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Building insulation
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Building insulation refers broadly to any object in a building used as insulation for any purpose. Whilst the majority of insulation in buildings is for thermal purposes, the term also applies to acoustic insulation, fire insulation, and impact insulation (eg. for vibrations caused by industrial applications). Often an insulation material will be chosen for its ability to perform several of these functions at once.
Thermal Insulation
Thermal insulation in buildings is an important factor to achieving thermal comfort for its occupants.
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Building insulation refers broadly to any object in a building used as insulation for any purpose. Whilst the majority of insulation in buildings is for thermal purposes, the term also applies to acoustic insulation, fire insulation, and impact insulation (eg. for vibrations caused by industrial applications). Often an insulation material will be chosen for its ability to perform several of these functions at once.
Thermal Insulation
Thermal insulation in buildings is an important factor to achieving thermal comfort for its occupants. Insulation reduces unwanted heat loss or gain and can decrease the energy demands of heating and cooling systems. It does not necessarily deal with issues of adequate ventilation and may or may not affect the level of sound insulation. In a narrow sense insulation can just refer to the insulation materials employed to slow heat loss, such as: cellulose, fiberglass, rock wool, polystyrene, urethane foam, vermiculite. But it can also involve a range of designs and techniques to address the main modes of heat transfer - conduction, radiation and convection materials., and earth or soil.
The effectiveness of insulation is commonly evaluated by its R-value. However, an R-value does not take into account the quality of construction or local environmental factors for each building. Construction quality issues include inadequate vapour barriers, and problems with draft-proofing. In addition, the construction properties and density of the insulation material itself is critical. For example, according to Leah Twings, Quality Compliance Manager of Textrafine Insulation, fiberglass insulation materials made from short strands of glass layered over each other is not as durable as insulation made from long entangled strands of glass.
Planning
How much insulation a house should have depends on building design, climate, energy costs, budget, and personal preference. Regional climates make for different requirements. Building codes specify only the bare minimum; insulating beyond what code requires is often recommended.
The insulation strategy of a building needs to be based on a careful consideration of the mode of energy transfer and the direction and intensity in which it moves. This may alter throughout the day and from season to season. It is important to choose an appropriate design, the correct combination of materials and building techniques to suit the particular situation.
In the USA
An initial estimate of insulation needs in the United States can be determined by the US Department of Energy's ZIP code .
Climate
Cold climates
In cold conditions, the main aim is to reduce heat flow out of the building. The components of the building envelope - windows, roofs and walls, and air infiltration are all important sources of heat loss; in an otherwise well insulated home, windows will then become an important source of heat transfer.. The resistance to conducted heat loss for standard glazing corresponds to an R-value of about 0.17W/m2/Ko (compared to 2-4W/m2/Ko for glasswool batts). Losses can be reduced by good weatherisation, bulk insulation, and minimising the amount of non-insulative (particularly non-solar facing) glazing. Indoor thermal radiation can also be retarded with spectrally selective (low-e, low-emissivity) glazing. Some insulated glazing systems can double to triple R values.
Hot climates
In hot conditions, the greatest source of heat energy is solar radiation.This can enter buildings directly through windows or it can heat the building shell to a higher temperature than the ambient, increasing the heat transfer through the building envelope.The Solar Heat Gain Co-efficient (SGHC) (a measure of solar heat transmittance) of standard single glazing can be around 78-85%.. Solar gain can be reduced by adequate shading from the sun, light coloured roofing, spectrally selective (heat-reflective) paints and coatings and various types of insulation for the rest of the envelope. Specially coated glazing can reduce SHGC to around 10%. Radiant barriers are highly
effective for attic spaces in hot climates . In this application, they are much more effective in hot climates than cold climates. For downward heat flow, convection is weak and radiation dominates heat transfer across an air space. Radiant barriers must face an adequate air-gap to be effective.
If refrigerative air-conditioning is employed in a hot, humid climate, then it is particularly important to seal the building envelope. Dehumidification of humid air infiltration can waste significant energy. On the other hand, some building designs are based on effective cross-ventilation instead of refrigerative air-conditioning to provide convective cooling from prevailing breezes.
Orientation - Passive Solar Design
Optimal placement of building elements (e.g. windows, doors, heaters) can play a significant role in insulation by considering the impact of solar radiation on the building and the prevailing breezes. (See Passive Solar Design) Reflective laminates can help reduce passive solar heat in pole barns, garages and metal buildings.
Construction
See insulated glass for discussion of windows.
Building envelope
The thermal envelope defines the conditioned or living space in a house. The attic or basement may or may not be included in this area. Reducing airflow from inside to outside can help to reduce convective heat transfer significantly .
Ensuring low convective heat transfer also requires attention to building construction (weatherization) and the correct installation of insulative materials .
The less natural airflow into a building, the more mechanical ventilation will be required to support human comfort. High humidity can be a significant issue associated with lack of airflow, causing condensation, rotting construction materials, and encouraging microbial growth such as mould and bacteria. Moisture can also drastically reduce the effectiveness of insulation by creating a thermal bridge(see below). Air exchange systems can be actively or passively incorporated to address these problems.
Thermal bridge
Thermal bridges are points in the building envelope that allow heat conduction to occur. Since heat flows through the path of least resistance, thermal bridges can contribute to poor energy performance. A thermal bridge is created when materials create a continuous path across a temperature difference, in which the heat flow is not interrupted by thermal insulation. Common building materials that are poor insulators include glass and metal.
A building design may have limited capacity for insulation in some areas of the structure. A common construction design is based on stud walls, in which thermal bridges are common in wood or steel studs and joists, which are typically fastened with metal. Notable areas that most commonly lack sufficient insulation are the corners of buildings, and areas where insulation has been removed or displaced to make room for system infrastructure, such as electrical boxes (outlets and light switches), plumbing, fire alarm equipment, etc.
Thermal bridges can also be created by uncoordinated construction, for example by closing off parts of external walls before they are fully insulated.
The existence of inaccessible voids within the wall cavity which are devoid of insulation can be a source of thermal bridging.
Some forms of insulation transfer heat more readily when wet, and can therefore also form a thermal bridge in this state.
The heat conduction can minimized by any of the following: reducing the cross sectional area of the bridges, increasing the bridge length, or decreasing the number of thermal bridges.
Materials
see Thermal insulation
There are essentially two types of building insulation - Bulk Insulation and Reflective Insulation. Most buildings use a combination of both types to make up a total building insulation system. The type of insulation used is matched to create maximum resistance to each of the three forms of building heat transfer - Conduction, Convection, and Radiation.
Conductive and convective insulators ('Bulk insulation')
Bulk insulators block conductive heat transfer and convective flow either into or out of a building. The denser a material is, the better it will conduct heat. Because air has such low density, air is a very poor conductor and therefore makes a good insulator. Insulation to resist conductive heat transfer uses air spaces between fibers, inside foam or plastic bubbles and in building cavities like the attic. This is beneficial in an actively cooled or heated building, but can be a liability in a passively cooled building; adequate provisions for cooling by ventilation or radiation are needed.
Radiant heat barriers
Radiant barriers work in conjunction with an air space to reduce radiant heat transfer across the air space. Radiant or reflective insulation reflects heat instead of either absorbing it or letting it pass through. Radiant barriers are often seen used in reducing downward heat flow, because upward heat flow tends to be dominated by convection. This means that for attics, ceilings, and roofs, they are most effective in hot climates.
They also have a role in reducing heat losses in cool climates. However, much greater insulation can be achieved through the addition of bulk insulators (see above).
Some radiant barriers are spectrally selective and will preferentially reduce the flow of infra-red radiation in comparison to other wavelengths. For instance low-emissivity (low-e) windows will transmit light and short-wave infra-red energy into a building but reflect back the long-wave infra-red radiation generated by interior furnishings. Similarly, special heat-reflective paints are able to reflect more heat than visible light, or vice-versa.
Thermal emissivity values probably best reflect the effectiveness of radiant barriers. Some manufacturers quote an 'equivalent' R-value for these products but these figures can be difficult to interpret, or even misleading, since R-value testing measures total heat loss in a laboratory setting and does not control the type of heat loss responsible for the net result (radiation, conduction, convection).
A film of dirt or moisture can alter the emissvity and hence the performance of radiant barriers.
Installation of insulation
Insulating buildings during construction is much easier than retrofitting, as generally the insulation is hidden, and parts of the building need to be deconstructed to reach them.
Home energy audit
A home energy audit is a service where the energy efficiency of a house is evaluated by a person using professional equipment (such as blower doors and infra-red cameras), with the aim to suggest the best ways to improve energy efficiency in heating and cooling the house.
This kind of service can often be facilitated by:
- Public utility companies, or their energy conservation department.
- Independent, private-sector companies such as energy services company, insulation contractor, or air sealing specialist.
- (US) State energy office.
Utility companies are usually eager to provide this service, as well as loans and other incentives to insulate. They also often provide incentives to switch, for example, if you are an oil customer considering switching to natural gas. It is possible to obtain simple energy audits (without the blower tests) from some utilities and US state agencies for free. An example is the , which provides simplified energy audits and compact fluorescents to homeowners at no cost.
Where to look for insulation recommendations:
- Local building inspector’s office.
- Local or state building codes.
- US Department of Energy. (U.S.A.)
- Home Energy Rating Schemes (Australia)
- Green Building Insulation (USA)
- Websites for any of the above.
See also
Materials
Design
Construction
Other
External links
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