1060mm, powder coated in any RAL colour, and fabricated to order at our Chelmsford facility in Essex.

The flat top surface gives a clean, horizontal profile at parapet level. On commercial offices, retail units, contemporary apartment buildings and NHBC-registered housing developments where a minimal parapet line is part of the specification, flat coping is the standard choice. It relies on the external leg drip detail and correctly sealed joints for weathertightness rather than a built-in surface slope. For projects where positive surface drainage is preferred, the 3mm sloping coping range provides the alternative profile in the same gauge.

At 3mm, this section is built for the long term. Commercial parapets face sustained wind loading at height, repeated thermal cycling and the full force of UK weather on exposed faces. The 3mm gauge is stiffer across its profile than the domestic 2mm equivalent, resisting deformation and wind uplift forces more effectively over a 25 to 30 year commercial service life. On a project where the coping is expected to perform without intervention for decades, getting the gauge right from the outset is the correct decision.

Key Benefits

• Heavy commercial gauge: 3mm aluminium is the correct specification for commercial buildings, exposed sites, elevated parapets and NHBC-registered new-build housing. Stiffer and more resistant to wind peel than 2mm.

• Fewer joints on long runs: a 3m section reduces joint count to the practical minimum. On a 12m parapet face, four 3m sections give three joints. Fewer joints means less sealant, fewer maintenance points and a cleaner installed line.

• Clean flat profile: horizontal at parapet level, suited to commercial and contemporary architecture where a minimalist coping line is specified. Consistent shadow line along the full parapet perimeter.

• 23 commercial width sizes: 510mm to 1060mm covers cavity wall commercial parapets from approximately 340mm to 890mm wide. If your size is below 510mm, the 2mm flat coping system is likely the right product.

• Any RAL colour: external grade polyester powder coat to any RAL specification. Order all system components in the same RAL for batch-consistent colour across lengths, corners, stopends and brackets.

• Concealed fixing: the 5mm bracket is fixed to the wall before the coping is installed. No fastener penetrates the face or top surface of the installed section.

• Made to order in Chelmsford: fabricated to the width and colour you specify at our Essex facility. Short UK lead times.

Technical Specifications

Material: 3mm grade aluminium

Profile: Flat coping

Length: 3m (3000mm)

External Leg: 75mm

Internal Leg: 75mm (equal both sides)

Sizes Available: 510mm, 535mm, 560mm, 585mm, 610mm, 635mm, 660mm, 685mm, 710mm, 735mm, 760mm, 785mm, 810mm, 835mm, 860mm, 885mm, 910mm, 935mm, 960mm, 985mm, 1010mm, 1035mm, 1060mm

Size Definition: Overall WIDTH of the coping profile (external leg tip to internal leg tip) -- NOT the run length

Sizing Formula: Wall width + 170mm = size to order

Wall Width Range: Approximately 340mm to 890mm

Finish: Polyester powder coating, external grade

Colour: Any RAL colour to order

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

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

Country of Origin: United Kingdom (Chelmsford, Essex)

How to Measure: Getting the Size Right

The most important step before ordering. The 23 sizes refer to the coping WIDTH, not the run length. Every section on this page is 3m long. The size must match the overall girth of your parapet wall.

Formula: wall width + 170mm = the size to order.

Measure the wall width at the top of the parapet from outside face to inside face. Add 75mm for the external leg, 75mm for the internal leg, and 10mm for each return (20mm total). That gives wall width + 170mm.

• 340mm wide wall: 340 + 170 = 510mm (smallest available size)

• 440mm wide wall: 440 + 170 = 610mm

• 615mm wide wall: 615 + 170 = 785mm

• 890mm wide wall: 890 + 170 = 1060mm (largest available size)

If the result falls between two available sizes, always select the next size up. If it falls below 510mm, the parapet wall is likely in the domestic range and the 2mm flat coping system may be more appropriate.

Where This Product Is Used

Commercial Flat Roof Parapets

The primary market for 3mm flat coping. Commercial buildings with perimeter parapets, including offices, retail units, healthcare facilities, warehouses and light industrial buildings across Essex, East London and the South East. On a commercial building with a 24m parapet perimeter, eight 3m sections cover the full run with seven joints and no waste. Use 2m sections for medium parapet faces between 2m and 5m, and 1m sections for short returns and final infill pieces.

NHBC New-Build Housing Developments

On NHBC-registered residential developments where the house type specification calls for 3mm flat coping on cavity wall parapets, the 3m section is the primary order length per plot or development phase. Ordering the full system from a single manufacturer, including the 5mm brackets, 90 degree corners, closed stopends and colour coded sealant, gives a colour-matched, single-source specification that supports the warranty position on completion.

Exposed and Coastal Site Parapets

Buildings near the Essex and Kent coastline, on hilltop sites, or where wind loading calculations place the site in an exposed category require 3mm specification throughout. The 3m section in 3mm gauge gives maximum joint reduction while meeting the commercial specification. Reduce 5mm bracket centres to 750mm on exposed sites rather than the standard 1000mm maximum.

Commercial Refurbishment and Replacement

When existing 3mm flat coping on a commercial building has failed, the replacement must be 3mm. A 2mm replacement is under-specified for the site conditions that required 3mm in the first place, and creates a profile mismatch at every junction. Order the 3m replacement sections alongside the matching corners, stopends and 5mm brackets from Chelmsford for consistent profile and colour across the repaired section.

Installation Overview

Mark out the 5mm bracket positions along the full parapet run before fixing anything. This is the correct bracket for all 3mm flat coping: do not substitute the 4mm bracket, which is for 2mm coping only. Fix brackets at maximum 1000mm centres, with one within 150-200mm of every run terminal, corner junction and stopend position. A 3m section needs a minimum of four brackets. On exposed sites, reduce to 750mm centres or follow the structural engineer's specification where wind loading has been calculated.

Press the 3m flat coping sections onto the brackets from the fixed terminal end of the run. Before butting each section up to the previous one, apply a continuous bead of colour coded sealant in the matching RAL to the internal face of the joint. The sealant bead at each joint is the primary weathertight seal between adjacent sections. Keep it continuous. On a long commercial run, work systematically along the parapet and do not skip ahead of the sealant.

Lock the coping to the brackets using colour coded metal fasteners in the matching RAL. Fit the appropriate 3mm 90 degree corner pieces at every change of direction and closed stopends at every run terminal. Apply a neat finishing sealant bead on all external joint faces. For mixed-level parapets with T-junctions, the 3mm T-junction piece is available from the same range.

Allow normal expansion gaps at joints according to the BS 6229 detailing requirements for the site conditions. On a long commercial run in full sun exposure, thermal movement in summer months is real and the sealant joint must be able to accommodate it.

Why Aluminium Flat Coping Over the Alternatives

Versus uPVC

uPVC becomes brittle with age, fades in UV, and has a shorter service life on exposed commercial parapets. Aluminium does not degrade under UV, holds its powder coat colour for decades, and does not become brittle in cold weather. On a commercial building where the coping is expected to last the life of the flat roof, aluminium is the correct long-term choice.

Versus Lead

Lead has been used on parapets for centuries but is heavy, expensive, and requires skilled installation to avoid cracking at folds and joints over time. Aluminium flat coping is lighter, faster to install, consistently dimensioned, and available in any RAL colour for a modern finish. On most commercial projects, aluminium is now the standard specification where lead was once used.

Versus Concrete or Stone

Concrete and stone copings are heavy, require separate mortar bedding, and can crack under freeze-thaw stress at joints. Aluminium is dimensionally consistent, lightweight, and installed with a concealed bracket system that allows controlled thermal movement. There are no mortar joints to open, no stone to crack, and no repointing requirement over the service life.

Why Choose Online Metal Store Ltd

We manufacture all our aluminium coping systems at Highlands Farm, Southend Road, Chelmsford, CM3 8EB. Every section, corner and stopend in the 3mm flat coping range is fabricated and powder coated at this facility, which means short lead times for projects across Essex, East London, the South East and the wider UK. There are no intermediaries and no imported stock: what we quote is what we make, and we make it to the specification you provide. If you have questions about any aspect of the system, our team is available on sales@onlinemetalstore.co.uk or by phone at +44 7907 239290, Monday to Saturday from 6:30am to 4:30pm.

Bespoke sizing is standard, not an extra. Every section is made to the width you specify. Powder coating is available in any RAL colour, and when you order all system components together (lengths, corners, stopends, brackets) in the same RAL at the same time, they are coated in the same batch and arrive colour-matched. The full 3mm flat coping system is available from this page, and the complete aluminium flat copings range covers both 2mm and 3mm systems with the same manufacturing and ordering process throughout.

Complete the System

This 3m section is the primary run length in the 3mm flat coping system with a 75mm external leg. For medium parapet faces and infill positions, the 3mm flat coping 2m length and 3mm flat coping 1m length are available in the same sizes, gauge and colour range. A complete installation also requires:

• 3mm Flat Coping 90 Degree Corner -- for every right-angle change of direction

• 3mm Flat Coping 135 Degree Corner -- for obtuse-angle changes of direction

• 3mm Flat Coping Closed Stopend -- for every run terminal end

• 3mm Flat Coping Stopend Upstand -- for upstand terminal details

• 3mm Flat Coping T-Junction -- for parapet run intersections

• 5mm Aluminium Coping Bracket -- the correct bracket for all 3mm flat coping

• Colour Coded Sealant 300ml -- required at every joint in the run

• Colour Coded Metal Fasteners -- for locking coping to brackets on commercial substrates

For the full overview of all aluminium coping systems stocked and manufactured, including the 2mm flat coping range and the complete sloping coping systems in both 2mm and 3mm, visit the Aluminium Copings overview page. To see a completed coping installation on a live UK project, read the aluminium coping case study.

Frequently Asked Questions

When should I use 3mm flat coping instead of 2mm?

Use 3mm when the project is commercial, when the parapet wall width produces a coping girth of 510mm or above, when the NHBC specification or structural engineer's notes require 3mm, or when the building is on an exposed site or at two or more storeys. For standard domestic extensions, garages and outbuildings in sheltered settings where the coping girth falls below 510mm, the 2mm flat coping system is normally the correct choice.

What is the difference between flat and sloping aluminium coping?

Flat coping has a level top surface that sits horizontally on the parapet, giving a clean horizontal profile at building level. Sloping coping has a built-in slope that tilts toward the external face and actively drains rainwater off the surface. Flat coping relies on correctly sealed joints and the external leg drip detail for weathertightness. Sloping coping adds surface drainage on top of that. Both systems use the same concealed bracket fixing method. For 3mm sloping coping, see the 3mm sloping coping range.

How many 3m sections do I need?

Work out the total linear metres of each straight parapet face separately. Divide by 3 and round up to get the 3m section count for that face. A 12m face needs four sections. A 10m face needs three 3m sections plus a 1m infill section rather than a fourth full 3m section. Add up the section counts across all faces. Corner pieces and stopends are counted per corner and per run terminal, not per linear metre.

What bracket do I need, and how many per section?

The 5mm aluminium coping bracket is the correct bracket for all 3mm flat coping. Do not use the 4mm bracket, which is specified for 2mm flat coping only. For a 3m section, you need a minimum of four brackets: one near each end and two intermediates at approximately 1000mm centres. On exposed sites or elevated buildings, reduce to 750mm centres or follow the structural engineer's specification.

Is this product anodised or powder coated?

Powder coated only. The finish is an external grade polyester powder coat available in any RAL colour. These products are not anodised. Any reference to anodising on the current product page is a factual error. Powder coating is the only available finish across the entire Online Metal Store Ltd 3mm flat coping range.

Can 3mm flat coping sections be cut to length on site?

Yes. Aluminium cuts cleanly with a fine-toothed hacksaw, a metal-cutting circular saw blade, or an angle grinder with an aluminium-rated cutting disc. Cut square to the profile and deburr the cut edge. Fit a closed stopend at any cut end that forms a run terminal rather than leaving the cut aluminium face exposed. Bear in mind that sections cut on site cannot be returned, so measure carefully before cutting.

What is the expected service life?

A correctly installed 3mm aluminium flat coping system with properly sealed joints and correctly specified 5mm brackets can be expected to perform for 25 to 30 years on a commercial building. Aluminium does not rust, does not rot, and the external grade powder coat does not fade significantly over this period. Periodic inspection of the sealant at joints is the main maintenance requirement: the aluminium itself requires no treatment.

Ready to Order or Need Some Advice?

Select your size from the dropdown above, choose your RAL colour, and add to basket. If you need help with sizing, want to discuss a full system order across multiple lengths and accessories, or have a project-specific question, contact us directly. Our team is available Monday to Saturday, 6:30am to 4:30pm, at sales@onlinemetalstore.co.uk or on +44 7907 239290. We can confirm the correct width size from your wall dimensions, advise on section mix for your run layout, and quote for the complete system including corners, stopends and brackets in your chosen RAL colour.

All sections are made to order at our Chelmsford facility with short UK lead times. Download our colour chart for the full RAL range, or call us if you need to match an existing colour on site.

Custom Fabricated Item: This is a made-to-order product. Please check your measurements carefully before ordering. Non-returnable unless faulty. See our Refund and Returns Policy for full details.