Definition

In an APC context, sustainable design considerations for buildings covers the decisions made at design stage that determine a building's environmental, social and economic performance throughout its whole life — from site selection, orientation and fabric specification through to materials, water management and adaptability. The Building Regulations Approved Document L sets the minimum regulatory standard; sustainability best practice, as evidenced by BREEAM Excellent or Outstanding, goes well beyond it.

Why this matters for Sustainability

  • Level 1 knowledge: you must be able to identify the principal sustainable design considerations and explain the impact each has on environmental performance.
  • Design decisions lock in long-term performance: a poorly oriented or under-insulated building incurs excess energy costs and carbon for decades. BREEAM assessment, MEES compliance and net zero claims all depend on design quality.
  • Planning authorities require sustainability statements for major developments, and occupier wellbeing — daylight, thermal comfort, air quality — is increasingly valued in commercial leasing.

Key principles

Site selection and orientation

The most fundamental sustainable design decisions are made before the building is designed. Site selection determines transport access, proximity to existing infrastructure, flood and overheating risk, and ecological constraints. Orientation affects passive solar gain, ventilation and daylighting. A south-facing aspect maximises winter solar gain but must be balanced against overheating risk through shading strategies such as brise soleil, deep reveals or high-performance glazing.

Building fabric: insulation, air tightness and glazing

Building fabric determines the rate of heat gain or loss. High insulation reduces heating demand; air tightness prevents heat loss through uncontrolled infiltration. Glazing affects both heat loss (U-value) and solar gain (g-value): triple glazing reduces U-values but increases embodied carbon and cost. Approved Document L and BREEAM set minimum fabric standards, but Passivhaus-level performance — air tightness below 0.6 ACH₅₀ — offers significantly better energy performance.

Water efficiency and drainage

Water-efficient fittings, rainwater harvesting and greywater recycling reduce consumption and associated carbon. Sustainable drainage systems (SuDS) — permeable paving, green roofs, swales and attenuation tanks — manage surface water run-off in line with planning requirements and the Flood and Water Management Act 2010. BREEAM awards credits for water efficiency and metering.

Materials, circular economy and adaptability

Material specification determines both embodied carbon and circular economy potential. Low-carbon materials — cross-laminated timber, recycled-content steel, low-carbon concrete — reduce upfront carbon. Designing for adaptability and disassembly extends building life, avoids premature demolition and enables end-of-life material recovery. The RICS whole life carbon assessment professional standard (2nd edition, 2023) provides the framework for measuring these decisions; circular economy principles are embedded in BREEAM materials credits.

Relevant RICS guidance and legislation

  • Building Regulations Approved Document L (conservation of fuel and power) — sets minimum energy performance standards for fabric and services in new and refurbished buildings.
  • Building Regulations Part O (overheating) — introduced requirements to limit overheating risk in new residential buildings in England.
  • RICS "Whole life carbon assessment for the built environment" 2nd edition (2023) — the professional standard for measuring and reporting embodied and operational carbon decisions.
  • BREEAM (BRE) — the primary UK voluntary certification scheme against which sustainable design quality is assessed.
  • Flood and Water Management Act 2010 — provides the statutory basis for sustainable drainage system requirements.
  • Climate Change Act 2008 (as amended 2019) — sets the net zero by 2050 target that drives sustainable design requirements.

Ethics and Rules of Conduct angle

Rule 2 of the RICS Rules of Conduct (effective 2 February 2022) requires members to maintain competence. Sustainable design standards evolve rapidly — fabric requirements, overheating risk assessment and embodied carbon benchmarks change as regulations develop. A surveyor reviewing a design must identify where it falls short of current and anticipated future requirements, not just minimum compliance. Rule 3 (integrity) requires honesty where a design is promoted as sustainable but does not meet the performance it claims, whether through greenwashing or optimistic energy modelling.

APC-style Q&As

Q (Level 1)What is the difference between U-value and g-value in glazing specification?

A U-value measures the rate of heat transfer through a building element (W/m²K) — the lower, the better the insulation. A g-value (solar factor) measures the proportion of solar energy passing through glazing, from 0 to 1 — lower admits less heat. Both must be balanced: low U-values reduce heat loss, but low g-values can reduce passive solar gain and daylighting, increasing artificial lighting demand.

Q (Level 1)What is a sustainable drainage system (SuDS) and why is it used?

A Sustainable Drainage System (SuDS) manages surface water run-off in a way that mimics natural drainage, rather than routing it directly to sewers. Examples include permeable paving, green roofs, swales and attenuation tanks. SuDS reduce flood risk, improve water quality by filtering pollutants, and can enhance biodiversity. They are required by planning policy and supported by the Flood and Water Management Act 2010.

Q (Level 2)Why is air tightness important in sustainable building design and how is it measured?

Air tightness limits uncontrolled heat loss through gaps in the building fabric, reducing heating demand and improving MVHR effectiveness. It is measured by an air pressure test recording leakage as air changes per hour at 50 Pascals (ACH₅₀). Approved Document L sets a maximum leakage rate for new buildings; Passivhaus requires below 0.6 ACH₅₀.

Q (Level 2)How does designing for adaptability contribute to sustainability?

Designing for adaptability extends a building's useful life by enabling reconfiguration without major demolition — avoiding the embodied carbon cost of premature replacement, which can take decades of operational savings to offset. Key features include flexible floor plates, raised access floors, accessible ceiling voids and structural grids that accommodate multiple layouts. The RICS whole life carbon assessment guidance recognises design for longevity as a key carbon reduction strategy.

Q (Level 3)A developer client asks you to review the sustainability credentials of a proposed new mixed-use scheme at outline planning stage. What design considerations would you assess and how would you advise them?

(example) I would assess site and orientation (passive solar gain, overheating risk under Part O); fabric (insulation, glazing and air tightness against Approved Document L and BREEAM Excellent targets); embodied carbon (a whole life carbon assessment under the RICS professional standard); and water (SuDS adequacy and water efficiency for BREEAM credits). Addressing all four at outline stage is substantially cheaper than late-stage design changes, and a strong sustainability statement reduces planning risk.