1.5mm Aluminium Inspection Chambers - 300mm x 300mm | Deck Version

A green roof that covers its drainage outlets with substrate and vegetation is a green roof that will eventually block. Once the outlet silts up, water backs up across the membrane, pooling builds, and the structural load increases until something gives. The GRO Green Roof Code is clear on this point: inspection chambers are required at every outlet to ensure they remain accessible and free of blockages. On living roofs across Chelmsford, Brentwood, Colchester and the wider South East, this is not optional, it is fundamental to the system working as designed.

An aluminium inspection chamber sits around the roof outlet, containing the growing substrate and border pebbles while allowing water to pass freely through the slotted sides into the drainage system. The lockable lid lifts off for routine inspection without disturbing the surrounding planting. It is a small component that prevents the single most common failure mode on green roof installations.

Product Overview

The 1.5mm aluminium green roof inspection chamber from Online Metal Store Ltd is a water permeable box designed to fit around roof outlets on living roofs, green roofs, blue roofs and podium decks. The 300mm x 300mm deck version sits on the roof deck surface (rather than against a parapet wall) and is available in four height options: 150mm, 200mm, 250mm and 350mm to match different green roof build up depths.

The chamber consists of a slotted base section, interlocking midsections that stack to achieve the required height, and a lockable lid for inspection access. Each component is custom fabricated at our Chelmsford, Essex workshop and powder coated in any RAL colour. For outlets positioned against parapet walls, the parapet version is also available. For larger outlets or higher build up depths, the 450mm x 450mm deck version provides a bigger chamber footprint.

Key Benefits

Keeps Roof Outlets Accessible and Clear

The chamber creates a protected zone around the roof outlet, preventing growing substrate, border pebbles and vegetation from entering and blocking the drainage system. The slotted sides allow water to flow freely into the outlet while containing the mass materials that would otherwise silt it up.

GRO Code Compliant

The GRO Green Roof Code requires inspection chambers at all drainage outlets on green roofs to ensure they remain free of blockages. This chamber meets that requirement, providing a clearly visible, accessible inspection point that maintenance teams can check during the twice yearly inspections the Code specifies.

Adjustable Height for Any Build Up Depth

With four height options (150mm, 200mm, 250mm and 350mm), the chamber accommodates both extensive green roofs with shallow substrate (80mm to 150mm) and semi intensive or intensive systems with deeper build ups. The interlocking midsections stack to match the exact finished level of the green roof surface.

Corrosion Resistant and Long Lasting

Aluminium does not rust, even in the permanently damp conditions found beneath green roof substrate. The powder coat finish adds further protection against the humic acids that leach from growing media over time. Where plastic chambers can become brittle and crack, aluminium holds its shape and strength for the full life of the roof.

Powder Coated in Any RAL Colour

The chamber can be colour matched to the surrounding roof furniture, coping or pebble border for a consistent finish. On visible roof terraces and amenity green roofs, this matters.

UK Manufactured with Fast Turnaround

Every chamber is fabricated at our workshop in Chelmsford, Essex. We manufacture to order and keep lead times short. Most orders leave within a few working days.

Technical Specifications

Material: 1.5mm aluminium

Type: Green roof inspection chamber, deck version

Chamber Size: 300mm x 300mm

Height Options: 150mm, 200mm, 250mm, 350mm

Construction: Slotted base section, interlocking midsections, lockable lid

Finish: Polyester powder coated in any RAL colour

Suitable For: Extensive, semi intensive and intensive green roofs, blue roofs, podium decks

Manufactured: Chelmsford, Essex, United Kingdom

Price: From £65.00 ex. VAT (£78.00 inc. VAT)

Choosing the Right Chamber

Two decisions determine which chamber you need: footprint size and height.

300mm x 300mm vs 450mm x 450mm

The 300mm x 300mm chamber suits standard roof outlets on domestic and smaller commercial green roofs. For larger outlets, multiple adjacent outlets, or where the specification calls for a wider inspection zone, the 450mm x 450mm deck version provides more space around the outlet.

Deck Version vs Parapet Version

The deck version sits on the open roof deck, away from walls. The parapet version is designed for outlets positioned against or near a parapet wall, with one open side that faces the wall. Check your outlet position before ordering.

Height Selection

• 150mm: Shallow extensive green roofs with 80mm to 120mm substrate depth.

• 200mm: Standard extensive green roofs with 120mm to 170mm substrate depth.

• 250mm: Deeper extensive or semi intensive systems with 170mm to 220mm build up.

• 350mm: Intensive green roofs, deeper podium deck systems, or blue green roof build ups over 220mm.

How to Install a Green Roof Inspection Chamber

Position the base section of the chamber directly over the roof outlet, on top of the waterproofing membrane. If a drainage board is being used, cut out a section above the outlet and place the chamber base directly on the drainage element with filter fleece on top.

Stack the interlocking midsections onto the base until the chamber reaches the finished level of the green roof surface. The sections click together and can be trimmed on site if needed to fine tune the height. Place the lockable lid on top.

In accordance with the GRO Code and FLL Guidelines, surround the chamber with a minimum 500mm pebble or shingle border, keeping vegetation clear of the inspection point. This ensures the chamber remains clearly visible and accessible for the twice yearly inspections the Code requires.

Where Green Roof Inspection Chambers Are Used

Extensive Sedum and Wildflower Roofs

On lightweight sedum blanket roofs and wildflower roofs across domestic extensions, garages and garden rooms in Essex and the South East, the 300mm chamber provides outlet protection without taking up excessive space on smaller roof areas.

Semi Intensive and Intensive Green Roofs

Deeper planting schemes on commercial buildings, schools and apartment blocks need taller chambers to match the greater substrate depth. The 250mm and 350mm height options serve these deeper build ups.

Blue Green Roof Systems

On blue green roofs designed to attenuate rainwater, inspection chambers are fitted at every outlet and at cascade points between upper and lower roof areas. These critical locations are prone to silt build up and require routine maintenance to keep the attenuation system functioning correctly.

Podium Decks and Roof Terraces

On podium structures over car parks, basements or commercial spaces, the inspection chamber provides access to drainage outlets beneath the landscaping or paving build up. The deck version sits on the structural slab and rises through the layers to the finished surface.

NHBC and Local Authority Projects

On NHBC registered new builds and local authority projects where green roofs are specified as part of a planning condition or biodiversity net gain requirement, inspection chambers demonstrate compliance with the GRO Code and provide auditable maintenance access points.

Frequently Asked Questions

What is a green roof inspection chamber used for?

An inspection chamber is a water permeable box that sits around a roof outlet on a green roof. It prevents growing substrate, pebbles and vegetation from blocking the drainage outlet, while allowing water to flow freely through the slotted sides. The lockable lid provides access for routine inspection and clearance without disturbing the surrounding planting.

Do I need an inspection chamber on a green roof?

Yes. The GRO Green Roof Code states that inspection chambers are required to ensure outlets are kept free of blockages. Without a chamber, the substrate and vegetation will eventually cover and block the outlet, causing water to back up across the membrane.

What is the difference between the deck version and the parapet version?

The deck version sits on the open roof deck away from walls, with slotted sides on all four faces. The parapet version has one open side designed to sit against a parapet wall where the outlet is positioned at the wall base. Choose based on where your outlet is located on the roof.

What height do I need?

The chamber height should match the finished level of the green roof build up. Measure the total depth from the waterproofing membrane to the top of the substrate or pebble border. This product is available in 150mm, 200mm, 250mm and 350mm. Choose the height that matches or slightly exceeds your build up depth.

Is an aluminium inspection chamber better than plastic for green roofs?

Aluminium does not become brittle in UV light, does not crack in frost, and resists the humic acids that leach from green roof substrate. Plastic chambers can degrade over time in these conditions. For a component that needs to last the full life of the roof (typically 25 to 40 years), aluminium is the more reliable long term choice.

Can the chamber be colour matched?

Yes. Every chamber is powder coated in any RAL colour before dispatch. On visible amenity roofs and roof terraces, colour matching the chamber to the surrounding coping or pebble border gives a cleaner finish.

Aluminium vs Plastic vs Polymer Concrete Inspection Chambers

Aluminium

Corrosion resistant, UV stable, and unaffected by humic acids from growing substrate. Powder coated in any RAL colour and manufactured to precise dimensions. The interlocking midsection system allows exact height adjustment. For the majority of green roof installations in the UK, aluminium is the best choice for durability, appearance and long term performance.

Plastic

Plastic chambers are cheaper upfront but degrade in UV exposure, become brittle in cold temperatures, and can crack under load. In the permanently damp, acidic conditions beneath green roof substrate, plastic deteriorates faster than in other applications. For any roof where the expected service life exceeds 15 years, aluminium is the more cost effective choice over the full life of the system.

Polymer Concrete

Polymer concrete chambers (such as those from specialist green roof system suppliers) are heavy, robust and very durable. They are typically specified as part of a complete system package from one manufacturer. Aluminium chambers are a lighter, more adaptable alternative that can be colour matched, height adjusted, and used across multiple green roof system types. Browse the full living roof accessories collection to see all available products.

Standards and Compliance

Inspection chambers on green roofs should be installed in accordance with the GRO Green Roof Code which requires inspection chambers at all drainage outlets and specifies twice yearly inspection of those outlets. The underlying flat roof should comply with BS 6229:2018 for flat roofs with continuously supported flexible coverings. The GRO Code also references the FLL Guidelines (the German green roof standard widely referenced in UK specifications) which require inspection chambers to be clearly visible and surrounded by a minimum 500mm ballast margin. Getting these details right protects the warranty, the building and the drainage system.