Landscaped roofs put green sheen on landmark city developments

In recent years, green roofs have become increasingly popular throughout the UK, with industry experts estimating that the number of ‘gardens in the sky’ being installed across the UK has risen by 40% since the start of the decade. Dave Maginnis, Managing Director at BriggsAmasco, highlights how these earthy installations are helping transform London’s landmark Battersea Power Station site – one of the largest redevelopment spaces in Europe – into a thriving mini-city.

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Planning from pallet to roof

BriggsAmasco installs two types of green roof systems – sedum and plug plant. Each has its challenges in terms of installation. The sedum mat is, generally, a more robust system to fit. It’s grown in a greenhouse before being rolled-up and transported to site. Good forward planning is essential to ensuring a smooth transfer from pallet to roof. A sedum mat will not survive on a pallet for longer than three days; therefore, the roof’s waterproof insulation should be in position in good time before its green layer arrives.

Plug plants arrive pre-potted and rooted – which is the same as buying from a nursery – and are planted onto a roof via a mixed substrate. An ecology report will determine how many plants are required per square metre, whilst the green layer is generally laid to a depth of between 70 and 100mm. The only potential issue with the installation of the substrate is people walking over it whilst it’s in situ. Plants need to be planted between April and September. Good logistics will again pay dividends to avoid projects finishing outside of these optimum times.

The main challenge of any roof installation is transferring the material – particularly the substrate – to the top of a building. For instance, laying a substrate to a thickness of 100mm across a 1000m2 roof, that’s a few tonnes-worth of bags that need taking to the roof. In such instances, the process is made easier – though not necessarily quicker – by spreading the load and using more bags. This increases the amount of lifts, but ensures a leaner operation. A hoist is often used to convey materials, a job that a crane could carry out far more time-effectively.

Following a project’s handover to the client, the green roof’s maintenance is provided by a qualified sub-contractor. A sedum roof doesn’t require a lot of maintenance. Generally, once established, it thrives in the temperate UK climate. Plug plants need to be nurtured and watered regularly – if not, the system will die.

Case study – Battersea Power Station

There can be no doubting the benefits a green roof brings to the environment. Aesthetically-pleasing and environmentally-friendly, it encourages a sense of health and wellbeing in a building’s occupants as well as adding a biodiverse layer to an otherwise grey, under- utilised space.

The breath-taking redevelopment of the Battersea Power Station site in London provides a fine example of how a green roof system is being employed in a thoroughly modern, residential and commercial complex. On behalf of main contractor, Carillion, BriggsAmasco was selected to install a multiple-level roof system for phase one of an eight-phase project which helped transform the derelict 39-acre Battersea Power Station site in south-west London into a thriving mini-city, replete with retail stores, restaurants and bars, a six-acre park, community theatre and residential apartments.

The initial phase involved 12 high-rise residential blocks to the west of the site. It comprised 850 residential apartments, as well as retail facilities, theatre space, business studios and two levels of parking. BriggsAmasco supplied six green roofs and two lower-level roofs consisting of limestone paving, which linked seamlessly with the internal spaces of the various winter gardens of the apartments. For all roofs, a Hydrotech Monolithic hot-melt membrane was fully-bonded to the substrate. The system provides excellent root protection and allows immediate access to waterproofed areas. Its membrane is designed to last a building’s lifetime, offering seamless, waterproof protection for podiums and highly-detailed water feature projects. Rigid extruded polystyrene insulation (XPS) provided the membrane’s insulation layer. Due to its compressive strength, XPS is ideal for specialist applications such as car park decks and inverted roofing. A plug plant system constituted the roof’s sustainable, green finish.

In addition to the main roofs and terraces, the project presented access and logistical challenges relating to numerous service risers which could have compromised the main works programme and that of other trade contractors. BriggsAmasco used its Exemplar cold-applied PMMA waterproofing to these areas. PMMA is a product that is durable, cost-effective and allows seamless integration with the complex facade interfaces.

BriggsAmasco completed the complex, multi-roof Battersea Power Station installation in April 2017. It has helped steer this formerly drab, derelict site towards a brighter future as one of the most attractive commercial/residential hubs in the capital. The company’s expert implementation of a number of waterproof green roof systems has added to the residential buildings’ sustainable credentials as well as off-setting the surrounding built environment by introducing a natural element which is pleasing to the eye and increases the wellbeing of the apartments’ occupants.

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