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Rooftop Development, Hove
Cityzen designed this rooftop residential development using Sterling OSB Zero as the principal construction material.
Competition

RIBAJ: Raise The Roof

Sponsored By
Judging Panel

Chaired by The RIBA Journal, the panel includes representatives from Norbord Europe, White arkitekter, HKS Architects and one of last year's winners.

We designed this pair of modern dwellings for the 2019 ‘Raise The Roof’ competition. Our rooftop development is deliberately distinct from the design of the existing building. It seeks to enhance historic features, whilst at the same time add its own architectural merit.

This project exemplifies how Cityzen responds to a client brief and the factors that can influence our design choices.

The competition sought “proposals for transforming redundant urban roof spaces to new uses, formed predominantly from OSB. This could be residential, mixed-use, commercial, or for communal/leisure purposes.”

We chose residential, as Brighton & Hove Council has set a target of 11,300 additional homes (minimum) across the city by 2030. This is a considerable challenge given the specific natural constraints to the city (the sea to the South, South Downs National park to the North, and surrounding towns to the East and West).

Appropriating urban roof areas is a way to maximise delivery within the city and increase its urban density. It would achieve much-needed housing stock without adding to the urban sprawl, and make use of existing infrastructures such as public transport routes (reducing car dependency). Rooftop developments provide new views of the city landscape, giving more residents a connection with nature (sea/sky/the Downs).

We were free to use an existing building of our choosing. Our nominated property was an Edwardian villa with available rooftop space for residential accommodation. It is one of many suitable flat roofs across the city, making our proposal viable on a larger scale.

The brief stated “pre-fabrication, panels or CNC fabrication may all be considered. Other materials may be used to clad and fit out the proposal but structural integrity is intended to be predicated on the use of Sterling OSB Zero.”

Sterling OSB Zero has lightweight yet high strength features, making it ideal for a sustainable, independent self-supported structure over an existing building. Our design uses OSB based modular SIPs for the roof, walls and floors. This offers excellent structural performance and, at the same time, constructive lightness. SIPs have increased thermal, acoustic and air tightness properties, so they also help with the building’s overall performance.

The new accommodation sits lightly over the existing building, recessed from the front façade, creating a front terrace with views to the sea. A central open patio provides a common space for the two dwellings. The patio forms the core of the internal layout, giving light to the rooms that are organised around it. Circular skylights feature in all of the bedrooms, giving a sense of space and connection to the outside world.

The new dwellings would be delivered to site in pre-fabricated panels and craned into place. The flooring consists of an independent grillage system to raise the rooftop development over the existing roof, to allow for drainage and services runs. Our design specifies a zinc finish for the roof, installed over breathable membrane and fixed with stainless steel clips. The exterior walls are clad with Lunawood Thermowood. Modular staircases provide independent access, as required by the brief.

Offsite construction in a factory environment reduces errors and doesn’t suffer from bad weather delays. This, along with quick assembly onsite, would minimise disturbance to the neighbours living below.

Norbord Sterling OSB Zero

Note: designs were not required to adhere to current building guidance. For more information about ‘air-rights buildings’ take a look at this article from Designing Buildings Wiki.