Sustainability Assessment, Measurement and Certification

Introduction and context

Sustainable construction requires more than the installation of efficient equipment or the use of environmentally preferable materials. It requires evidence that a project reduces environmental burdens, supports human well-being, remains economically viable and performs as intended throughout its life cycle. Sustainability assessment provides the methods for producing that evidence. It includes the selection of indicators, measurement of performance, comparison with benchmarks, verification of claims and communication through certification systems.

In practice, sustainability assessment operates at several levels. A material may be assessed through a life-cycle assessment; a building may be assessed for energy, water, indoor environmental quality and ecological impact; an infrastructure project may be assessed for resilience, community value and whole-life carbon. Post-occupancy evaluation then tests whether predicted outcomes have been achieved after use begins. Certification systems such as LEED, BREEAM, EDGE, Envision and national schemes organise these assessments into structured frameworks.

Assessment is not automatically synonymous with sustainability. A project can obtain a certificate while performing poorly in actual operation, especially where design predictions are inaccurate, credits are selected strategically, or operational data are unavailable. At postgraduate level, therefore, sustainability assessment must be understood as both a technical activity and a governance process involving boundaries, assumptions, evidence, incentives and professional ethics.

Learning objectives

By the end of this chapter, the learner should be able to:

1. Explain the purpose, scope and limitations of sustainability indicators and assessment systems.

2. Select appropriate environmental, social and economic indicators for a construction project.

3. Apply benchmarking, normalisation and basic performance-gap analysis.

4. Compare the logic and application of LEED, BREEAM, EDGE, Envision and national rating systems.

5. Design a post-occupancy evaluation programme.

6. Critically assess certification evidence, greenwashing risks and ethical responsibilities.

7. Recommend an assessment and improvement strategy for a building or infrastructure project.

1. Foundations of sustainability assessment

1.1 Assessment, measurement, benchmarking and certification

These terms are related but not interchangeable.

Measurement is the observation or calculation of a performance quantity, such as annual electricity consumption, potable-water use, construction waste diversion or occupant satisfaction. Measurement may use meters, surveys, site records, laboratory tests, simulations or life-cycle databases.

Assessment is the interpretation of measured or estimated data against objectives, criteria or reference conditions. It asks whether performance is acceptable and why.

Benchmarking is systematic comparison with a reference group, standard, target, baseline or best-performing case. A benchmark may be regulatory, historical, peer-based or aspirational.

Certification is a formal statement by an authorised or recognised body that a project has met defined requirements, usually after documentation review, audit or third-party verification. Certification is evidence of conformity with a system; it is not a guarantee that every sustainability outcome is optimal.

A sound assessment process should answer five questions:

• What is being assessed?
• Over what life-cycle period and geographical boundary?
• Which indicators represent the intended outcomes?
• What evidence supports the result?
• How will uncertainty and underperformance be managed?

1.2 Dimensions of performance

The conventional three-dimensional model considers environmental, social and economic performance. Contemporary practice adds governance and resilience because decisions, accountability and response to disruption strongly influence long-term outcomes.

Environmental indicators may include operational energy, embodied carbon, water withdrawal, waste generation, land disturbance, biodiversity impact, air emissions and refrigerant leakage. Social indicators may include thermal and visual comfort, indoor air quality, accessibility, health, safety, labour conditions, community displacement and user participation. Economic indicators include capital cost, operating cost, maintenance cost, productivity, asset value and life-cycle cost. Governance indicators include transparency, stakeholder engagement, procurement integrity, data quality and responsibility for monitoring.

Indicators should be relevant, measurable, comparable, sensitive to project decisions, and difficult to manipulate. A large number of indicators does not necessarily produce a better assessment. A smaller set of material indicators, supported by reliable data, may be more useful than an extensive checklist of weakly related credits.

1.3 Leading and lagging indicators

Leading indicators measure actions or conditions expected to influence future performance. Examples include the percentage of design decisions subjected to life-cycle analysis, commissioning completion, worker-training hours, and the proportion of construction waste segregated at source. Lagging indicators measure outcomes after they occur, such as actual energy use, accident frequency, complaints, carbon emissions or water consumption.

A robust management system uses both. Leading indicators support early intervention, whereas lagging indicators test whether intervention worked. Reliance only on leading indicators can reward intentions without results; reliance only on lagging indicators may identify failure too late.

2. Indicator design and performance measurement

2.1 Defining an indicator

An indicator should have a clear name, unit, boundary, data source, frequency, responsible party, baseline and target. For example:

Operational energy intensity = annual delivered energy / conditioned floor area.

If annual delivered energy is 1,200,000 kWh and conditioned floor area is 10,000 m², energy intensity is:

1,200,000 kWh ÷ 10,000 m² = 120 kWh/m²·year.

The unit is kWh/m²·year. The indicator is meaningful only when the area definition, occupancy, operating hours, climate and energy accounting method are stated. Comparing a hospital with a lightly occupied office without adjustment can produce a misleading conclusion.

For a general intensity indicator:

Intensity = total measured quantity / relevant activity or service denominator.

The denominator may be floor area, occupant-days, tonnes of product, lane-kilometres or service users. Choice of denominator is a technical and ethical decision because it affects apparent performance.

2.2 Absolute and intensity-based indicators

Absolute energy or emissions indicate total environmental burden and are essential for climate and resource accounting. Intensity indicators support comparison between differently sized projects. Both should be reported where possible. A project may reduce intensity while its total emissions increase because the building has expanded or occupancy has grown.

For carbon, a simplified operational calculation is:

Operational emissions = Σ(Eᵢ × EFᵢ)

where Eᵢ is the quantity of energy carrier i consumed and EFᵢ is its applicable emission factor. Units must be consistent, such as kWh multiplied by kg CO₂e/kWh. The calculation assumes that the emission factors represent the selected reporting boundary and period. Grid factors may vary by location and year; therefore, the source and vintage of each factor must be documented.

Embodied-carbon assessment requires a life-cycle boundary. Common stages include product manufacture, transport, construction, use, replacement, demolition and end-of-life. Results may be reported as kg CO₂e per m² of floor area or per functional unit. Comparing studies without checking system boundaries, service life, databases and allocation rules is unreliable.

2.3 Baselines and targets

A baseline is the reference condition against which change is evaluated. It may be the existing building, a code-compliant reference building, a conventional design, or a historical average. The baseline must be defined before results are known. Otherwise, the assessor may select a favourable comparison after the fact.

A target should specify the metric, value, time horizon and scope. “Reduce energy use substantially” is not a verifiable target. “Reduce annual delivered energy intensity by 30% relative to the documented code baseline by the second year of operation” is more useful, although the baseline model and occupancy assumptions must still be disclosed.

2.4 Normalisation and uncertainty

Normalisation adjusts data to improve comparability. Energy may be normalised by floor area, degree-days, occupancy or operating hours. However, every adjustment introduces assumptions. Over-normalisation can conceal genuine operational problems.

Measurement uncertainty arises from meter accuracy, missing data, estimation methods, changing occupancy and inconsistent definitions. A professional report should distinguish measured values from modelled values and estimates. It should record data quality, confidence level and material assumptions. Where uncertainty could change a decision, sensitivity analysis is appropriate.

3. Benchmarking and performance-gap analysis

3.1 Types of benchmark

Benchmarks include:

• Regulatory benchmarks, such as energy codes or environmental limits.
• Design baselines, used to compare proposed performance with a reference model.
• Historical benchmarks, comparing current performance with previous years.
• Peer benchmarks, comparing similar buildings or projects.
• Best-practice benchmarks, representing high-performing examples.
• Science-based targets, derived from climate or resource constraints rather than average practice.

A regulatory benchmark is a minimum compliance threshold, not necessarily a sustainability target. A peer benchmark may reflect common inefficiency. Best practice may not be transferable because of climate, use, cost or technology differences.

3.2 Predicted versus actual performance

The performance gap is the difference between predicted and measured outcomes. For an indicator where higher performance means lower consumption, a simple relative gap can be expressed as:

Performance gap (%) = (Actual − Predicted) / Predicted × 100

If predicted energy use is 100 kWh/m²·year and measured use is 125 kWh/m²·year, the gap is 25%. This equation is a descriptive comparison, not a causal diagnosis. It assumes that predicted and actual values have comparable boundaries, weather conditions, occupancy and operating periods.

Performance gaps may result from inaccurate models, optimistic schedules, equipment faults, control-system overrides, inadequate commissioning, occupant behaviour, changed space use, poor maintenance, metering errors or procurement substitutions. The appropriate response is investigation rather than immediate attribution to occupants or designers.

3.3 Measurement and verification

Measurement and verification (M&V) establishes whether an intervention produced claimed savings. A credible M&V plan defines the measurement boundary, baseline, routine and non-routine adjustments, metering arrangements, reporting period and treatment of missing data. Baseline conditions may need adjustment for weather or occupancy so that the comparison is fair.

Commissioning verifies that systems are installed, calibrated and operated according to the design intent. Recommissioning repeats this process during operation. Continuous commissioning uses operational data to identify drift. These activities are especially important because certification documentation is often completed before long-term operation is observable.

4. Post-occupancy evaluation

Post-occupancy evaluation (POE) is a systematic study of a completed and occupied facility. It investigates technical performance, user experience and organisational operation. POE may be conducted shortly after occupation, after a full seasonal cycle, or repeatedly over the building’s life.

A comprehensive POE has four stages:

1. Planning: define objectives, stakeholders, confidentiality arrangements, sample and indicators.

2. Data collection: obtain utility data, indoor environmental measurements, maintenance records, interviews, surveys and observations.

3. Analysis: compare results with design targets, standards, benchmarks and user expectations.

4. Feedback and action: communicate findings, assign corrective actions and verify improvement.

Methods include spot measurements, continuous sensors, building-management-system data, occupant questionnaires, interviews, walkthroughs and document reviews. Surveys should be designed to reduce response bias and protect privacy. A small number of dissatisfied respondents does not prove overall failure, while a high satisfaction score does not prove low energy use.

POE is most valuable when treated as organisational learning rather than fault-finding. Findings should feed into facilities management, future design briefs, commissioning procedures and procurement requirements. A limitation is that user perceptions are influenced by expectations, culture, season and acclimatisation; they should therefore be interpreted alongside physical measurements.

5. Certification and rating systems

Rating systems provide common terminology, criteria, documentation routes and market recognition. Their scoring structures differ, and direct comparison of certificate levels across systems is generally invalid.

5.1 LEED

LEED, developed by the U.S. Green Building Council, is a points-based system applied to various building and neighbourhood types. Its categories have included location and transportation, sustainable sites, water efficiency, energy and atmosphere, materials and resources, indoor environmental quality, innovation and regional priority. Certification levels are determined by achieved points, subject to prerequisites and documentation review.

LEED’s strengths include broad international recognition, a substantial technical framework, attention to integrative design and market visibility. Limitations may include documentation burden, dependence on project-type rules, variable operational follow-through and the possibility of optimising points rather than total environmental benefit. The applicable version and reference standards must always be checked because requirements evolve.

5.2 BREEAM

BREEAM originated in the United Kingdom and assesses management, health and well-being, energy, transport, water, materials, waste, land use and ecology, pollution and innovation. It uses weighted categories and performance levels, with assessment commonly involving licensed professionals and evidence review.

BREEAM is noted for its life-cycle perspective, management emphasis and adaptability to different asset types. Its challenges include complexity, assessor dependence and the need to interpret criteria in local contexts. As with other systems, a rating reflects the selected methodology and evidence, not every dimension of sustainability.

5.3 EDGE

EDGE, developed by the International Finance Corporation, focuses on resource efficiency, particularly reductions in energy use, water use and embodied energy in materials, relative to a local baseline. Its streamlined approach and software support make it particularly relevant to emerging markets and projects seeking measurable efficiency improvements.

EDGE can be valuable where cost, simplicity and resource savings are priorities. Its narrower scope means that social, ecological, governance and broader resilience issues may require supplementary assessment. Baseline assumptions and local utility conditions must be examined carefully.

5.4 Envision

Envision is designed primarily for infrastructure. It addresses quality of life, leadership, resource allocation, natural world and climate resilience. It encourages consideration of community outcomes, stakeholder engagement, ecological systems, life-cycle resource use and resilience beyond the project boundary.

Its strength is its infrastructure-wide perspective, which is not limited to building energy and water. Its application requires professional judgement because infrastructure benefits, impacts and alternatives are often distributed across regions and decades. Evidence of meaningful stakeholder participation is more important than merely recording consultation events.

5.5 National and regional systems

National systems may be better aligned with local climate, regulations, construction practice, materials, cultural expectations and utility conditions. Examples include systems developed by national green-building councils or public agencies. They may address local priorities overlooked by international schemes, but their market recognition and technical resources vary.

Selection should consider project type, location, client objectives, regulatory requirements, assessor availability, data capability, cost and the outcomes that matter most. Certification should be selected after defining sustainability objectives, not used as a substitute for defining them.

6. Critical evaluation and greenwashing risks

Greenwashing occurs when environmental or social performance is presented as better than the evidence supports. It may be deliberate or arise from weak methods and careless communication. Common forms include:

• highlighting a minor improvement while concealing major impacts;
• confusing design intent with operational results;
• reporting percentage improvement without stating the baseline;
• using a certificate as proof of net-zero or universal sustainability;
• relying on vague labels such as “eco-friendly”;
• excluding embodied carbon, construction impacts or tenant energy;
• purchasing offsets while failing to reduce direct emissions;
• counting stakeholder meetings without demonstrating influence;
• using outdated or non-comparable data.

Certification can reduce greenwashing through defined criteria, evidence requirements and independent review, but it cannot eliminate it. Risks increase when credits are traded as marketing commodities, when evidence is selectively disclosed, or when assessors face conflicts of interest.

Good practice requires claims to be specific, current, verifiable and proportionate. A project should state what was measured, during which period, against which baseline, by whom and with what uncertainty. Environmental claims should not imply broader social or climate benefits than the evidence supports. Professional codes of conduct require honesty, competence, disclosure of limitations and avoidance of misleading statements.

7. Integrated assessment workflow

A project team can implement the following workflow:

1. Establish purpose and decision context. Identify whether the assessment supports design selection, financing, compliance, operation, disclosure or certification.

2. Map stakeholders and material issues. Include owners, users, communities, regulators, contractors, operators and affected ecosystems.

3. Set boundaries and functional units. Define life-cycle stages, geography, assets, users and exclusions.

4. Select indicators. Combine outcome indicators with leading management indicators. Avoid double counting.

5. Define baselines and targets. Document assumptions before modelling or measurement.

6. Assign data ownership. Identify who measures, checks, stores and approves each data set.

7. Integrate assessment into design. Use energy, daylight, water, carbon, cost, resilience and social analyses before major decisions are fixed.

8. Verify construction and commissioning. Confirm materials, equipment, controls, meters and installation quality.

9. Measure operation. Conduct M&V and POE after occupation and over representative seasons.

10. Report transparently and improve. Publish results, limitations, corrective actions and revised targets.

Digital tools can support this workflow. Building information modelling can link quantities to material and carbon databases; smart meters can reveal operational trends; digital twins can support scenario analysis; and dashboards can communicate indicators. Artificial intelligence may assist anomaly detection, forecasting and document checking. However, AI outputs depend on data quality and model assumptions. It should not replace professional verification, stakeholder judgement or accountability. Privacy, cybersecurity, interoperability and bias must be addressed when occupant or operational data are collected.

8. Illustrative applied case: performance gap in a certified office building

Background

An illustrative 12,000 m² office building achieved a recognised green-building certification at design completion. Its energy model predicted annual delivered energy intensity of 95 kWh/m²·year. After the first full year, utility records indicated 132 kWh/m²·year.

Problem

The owner assumed that certification guaranteed the predicted performance. Occupants reported overheating in perimeter offices, while facilities staff reported frequent complaints and manual overrides of the building-management system.

Analysis

The initial performance gap was:

(132 − 95) / 95 × 100 = 38.9%.

The team first checked whether the boundaries matched. Both figures included landlord electricity and central plant energy, but tenant plug loads had been estimated in the model and measured directly in operation. Occupancy was 12% higher than assumed, and operating hours were longer on several floors. These factors explained part, but not all, of the difference.

Trend data showed that the cooling plant operated simultaneously with perimeter heating during mild weather. Several temperature sensors were poorly calibrated, and night-time schedules had been overridden. A sample POE found that occupants valued daylight but experienced glare and thermal discomfort. The problem was therefore not simply excessive occupant behaviour; it involved controls, commissioning, assumptions and user interaction.

Approach and solution

The team established an adjusted baseline using actual occupancy and operating hours, calibrated sensors, corrected control sequences, restored schedules, improved shading control and recommissioned the air-handling units. Facilities staff received training, and occupants were given clear guidance on local controls. The project also introduced monthly reporting of energy intensity, peak demand, comfort complaints and unresolved faults.

Outcome

After six months, annualised energy intensity had fallen to 108 kWh/m²·year. The remaining difference from the original prediction was not described as a failure of occupants. Instead, the owner reported the adjusted baseline, interventions, uncertainty and continuing actions. Thermal-comfort complaints decreased, although a complete second-year evaluation was required before claiming stable performance.

Learning points

The case demonstrates that certification at completion is not equivalent to operational success. Boundary checking, commissioning, POE, transparent reporting and facilities-management capability are essential. It also shows why a single energy metric should be supplemented with comfort, controls and user data.

9. Challenges, limitations and governance

Assessment systems simplify complex realities. Point-based systems may reward discrete features even when interactions between systems produce unintended consequences. Life-cycle models depend on databases and assumptions that may be uncertain. Social outcomes are difficult to quantify and can be reduced to procedural evidence. Benchmarks may penalise innovative projects or reward poor local norms. Certification costs may exclude small organisations and communities.

Data governance is increasingly important. Metering must be accurate and maintained; data definitions must remain stable; access rights must be clear; and personal information from occupancy sensors or surveys must be protected. Public reporting should distinguish verified data from estimates and should preserve an auditable record of revisions.

Governance should also address conflicts of interest. The client, assessor, designer and certifier may have different incentives. Independent review, separation of design and verification roles, peer review of material claims and disclosure of commercial relationships can strengthen credibility. Public-sector projects may need procurement clauses requiring operational disclosure, commissioning, POE and corrective action rather than only a design-stage certificate.

10. Best-practice principles

Effective sustainability assessment follows these principles:

• begin with outcomes and material impacts, not available credits;
• define boundaries, baselines and functional units explicitly;
• combine absolute and intensity-based reporting;
• integrate environmental, social, economic and resilience considerations;
• use measured operational data wherever feasible;
• involve operators and users before design decisions are finalised;
• verify installation, controls and commissioning;
• repeat assessment during operation;
• disclose uncertainty, exclusions and failed targets;
• avoid double counting and unsupported claims;
• treat certification as a management tool, not an end in itself;
• link assessment results to budgets, responsibilities and corrective actions.

Chapter Summary

Sustainability assessment converts broad objectives into indicators, evidence and decisions. Measurement records performance; assessment interprets it; benchmarking provides comparison; and certification provides structured, often independently reviewed recognition. Reliable indicators require clear boundaries, units, baselines, denominators, data ownership and uncertainty statements. Both absolute and intensity-based results are important.

Performance gaps between predicted and actual outcomes are common and may arise from modelling assumptions, changed occupancy, controls, commissioning, maintenance, metering and user interaction. Post-occupancy evaluation combines technical data with user experience and provides a route for learning and improvement. LEED, BREEAM, EDGE, Envision and national systems differ in scope, geography, evidence and emphasis; their rating levels should not be treated as directly equivalent.

Greenwashing is controlled through material indicators, transparent baselines, verified evidence, honest communication and disclosure of limitations. Digital tools and AI can improve monitoring and analysis but cannot replace professional judgement, ethical governance and accountability. The most credible assessment is continuous: it begins with project objectives, informs design and construction, measures operation, investigates gaps and drives corrective action.

Key Terms

Indicator: A defined measure used to represent a condition, impact or outcome.

Benchmark: A reference value or performance group used for comparison.

Baseline: The documented reference condition against which change is assessed.

Normalisation: Adjustment of data to improve comparability using a relevant denominator or condition.

Performance gap: Difference between predicted and measured performance.

Life-cycle assessment: Evaluation of environmental impacts across defined life-cycle stages.

Embodied carbon: Greenhouse-gas emissions associated with materials and processes other than, or including, operation depending on the stated boundary.

Operational carbon: Emissions associated with energy used during operation.

Functional unit: Quantified reference unit used to compare life-cycle performance.

Measurement and verification: Process for determining whether an intervention achieved claimed savings.

Commissioning: Verification that systems are installed and operate according to design intent.

Post-occupancy evaluation: Systematic assessment of a facility after occupation.

Certification: Formal recognition that defined requirements have been met.

Greenwashing: Misleading presentation of environmental or sustainability performance.

Materiality: Significance of an issue to environmental, social, economic or organisational decisions.

Leading indicator: Measure of an action or condition expected to influence future outcomes.

Lagging indicator: Measure of an outcome after it has occurred.

Life-cycle boundary: Stated limits defining which processes, stages and impacts are included.

Recommissioning: Reassessment and optimisation of operating systems after initial commissioning.

Review Questions

Short Answer Questions

1. Distinguish measurement, assessment, benchmarking and certification.

2. Why should absolute and intensity-based indicators both be reported?

3. State two causes of the building performance gap.

4. What is the purpose of post-occupancy evaluation?

5. Identify two common forms of greenwashing.

Long Answer Questions

1. Explain how an assessment team should select indicators for a major building project.

2. Compare the strengths and limitations of LEED, BREEAM, EDGE and Envision.

3. Describe a complete measurement-and-verification process for an energy-efficiency project.

4. Discuss the role of baselines, boundaries and uncertainty in sustainability reporting.

5. Explain why certification does not guarantee sustainable operational performance.

Analytical / Application Questions

1. A building predicted at 110 kWh/m²·year records 143 kWh/m²·year after occupation. Calculate the relative performance gap and identify the additional information needed before diagnosing its cause.

2. Design a POE programme for a university building that has high energy use and low occupant satisfaction. Specify data sources, indicators, timing and corrective-action procedures.

3. A developer advertises a project as “net-zero and fully sustainable” because it has obtained a high rating and purchased offsets. Critically evaluate the claim and propose a transparent alternative disclosure.

Multiple Choice Questions with Answers

Question 1

Which statement best distinguishes certification from assessment?

A. Certification is the measurement of raw project data.

B. Certification is formal recognition of conformity with defined requirements.

C. Certification is always a guarantee of excellent operational performance.

D. Certification eliminates the need for benchmarking.

Correct Answer: B. Certification is formal recognition of conformity with defined requirements.

Question 2

A building uses 1,200,000 kWh annually and has 10,000 m² of conditioned floor area. What is its energy intensity?

A. 12 kWh/m²·year

B. 120 kWh/m²·year

C. 1,200 kWh/m²·year

D. 12,000 kWh/m²·year

Correct Answer: B. 120 kWh/m²·year

Question 3

Which is a lagging indicator?

A. Commissioning completion rate

B. Hours of worker training

C. Measured annual operational energy use

D. Percentage of design reviews completed

Correct Answer: C. Measured annual operational energy use

Question 4

If predicted energy use is 100 kWh/m²·year and actual use is 125 kWh/m²·year, the relative performance gap is:

A. 20%

B. 25%

C. ั30%

D. 125%

Correct Answer: B. 25%

Question 5

Which system is primarily designed for infrastructure assessment?

A. EDGE

B. LEED for Homes

C. Envision

D. A building energy code

Correct Answer: C. Envision

Question 6

What is a principal purpose of post-occupancy evaluation?

A. To replace all design-stage analysis

B. To test actual building performance and user experience after occupation

C. To award planning permission automatically

D. To avoid measuring utility consumption

Correct Answer: B. To test actual building performance and user experience after occupation

Question 7

Which practice most directly reduces greenwashing risk?

A. Reporting only the highest percentage improvement

B. Using vague claims without a baseline

C. Disclosing boundaries, data sources, assumptions and uncertainty

D. Treating a certificate as proof of every sustainability claim

Correct Answer: C. Disclosing boundaries, data sources, assumptions and uncertainty

Question 8

Operational carbon emissions can be estimated, under stated assumptions, by:

A. Multiplying energy use by applicable emission factors and summing carriers

B. Dividing floor area by occupancy

C. Adding capital cost to maintenance cost

D. Subtracting predicted energy from actual floor area

Correct Answer: A. Multiplying energy use by applicable emission factors and summing carriers

Question 9

Why may a regulatory benchmark be insufficient as a sustainability target?

A. It is always more stringent than best practice.

B. It represents a compliance minimum rather than necessarily an ambitious outcome.

C. It cannot be measured.

D. It applies only to social indicators.

Correct Answer: B. It represents a compliance minimum rather than necessarily an ambitious outcome.

Question 10

Which action is most appropriate when a certified building shows an operational performance gap?

A. Blame occupants without investigating data

B. Ignore the gap because certification was achieved

C. Check boundaries and assumptions, then investigate controls, commissioning and operation

D. Change the baseline after seeing the result to remove the gap

Correct Answer: C. Check boundaries and assumptions, then investigate controls, commissioning and operation