James Leathem, project architect, Rogers Stirk Harbour + Partners
The redevelopment of the bullring in the Montjuïc area of Barcelona transformed the 1890s building into a mixed-use development topped by a dome made of timber and glass. This is raised on steel columns around the perimeter, so that it appears to float above the facade.
The dome rises above the bullring’s top floor, which encloses a space for sports events or other shows. The timber gridshell and steel ring beam structure, designed with subcontractor Finnforest Merck, is constructed using a matrix of glulam beams that form a triangular lattice. At the crown, a steel circular ring beam encloses a 30m-diameter oculus.
Initially we looked at using steel for the gridshell as well, but this was ruled out by our structural engineer, Expedition Engineering, due to the dome’s diameter.
The council restricted the height we could build to, so the dome took on a very flat profile and the structure had to work harder due to the large circumference and the tolerances required. Finnforest was able to refine the design to create much thinner and lighter members than planned.
The dome is doughnut shaped and stiffened by two tubular steel ring beams around the perimeter and the interior oculus. These beams have connections to support all the glulam timber members. They absorb all the stresses generated by the timber lattice, and hold the members in high tension and compression.
The structure is given horizontal rigidity by the Finnforest Kerto-Q panels, which are cut into triangular shapes and laid across the top of the gridshell. Initially, we planned to use plywood, but Finnforest said Kerto would increase structural stiffness, allowing us to reduce the size of the glulam beams. Kerto panels get their strength from a homogeneous bonded structure of 3mm-thick spruce veneers glued together to form a continuous panel.
Specifying green roofs
01 Ensure design compliance
A green roof design must comply with all relevant structural criteria, with a key focus on waterproofing, drainage, fire, irrigation, safety and access. It must also meet the appropriate Eurocodes, particularly EN1991 Eurocode 1: Actions on structures.
02 Specify the roof correctly
Green roofs can be extensive, semi-intensive, intensive extensive, or biodiverse. A green roof will need sunlight, moisture, drainage, aeration to roots and nutrients. It will also need a root-resistant material, a moisture retention/protection layer, a drainage/reservoir layer, a filter layer and a growth medium.
03 Make sure it is installed competently
Installation of all green roof system components should be undertaken by a fully trained contractor accredited by the National Federation of Roofing Contractors. Contractors should be trained in site preparation, system components, growth mediums, planting programs, plant and plant support system installation and maintenance.
04 Maintain the roof after installation
Green roofs require sustained maintenance to ensure good health. The installing contractor should remain responsible for maintenance for around 12-15 months and carry out irrigation, fertilisation, plant management and general clearance and removal.
05 Consult the code
The Green Roof Code from the Green Roof Organisation provides best practice on design, specification, installation and maintenance, plus details of British Standards and regulations. It has been developed in partnership with the Environment Agency, the Homes and Communities Agency, manufacturer Bauder, and others. It will be reviewed and updated annually.
US-German solar system manufacturer, Solyndra, has collaborated with Swiss-based roofing company Sika to promote the use of Sika’s reflective roofing membranes with Solyndra’s photovoltaic systems. Solyndra’s proprietary system uses pipe-shaped PV panels to collect solar energy more uniformly over the day and can be orientated in almost any direction. The panels can be installed without specialist fixings or penetrating flat roof surfaces. The system can operate in gales of up to 130mph without added mounts.
A Turkish supplier Sahtas is looking to enter the UK market with its traditional terracotta roof tiles, made by hand-throwing the clay onto sand-dusted wooden moulds. Its tiles come in many colours, blends and profiles with a range of fittings including ridges, peg tiles, and vents. At the company’s Izmir factory, local clay is combined with modern techniques to produce a product to ISO quality standards. These tiles have an insurance-backed 30-year guarantee and are tested to BS EN standards for flexural strength, resistance to frost and permeability to water.
Marley Eternit relaunched its Mendip roof tile which can be installed at pitches of just 15 degrees, 7.5 degrees lower than previously recommended. The concrete interlocking tiles have been subjected to thorough testing including wind-driven rain. The company says the tiles are ideal for the domestic extension market, as they are suitable for fixing below first floor windows, and available in five colours to match existing tiling. The tiles measure 330mm x 420mm and are available in two finishes: smooth and granular.