Climate and sustainability

Sustainable Development – passive design

Goal: Achieve an optimal active design approach

What do we mean by ‘passive’ design?

^p138. Passive design (not to be confused with ‘Passivhaus’ which is covered later) advocates design choices to maximise the efficient use of resources available from the natural environment. This can be for heating, cooling and ventilation in order to create comfortable conditions inside buildings. It can be achieved by harnessing environmental conditions, such as solar radiation, cool night air and air pressure differences to drive the internal environment. Passive measures do not involve mechanical or electrical systems.

^p139. Passive design choices are considered very sustainable as they emit no carbon and utilise the renewable resources of the natural environment. They also help lower the operational costs, require little to no maintenance and last the lifespan of a building.

^p140. You need to identify early on in the design process what passive design opportunities are available in a scheme and how these can be maximised. These should be considered not just for new development but also include refurbishment and upgrading of buildings, as well as expansions to buildings.

Factors to consider:

Landscape
Re-use of materials
Siting / Orientation and Internal layout
Scale and massing (thermal massing)
Sunlight (lighting and solar radiation)
Shading (natural and constructed)
Passive ventilation

Passive design choices

Orientation (South by South East)

Use landscaping as natural shading

Use passive solar gain and thermal massing

Use passive ventilation

Use night purging to cool

Figure 57: Factors to minimise carbon emissions through passive systems

Sustainable Development – Active design

Goal: Achieve an optimal active design approach

What do we mean by ‘active’ design?

^p141. ‘Active’ design uses mechanical and electrical systems (conventional electricity and natural gas) to keep the environment of a building comfortable. This includes the heating, cooling, lighting or heated water for a scheme or building. Buildings will generally include both active and passive measures. Active measures are considered less sustainable than passive design measures as they contribute to carbon emissions; however, they can utilise a mixture of renewable and non-renewable energy resources and be optimised to operate on more sustainable sources.

^p142. It is useful to identify early on in the design process, opportunities to minimise the carbon emissions of active systems by prioritising renewable energy sources rather than non-renewable ones.

Factors to consider:

Insulation
Airtightness
Solar-electrical power (battery storage)
Solar-thermal energy (thermal storage)
High efficiency Heating, Ventilation and Air Conditioning systems (HVAC)
Air Source Heat Pumps (ASHP)
Ground Source Heat Pumps (GSHPs)
Water Source Heat Pumps (WSHPs)
Electric charging (vehicle charging)

Active design choices

Thermal resistances and shading

Solar electrical power

Airtightness

High efficiency Heating

Insulation

Figure 58: Factors to minimise carbon emissions through active systems

What to consider in your design approach?

^p143. Capturing waste energy in the form of heat or using smart local energy networks to distribute excess on-site energy where demand is needed, can also be used as an active approach to these systems.

^p144. Consideration should be given to linking energy solutions with large consumers (or generators) adjacent to the site, particularly where an infill site is concerned.

^p145. This may give an energy scheme sufficient scale to merit a more sustainable and economically sound approach to be realised.

^p146. An energy plan/ statement should be prepared and demonstrate how sustainable technologies might be used with, or instead of, more conventional forms of energy, such as natural gas.

^p147. Provide the maximum opportunity to incorporate active solar energy systems (either thermal or for power generation) thereby reducing energy demand.

^p148. Technologies to be considered within the plan should include (but not be limited to): solar photovoltaics (PV), solar thermal, heat pumps (air, ground or water if near a watercourse or river), hydro, wind and fuel cells.

A balanced approach

^p149. Development should demonstrate a balanced design approach to achieve sustainability, factoring in both passive and active solutions whilst considering local character. Consideration should be given to linking energy solutions with large consumers (or generators) adjacent to the site, particularly where an infill site is concerned.

^p150. As a rough guide the key aspects to consider using both passive and active design approaches to sustainability include:

Existing built fabric should be re-used as much as possible;
For new construction, minimise the number of resources, including energy needed as well as minimising waste;
The materials used for construction are sustainable, low carbon and locally sourced or manufactured;
Buildings use or have the potential to use renewable energy sources;
The design of a building is optimised towards energy efficiency;
Buildings have a long lifespan and can be easily adapted or re-purposed.

Examples of design responses

Orientation: Orientation, layout of habitable rooms, and window size should be carefully considered in relation to the sun path.
Rooms that are most frequently occupied should benefit from a southerly aspect with appropriate measures to avoid overheating in place.
Rooms that include a concentration of heat generating appliances (e.g. kitchens) or are less frequently occupied (e.g. bathrooms) should be located in the cooler part of the building, generally the northern side.
Conservatories and atria can be used to assist natural ventilation in the summer by drawing warm air upward to roof vents and to collect heat during the spring and autumn.
Deep projections that overshadow windows should be avoided, particularly on south facing elevations. Projections should be sized appropriately so that they provide shading from the sun during the hottest part of the year but allow solar gain in the colder months.
A higher proportion of glazing on north facing elevations can increase natural lighting without significantly increasing solar gain, thereby minimising excessive heat gain.
Where there is a chance that overheating could occur (e.g. due to large expanses of glazing on roofs and south facing elevations), design measures such as roof overhangs, brise soleil, external shuttering, photochromatic and thermochromic glass and a lighter colour palette can help.
Zonal heating, ventilation systems and controls can be used allowing areas subject to high solar gain to occupy their own temperature control zone. Dynamic controls reduce energy waste.
Use of materials to build in thermal mass to absorb excess heat during warmer periods and release it slowly during cooler periods (e.g. day/night, summer/winter).
Buildings should be designed for passive ventilation: Cross ventilation with windows located on opposite walls and/or roof mounted turbines or wind cowls that assist with circulation of air by drawing air through windows or top floor openings and;
passive stack ventilation (PSV) that uses pressure differences to draw in fresh air from outside should replace rising warm air which is released from the top of the building. A heat exchanger can be placed where the air escapes the building to reduce heat loss.

Combining active and passive design approaches to reduce the carbon emissions of a dwelling.
To see more technical guidance for homeowners on these aspects see:

Planning Portal - common projects

Figure 59: Combining active and passive design approaches can reduce the carbon emissions of a dwelling.

Example of an extensive green roof (Maidenhead)

Passivhaus with Photovoltaics (Southmoor, from Greencore Construction)

Ensure the scheme:

uses tree planting in open spaces and streets to mitigate heat island effects;
maximises the reuse and recycling of materials including materials existing on site;
optimises the orientation of buildings to utilise solar gain and shading;
optimises natural ventilation techniques to improve the wellbeing and comfort of internal environments and further reduce energy needs;
includes water harvesting and storage provision for all major and minor development types;

We strongly encourage:

the use of renewable energy technologies to reduce the site’s conventional energy needs;
the use of solar technology on roofs for all commercial, non-commercial, industrial buildings, and solar canopies in parking areas **;
the use of solar technologies on roofs for residential developments;
the reuse and recycling of materials including materials existing on site.

Note: All design principles are applicable to all scales of development unless otherwise specified; *minor applications, **major applications

Sustainable Development – passive design

Goal: Achieve an optimal active design approach

Figure 57: Factors to minimise carbon emissions through passive systems

Sustainable Development – Active design

Goal: Achieve an optimal active design approach

Figure 58: Factors to minimise carbon emissions through active systems

Figure 59: Combining active and passive design approaches can reduce the carbon emissions of a dwelling.

Design principles - sustainable development