At the end of last week’s ToT on the history of sustainability we arrived at our current dilemma: finding the ‘Goldilocks’ density.

How to balance the operational and embodied energy of a well-designed building with the transport, infrastructure and environmental impacts? Planning issues of location and dwelling density become crucial in determining the overall carbon footprint.

In low density suburbia or remote areas, the best designed homes will still have high overall carbon demands, a result of increased transport and infrastructure energy costs. An isolated passive solar home, no matter how high performing or autonomous, is NOT sustainable as it is miles away from the community services the occupants need.

High density buildings in urban locations save on travel and infrastructure costs, but operational energy soars for uses such as basement ventilation, lifts and air conditioning, with little opportunity to offset the demand from solar PV on the limited roof (and sometimes wall) areas. High -rise apartments are NOT sustainable given high energy demands and limited solar gain.

The ‘just right’ typology for sustainable homes is somewhere in the middle, in both senses. The ultimate solution is well-designed and close to services: walking / cycling distance of community facilities; four to six storeys; ‘low and close’ in form and plan; passive-based; 70% site coverage; accessible; minimal basements; high envelope standards; and maximised solar PVs to make it carbon neutral operationally.

The key considerations as summarised in the diagram:

SITING

  • Max 800m to retail + health services – meaning less transport carbon.
  • Max 400m to public transport to get to employment and education.                                                      

FORM

  • Low scale in consideration of the neighbours’ amenity.
  • 3-4 storeys maximises the occupants use of stairs (up and down).
  • 5-6 storeys are stepped for better amenity to southern neighbours.
  • Minimise ground floor parking, share cars only.
  • Minimise basements to a single level, naturally ventilated.

LANDSCAPE

  • Optimise 70% site coverage for landscape and deep soil.
  • Balance community space on site, with local parks.
  • Areas for plants for food on the ground, and roof.
  • Maximise rainwater collected, stored and used on site.

PLANNING

  • Well oriented plans for light and sunlight for amenity.
  • Plans for better livability – wide doors and corridors.
  • Use ground floor for garden apartments or live/work spaces.
  • Maximise security in apartments with surveillance.
  • Maximise safety in apartments in fall heights.

ENVELOPE + INTERIOR

  • Glazing sized between 10 and 20% of floor area.
  • Vertically proportioned glazing for depth of light.
  • Double glazed for thermal comfort / lower energy costs.
  • ‘Outsulation’ everywhere to improve thermal comfort.
  • Reflective and bulk ‘outsulation’ to reduce AC demand.
  • Heavy internal thermal mass improves thermal comfort.
  • Concrete ceilings with X-Vent lowers AC demand in summer.
  • Cross ventilation wherever possible, ceiling fans everywhere.
  • Maximise corner apartments (good X-vent and light).

CONSTRUCTION

  • Use standardised factory-based systems for all components.
  • Construction in prefab, either kit of parts or full volumetric.
  • Avoid painted surfaces externally (less maintenance).
  • Careful use of brick and concrete (high embedded energy).
  • Or consider CLT with lightweight claddings and ‘outsulation’.

SERVICES

  • Air-conditioning in every apartment (for thermal comfort).
  • All services (AC heat pumps etc) within apartment footprint.
  • Pelmet LED lighting (no downlights or ceiling penetrations).
  • Minimise communal services / equipment (maintenance  access).
  • Big lifts for emergencies and furniture movements.
  • All electric appliances, everywhere (no gas).
  • Communal heat pump HWS, no individual storage.
  • Maximum areas of solar PVs on the roof.

If you think this looks a lot like a recipe for an up-dated version of the traditional three-storey, red-brick walk-up flats, you’d be correct. Reviled aesthetically, they have always been the most sustainable housing, despite being so far from the ideal environmental home envisaged when ‘passive solar’ was the go-to solution after WW2.

In the intervening 80 years we’ve discovered that there is no such thing as a fully sustainable home in perpetuity. The mere act of building anything is considered by many to be unsustainable.

But this is the best solution we have for now.

Title image: Diagram illustrates the key considerations in making the most sustainable form of home. Image by TW.

Next week: We will look at upgrading 3-4 storey red-brick walk-up flats, improving the building fabric of the existing, and new services, to make them THE MOST sustainable ever.

This is Tone on Tuesday #212, 11 June 2024, Some of this article and diagram was first published in the NSW Architecture Bulletin, Housing for All, Vol 80, No 2, 2023-4. It was written by Tone Wheeler, architect / Adjunct Prof UNSW / President AAA. The views expressed are his. Past Tone on Tuesday columns can be found here. You can contact TW at toneontuesday@gmail.com.