- Building insulation
Building insulation refers broadly to any object in a building used as
insulationfor 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. Often an insulation material will be chosen for its ability to perform several of these functions at once. Other types of insulation are designed to withstand high vibrations, and support heavy industrial applications such as LNG tasks.
Thermal insulationin buildings is an important factor to achieving thermal comfortfor 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 ventilationand 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, vermiculiteBut it can also involve a range of designs and techniques to address the main modes of heat transfer - conduction, radiation and convection materials. [ [http://www.buildingscience.com/documents/digests/bsd-011-thermal-control-in-buildings/ BSD-011: Thermal Control in Buildings] ] [ [http://www.greenhouse.gov.au/yourhome/technical/fs16a.htm Your Home Technical Manual - 1.6a Insulation Overview] ] , 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.
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 [http://www.ornl.gov/~roofs/Zip/ZipHome.html insulation calculator] .
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 [ [http://www.direct.gov.uk/en/Environmentandgreenerliving/Greenerhome/DG_064374 Insulating and heating your home efficiently : Directgov - Environment and greener living ] ] [ [http://www.allwoodwork.com/article/homeimprovement/reduce_your_heating_bills.html Reduce Your Heating Bills This Winter - Overlooked Sources of Heat Loss in the Home ] ] ; in an otherwise well insulated home, windows will then become an important source of heat transfer. [ [http://www.climatechange.gov.au/yourhome/technical/fs18a.htm Your Home Technical Manual - 1.8a Glazing Overview ] ] . The resistance to conducted heat loss for standard glazing corresponds to an R-value of about 0.17W/m2/Kohttp://www.wers.net/documents/Rehau_NFRC_Dec_2007.pdf] (compared to 2-4W/m2/Ko for glasswool batts [http://www.ecopink.com.au/pdf/Pink_Batts.pdf] ). 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 glazingsystems can double to triple R values.
In hot conditions, the greatest source of heat energy is solar radiation. [At latitudes less than 45 degrees, winter
insolationrarely falls below 1kWh/m2/day and may rise above 7kWh/m2/day during summer. (Source:www.gaisma.com) In comparison the power output of an average domestic bar radiator is about 1kW. Therefore the amount of thermal radiation falling upon a 200m2 house could vary between 200-1400 home heaters operating continuously for one hour.] 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. [Re-radiation of heat into the roof space during summer can cause sol-air temperatures to reach 60Co] [http://www.fsec.ucf.edu/en/publications/html/FSEC-CR-1220-00-es/roofing.pdf Comparative Evaluation of the Impact of Roofing Systems on Residential Cooling Energy Demand in Florida ] ] The Solar Heat Gain Co-efficient (SGHC) [ [http://www.wers.net/faqs#shgc Windows Energy Ratings Scheme - WERS ] ] (a measure of solar heat transmittance) of standard single glazing can be around 78-85%. [http://www.gjames.com.au/brochure/glassperformance.pdf] . 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 [ [http://www.fsec.ucf.edu/en/publications/html/FSEC-EN-15/ Florida Solar Energy Center ] ] . 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.
insulated glassfor discussion of windows.
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 [ [http://www.ornl.gov/sci/roofs+walls/whole_wall/airtight.html BERC - Airtightness ] ] .
Ensuring low convective heat transfer also requires attention to building construction (
weatherization) and the correct installation of insulative materials [ [http://www.eere.energy.gov/buildings/info/design/integratedbuilding/buildingenvelope.html DOE Building Technologies Program: Building Envelope ] ] [ [http://www.energystar.gov/ia/new_homes/features/VEFraming1-17-01.pdf V-E Framing ] ] .
The less natural airflow into a building, the more
mechanical ventilationwill be required to support human comfort. High humiditycan be a significant issue associated with lack of airflow, causing condensation, rotting construction materials, and encouraging microbial growth such as mouldand 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 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 bridgeis 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 glassand 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 areaof the bridges, increasing the bridge length, or decreasing the number of thermal bridges.
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 [Design of Low Cost Passive Cooling Systems, ThinkCycle Open Collaborative Design, http://www.thinkcycle.org/tc-notes/note-view?topic_id=27256 ] 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 most effective 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 some role in reducing heat losses in cool climates. However, much greater insulation can be achieved through the addition of bulk insulators (see above). Because they primarily block downward heat flow, radiant barriers can allow more night heat loss than bulk insulation.
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.
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 [http://www.energytrust.org/residential/hes/review.php Energy Trust of Oregon program] , 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) [ [http://www.climatechange.gov.au/yourhome/technical/fs110.htm Your Home Technical Manual - 1.10 Rating tools ] ]
* Websites for any of the above.
Installing building insulation
Building insulation materials
Zero energy building
Passive solar design
Passive solar building design
* [http://www.periodhomeandgarden.co.uk/Features/tabid/63/articleType/ArticleView/articleId/74/Insulate-your-home-and-let-it-breathe.aspx Article on insulation for older properties]
* [http://www.thermapan.com/benefits/insulationmovie.html Rvalues: Myths and Reality ]
* [http://diy.17things.com/how-can-i-insulate-an-old-house.html Building Insulation types and methods of installation]
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