Case study

Trinity Square, Newcastle GatesheadMulti-surface podium with sustainable drainage (SUDs)

Zoontjens, trading as Cityroofs and working in partnership with Pithcmastic PBM for the Main Contractor Bowmer and Kirkland, was responsible for realising the Landscape architect’s and planners concept of a complete ‘elevated landscape’ podium across the roof of a major new retail development, providing a range of level external spaces serving new student residences. At the same time, efficient surface water drainage, source control and attenuation were required, delaying discharge to the sewer, and service runs accommodated below the podium. Zoontjens and Partners assisted with the detailed design, procurement and installation of the complete podium, working within the challenging constraints of a major building project.

IntroductionTrinity Square is a £100m mixed-use commercial development designed by architects 3DReid on a prominent hilltop site overlooking the River Tyne, in the heart of Gateshead. It replaces a 1960s shopping centre and well-known ‘Brutalist’ concrete multi-storey car park that featured prominently in the iconic 1971 film ‘Get Carter’. As well as creation of a new vibrant town square ready for the influx of fresh students in Autumn 2014 - including shops, cafés, bars and restaurants – the redevelopment features a large 150,000 ft2 ‘Tesco Extra’ retail store with under-croft car parking for the whole town.

Above the store is a new student village for Northumbria University Newcastle, providing accommodation for around 1,000 people. The village comprises a sequence of residential blocks - surmounted with curved canopy roofs, terminating at either end with brise-soleils screens – rising up from a massive podium which provides access and a diversity of outside spaces for the enjoyment of residents.

Residential blocks rise up from the podium over the new retail store

Project: Trinity square, Gateshead Focus on: Multi-surface podium with sustainable drainage (suds) Completion: 2014 Paving: 5000 sqm Green/Brown roofs: 3000 sqm

The podium and student village sit above the store entrance off the new Town Square

Developer: Spenhill Developments Architect: 3DReid Landscape architect and planner: Fairhurst Main contractor: Bowmer and Kirkland Roofing contractor: Pitchmastic

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Layout Plan of the student village podium serving the residential blocks (shown in brown) 1 Roof surfacing to be inaccessible to student to allow habitat creation 2 Access for maintenance only 3 Bin / Bikes 4 Sports Court

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Landscape designAccess to the student village podium is by lift in the north eastern corner, leading straight onto larger scale paved areas for meeting, recreation and serving communal areas, with an enclosed ball court immediately adjacent. The podium is characterised by a straight central avenue running the length of the site splitting the residential blocks. A secondary route runs along the north western edge of the podium providing access to bin and bike stores.

Running perpendicular to the avenue are pairs of courts, each finished with a mixed palette of materials defining smaller areas for resident’s use, clustered around entrances to the blocks. Some areas are shielded by vegetated screens and incorporate shrub planting, which is also concentrated along the block facades. Surfaces include Zoontjens’ Dreen® concrete paving slabs in a variety of sizes, colours and laying patterns, as well as hardwood timber decking and artificial turf.

Moving away from the more heavily used circulation and communal spaces, areas of wildflower and Sedum planting, are introduced to encourage biodiversity - some accessible only for maintenance.

Lift access for residents leads onto larger scale communal areas of Zoontjens’ concrete specialist paving solution, together with hardwood decking serving a café.

key

Coloured slabs Buff and charcoal coloured Dreen® slabs (with drainage slots clearly visible) are used for the secondary route running along the Newcastle- facing side.

Biodiversity Sedum and wildflower

planting, as well as a ‘Brown Roof’, will

encourage biodiversity once established.

Secondary route The secondary route serves an enclosed ball court, as well as bike/bin stores.

‘Panels’ of paving The central avenue is

identified by ‘panels’ of paving with a structured layout of

exposed aggregate slabs and narrow bands of smaller

charcoal concrete paving.

Courts Courts between residential blocks include areas of Dreen® paving and artificial turf for residents’ use.

Variation in materials Clustered around block

entrances are smaller areas differentiated by hardwood

decking and variations in Zoontjens paving sizes, textures and colours,

with raised planters, seating and vegetated screens.

Podium design realisationZoontjens realised the architects’ design for the podium landscaping using its own system, rather than the sealed surface of mortar-jointed paving originally conceived, to achieve key objectives including:- The seamless application of a complex palette of hard and soft

landscape materials and surfaces- Completely level surfaces for easy access and enjoyment by all, with

efficient localised surface water drainage - A sustainable drainage system (SuDS) for rainwater providing source

control and attenuation, delaying discharge to the sewer- A well-insulated, protected and durable roof to the retail store below- Accommodation of extensive service runs below the podium. This

was the main reason for such an extensive build up, and enabled all the other design criteria to be fulfilled. This is also the reason why a mortar solution would not work.

The resulting design makes extensive use of Zoontjens systems to provide a flexible, ‘floating’ deck of permeable surfaces allowing rainwater straight into a ‘tank’ below. Here, it is attenuated within drainage layers of special water-retention boards, effectively encasing (top, bottom and laterally) 395mm deep sections of EPS thermal insulation. This system then sits on top of 140mm XPS insulation over the water-proofed roof structure. This ‘inverted roof’ ensures that the roof membrane is protected from damage and weather.

The paved surfaces are generally Zoontjens’ Dreen® paving where high quality concrete slabs, incorporating special drainage slots, are installed on adjustable supports and locked in place to form a united structural surface able to accommodate level differences below. A service corridor 400mm deep runs the length of the central avenue, with thermal insulation performance continuity maintained, and access is easily achieved if needed by simply lifting paving slabs.

The flexibility of the Zoontjens system enabled a number of challenges to be overcome, including creation of access ramps up to building entrances using adjustable paving supports and also the numerous interfaces between various forms of paving in small areas.

The logistics of installation also proved challenging with all materials having to be craned onto the podium at specified times, sometimes at night: despite this, some 200 deliveries from Zoontjens in The Netherlands to site were virtually all on time.

The Dreen® Slab system Zoontjens Dreen® Slab is a high quality paving system developed specifically for flat roofs. It combines attractive appearance and trouble-free rainwater disposal with impressive strength and structural stability. It offers an extensive choice of slab sizes, colours and surface textures – including exposed fine aggregate finishes.

Once installed, the slabs become a homogeneous surface with an integral rigidity which means they cannot move or distort. Corners of slabs are supported by unique Comfix locking discs on adjustable supports, in a way that completely eliminates the possibility of horizontal displacement. Dreen® offers a wide range of benefits for rooftop paving, including:- effective drainage without ponding, via

slots formed by slab edges- maximum strength and stability, while

allowing free flow of water beneath- protection of the roof membrane from

damage and the effects of weather- restraint for loose-laid insulation below:

ideal for inverted roofs - choice of systems for fixed or adjustable

slab height with levelling- accommodation of rooftop services

within the void beneath adjustable height systems

- ease of access for maintenance by simply lifting slabs.

Inset access covers enable paving patterns to continue uninterrupted.

Typical Dreen® paving installation over inverted roof build-up.

‘Soft’ landscape surface installations over inverted roof build-up.

Dreen® Slabs and adjustable supports on the water-retention boards.

Key

1 Zoontjens Lid Lightweight Extensive Green Roof System to meet W.A. Fairhurst speciafication.

2 Rigid High Flow Drainage Board. 3 EPS Filcor / Filshield filler boards. Boards to have

rebar dowels between boards to ensure boards are ‘knitted’ together and have no uplift.

4 Block Paving / Landscaping to Pitchmastic PmB / Zoontjens Specification.

5 High flow drainage board (vertically laid and staggered across full length of podium).

6 Service trench for incoming and outgoing services to Student Accommodation Blocks. Trench sat onto High Flow Drainage Board.

7 Pitchmestic Blueshield PmB waterproofing system, nominal 2mm thick

8 140mm thick Roofmate extruded insulation Boards (of equal and approved)

9 Rigid High Flow Drainage Board

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Sedum Green Roof Detail

Tesco Retail Unit

Transition Detail Wildflower Roof Detail Brown Roof Detail

Sustainable drainage designThe rooftop rainwater drainage system was designed by John Knapton Consulting Engineers Ltd., for Zoontjens. The design aims to reduce the peak runoff from the roof by detaining the water within a water-retention material installed at two levels within the build-up of the roof deck. Calculations were made for the required capacity to accommodate storms of various durations and the time required to discharge the water from various lengths of storm until 50% of the storage capacity became available for a possible second storm.

Experience and historic evidence shows that the shorter the duration of the storm, the greater its intensity and it is common practice to consider storms of durations between 5 minutes and 24hr. The volume of water retention material required for attenuation storage was calculated using drainage design calculations based on the Wallingford Procedure (HR Wallingford, 2000).

Two additional layers of water-retention material were provided at the lower level at each gulley, giving three layers directly over the roof insulation board and one layer above the EPS. Vertical water-retention boards surround each of the 13 inspection chambers, connecting the upper layer to the three lower layers.

Key

1 Rigid High Flow Drainage Board. 2 EPS Filcor / Filshield filler boards. Boards to have rebar dowels between boards to ensure

boards are ‘knitted’ together and have no uplift. 3 Block Paving / Landscaping to Pitchmastic PmB / Zoontjens Specification. 4 High Flow Drainage Board (vertically laid and staggered across full length of podium at 20m centres). 5 Pitchmestic Blueshield PmB waterproofing system, nominal 2mm thick 6 140mm thick Roofmate extruded insulation Boards (of equal and approved)

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P.O. Box 61, 5000 AB Tilburg, The NetherlandsT +31 (0)13 5 379 379, F +31 (0)13 4 550 527, E info@zoontjens.co.uk

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Case study produced by: Hodsons Ltd. www.hodsons.comPhotos: Chris Hodson

about ZoontjensZoontjens is a CRH company, combining the strengths and support of a major international organisation with dedicated expertise over 35 years in rooftop paving solutions. Our products and systems satisfy every situation, ranging from rooftop car parking and heavy goods vehicle access to pedestrian areas and elevated landscapes. We offer a complete service package and operate as lead contractor in specialist roofing projects around Europe. We take care of detailed design, delivery, installation and maintenance, and are responsible for the warranty on the roof systems.