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resourceO5 newsInsulation
Insulation is a fundamental part of any energy efficiency strategy for buildings, with insulation products playing significant energy-saving roles in homes, office buildings, businesses and manufacturing plants.
Insulation levels There is a wide range of guidance available to give architects, specifiers, installers and others the information needed to specify adequate insulation for most typical UK building types - for both new building and refurbishment projects.
For example, the following advice on the likely levels of insulation needed to meet current best practice for new housing, has been extracted from Effective use of insulation in dwellings, advice published through the Energy Efficiency Best Practice in Housing programme.
The insulation levels needed to satisfy the Best Practice specification for new homes is expressed in terms of U-values for the main structural elements of the buildings - walls, roofs, etc. U-values measure the rate of energy loss through these elements. This can be slowed, and the U-value reduced, by incorporating more insulation in the building elements.
The Best Practice specification for new housing includes Carbon Index (CI) targets. The Index is an indicator of the carbon dioxide emissions associated with space and water heating. It is expressed on a scale of 1-10, the higher the number the better the performance. The CI for a building is obtained from the government's Standard Assessment Procedure (SAP) which is required for all new dwellings in the UK.
The Carbon Index is determined by a number of factors including:
The greater the exposed surface area compared with floor dimensions, the more insulation will be needed to achieve the same CI. For example, a semi-detached dwelling will need more insulation than a mid-terrace property. The index can be used to compare performance between dwellings because it is expressed in terms of emissions per square metre of floor area.
Changes to one factor will mean that changes must be made to others to achieve the same CI. This gives some flexibility to the design process, while the inclusion of maximum acceptable U-value for walls, floors, roofs and glazed areas in the specification, ensures that good insulation levels are always achieved. Where wet heating systems are used, minimum boiler efficiencies also have to be achieved.
The main features of Best Practice specification are given in Tables 1 and 2.
Table 1: Carbon Index requirements for various domestic heating fuels
Table 2: Limit factors for exposed structural elements and for heating boilers
Some of the factors influencing a building's Carbon Index are site specific and fixed, such as site layout and building orientation. Once these have been determined for a building, adjustments to the specification to achieve the appropriate CI may be needed. But some general conclusions can be drawn from the examples in Tables 3-5 about the relationship between the insulation levels given in the specification and the Carbon Index achieved:
Table 3: Two-bedroom flat - floor area 61m2
* for ground floor and top floor flats as applicable
Table 4: Semi-detached house - floor area 89m2
Table 5: Detached house - floor area 104m2
* mechanical ventilation with heat recovery also assumed here
Selecting 'green' insulation In addition to specifying the right level of insulation, there is the choice of insulation type to be made from a wide range of materials, some of which are in themselves more environmentally friendly than others. One source of advice on selecting insulation and other building materials to reduce environmental impacts, is 'The Green Guide to Specification' (and 'The Green Guide to Housing Specification') which provides an environmental profiling system.
The Green Guide contains typical building materials and components listed against a simple environmental rating scale from A (good) to C (poor). For each material a range of different environmental impacts are individually scored and an overall Summary Rating given.
The Green Guide lists a wide variety of insulation types, a number of which have an 'A' Summary Rating. These include materials such as low-density mineral wool, expanded polystyrene (EPS), pentane blown polyurethane, corkboard and recycled cellulose.
Mineral wool According to the 'Green Guide to Housing Specification', lower-density mineral wools should be used in preference to denser mineral wools where possible as the environmental impact increases proportionally with their weight, while their conductivity is relatively unaffected by density.
Mineral wool is made from molten glass, stone or slag that is spun into a fibre-like structure. Its thermal, fire and acoustics properties derive from its structure, a mat of fibres which prevent the movement of air, and from its chemical composition.
Expanded Polystyrene Polystyrene is extracted from oil through a process called polymerisation. Expanded polystyrene starts as small spherical beads containing an expanding agent - a hydrocarbon that does not contain halogens and does not damage the ozone layer.
Pentane blown polyurethane The basic polyurethane chemistry was developed by Otto Bayer in the 1930s. Polyurethanes are formed by reacting a polyol with a diisocyanate (or a polymeric isocyanate) in the presence of catalysts and additives. As a variety of diisocyanates and polyols can be used, a range of materials can be produced - flexible foams, rigid foams, coatings, adhesives, sealants, etc - for various uses. Rigid polyurethane foams are used as insulation in buildings.
The Green Guide to Specification notes that low density expanded polystyrene (see above) and pentane blown (zero ozone depletion potential) polyurethane can be used where intrinsic strength is required, and both offer good environmental performance.
Corkboard Corkboard was invented in the late 19th century, mainly to insulate cold storage areas in buildings and other locations requiring efficient insulation. It consists of various sizes of cork granules compressed together under a high temperature causing the granules to expand and giving them a dark brown colour.
Cork is a natural product derived from the bark of the cork tree - a species of oak, Quercus suber. It is an evergreen grown commercially in areas bordering the Mediterranean Sea. After the bark is harvested it can regenerate, leaving the tree unharmed.
Recycled cellulose Cellulose insulation is made from recycled wood fibre, primarily newspaper. Typically, one hundred pounds of cellulose insulation contains around 80 to 85 pounds of recycled newsprint. The remainder is made up of fire retardants.
When cellulose is blown or dense-packed into walls and ceilings, it takes on almost liquid-like properties which means it can flow into cavities and around obstructions to fill walls and seal cracks and seams.
Further information Several free-to-download publications covering all aspects of insulation use in buildings are readily available. For example the Energy Saving Trust's, Energy Efficiency Best Practice in Housing website www.est.co.uk/bestpractice/publications provides guidance such as 'Effective use of insulation in dwellings' (CE23) and 'Insulation material chart - thermal properties and environmental ratings' (CE 71), among many other publications.
For non-housing buildings, the Carbon Trust site www.thecarbontrust.co.uk/energy offers wide ranging energy efficiency advice.
'The Green Guide to Specification' and the 'Green Guide to Housing Specification' can be purchased from www.brebookshop.com.
Advanced insulation products and materials will be on display at resource05, a major low-carbon technology event in September this year - see www.resource05.com.
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