Bioclimatic Design and Ecological Foot Printing

Understanding and Accounting for The Environmental Impact of our Buildings
Michael P.G. Haslam, Solearth Ecological Architecture

As a designer or builder it is important that we are aware of the energy consequences of decisions made in the siting of a building, its form and the material choice. This is particularly important when we consider that buildings in the western world consume 40% of all resources and contribute 40% of all pollution created.

To give a stronger global perspective to this we should see these figures in the context of Eco-(logical) foot-printing which is about the fundamental inter-dependence of living together on our planet. If every person consumed as much as the average person in the UK and Ireland we would need three planet earths to support us. Eco-foot-printing actually refers to the area required to support the lifestyle of an individual or community. Calculations of Eco-foot-printing show that the global average foot-print is 2.85 hectares per person, for the UK and Ireland it is 6 hectares whilst the USA average is 12 hectares per person. However, with a global population of 6 billion and a productive area of the planet at 11.3 billion hectares we are left with an available average of 1.9 hectares per person. We started to exceed our sustainable capacity in the 1970s and since then we are eating into our natural capital.

With buildings contributing so highly to our energy demands it is important we look at strategies to reduce their Eco-footprint. The reduction of energy requirements through increased efficiencies to a point where renewable energy is a viable option for all our demands is of primary importance. To maximise the use of local, reclaimed and recycled materials must also be considered as well as a reduction in water consumption through greater efficiency and water recycling.

We must also look at our community designs if we are to reduce our Eco-foot-print – creating communities that are less dependent on the car. This can be achieved through integration of housing with services such as schools and places of employment and through measures such as good connections to public transport and car pooling. Finally, the integration of lifestyle with the local material cycles and energy flows, such as shopping for local goods and composting and recycling.

Building design can and should facilitate all these aspects; at the early design stage some simple decisions can help save energy usage later on. Bioclimatic design - which looks at the appropriate passive design strategies to achieve internal comfort conditions - indicates that in our temperate maritime climate, passive solar design can help make these energy savings.

The principle elements of passive solar design are:

  • Site planning
  • Building form
  • Sunspaces
  • Internal planning
  • Thermal mass
  • Insulation
  • Glazing and window design

We can look at these in more detail:

Passive solar site planning guidelines show that to maximise solar access and its benefits the principle façade of a building should be orientated to be within 30¼ of south. Furthermore, that the winter sun shadow is five times the height of any obstruction – such as a neighbour’s house – which means optimising the positioning and spacing of properties.

Building form should be compact in order to retain heat through presenting less external surface; and as heat rises, two stories becomes more optimal than one.

Glazed sunspaces are the principal gathering elements of solar heat throughout the year; they are however seasonal rooms and should be moved into and opened up as solar temperatures allow. They should not be heated by any means other than the sun. Heat generated in the sunspace can be used throughout the rest of the house either through pre-warming air and allowing it to circulate into the other rooms, by conduction or by radiant heat from the warmed thermal mass of the house.

Internal planning looks at zoning of spaces, setting living spaces to the south and service spaces to the cooler north. The creation of buffer zones to northerly or wind exposed elevations -utilising storage spaces or porches- helps to protect the warmer core of the house.

Thermal mass concerns the use of light-weight or heavy-weight construction. Heavy-weight, for example masonry buildings, tend to heat up more slowly but cool down more slowly too and are suited to regular occupation. Light-weight buildings are faster to warm but also faster to cool so are better suited to intermittent occupation. Wall area is the most efficient absorber of the sun’s warmth and thus a useful position for thermal mass; a darker surface will increase absorption.

Insulation should exceed present Building Regulations – super insulating buildings with 300mm of insulation coupled with a high degree of air–tightness means that up to 60% of a building’s heat can actually be gained from the occupants and waste heat from their appliances – in addition to retaining the sun’s heat for longer.

Glazing distribution is important because - even whilst using high efficiency double glazing – windows are still the weaker area of a building’s envelope in terms of heat loss. It thus makes sense to reduce window openings to the north and have 65% of windows to the south with 15% each to east and west. Night time insulation of windows and sunspaces is equally important.

Through these passive solar design strategies a 30% useful solar heating contribution to the annual house needs can be attained even in north-western Europe. Coupled with high levels of insulation and the correct balance of thermal mass, significant reductions in energy use demands can be achieved. This is a major step towards reducing our Ecological-foot-print and in combination with other strategies such as good community design and material choice we can really start to live sustainably.