Sika-Trocal Integral To State-Of-The-Art Blackwall Tunnel Ventilation System

The four futuristic ventilation shafts on London’s Blackwall Tunnel would not be out of place on the set of the upcoming James Bond film.  Forming part of Transport for London (TfL)’s three-year refurbishment of this vital link across the Thames, Sika-Trocal single ply membrane was specified for its versatility and long term waterproofing performance in the much needed upgrade of the 114 year old tunnel and its unusual ‘flying saucer’ ventilation domes.

Faced with the challenges of designing and installing a waterproofing system for a domed roof that features opening mechanical petals, Architects Acanthus LW worked with specialist contractor Robertson Roofing, to come up with an innovative solution for this unusual single ply membrane application.

Main contractor BAM Nuttall was awarded the contract from TfL for the refurbishment of the northbound carriageway which involved a complete upgrade of the tunnel’s emergency walkways and systems. As part of the project, new ventilation equipment is being installed, fire and life safety systems upgraded and a state-of-the-art communications systems incorporated, including high quality lighting, CCTV surveillance, radio-interrupt systems and variable message signs to convey quick appropriate information to tunnel users.

Appearing at ground level as raised concrete domes, a distinctive feature of the ventilation domes are the curved ‘petal’ sections which presented their own challenges for Robertson’s installation team.  The area build-up to the domes comprised a plywood deck shaped to form a dome profile over the lower perimeter area and the eight individual vent petals.  Onto the plywood, the team installed a layer of Sika-Trocal S-felt type A protection fleece which was mechanically fixed using Sika-Trocal laminated metal discs.  This was followed by a layer of Sika-Trocal Type S 1.5mm thick light grey membrane bonded to the Sika-Trocal laminated metal discs.

The Sika-Trocal type S membrane was installed in a manner to ensure the layout of flaps gave the best aesthetic appearance to the finished roof.  The domed roof shape also required Sika-Trocal laminated metal detailing to follow the curved line of perimeter gutters and vent segments.  In addition the installation team were required to create and install a Sika-Trocal secret gutter around the base of the vent petals and a curved perimeter gutter to follow the profile of the existing curved concrete parapet at the base of the new plywood dome.

The team worked through a learning curve on the first shaft with regard to finding the best method of installation to the area and difficult detailing, and were then able to complete the Sika-Trocal works to the other three shafts in a seven day programme per shaft.

Offering exceptional weather proofing and durability, the Sika-Trocal type S membrane was ideally suited to the curved dome shape of the ventilation shafts. 

Used in Great Britain since 1972, Sika-Trocal Type S family of membranes have been recognised for proven longevity with British Board of Agrément (BBA) Certification. As a result, the BBA has given all the Sika-Trocal Type S membranes a stated life expectancy ‘in excess of 30 years’.

At 1364 metres long, the Blackwall Tunnel carries one of London's busiest commuter roads, the A102, under the River Thames between the boroughs of Greenwich in the south and Tower Hamlets in the north.  The installation of the Sika-Trocal Type S system has ensured the longevity of the tunnel’s ventilation system for many years to come.

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