Applying design codes for modular construction methods on large-scale developments
Nov 24, 2020
This case study is based on work carried out during a year-long placement as Principal Urban Design Officer for Greater Cambridge Shared Planning Service (GCSPS) between April 2019 and March 2020.
It consolidates the challenges and some practical reflections from using design codes to review the reserved matters application for Northstowe Phase 2A, and to explore the different ways of negotiating, reviewing and applying design codes for developments that use modular construction methods.
DESIGN CODES IN GREATER CAMBRIDGE
Design codes have been used in the development within Greater Cambridge since 2007 for the sites Trumpington Meadows (approved 2010) and Clay Farm (approved 2011). In May 2012, South Cambridgeshire District Council and Cambridge City Council jointly published informal guidance on using design codes for strategic Development Sites within the ‘Cambridge Fringe’ areas. Since the 2012 guidance was prepared, other codes have been produced for development sites within the Greater Cambridge area, with varying degrees of success in terms of improving the quality of design at the reserved matters application stages and of ensuring the quality of materials and details used in construction. These include Eddington, Cambourne, Northstowe New Town, Northwest Cambridge and ‘Wing’.
Design codes were useful in securing the design quality of Northstowe 2A during the reserved matters planning application process, however, GCSPS needed to adopt a flexible approach to applying the approved codes to maximise the potential benefits of off-site modular construction methods.
NORTHSTOWE PHASE 2 CASE STUDY
Northstowe is a development of 10,000 homes, with a new town centre as well as education, leisure and employment facilities on the site of the former RAF Oakington base and surrounding farmland between Cambridge and Huntingdon. The site is being delivered jointly by the master developers, Homes and Communities Agency (HCA), and Gallagher over a period of 15-20 years. Phase 1 of the development received outline planning permission in April 2014 (S/0388/12/OL) and, following subsequent successful reserved matters applications, is currently under construction. Outline planning permission for Phase 2 was granted in January 2017 (S/2011/14/OL) and outline planning applications for Phase 3A and 3B are currently being determined (3A: 20/02171/OUT and 3B: 20/02142/OUT).
A hybrid planning application for Phase 2A (S/3499/19/RM) was submitted by the developer, Urban Splash, comprising of reserved matters for 406 dwellings, including affordable housing provision, non-residential floorspace, landscaping, open space and associated infrastructure. Proctor and Matthews architects masterplanned the site, and the modular homes were designed collaboratively by Proctor and Matthews and shedkm. The scheme received planning permission in February 2020 and won a housing design award in July 2020.
Two design codes were relevant to the review of the reserved matters application for Phase 2A:
Northstowe Phase 1 Design Code, by HCA and Gallagher and HCA. This includes strategic principles for the entire development along with specific codes for Phase 1. The Phase 1 design code was approved in May 2014 to discharge Condition 8 of the Phase 1 outline application.
Northstowe Phase 2 Design Code, by Tibbalds and Chris Blandford Architects. This was approved in April 2017 to discharge Condition 9 of the Phase 2 outline application.
CHALLENGES OF APPLYING DESIGN CODES AT NORTHSTOWE
The design codes produced for Northstowe did not consider that Phase 2A would be built using off-site using modular construction practices. This method of construction has very specific economic, structural, and material requirements that presented challenges when negotiating, reviewing and applying the existing design codes during the planning process for Phase 2A.
The main challenges were:
Modular construction relies on a limited number of house types and it can be prohibitively expensive to include features such as corner windows, gables or bay windows that are often prescribed through design codes that are developed with traditional construction techniques in mind.
The timber frame structure used for the Phase 2A dwellings is most efficient when houses are arranged in terraces. This can make variation in building forms and elevations difficult to achieve, leading to repetitive street typologies across larger sites. A good design code cannot replace the role of a skilled architect when it comes to the detailed design of streetscape features.
Modular construction allows the home buyer a degree of flexibility over the internal layout of each house, for example, there is the option for the living room and kitchen to be on the ground or upper floor. By specifying that living spaces should be on the ground floor, the design codes for Phase 2A did not allow for this flexibility.
The material palette in the design codes specified traditional materials that did not consider the opportunities for innovation afforded by modular construction processes; for example, ceramic tiles were more suitable as the primary cladding material for houses in Phase 2A, rather than the brick prescribed in the design code.
The design codes for Northstowe are overly focused on prescribing too many specific character areas. Ultimately the character of development parcels within Phases 1 and 2 differ on account of the methods of construction (modular vs traditional) and the ambition of the developer and design team rather than the prescriptions of the design code.
The vast amount of information contained within the two sets of design codes relevant to Phase 2A was overwhelming. Much of the site-wide information from the Phase 1 design code was repeated in the Phase 2 design code.
There was conflicting information in the outline planning permission and the design codes. For example, the storey heights in the Phase 2 design code are not consistent with the outline parameter plans.
The actions set out above gave GCSPS officers and Members the confidence to adopt a flexible approach to design code compliance during the review of the reserved matters planning application.
GCSPS officers permitted flexibility over superficial elements of the design code (materials, features, ground floor uses), which, if applied according to the approved design code, would have been prohibitively prescriptive in the context of modular construction practices.
At the same time, officers maintained the importance of the strategic design codes to ensure that the principal elements of the masterplan remained embedded in the proposals as they developed. For example, the Northstowe design codes included useful specifications for the architecture of the busway, which extended beyond Phase 2A into the adjacent development parcel. The code also specified different edge conditions that were important for the character and integration of Northstowe within the wider context by prescribing areas where development should follow a consistent building line that forms a clearly defined built edge to the countryside, and setting maximum storey heights along the sensitive boundary with an existing settlement. At the scale of individual dwellings, the design code set out principles for the effective integration of car parking, bicycle storage and bin storage.
Applying this approach to the Reserved Matters submission for Phase 2A resulted in the following outcomes:
The design codes allowed GCSPS to control key elements of the strategic design in the reserved matters planning applications, while also allowing the flexibility for innovative design solutions to develop through the detailed design process. This approach resulted in a quality of design that exceeded the expectations of the design codes and outline applications.
Communicating the added benefits of modular construction resulted in the council purchasing the affordable housing at Nothstowe 2A.
Phase 2A received planning permission in February 2020.
Phase 2A received a Housing Design Award in July 2020.
The complexities of modular construction (repetitive form and structural limitations and flexibility of elevations) mean that a good design code cannot replace the role of a skilled design team and skilled and well-resourced built and natural environment professionals within the local planning authority.
A concise, strategic design code that is updated as development progresses through phases is more useful than several overly prescriptive documents that repeat information.
Design codes that prescribe street sections across different parts of the site are particularly important for developments that use modular construction methods to ensure variation across development.
A benefit of modular construction is that it can give residents a choice over the internal layout of their house. This means that design codes must allow for this flexibility in terms of ground floor uses and elevations. If successful, this can provide subtle variation across the elevations of modular developments that enhance character.