Large Venting Rooflights Installed at Cambridge University

Roof Glazing by IQ Integrated into St Johns College Renovation

IQ Glass have just completed our largest venting rooflight installation ever. The five large venting rooflights were an integral part of the cafe and community renovation at St Johns College, Cambridge University.

oversized venting rooflight on a roof with a man in a high vis stood to the left of it

The new cafe, buttery dining room and bar are located within the south west corner of the Second Court building of St Johns College. The Grade I Listed building was built in 1599 and housed an existing buttery dining room that had been built in the 1970’s. The renovation – led my architects MCW – occupies the historic Kitchen Lane which lies along the boundary between St Johns College and Trinity College.

A large element of the successful planning application for the historic building extension, was the drive to create both a freestanding structure that protected the existing historical buildings as well as an energy efficient build that strove towards the College’s commitment to carbon reduction.

The design and specification of the building envelope was therefore a significant element of the build and design.

Designing the Large Venting Rooflights

IQ Glass were approached to provide the bespoke roof glazing as part of the build.

The design intent by MCW was to create a ‘funnel’ of light through the oak structure. The bespoke timber roof curves upwards towards the location of each rooflight which was required to be both frameless, high performing and opening for ventilation.

In addition to the high specification requirements and the large opening sizes wanted, none of the rooflights were square.

Each rooflight within the cafe design was an irregular trapezium, with two parallel sides and corner angles ranging from 99 degrees to 81.

hand sketch of a non square rooflight bespoke detail

We began by using our A.R.E.S. rooflight system as the basis for all the designs. This venting rooflight is a thermally broken aluminium framed vent. Not only is it minimally designed from an external perspective – which was important for such a sensitive location - all motors are integrated into the frame so creates a frameless interior design as well.

As IQ fabricate these ourselves, it allowed us much greater flexibility over the design and possibilities of the roof glazing.

Working with MCW the team at IQ investigated and modelled the sizes of rooflight wanted within the design to ensure that the weight and weight distribution were able to be fully handled by the motors integrated into the frame.

The largest of the opening rooflights was 3.2m wide by 2.6m long, using a glass unit that weighed approximately 399kg.

In order to achieve this large venting rooflight size, we used four integrated chain drive motors in the longest edge to provide an even distribution of force along the opening edge as well as enough power to lift the large glass panel.

The smaller rooflight design weighed approximately 249kg and three integrated motors were used along the longest 2.3m edge of the opening rooflight.

a hand sketch of a bespoke rooflight detail for a frameless opening design

Electronic Controls of the Large Venting Rooflights

In order to achieve maximum flexibility over the ventilation of the cafe space, each rooflight was wired independently back to a control box with one wall mounted switch for each rooflight.

A rain sensor and wind sensor were also integrated into the design to ensure that the large opening rooflights closed automatically in rainy or windy weather.

an internal view of a large opening rooflight in a timber roof

Completed Design of the Large Venting Rooflights

The large venting rooflights in the timber roof structure were angled towards Trinity College in order to capitalise on all natural light available to the new space which was surrounded by buildings. Each large venting rooflight sits within the bespoke oak roof structure, funnelling light into the eating areas.

The aluminium framing was finished in RAL 7021 with the glass stepped over the frame for an all-glass external design.

a large auto rooflight on the top of an extension to a listed building

All motors are built into the fixed frame of the A.R.E.S. rooflight so these are always hidden, allowing a modern and minimal internal finish.

Within the rooflight frames, the glass was double glazed, with a solar control coating to protect against overheating. The internal pane of the DGU was a laminated panel with a strengthening interlayer to strengthen the glass at the large size.

In addition to the large venting rooflight designs, IQ also provided a tricky strip rooflight that spans between the new freestanding timber structure and the wall of the listed building. The frameless strip rooflight was designed to intricately cut around the features of the existing building, alternating between widths of 0.4m to 0.8m across the 35m length.