Circular walk-on rooflight design and installation, London

Product: Bespoke Glazing – Walk On Rooflight

Application: 1 Blackhorse Lane, London E17

Contractor: JJ Rhatigan

Architect: AHMM

Circular walk-on rooflight design and installation

1 Blackhorse Lane, London E17

Main contractor, JJ Rhatigan, appointed Glasstec Systems to design and install an enormous, circular walk-on rooflight on a mixed-use development at 1, Blackhorse Lane, Walthamstow.

The project

1 Blackhorse Lane is a 10-storey development of 321 studio apartments, with shared amenities to the ground floor including a public café and a convenience store. There is also a purpose-built music and comedy venue, The Standard, which replaces the vacant pub and entertainment site of the same name.

The brief

• The glass was to be triple glazed with polished edges, measuring a diameter of 4800mm
• The ‘Class 1’ specification for walk-on rooflights required that it be manufactured for walking on infrequently for access to maintenance areas, not for everyday foot traffic
• Architects, Allford Hall Monaghan Morris (AHMM), wanted as little as possible of the central support beam to be visible
• AHMM also requested that the structural steel frame be hardly seen to maximise the amount of glass on show.

Glasstec Systems’ design solution

Glasstec Systems’ design of the walk-on rooflight was based on splitting the structure into two panes of glass, with each pane weighing 1200kg, resulting in an overall weight of just under 2.5 tonnes. The circle was manufactured as an inner and outer fame, made in quadrants.

The outer pane

The outer pane was produced using 3 x 10mm panes of clear toughened, low iron glass. For additional strength and to produce a thinner glass, we used 1.5mm SentryGlas® interlayers which are stronger and more rigid than traditional PVB (Polyvinyl Butyral). We also applied 100% Black Frit, a solid, opaque black ceramic paint, to permanently fuse the outer pane to the centre glass surface. For the insulated cavity, we used argon gas and a black 14mm spacer bar for thermal efficiency and to prevent condensation. We then sealed the cavity with silicone.

The centre and inner panes

The centre pane was produced from 6mm clear toughened, low iron glass, while the inner pane was manufactured using 9.5mm clear heat strengthened, low iron laminated glass. A 14mm space bar and argon gas were used for the cavity between the two panes, with a silicon seal.

Meeting the architect’s aesthetic vision

To meet the architect’s request for minimal visibility of the central support beam, we worked with our structural engineer, Marco Rossi, to design a cross beam that was only 60mm wide, weighed 200kg and spanned five metres. Despite its minimal size, the beam could easily accommodate the 2.5 tonne load.

We were also able to expose just 6mm of the structural steel frame from above to allow as much glass as possible to be displayed, as requested.

Challenges of the installation

The installation of the frame over the 5 metre diameter void was a huge challenge, from both a safety and logistical perspective, that required harness work for the installation team. Precision positioning took a full day, to ensure the frame was correctly interfaced with an external bar feature.

However, the major challenge of this project was lifting the glass into position. Many factors can affect the lifting of glass by crane, especially when each panel weighs 1140kg. The weather is a significant factor, as wind and rain can be highly disruptive and dangerous when lifting such large panels of glass over a building. Safe and experienced handling is critical for such complex manoeuvres.

We co-ordinated the glass lifting in collaboration with the JJ Rhatigan team and the lifting company. Using a mobile crane, an articulated lorry and the largest possible glass vacuum, the 15 strong team including supervisors needed to be on site for 5.30am to lift the glass into place safely and with expert precision. The positioning was professionally executed, without incident.

Project outcomes

The success of this project was down to design, innovation, detailed planning, technical expertise, and also teamwork with our fellow contractors. Working together to achieve the installation without any problems on a site located on such a busy corner of Blackhorse Lane and Forrest Road opposite a busy station, was a significant achievement and hugely rewarding.

JJ Rhatigan has acknowledged the effectiveness of the Glasstec Systems rooflight in enhancing a particular highlight of the project: “A standout feature is the striking double-height spiral staircase beneath a 5-metre-diameter rooflight, creating a dramatic central focal point.”

It was a pleasure to work with JJ Rhatigan and we hope to collaborate with the team again.

Why work with Glasstec Systems?

Glasstec Systems is a team of structural glass specialists with vast experience in multi-contractor renovations and new build projects.

Do you need structural glazing for an upcoming residential or commercial project? Get in touch with Glasstec Systems to find out how we can work together.