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• Introduction
• Sustainability & Housing
• Planning, Community & Sustainability
• The Site & The Dwelling
  • Climate And Orientation
  • Solar Energy: maximising passive solar gain
  • Wind: Design With Form, Layout And Land Cover
  • Precipitation: Design For The Effects Of Climate Change
  • Temperature: Using Landcover To Modify Extremes
  • Site Contamination
  • A Sense Of Place
• Energy Use
• Resource Conservation
• Healthy Dwellings
• Maintenance & Rehabilitation
• Finance & Management
• Useful Addresses
• Bibliography
• Selected Reference Material
• Case Studies
• Acknowledgements

3. The Site And The Dwelling

When taken together, site, resources, energy and health are inseparable aspects of design consideration with each affecting the other. As a result, each aspect should always be considered in relation to the others. For the sake of convenience, however, it is useful to refer to these headings individually. The following four chapters deal with these four different aspects of dwelling design and cover all types of housing activity. Chapter Seven summarises aspects that are :

Box 3.1 The Principles of sustainable design for dwellings

1. HOLISTIC APPROACH — An integrated design approach is preferable to a fragmented one; everything is connected to everything else
2. SITE — The specific nature of a place controls sustainable design
3. ENERGY USE — Reducing energy use is more cost effective than producing or reclaiming it
4. RESOURCE USE — Aiming for durability and re-use is more efficient than recycling products and materials
5. HEALTH — A sustainable environment is a healthy one for people
6. SIMPLICITY — Simple solutions are better than those which are complicated, over-designed or rely on “technical fixes”
7. EFFICIENCY — Good sustainable design produces multiple benefits from one feature
8. PARTICIPATION — Sustainable design involves the user at all stages

3.1 Climate And Orientation

Climate is a key factor in sustainable design and its variation (Figures 3.2 - 3.3) has great influence on the effectiveness of housing in terms of social activity, human comfort, health, physical resource use and energy use. The correct orientation of housing layouts and the plan of the individual dwelling will ensure an optimal response to the climate (see Section 3.1.1 and Box 3.2). Even in existing housing or tight urban locations where orientation is restricted, it is still possible to significantly improve the response of the dwelling to the climate (see Section 3.1.2).

The four key site variables in the Scottish climate for optimising sustainable design are:

• Solar Energy
• Wind
• Precipitation
• Temperature

3.1.1 Solar Energy: maximising passive solar gain

Scotland has ample sunshine to make its use worthwhile in a variety of ways in housing for heating purposes. The heating season in Scotland is longer than in England which makes the use of solar energy more cost effective in Scotland than in England in terms of reducing heating bills¹. Even on cloudy days approximately 30% of solar radiation can be usefully harnessed for lighting and energy use.

The following benefits can be obtained from using solar energy:

• the building form itself can capture solar energy for heating and save around 10-15% on annual heating costs

• mechanical systems which capture solar energy for the heating of hot water can save up to 50% on annual hot water costs (see Table 4.3)

• both passive and active modes of solar heating can be retrofitted to old stock

• active solar water heating using solar water panels has an average financial payback of 10 years, well within the life of the panel itself (see Table 4.3)

• retro-fitted sunspaces (Figures 3.4 - 3.10) can save energy and offer an additional low cost amenity space for three seasons of the year.

Passive solar gain is the use of solar energy for heating by using the dwelling layout and form to capture and store the sun’s heat for use both in the day and evening². Ideally, housing should lie roughly on an east/west axis with habitable rooms to the south (Figure 3.4). This layout is not always possible due to planning constraints, but should be adopted wherever practical.

The main method of capturing and storing solar energy is through large south facing windows situated in a highly insulated dwelling but an additional means is through using sunspaces. These are highly glazed south facing amenity areas or porches which are either added or incorporated in to the dwelling layout to enhance passive solar gain and reduce heat loss. There are four ways in which sunspaces save energy:

• Thermal Buffering
• Pre-heated Ventilation
• Draught lobby
• Evening heating

Energy gathered during the day will be lost in the evening, if sunspaces are not effectively insulated from the outside. It is a matter of training the occupier to ensure that any shutters or insulated blinds in sunspaces are closed at night to prevent heat loss. Airways through doors, windows or ventilators between the sunspace and living area should also be closed off once it is apparent that the sunspace is cooler than the living area.

Passive solar gain methods must also be established in tandem with daylighting design in order to ensure optimum performance (see Section 4.2.2). There are a number of methods and tools available to help carry out these calculations. One of the best known is BREDEM³. Method 5000⁴ is a simpler version. There are also numerous “shareware” solar gain tools on the internet⁵.

Careful siting of deciduous trees can stop overheating of south facing rooms and conservatories in the summer with full leaf shade, while allowing more light to penetrate in the winter due to less foliage. Care must be taken not to over shade with trees as even in winter deciduous trees can take away up to 50% of daylight when densely planted (Figure 3.11).

Box 3.2 Passive solar gain: pointers for good practice

• Site layout should provide access to sunshine for as many dwellings as possible and avoid overshading (See figure 3.12)

• housing layouts should be orientated within 30 degrees of due south wherever possible in order for the solar gain to be useful

• plan cooler service spaces on the north side and habitable rooms needing warmth on the south side

• make sure the building is well insulated and relatively airtight

• allow for adequate and controllable ventilation to avoid overheating in summer

• incorporate draught lobbies to minimise heat loss

• glazing should be optimised with a 70:30 ratio of glazing from south to north elevations to maximise passive solar gain

• provide thermal mass where possible to absorb solar gain (up to 100mm blockwork is effective) and avoid overheating

• the use of conservatories or sunspaces purely for energy reasons is not effective unless they are a cheap, unheated, preferably single glazed (which uses considerably less material resources than double glazing and doesn’t rely on vulnerable sealants), three season amenity space

• narrow width sunspaces (under 1500 mm wide) are preferable to room sized ones or conservatories to prevent them from being treated as an additional room and being heated

• provide full separation and insulation between sunspaces and the main dwelling

• provide structural overhangs, external shutters and internal blinds to prevent both overheating in summer and heat loss at night

• cover as much of the south facing wall as practical with a sunspace to act as a thermal buffer

• use deciduous trees and planting to provide partial shade to sunspaces in the summer

3.1.2 Wind: Design With Form, Layout And Land Cover

Even if an urban development site does not offer much opportunity for passive solar gain, all housing can benefit from design for shelter as wind chill contributes significantly to energy loss. Generally, the best orientation for solar gain is also the best for preventing heat loss due to prevailing wind chill from the southwest and north east (Figure 3.13). Regional wind data can be obtained from the Meterological Office⁶ but site measurements and analysis will give a more accurate picture for design purposes⁷.

Housing form can reduce the effect of windchill and heat loss. The ideal form for housing will minimise surface area for heat loss but retain surface variation and texture to increase wind drag. One of the most energy efficient forms of housing is the tenement block. Terraced two storey housing is also very effective. The least effective are the semi-detached and detached house (Figure 3.14 and Figure 3.4A). Providing external structures such as porches, trellising and fencing can all help to reduce wind speeds without increasing heat loss from the building. Vegetation, carefully planned, can act as a “third skin” on appropriate walls of buildings by providing wind drag and an additional thermal buffer. In effect it becomes “free” and renewable insulation material with minimal manufacturing costs⁸ (Figure 3.15).

Housing layouts should be self-sheltering wherever possible. The traditional Scottish village (Figure 3.16) provides a good rural example of this with the tight layout of buildings creating a milder micro-climate and helping to shelter the inner faces and entrances of the buildings. The traditional Victorian tenement block provides an urban example of the same principle.

The use of trees combined with planting and fencing in garden areas also provides some degree of wind shelter through landcover. The most effective height for trees is the height of the dwelling and placed 1-3 heights away, or 3-4 heights where solar access is required⁹(Figure 3.17). Larger shelterbelts of trees can provide the same effect over a whole housing development. There may be a conflict with the need for visibility and observation when providing planting. This can be overcome by planning lines of vision along public routes from the housing.

Box 3.3 Reducing wind chill and heat loss: pointers for good practice

• avoid exposed, windy sites and take advantage of any shelter offered by a site

• visit site to establish local wind conditions and design for these

• orientate housing to minimise wind chill by presenting narrow ends to the prevailing wind

• minimise surface to volume area of buildings by maximising use of terrace or tenement layouts and using compact forms

• use shared party walls to reduce heat loss through the building envelope

• increase shelter and wind drag through use of planting and external structures

• design housing to be self-sheltering

• avoid housing layouts and forms that accelerate the wind

• use evergreen planting to increase effectiveness of shelterbelts in winter but avoid overshading

3.1.3 Precipitation: Design For The Effects Of Climate Change

Housing developments should be “future proofed” against increased precipitation and storm frequency¹⁰ with suitably robust layout and detailing. Consultants should be asked if they have taken the predicted effects of global climate change, such as increased storms and precipitation, into account¹¹(see Box 3.4).

Box 3.4 Taking account of global climate change: pointers for good practice

• check existing water table and natural patterns of drainage

• calculate rainwater guttering and pipework on the basis of up to 30% increase in precipitation

• use soft landscaping to reduce storm water runoff and help the rain to percolate naturally back into the water table¹² (Figure 3.19)

• use porous paving schemes to allow water to flow down through hard landscaping directly into the water table to minimise drainage requirements and relieve pressure on existing drainage (Figure 3.20)

• retain robust roofing details including sarking in preference to battens

• ensure all details take account of increased intensity and number of storms

• preserve and increase planting of trees to absorb CO₂ to help reduce global climate change

3.1.4 Temperature: Using Landcover To Modify Extremes

Large urban areas in Scotland create particular local climates which trap pollution, have less solar radiation, and are generally warmer than the surrounding countryside by several degrees. Planting modifies heat difference by trapping solar heat and providing cool air through transpiration. Hard landscaping in the immediate vicinity of the dwelling can also capture solar heat during the day and re-radiate it in the evening which helps to even out daily temperature swings (see Case Study No.5).

To replenish the oxygen we use up, each human needs 30 m² of planting, either in housing schemes or elsewhere. Trees are effectively the “lungs” of the Earth. They not only clean air by removing 75% of dust particles, they oxygenate it, and remove carbon dioxide as well as sulphur monoxide¹³. Meanwhile their roots break down the soil, take up nutrients and provide the soil with nutrients in return through dead leaf mould. Scotland’s major cities have some of the highest concentrations of air pollutants in Europe, principally arising from traffic. In inner city areas the use of trees and other planting can act as a pollution filter between housing and busy, congested roads.

Trees are also of high amenity value and can form a focus for community involvement by combining community woodland development with housing¹⁴. Many of our housing estates have few trees because landscaping is traditionally the first cost saving to be made. This is shortsighted given the environmental benefits that trees and planting in generally can generate.

Box 3.5 Soft and hard landscaping : pointers for good practice

• require contractors to preserve biodiversity

• minimise hard landscaping and encourage the use of deciduous trees to enhance microclimate

• preserve existing mature trees and wildflower areas as much as possible

• increase planting generally to increase opportunities for local wildlife to proliferate

• set aside wild areas using native plants and trees with minimal cultivation to encourage local biodiversity

• provide corridors of linked planting to allow cross-pollination and provide routes for wildlife

• establish which parts of the site are optimum for growing vegetation and allow re-development to take place on the least ecologically promising part of the site

• replace soil sterilised by additional housing with soil and plant cover on the roofs of the housing (Figure 3.21) where suitable

• use planting as pollution filters and sound barriers between busy, congested roads and housing developments

• use hard landscaping on south side of building as thermal mass to modify climate

3.2 Site Contamination

The increasing use of brownfield sites often means dealing with contaminated sites. Consultants should establish an accurate site history using local records and carry out a contamination survey where necessary.

Site de-contamination can be carried out in a number of ways:

• scrape clean and removal of toxic soil
• capping the contaminated soil
• chemical de-contamination
• biological de-contamination

The most benign method involving least energy is biological de-contamination using toxin-neutralising plants such as willow saplings and reeds(Figures 3.22 - 3.23).

This takes time, however, and requires careful pre-planning. Intensive treatment for on site de-contamination using enhanced chemical compositions can be quicker but uses a more energy intensive product. Capping the contamination does not get rid of the problem but may be a cost effective solution if contamination is not severe. Scraping the site clean is a last resort but may be required if contamination is particularly severe. Consultants should balance the cost of de-contamination process against the environmental impact of the de-contamination process itself.¹⁵

3.3 A Sense Of Place

The final ingredient when designing sustainably for a given site is to understand the existing nature of the locality. Physical, historical, cultural and archeological features all inform a sense of place and should also be taken into consideration when applying a holistic approach to site development. Sustainable design is as much about sustaining our history as it is about sustaining our environment.

Site Checklist-Key Areas

• Climate
  • carry out comprehensive climate analysis
  • maximise passive solar gain (see Box 3.2)
  • provide shelter by modifying housing layout and form (see Box 3.3)
  • take account of global climate change (see Box 3.4)
• Land cover
  • protect and enhance existing vegetation (see Box 3.5)
  • make provision for contaminated site remediation
• Sense of place
  • note historical, cultural or archeological features on the site
  • identify physical influences on local building style

Footnotes