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

On green roofs with parapet walls, the drainage outlets are almost always positioned at the base of the wall where the roof membrane turns up to form an upstand. It is the lowest point, where water naturally collects, and where growing substrate, pebbles and organic debris are most likely to wash into the drainage system. Without a chamber around that outlet, the substrate migrates into the drainage point and blocks it. Once blocked, water builds up behind the parapet, loading the structure and saturating the growing medium until the planting fails or the membrane is compromised.

The parapet version of the inspection chamber is designed specifically for this situation. It sits against the wall with one open face towards the parapet upstand, containing the substrate on three sides while allowing water to flow through the slotted walls into the outlet. The lockable lid gives maintenance teams clear access for the twice yearly inspections the GRO Green Roof Code requires. On green roof projects across Chelmsford, Brentwood, Colchester and the wider South East, this is the detail that keeps the drainage working as designed.

Product Overview

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

Unlike the deck version which has slotted sides on all four faces and sits on the open roof deck, the parapet version has one open face designed to butt against the parapet wall where the outlet is positioned. The chamber consists of a slotted base section, interlocking midsections that stack to the required height, and a lockable lid. Every component is custom fabricated at our Chelmsford, Essex workshop and powder coated in any RAL colour. For larger outlets or higher build up depths, the 450mm x 450mm parapet version provides a bigger footprint.

Key Benefits

Designed for Parapet Wall Outlets

The open face sits flush against the parapet upstand, creating a three sided enclosure around the outlet. This allows the membrane to dress up the wall without obstruction while the chamber contains the substrate and pebble border on the remaining three sides. No other chamber type provides this wall interface.

Keeps Outlets Clear and Accessible

The slotted sides allow water to flow freely into the outlet while preventing substrate, pebbles and organic debris from blocking the drainage point. The lockable lid lifts off for routine inspection without disturbing the surrounding planting or pebble margin.

GRO Code Compliant

The GRO Green Roof Code requires inspection chambers at all drainage outlets to ensure they remain free of blockages. This chamber meets that requirement and provides a clearly visible inspection point for the twice yearly maintenance checks the Code specifies.

Adjustable Height for Any Build Up Depth

Four height options (150mm, 200mm, 250mm, 350mm) cover everything from shallow extensive sedum roofs to deeper intensive and blue green roof systems. The interlocking midsections stack to match the exact finished level of the green roof surface.

Corrosion Resistant in Permanently Damp Conditions

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

Powder Coated in Any RAL Colour

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

UK Manufactured with Fast Turnaround

Every chamber is fabricated at our workshop in Chelmsford, Essex. We manufacture to order and keep lead times short.

Technical Specifications

Material: 1.5mm aluminium

Type: Green roof inspection chamber, parapet version

Chamber Size: 300mm x 300mm

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

Construction: Slotted base section, interlocking midsections, lockable lid, one open face for parapet wall

Finish: Polyester powder coated in any RAL colour

Suitable For: Parapet wall outlets on 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

Parapet Version vs Deck Version

Use the parapet version when the roof outlet is positioned at the base of a parapet wall or against any vertical upstand. The open face of the chamber sits against the wall, and the remaining three slotted sides contain the substrate. Use the deck version when the outlet is on the open roof deck, away from any wall. The deck version has slotted sides on all four faces.

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 parapet version provides more space around the outlet.

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 Parapet Inspection Chamber

Position the base section of the chamber over the parapet wall outlet with the open face against the wall. The membrane should dress up the parapet upstand behind the chamber. Place the base directly on the waterproofing membrane or, where a drainage board is in use, on top of the drainage element with filter fleece over the outlet.

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. Place the lockable lid on top.

In accordance with the GRO Code and FLL Guidelines, maintain a minimum 500mm pebble or shingle border around the chamber, keeping vegetation clear. This ensures the chamber is clearly visible and accessible for routine inspection.

Where Parapet Inspection Chambers Are Used

Flat Roofs with Parapet Walls

On buildings with parapet walls, drainage outlets are positioned at the base of the wall where the roof membrane turns up to form the upstand. This is the natural collection point for water on any flat roof. On green roofs across Essex, Kent and the Home Counties, every parapet outlet needs a chamber to keep the substrate out of the drainage system.

Extensive Sedum and Wildflower Roofs

On lightweight sedum blanket and wildflower roofs with parapet walls, the 300mm chamber provides outlet protection without taking excessive space on smaller domestic roof areas. The 150mm and 200mm height options suit the shallow build up depths typical of extensive systems.

Blue Green Roof Attenuation Systems

On blue green roofs designed to attenuate rainwater, inspection chambers are required at every outlet and at cascade points between roof levels. Parapet outlets on these systems are critical drainage points that are especially prone to silt build up and require routine access for maintenance.

Commercial and Public Buildings

On commercial buildings, schools, care homes and apartment blocks where green roofs are specified as part of a planning condition or biodiversity net gain requirement, parapet inspection chambers provide the auditable maintenance access points that building managers need.

Podium Decks and Roof Terraces

On podium structures where landscaping or paving sits above a structural slab with parapet walls, the chamber protects drainage outlets beneath the build up. On amenity terraces, colour matching the chamber to the coping or pebble border keeps the visible detail clean.

Frequently Asked Questions

What is a parapet inspection chamber used for on a green roof?

It is a water permeable box that sits around a parapet wall outlet on a green roof. It contains the growing substrate and border pebbles on three sides while allowing water to flow through the slotted walls into the outlet. The open face sits against the parapet wall. The lockable lid provides access for routine inspection and clearing.

When do I need a parapet version instead of a deck version?

Use the parapet version whenever the roof outlet is positioned at or near the base of a parapet wall or vertical upstand. The open face of the chamber sits against the wall, allowing the membrane to dress up behind it. Use the deck version when the outlet is on the open roof deck, away from any wall.

Do I need an inspection chamber at every parapet outlet?

Yes. The GRO Green Roof Code requires inspection chambers at all drainage outlets on green roofs. Every parapet outlet needs a chamber to prevent substrate from entering and blocking the drainage system, and to provide access for the twice yearly inspections the Code specifies.

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. Choose from 150mm, 200mm, 250mm or 350mm. Select the height that matches or slightly exceeds your build up depth.

Is an aluminium parapet chamber better than plastic?

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 in these conditions over time. For a component that needs to last the full life of the roof (25 to 40 years), aluminium is the more reliable choice.

Aluminium vs Plastic vs Polymer Concrete Parapet Chambers

Aluminium

Corrosion resistant, UV stable, and unaffected by humic acids. Powder coated in any RAL colour. The interlocking midsection system allows exact height adjustment. Lightweight and easy to handle on site. For the majority of green roof installations in the UK, aluminium is the best choice.

Plastic

Cheaper upfront but degrades in UV exposure, becomes brittle in cold, and can crack under load. In the permanently damp, acidic environment beneath green roof substrate, plastic deteriorates faster than in other applications. Not recommended for roofs with a design life exceeding 15 years.

Polymer Concrete

Heavy, robust and durable, but typically only available as part of a complete system package from specialist green roof suppliers. Aluminium chambers are a lighter, more adaptable alternative that can be colour matched, height adjusted, and used across multiple 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. The underlying flat roof should comply with BS 6229:2018 for flat roofs with continuously supported flexible coverings. The FLL Guidelines (referenced in the GRO Code) require 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.