Stage 4
Technical Design
Chapter overview
The Developed Design will have been signed off by the client. Stage 4 is the opportunity to consolidate and address all statutory requirements and to ensure that the Developed Design and its Sustainability Strategy will meet or exceed the Sustainability Aspirations that were set in the Final Project Brief.
This is the point at which the detail is considered and robust means of communication, consolidation and review between members of the project team are vital. This process should not be rushed.
Responsibility for management of the Sustainability Strategy should be clearly allocated. This is crucial if there have been changes in the project team or in the project management. As new project team members are appointed, it is important to ensure that everyone involved understands the issues to date and is adequately trained to implement the requirements. This would be a good time to revisit the original Sustainability Aspirations to remind the project team and inform new team members of the underlying reasons for the sustainability targets that have been set and how the Project Strategies are expected to achieve these.
Key coverage in this chapter is as follows:
Introduction
The Developed Design will have been audited at Stage 3 against the Final Project Brief, the Sustainability Strategy and the Sustainability Aspirations. These, along with any key performance indicators (KPIs), should be clearly identified in the preparation of the detailed specification etc, together with the mechanism for providing evidence that they have been met. The Technical Design should be developed and tested against the six strategic sustainability considerations identified in the Introduction to this guide.
By the end of Stage 4, sufficient information will have been produced to demonstrate compliance with the various Building Regulation requirements in the UK (depending on the chosen procurement route), issue tenders and complete any formal Sustainability Assessment processes. The responsibilities for delivering on the Sustainability Strategy and the Sustainability Aspirations will have been clearly assigned. Any training requirements should have been addressed to ensure that everyone involved understands the Sustainability Strategy, why it is being pursued and the holistic nature of the process, which means that even minor changes can have disastrous outcomes.
Any carbon/energy declarations initiated at Stage 3 must be updated as part of a Building Regulations submission and the design stage sustainability assessment and a climate impact assessment should be prepared.
During Stage 4, forethought is required about key elements, such as airtightness testing regimes, thermal integrity testing and materials specification to ensure that they are addressed and are in line with the required Sustainability Strategy and Sustainability Aspirations.
Any perceived variations from the norm in terms of materials specification will require special consideration as contractors may not understand the importance of the specified materials, or where to source them. This might either lead to additional expense or substitutions that could undermine the Sustainability Strategy.
The consequences of any changes to the specification or design need to be clarified and Change Control Procedures discussed in order to ensure a clear line of enquiry and information that does not disrupt the Project Programme or Project Budget in the event of queries. Contributions by specialist subcontractors must clearly demonstrate compliance with the agreed Sustainability Aspirations.
Looking ahead to project completion, the building Handover Strategy and monitoring strategy – including the people to be involved and their contractual responsibilities – and the required monitoring technologies should have been identified for inclusion. The format and content of the Part L log book, or equivalent, is to be agreed and this requires a non-technical user guide to be drafted.
The Sustainability Checkpoints at the end of this stage require that sufficient technical information is available to demonstrate:
In addition, it is important that the Sustainability Aspirations are reviewed and that the project team as a whole remains both aware of and committed to them.
What are the Core Objectives of this stage?
The Core Objectives of the RIBA Plan of Work 2013 at Stage 4 are:
The Core Objective at Stage 4 is to ensure that the final design and follow-on design work by specialist subcontractors reflect the Sustainability Strategy and will meet or exceed the Sustainability Aspirations.
Reviewing the previous stages
At Stage 4 it is important to review the previous stages in order to communicate and reassert to everyone involved, in particular new members of the project team, the contents and logic behind the Sustainability Strategy that is being followed and the Sustainability Aspirations that must be achieved. This is also the time to discuss and agree responsibilities with regard to the Sustainability Checkpoints.
Why is awareness of a holistic design approach important at this stage?
It is important that the project team understands that some elements of the design may be fulfilling multiple purposes and so value engineering based alterations at this stage or later need very careful consideration.
Value engineering and holistic design 
- The thermal mass of the building may have been modelled to eliminate the need for heating in all or part of the building and reducing the thermal mass may reintroduce a need for expensive equipment as well as a space to accommodate it.
- Overhangs may have been incorporated to minimise solar penetration and prevent a cooling load; their removal will increase the servicing requirement.
- Landscaping may have been designed as an integral part of the environmental strategy to reduce heat gains or glare or to protect from wind. Changing this may expose the building to environmental pressures that will need to be remedied by other means.
- The materials specification may incorporate an element of hygroscopic mass to buffer moisture and maintain a healthy indoor climate; substitution may undermine this element of the Sustainability Strategy.
What are the implications for the Cost Information?
By Stage 4, the Sustainability Aspirations should be fully integrated with the perception of project quality and cost effectiveness so that they cannot be compromised. The project team should also be aware of the potential knock-on implications of value engineering on performance and sustainability targets and the need to examine changes carefully to ensure that they do not give rise to additional complications.
Following the preparation of the detailed specification, the project’s cost consultant can create a detailed elemental cost plan and this should be agreed with the client. In the event of the need for value engineering, revisit the schedule of possible reductions identified at Stage 3: page 139. This should have clearly identified any aspects of the design where cost reductions would seriously undermine environmental objectives.
Specific Project Strategy tasks for consideration at the Technical Design stage
Ensure that the consultation is progressing
Ensure that the affected community is aware of the project progress and timescales and recognises that their input is a valued part of the process. Any specified requirements for consultation to be undertaken as part of a formal sustainability assessment should be addressed and protocols strictly followed.
Coordination of the passive design strategy
Revisit the guidance given at Stage 3 to ensure that there are no conflicts between the various requirements, and that only the most efficient and resource-conserving systems (conveying, heating, cooling, water, lighting) have been specified (and without oversizing).
A hybrid ventilation strategy and implications for building operation 
A hybrid ventilation strategy was developed for an Environmental Education Centre to meet the sustainability target for energy use, which exploited the opportunities afforded by the site and the massing of the building. The main space has a high ceiling to enhance air quality in the occupied zone. It is naturally ventilated with passive stack ventilation for most of the year and a back-up mechanical system for use when the building is busy and the weather cold. This allowed the maximum output of the heating system to be reduced by 35%, making it cheaper to install and run.
The units are controlled by a manual ‘on’ and a timed ‘off’ switch and they are linked to movement detectors in the spaces they serve. Their fan speed slows as the CO2 level in the extracted air reduces. Essentially, the control systems are designed to minimise their use, avoiding the possibility of the systems running when they are not required.
This system relies on the building users learning how the building actually performs in certain circumstances and actively managing the building, by opening and closing windows in response to changing conditions or using the mechanical system when it is cold.
What are the important aspects of the materials strategy at this stage?
A strategic approach to the assessment of environmental credentials of suppliers and contractors, including a prequalification statement for materials and products, will be helpful in the development of the project. During this process certain materials may be excluded and others chosen and this must be communicated clearly in the contract documentation as any changes could potentially undermine the Sustainability Strategy.
The use of materials with minimum chemical and mechanical transformation, and therefore low embodied energy and pollution, may be a strategic consideration for certain clients. Some organisations have a proactive approach to indoor environmental health to avoid building-related ill-health and therefore favour non-toxic, healthy and hygroscopic materials. Others may have specific exclusion lists of toxic materials (Red Lists) that might be associated with health risks or considered difficult to dispose of at the end of their useful life, with consequent implications for whole-life costs. Identify any significant lead times for environmentally benign materials, products or systems and ensure that these are highlighted in any tender documentation:
- Appraise the availability of local materials and confirm that they are suitable in terms of the Sustainability Strategy.
- Research environmental performance and provenance of materials and components. Be attentive to potential pollutants in those from recycled sources.
Energy requirements
The Project Strategies will be sufficiently detailed to allow energy calculations to be refined, regulatory submissions made and the anticipated energy demand checked against the Sustainability Aspirations. The importance of the form and fabric, as well as any controls, needs to be understood within the project team and communicated to new members, particularly the contractor, who has the responsibility for delivering the project on site, particularly where there is a need for special attention to certain aspects of the construction, such as ensuring airtightness.
The energy consumption of all components should be considered with attention to regulated and unregulated loads, including domestic hot water, small power and artificial lighting, pumps and fans as these may constitute a significant proportion of the overall energy consumption in use.
Ensure that artificial lighting and daylighting strategies and controls are mutually supportive in delivering low energy consumption.
Testing
Identify specific aspects of the construction phase where performance to a defined standard will require testing and validation, including airtightness, thermal integrity and ventilation.
It is important to plan for the delivery of the airtightness strategy, which requires consideration of the air barrier strategy at this stage.
Airtightness requirements
The project specifications must detail:
- the air leakage target and the air barrier strategy
- the requirements for various work packages to incorporate particular items of work that contribute to the airtightness of the building
- the project requirements for air barrier drawings, checks of air leakage design, site air leakage audits and preliminary and acceptance air leakage testing
- requirements for management strategies to ensure that workmanship is satisfactory to achieve the airtightness target
- responsibilities for works, particularly in the event that the result of the air leakage testing is unsatisfactory and remedial sealing and additional air leakage testing are required.
A robust air barrier strategy
The air barrier strategy is a summary of the fabric choices that facilitate the achievement of the airtightness target. The first principle is to adopt a single layer, with junctions between materials as necessary. Multiple layers merely increase the scope for divided responsibilities and failures in workmanship. The strategy must not be undermined over time and due to lack of robustness. Ideally, the air barrier strategy will be summarised on a drawing to ensure that it is effectively communicated and incorporated into site inductions.
Identifying a contractor that can and will address sustainability
It is vitally important to ensure that the contractor has the ability and attitude to address sustainability issues enthusiastically. Preparation of prequalification questionnaires (PQQs) for the potential contractor should clearly address sustainability and refer specifically to the Sustainability Strategy and Sustainability Aspirations. The KPIs should be identified and allow for discussion on responsibilities. For non-traditional procurement processes this may happen at an earlier stage. The track record of the contractor should be identified and an open discussion should identify any concerns connected with innovation and the extent of any training required. Various procurement routes are discussed at Stage 1 and Table 4.1 highlights the pros and cons of each.
| PROS | CONS | |
| Traditional contract | The client signs off all design decisions, including changes made during construction, the exception to this being Contractor Designed Portions, which are aimed at passing Technical Design responsibility for specific trades to the main contractor | The contractor’s team is identified and contracted after the majority of design decisions are made, which limits their input. Where Contractor Designed Portions are included, those designing these elements of the Technical Design are usually far removed from the Design Concept and the Sustainability Strategy |
| Design and build (including contractor-led) contract | Design risk is moved from the client to the contractor, giving more cost certainty | The design team’s responsibility is to make a profit for the contractorwithin the scope of the Employer’s Requirements |
| Management contract | Programme risk is moved from the client to the contractor, but the client retains sign off on all design matte rs | The client relinquishes cost certainty and, as the design process continues during construction, it may be difficult to retain a focus on the Sustainability Strategy |
| Self-build | The client retains complete control | The client has sole responsibility |
Include schedules of the necessary reporting procedures in the contract documents. Identify the information required from the contractor to assess contractor-designed elements that must meet the Sustainability Aspirations. Agree responsibilities and routines for data recording to monitor performance.
Review the final details, including subcontractors’ packages for airtightness and continuity of insulation.
Complete consultation with specialist subcontractors with regard to all Technical Design issues and review information packages to check that they are coordinated, complementary and support all components of the Sustainability Strategy.
Pre-tender discussion
When a traditional procurement route is being used, it is increasingly common to invite bidding contractors to a pre-tender meeting where questions concerning the information packages can be asked in a forum of open and shared enquiry. This allows all the bidding contractors to seek guidance on issues, standards and expectations with which they might be unfamiliar and reduces the risk of a pricing strategy that reflects unnecessary concerns and inflated perception of risks. Typically, questions might concern:
- sequencing
- airtightness standards and test procedures
- project strategies
- materials, including sources and lead times for unfamiliar items
- handover expectations
- post-handover involvement
- Change Control Procedures
- lines of responsibility for sustainability issues
- post-occupancy monitoring requirements
- similar projects.
These questions are equally relevant for other forms of procurement in the early stages.
The sustainability aspects of the Final Project Brief, Sustainability Strategy and Sustainability Aspirations need to be on the agenda of all progress meetings. The requirements of any formal sustainability assessment being sought will also need to be reviewed to ensure that the appropriate time to undertake these is not missed.
Reviewing and updating the Handover Strategy
Thinking ahead to Stages 6 and 7 (handover, commissioning and building management) is vital at this stage to ensure that the building will operate as intended.
Revisit the Handover Strategy. Specifically, discuss the issues of building management and determine the set points of user controls to achieve efficiency and comfort with the person(s) responsible for managing the completed building to ensure that they are fully in agreement with the requirements and the strategy.
Review the control systems to ensure that they are appropriate and intuitive and not overly complex. If possible, involve building management and users in reviewing the environmental control systems, including manual and automatic controls to ensure that they are fit for purpose. Engage the eventual users or their project team representative in a discussion about the required contents of a simple, appropriate user guide.
User guides
A full set of operating and maintenance manuals can be very intimidating. They are necessary in so far as they contain all of the information required to run, maintain and eventually replace the building services, but they provide too much information in too technical a format to be useful as a day-to-day guide.
A user guide has a different aim. Written in plain English, it explains, as simply as possible, the services strategy – why the various services have been installed, what they are supposed to do, when they are meant to be used and how to tell when they are not working properly.
Sensors and monitoring equipment for movement, lighting levels, temperature, CO2, relative humidity etc are rapidly becoming more affordable. Such sensors may well be linked to the building energy management system (BEMS) and used to control different systems in a coordinated way.
Modern electronics and computing power have allowed for increasingly sophisticated control systems to be developed, which can often be controlled remotely. However, where projects do not warrant a trained building management team or it cannot be guaranteed that the end user will be proactive in controlling the building, then simpler controls, ideally of the ‘manual on and manual/auto off’ type, may prove just as efficient in practice. If appropriate, arrange for specialist training and/or the provision of non-technical guidance on the control systems.
Involve the client/users/building managers in discussions on issues concerning maintenance and operation in order to ensure that procedures are fully planned, affordable and adequate, with minimum adverse environmental impact. Agree any technical requirements to support the monitoring strategy, including the monitoring technology – both data gathering and analysis – and ensure that this is agreed in the budget, with responsibilities and personnel clearly identified.
Reviewing and updating the Health and Safety Strategy
Update the Health and Safety Strategy and organise any training required in the use of innovative materials or components with which the project team may be unfamiliar.
What factors are important in reviewing the Design and Project Programmes and Change Control Procedures?
At this stage, the supply of any specialist materials and products should have been coordinated. A chain of command for approval of any change requests should be in place to ensure that these do not undermine the Sustainability Strategy or create delays.
How does sustainability impact on the Key Support Tasks at Stage 4?
The RIBA Plan of Work 2013 lists eight Key Support Task at Stage 4. The Sustainability Strategy, Construction Strategy and Handover Strategy remain fundamental to achieving the Sustainability Aspirations and are dealt with in detail at this stage. Of the remaining five tasks, four revisit the Key Support Tasks listed at Stage 3 and require the project team to review, update and take action as necessary.
What are the Sustainability Checkpoints at Stage 4?
- Is the formal sustainability assessment substantially complete?
- Have details been audited for airtightness and continuity of insulation?
- Has the Building Regulations energy submission been made (this is Part L in England and Wales, Part F in Northern Ireland and Section 6 in Scotland) and the design stage carbon/energy declaration been updated and the future climate impact assessment prepared?
- Has a non-technical user guide been drafted and have the format and content of the Part L or equivalent log book been agreed?
- Has all outstanding design stage sustainability assessment information been submitted?
- Are building Handover Strategy and monitoring technologies specified?
- Have the implications of changes to the specification or design been reviewed against the agreed Sustainability Strategy and sustainability targets and captured in the Change Control Procedures?
- Has compliance with the agreed Sustainability Strategy and sustainability targets for contributions by specialist subcontractors been demonstrated?
Climate impact assessment
There is general consensus that the UK climate has changed and will continue to change, the prevailing trend being towards warmer, wetter winters and hotter, drier summers with an increasing number of extreme weather events.
These trends are reflected in the quinquennial review of those Eurocodes which relate to structural loadings for wind and snow.
Simply put, buildings in the future will have to cope with greater solar gains, exacerbated by the presence of heat islands in urban centres, and withstand more adverse weather for a greater proportion of the time with shorter recovery periods between.
Any Sustainability Strategy has to look ahead to the conditions that may prevail throughout the building’s lifetime and not just those that predominate during design and construction.
What are the Information Exchanges at Stage 4 completion?
In the required review and update of the Sustainability Strategy, include specific reference to the Handover Strategy, building management, the controls and commissioning strategies and to future monitoring. Identify the person or people responsible for all of these aspects. Ensure that the project team remains fully aware of the Sustainability Strategy as it develops throughout the project.
4 Chapter summary
At the end of Stage 4, any formal sustainability assessments that were required will be complete. These may take the form of an agreed approval in respect of certification requirements or may be a review against the original Sustainability Strategy, Final Project Brief and Sustainability Aspirations.
All regulatory aspects will have been addressed and the necessary submissions and approvals received. The future users and building managers will have been identified and appropriate technical and non-technical user guides drafted, along with the requisite Handover Strategy. Any monitoring equipment will also have been agreed and costed.
Compliance with the agreed Sustainability Aspirations and KPIs by contractors and any specialist subcontractors will have been clearly and explicitly demonstrated.
The contractor will be aware of the implications of changes to the specification, and the procedures for raising issues about any changes and timely response will be clearly stated.