Stage 2: Assess and Plan
The second step of the whole building approach is to assess and plan.
Assimilating information, identifying opportunities and constraints
An important first step in the assessment process is to review all contextual information collected in Stage 1: Gather Data and Surveys to ensure it is thoroughly understood and considered.
Opportunities and constraints should be identified and recorded. These will vary widely depending on context. For example:
- some interventions may be easier and more economical to undertake when a building is being repaired, altered, extended, or the services replaced
- where buildings must remain occupied, the level of disruption and relative cost may be prohibitive
- building use and occupancy levels will influence decisions around feasibility of interventions
- where a building was in poor condition, necessary time may be needed following repair works for damp fabric to dry naturally prior to other works being undertaken
- if a building is listed or in a conservation area, the range of acceptable improvements must consider heritage designation and significance
- budget and grant funding opportunities are key factors to consider
Appraising options, identifying interventions
All possible mitigation and adaptation interventions should be appraised in response to the specific context, opportunities, and constraints of the project. Interventions should be assessed to establish associated technical risks, benefits and cost effectiveness, and appropriateness. They should also be evaluated against the project objectives. This includes:
Risk based assessment
Risk based assessment helps identify the technical risks of available interventions to establish which, if any, are suitable and applicable, accounting for the building's context. This might include undertaking moisture, overheating and/or climate risk assessments.
The same high-level principles that apply to the repair of historic buildings should also be considered throughout assessment, design and specification of interventions:
- Only techniques and materials that have been demonstrated to be appropriate to the building fabric should be used. These will normally be the same as the original or host material. When this material is no longer available or appropriate, the intervention should employ a material that has compatible properties, both technically and aesthetically, and has been proven
- Interventions should maximise the life expectancy of significant building fabric consistent with sustaining its significance
- Interventions should be technically feasible, practicable and should not prejudice future interventions when they become necessary
- All works should be adequately recorded, and the records made available for others who may take on the building in the future
- Interventions should contribute to, or at least not compromise, future climate resilience, management, and maintenance
Cost benefit analysis
Cost benefit analysis of available interventions helps establish which, if any, are beneficial, cost and carbon efficient, accounting for the building's context, including climate change resilience.
This should identify whether interventions for energy efficiency or climate resilience have an economic pay-back period and the whole life carbon cost of implementation does not exceed the operational carbon reductions archived. This should be identified if installed on its own and/or as any recommended package(s).
This should identify any benefit in implementing adaptation measures to safeguard the efficacy of mitigation measures. For example, including external solar shading or securing thermal inertia, to ensure energy and carbon savings are not undermined by future cooling needs.
There are a number of standards in use or development which aim to define 'Net Zero' and measure whole life carbon (WLC) in the construction industry, however there is not yet a nationally adopted method. Current tools and methodologies to do this include:
Heritage Impact Assessment
Mitigation and adaptation interventions to a historic building may impact the building's significance. The benefit of interventions need to be carefully considered and balanced against impact on heritage assets.
A Heritage Impact Assessment helps establishes the best way to accommodate change to heritage assets and which, if any, interventions are justifiable, accounting for the building's designation and significance.
Heritage Impact Assessments go further than Statements of Heritage Significance by detailing the impact of a proposal(s) on significance. More information can be found in Statements of Heritage Significance: Historic England Advice Note 12.
A resulting Heritage Impact Assessment should provide appropriate and proportionate information needed to understand the impact of the proposals on the significance of any heritage assets affected. Local authorities have a requirement for this type of assessment and statement to be submitted with applications for designated heritage assets and provide guidance on how to complete them.
This can give decision makers the information they need to understand the reasons for a proposal and to weigh up the risks and benefits. Good information, available from the outset, can speed up decisions, reduce costs and lead to better overall design.
Whole life carbon and environmental impact assessment
Whole life carbon, resource intensity, and environmental impact of mitigation or adaptation choices should be factored into decisions, not just the potential saving in operational energy and carbon. Some alterations can cost more in energy and carbon than they save during their service life.
Making energy efficiency improvements to existing buildings has been shown to be at least 4% better (and in some cases up to 60%) than if you were to demolish and replace when considering carbon within a whole life cycle analysis. Considering lifecycle analysis also allows you to consider the environmental sustainability of your choices more widely, which can support any climate resilience measures you take, as well as the whole building approach.
Energy Sufficiency is an essential part of a sustainable energy future. The principle prioritises a shift away from efficiency alone and towards using less energy in absolute terms to deliver well-being within planetary boundaries.
Learn more:
Determining priorities
The measures finally selected need to form a coherent and well-integrated package. For example, fabric improvements that reduce air infiltration should be accompanied by a ventilation strategy to remove excess moisture and maintain indoor air quality.
Interventions should prioritise occupant and building health. It is important to consider the interactions between the measures at every stage to ensure they are properly integrated. A successful whole building approach does not mean all work must be undertaken in one phase but can be undertaken over a period of years where appropriately planned. Undertaking works phases can:
- suit budget or funding constraints
- allow savings from early energy efficiency improvements to fund later interventions
- enable interventions to be incorporated with planned maintenance or improvements
- prevent unnecessary capital and carbon expenditure at any stage
- ensure single measures funded by grants or other financial incentives fit into a robust whole building approach
- minimise the potential for negative issues caused by isolated single measure or fabric first approaches, such as increasing moisture risk, causing mould growth and reducing internal air quality
Historic England guidance summarises practical energy efficiency improvements and considers their respective benefits and technical risks. The measures are arranged in order of priority and represent a step-by-step approach to energy efficiency improvements, setting out an 'energy efficiency hierarchy'.
Producing a plan
A plan should not be a fixed document, it must remain dynamic and iterative to allow later phases to be adapted as new information arises. This enables the plan to be adjusted in response to any gains made and allows time to uncover and deal with unintended issues or if anticipated outcomes are not being achieved.
The plan should set out suitable and practicable short-, medium- and long-term interventions that ensure they are properly phased, integrated and technically compatible.
For a scheme to be successful, adequate and timely, funding and access to appropriate professional expertise and practical skills will be needed. The plan should be realistic and allow sufficient time to prepare the detailed design and specifications, obtain any necessary statutory consents and carry out the work.
The plan should be appropriate in its level of detail and interventions and should be passed to successive occupants or owners. As well as information needed under the Building Safety Act, it should set out:
- key building information including the energy performance of the existing building and basis on which this has been estimated or measured
- project aims and objectives, opportunities and constraints within its context
- risks-based assessment and cost-benefit analysis and their conclusions
- Heritage Impact Assessment and its concluding statement
- scope of interventions therefore proposed and their interdependencies
- phasing of interventions proposed and quality assurance process to minimise risks, unintended consequences, and the performance gap
- a plan for monitoring and reporting energy and carbon consumption
The performance gap
Measures installed to reduce energy use in new and existing buildings sometimes fail to achieve the savings predicted. The reasons for this 'performance gap' include:
- failure to address repair and maintenance needs of the building prior to intervention
- incorrect assumptions about the thermal performance of existing buildings
- inaccuracies in the data and models used to predict energy performance
- energy consumption in a building prior to improvement is overestimated (pre-bound effect)
- inadequate design and specification of improvements
- poor installation, integration, and commissioning of improvements
- ineffective or confusing control systems
- building occupancy and patters of use occupant behaviour- 'comfort taking'
A 'rebound effect' may occur when energy efficiency improvements lead to behaviours that increase energy consumption. For example, when a heating system becomes less expensive to run, it may be used more frequently or at higher temperatures than before. Savings may also be less than expected if the energy consumption in a building prior to improvement is overestimated.
