New buildings
Energy efficiency and other eco-friendly features need to be built into the design of a building from the very beginning, i.e. at the planning stage long before any detail designs are undertaken. To build in energy efficiency later in the design process becomes progressively more difficult. Some environmental considerations, such as orientation with respect to the sun, are fundamental and are frequently generators of the design itself. Take advice from a professional who is sympathetic with your aims - you do not have to accept common solutions designed to the minimum standards.
Consider all aspects of the design. A sustainable building is not only energy efficient but aesthetically pleasing, well detailed, weatherproof, built of durable materials, adaptable to new uses in the future and has character. If attractive it will be loved, used and maintained, and hence it will endure and save energy long into the future.
when planning a building consider:
- Its position and orientation to make best use of available solar energy, shelter and natural light as well as considering views and relationship to other elements on the site.
- Availability of renewable sources of energy, including solar power in its various forms, wind power and coppiced wood.
- Sustainable drainage and water conservation issues. This may include the use of soakaways rather than public stormwater drainage, composting toilets, recycling of grey water and on-site water treatment.
- The heating strategy for the building. You may choose to design a building that is so well insulated that a heating system is unnecessary. Eliminating the cost of a heating system will offset the cost of the extra energy saving measures.
Sustainable construction is a wide subject and includes green materials, response to the environment and the items mentioned above. This page concentrates primarily on energy conservation as this the greatest single issue. The success of any design, however, will naturally depend of a wider set of factors and the realisation of a wholistic solution. The following section will outline what is required to achieve a zero heating standard building which is defined in the Building a Sustainable Future: Homes for an Autonomous Community, BRESCU, Garston, UK. October 1998
Zero Heating Standard
Zero heating is achieved by super insulating all the external elements in your building and using high performance glazing. (A zero heating house may possibly have back up heating for use in exceptional circumstances.) The U-values and insulation levels required are tabulated below.
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Zero Heating Standard |
||
|
Element |
U-value (W/m2K) |
Insulation |
|
Roof |
0.08 |
500mm cellulose fibre |
|
Wall, external |
0.14 |
250mm full-filled cavity |
|
Ground floor |
0.10 |
300mm expanded polystyrene |
|
Windows, doors, rooflights |
1.70 (overall value for whole element) |
Triple-glazed windows with two low-emissivity panes and krypton gas filling. Doors with insulation sandwich construction |
|
Hot water cylinder |
150 mm layer of insulation, including base and connecting pipes. |
|
(The lower the U-value the better the insulation)
There are an increasing number of such buildings now being built in this country. Good examples of this type of house is BedZED, a new housing development at Beddington by Bill Dunster Architects and also the Autonomous House in Southwell by Brenda and Robert Vale.
BedZED, Beddington Zero Energy Development
Having greatly reduced heat loss through the fabric of the building, heat loss through ventilation needs to be tightly controlled. New buildings are now required to be pressure tested for air tightness. Bear in mind that heating, ventilation and condensation control go hand in hand, and that professional advice may be required to achieve the best energy performance, avoid the risks (such as condensation) and comply with the regulations.
The other ways in which building energy consumption may be reduced include
- Hot water heating efficiency and fuel type. Remembering that electrical power is many times 'dirtier' than gas or oil.
- The efficiency of household appliances, white goods etc.
- The habits and lifestyle of its occupants.
- The users understanding of the design of the building and thus how it is best managed to get the best environmental performance, i.e. opening of windows, use of fans, closing of shutters etc.
Construction details
Walls
An insulating wall construction can be achieved using a timber frame construction of sufficient wall thickness to accommodate the required insulation, i.e. 250mm. Examples of this form of construction include those employing the Walter Segal method and more recently buildings by Architype.
The other characteristic of a wall which is important from an energy and comfort standpoint is its thermal capacity, i.e. its ability to store heat (or cold). If the thermal mass of a wall is located on the inside of the insulation layer it will stabilise internal temperatures. Thermal mass will prevent overheating in summer and temperatures dropping too low overnight in winter. Utilising thermal mass reduces the need for heating in winter and air conditioning in summer.
In order to maintain comfortable temperatures without heating through the bleaker winter periods, it is necessary to incorporate a significant amount of thermal mass as well as the necessary insulation within a building construction. The useful thickness of thermal mass typically in the form of brick or dense concrete block, incorporated in the inner leaf of the wall can vary between 100 and 300 mm. The greater the thermal mass the more stable internal temperatures will remain.
A typical construction may consist of 200 mm dense concrete block inner leaf, 300 mm insulation and an external weatherproof layer. The outer skin of the building need not be brick, it can be any suitable weatherproof finish such as render, timber cladding etc. The extra wall thickness will need to be considered early in the design process.
Sample of wall construction at Beddington Zero Energy Development
Thermal mass is also useful in reducing the need for cooling during warm periods. Offices subject to high internal heat gains from IT equipment can be kept cool by thermal mass normally in the form of an exposed concrete ceiling. The floor slab is cooled at night by outside air. The coolth stored in the slab helps maintain cool and stable temperatures during the following day.
For further information on offices and other building types click here to visit Action Energy
Roofs
Heat flows upwards making the roof the most important element to insulate. It is a part of the building in which a significant amount of insulation can be incorporated without too much difficulty. To achieve a super insulated roof with a U-value of 0.08 W/m2K approx. 500mm of insulation is required.
The risk of condensation needs to be controlled by an appropriate vapour check and ventilation or breathable construction. Ideally thermal mass will be incorporated in the top floor ceiling. Alternatively thermal mass can be included in the intermediate floors in the form of concrete floors.
Breathing roof construction
incorporating breathable roofing felt
Ground Floor
A ground floor is an excellent opportunity for thermal mass possibly benefiting from direct solar gain through south facing windows. The thermal mass needs to be located above the insulation layer and exposed to the interior air enabling heat exchange.
A ground floor is an excellent opportunity for thermal mass possibly benefiting from direct solar gain through south facing windows. The thermal mass needs to be located above the insulation layer and exposed to the interior air enabling heat exchange.
Approx 300mm of insulation will be required to achieve super insulation standard U-value of 0.10. A rigid product such as expanded polystyrene will be suitable for solid floors. A suspended floor can be insulated with a greater range of products including the more environmentally friendly ones such a cellulose (from recycled newspaper).
Mass of floors and walls storing direct solar radiation
Windows
Windows are a critical element in the design. Windows
- give views and a sense of connection with the wider environment.
- are one of the means to ventilate a room.
- lose heat more rapidly than any other surface.
- facing south provide a significant amount of solar gain - a very welcome source of heating in winter, but requiring shading in summer to prevent overheating.
The design of a low energy house will seek to capitalise on the solar gain through windows during the winter period. In order to do so, these south facing windows will require an unobstructed view of the low winter sun during the middle of the day. This source of energy is valuable in enabling a zero heating house to remain comfortable through the winter.
Generally windows lose more heat than they gain. A low energy house will have less glazing than an average house. The majority of the glazing will be south facing. North facing windows will be quite small; just sufficient to provide a visual link with the external environment and to provide some natural lighting.
First floor plan - reduce size of the north facing windows to minimise heat loss. Plan taken from 'Passive solar house design' General Information Leaflet 25, Building Research Establishment
The windows need to have a high thermal specification. Standard windows have a relatively large U-value. To improve this, windows will need to be double, triple, or even quadruple glazed, with a reasonable sized cavity, have layer(s) of low emissivity glass and possibly be gas filled. Insulated shutters and curtains can decrease the heat loss from windows, especially those of poor thermal performance. See Windows under section on Existing Buildings.
Zero CO2, Zero heating and autonomous standards
An abstract from Building a Sustainable Future: Homes for an Autonomous Community
- A zero CO2 house creates no net emissions of CO2 on an annual basis. This means that it must obtain its heat and power from renewable energy. It may do this by buying electricity on a ‘green tariff’ from a company generating renewable energy. If the house makes use of any non-renewable energy sources, it must have its own renewable energy system of sufficient capacity such that, during any year, it can export enough renewable energy to compensate for the CO2 emissions associated with other imported energy.
- A zero heating house normally obtains all its space heating needs from its occupants and their activities, combined with solar and other casual heat gains. The definition of performance will be based on the calculated performance of the house when analysed using BREDEM-8 or BREDEM-12 developed by BRE. The zero heating calculation assumes that the house is occupied by its designated number of residents (based on provided bed-spaces), that low-energy appliances are used, and that all lights are compact fluorescent lamps (CFLs). These latter requirements are to avoid the use of high appliance and lighting loads to boost available heat gains. A ‘nominal zero heating’ house may have a heating system installed to cope with the higher temperatures or heat demands associated with, for example, babies and young children, elderly or disabled occupants, under-occupancy, illness, and periods of extreme weather.
- An autonomous house must meet the zero CO2 and zero heating standards defined above, but it must achieve this by the use of on-site renewable energy generation, which may be a stand-alone system or grid-linked. It must not use any mains services apart from electricity and, if it is linked to the electricity grid, in any year it must export sufficient renewably generated electricity from its own system to balance its intake from the grid. In addition, it must provide its entire water supply and treatment services from the resources it can collect from its site, without the need for mains connections, and it must process its own waste water and sewage within the confines of its site. No waste water or sewage discharges of any kind must leave the curtilage of the site, including surface water run-off. (In this context, ‘the site’ may be taken as the boundary of the housing estate to allow communal autonomous solutions to be proposed.)
All three standards are designed to include ‘low embodied energy’ construction, where ‘embodied energy’ is all the energy used to produce and transport the physical fabric of the building. In addition, they will be powered by renewable energy, so that they provide a net zero CO2 emission standard during operation. It is expected that the forthcoming ‘green tariff’ offered by electricity companies will allow consumers to purchase, direct from the grid, energy produced from renewable resources. Homes built to any of the three standards will offer low-pollution living conditions, as well as emitting lower levels of pollutants to the atmosphere. Non-toxic materials offering minimum emissions of, for example, formaldehyde, volatile organic compounds and solvent vapours will be used in houses. Because electricity is used for cooking there will be fewer pollutants (carbon monoxide, oxides of nitrogen) in the house caused by combustion.
A well-controlled ventilation system (either a passive stack system with humidity control intakes and extracts, or a mechanical system with heat recovery) will ensure that the indoor air quality remains healthy. This means that great care must be taken in the detailing and construction of joints between elements and components to avoid unwanted air infiltration; and the completed house must be pressure tested to ensure the required performance is achieved. The hot water cylinder will be superinsulated to minimise heat loss; while the demand for hot water will be reduced because such houses will have aerating taps for use in basins and showers, in preference to baths (maximum flow rate 6 litres per minute). The compact design of the hot water system will lead to greater efficiency, and all hot water pipework will be fully lagged. In addition, appliances in all dwellings will need to be the most energy and water efficient listed in the EU rating scheme, and the lighting will use CFLs throughout.