Cost model: School extensions

Introduction

Davis Langdon has published cost models in Building since 1994 and more than 60 cost models and updates have appeared since then. However, most of these have covered large-scale projects. Recent reader feedback has led to the development of a mini-cost model series, focused on projects up to about £1m in value.

With the continued high levels of spending on education this first model looks at the primary schools sector, with the spotlight on classroom block extensions. The government's continued commitment to investment in school buildings has led to a total capital expenditure of £5.2bn in 2005/06, of which £500m will fund improvements to primary schools.

Design issues

Designers of schools face a number of challenges. Design for children is the key issue, and design quality, flexibility, sustainability and whole-life value are also high on the agenda. The advancement of ICT in the national curriculum, increased security concerns and a desire to make greater community use of school facilities have all gained greater significance in the past few years.

Building Bulletin 99: Briefing Framework for Primary School Projects, published by the Department for Education and Skills last year, provides details of the latest accommodation standards for schools to meet modern curriculum needs. The key issues raised by the guidance reflect wider changes in the organisation of the classroom:

• Changing teaching methods, including more interactive teaching, pupil-focused development and wider use of new technology, providing a stimulating learning environment.
• Provision of multipurpose space, including practical study rooms and space for small group teaching.
• Sizing and equipping rooms to enable a range of group sizes to be taught effectively in a single space. This may mean using moveable furniture and so on. A current example of this is the debate as to whether to have computers located in shared ICT suites or in larger classrooms and the consequent effects on floor areas, furniture, storage and so on.
• Providing for long-term flexibility, including:

Room layout - particularly narrow rooms that are difficult to space-plan as classrooms

Storage - sufficient, well-located, secure and non-secure storage for teaching equipment

Design for long-term adaptation - for example, using drywall partitions rather than load-bearing blockwork

Achievement of a cost-benefit balance when investing in high-cost solutions such as moveable partitions.

• Providing direct access to the outside for play and outdoor activities, including habitat areas and so on.
• Special educational needs may require the provision of additional spaces such as learning support rooms for one-to-one teaching.
• Security - balancing safety and security with a welcoming and attractive environment is an increasingly important topic, with greater concerns about the security of pupils and valuable teaching equipment. Control of access, avoidance of concealed spaces, use of monitoring devices and lockable storage are typical responses.
• Sustainability - schools are officially expected to achieve BREEAM ratings of at least "good" but, as projects such as Kingsmead school in Cheshire have demonstrated, clients can set much more ambitious targets. Design criteria are laid down in Building Bulletin 93, including requirements for acoustic and energy calculations. In developing a sustainability strategy, a balance must be reached between the use of robust materials, ease of maintenance and capital-vs-whole-life cost.

CABE's design principles

In addition to the practical issues raised by Building Bulletins, CABE has contributed to the school design debate by putting forward these key design principles:

• Good, clear organisation
• Spaces that are well proportioned, efficient, fit for purpose and meet the needs of the users
• Generous and well-organised circulation
• Appropriate levels of natural light and ventilation that offer good environmental conditions
• Attractive design
• Good use of the site that offers a civic building presence
• Appropriate levels of security with a variety of attractive external spaces
• Robust materials that are durable and attractive
• A layout that offers broad community access and use out-of-hours where appropriate
• Flexible design that will facilitate changes in policy and technology, which allows expansion or contraction where appropriate.

Pupils at Springhill Catholic Primary School in Southampton swarm around their new classroom block, designed by architecture plb

Floor area allowance and planning

Last year's Building Bulletin 99: Briefing Framework for Primary School Projects supersedes the previous guidance published in 1996. Although classroom sizes are the same, there is greater emphasis on having enough space for practical activities and on the requirements of pupils who have special educational needs or disabilities. The main change in BB99 is a move away from area calculations to a more planning-oriented process that defines the brief and key design criteria of the school first.

At present, typical primary school classrooms are planned for 30 pupils. Under the national curriculum, primary school pupils spend most of their time in their classbase, but will also work in smaller groups with specialist teachers and resources that benefit from some variation in classroom size. Indicative areas for classrooms are as follows:

• Standard classrooms are 57 m2 - able to accommodate most activities
• Large classrooms are 63 m2 - suited to all activities and recommended for foundation-stage classes
• Small classrooms are 50 m2 - suited to numeracy and literacy activities. Use of smaller rooms means that further shared teaching areas will be needed to provide facilities such as a wet area or book corner.
• Specialist practical activities used when teaching science, design and technology, art and so on are typically taught in large or standard classrooms, or in shared teaching areas. If a dedicated room is used, a minimum of 24 m2 should be allowed.
• Allowances for circulation, administration, storage and so on need to be added to calculate overall areas and costs. An allowance of 30% is typically added for WCs and circulation. Areas based upon need should also be added for storage and so on.

Building services design criteria

The main design parameters for services are detailed in Building Bulletin 87: Guideline for Environment Design in Schools, published in 2003.

Typical criteria include:

• Heating to classrooms and administration areas to achieve 18°C , with 15°C in circulation and washroom areas.
• Ventilation rates of 8 litres/s/person in teaching areas and six air changes per hour in washrooms.
• Lighting to general areas of 300 lux, increasing to 500 lux for some practical work spaces. Entrance halls and stairs require 175-250 lux.
• Cold water storage should not exceed 25 litres per occupant. It is recommended that hot water temperature is limited to 43°C.

The single-storey extension at Springhill School is typical of the smaller projects being built across the country.

Cost drivers for classroom extensions

• Gross internal floor area
• Number of storeys - proportions of substructure and roof costs
• Wall-to-floor ratio
• Extent of cellularisation
• Degree of in-built flexibility required
• Potential impact of ground conditions on developed site
• Building envelope performance - future impact of Part L
• Influence of the existing building on the design solution
• Requirements for services content - ability to use existing plant capacity, need for additional WCs and so on
• Enhanced finishes, equipment and security to facilitate community use.

Procurement and construction issues

Working on an occupied site introduces a number of health and safety and co-ordination constraints that a contractor will need to address and that may increase preliminary costs These include:

• Stakeholder liaison - dealing with head teachers, parent representatives and so on
• Programming the works - to achieve a fixed completion date for the academic year and to minimise disruption to school activities
• Access and working hours - restrictions on the site access routes, delivery times and noisy work, including quiet times for exams
• Security and health and safety - the critical need to prevent access to the site by pupils, to manage the site to minimise risks from waste and so on, together with the typical risks found on a brownfield site.

Management of project abnormal costs and claims for additional funding is a key issue with respect to affordability and sources of additional funding. On extension projects, in addition to typical abnormals associated with ground conditions, works associated with the existing building may generate additional entitlement. These might include demolition and alteration works and planning-imposed design solutions such as matching building heights or roof materials. Other areas where abnormals funding can be secured include onerous requirements to meet BB93, requirements for specialist consultants, exceptional special needs provisions and so on.

Classroom extension cost breakdown

This cost model is based on a single-storey, three-classroom extension to a primary school. An additional room for teaching up to five pupils or for use as a special educational needs base is included. Gross internal floor area totals 310 m2 of accommodation including a 20% allowance for circulation.

The extension is a traditional brick cavity build with strip foundations and pitched tiled roofing. Access is provided from the existing school via a connecting lobby. Subdivision is by load-bearing, blockwork partitions. M&E services include heating, hot and cold water and limited extract ventilation. The scheme complies with Part L (2002).

Unit rates are as at first quarter 2006, based on a South-east location, derived from lump-sum competitive tenders. The building only cost, £1277/m2, compares with the costs collected by BCIS for horizontal school extensions, which range from £1150/m2 to £1450/m2.

The costs exclude enabling works, demolitions, external works and services. Non-fixed furniture and equipment and ICT cabling are also omitted, as are professional fees and VAT. Unit rates should be adjusted for location, site conditions, programme and procurement route.

(See graphs)