Building insulation
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The goal of insulation used in building construction is to slow down heat transfer. The same materials are required to keep buildings cooler in hot climates, or warmer in cold climates; methods may be different because of the necessity to manage humidity buildup differently. Occupied buildings always need to evacuate humidity. No substance can stop heat transfer from occurring.
As more insulation is installed, more comfort (thermal and soundproofing) is created, and operating costs are lowered. There is no objective test or standard for thermal insulation, although ASHRAE Standard 55 defines thermal comfort goals. The three means of Heat-transfer resistance reduce radiative, conductive and convective losses and gains. Local custom often determines the methods used to achieve comfort level goals.
In some climates, large thermal mass can be used to damp daily swings in temperature. Adobe, earth, stone, and concrete are poor insulators but serve the purpose of regulating indoor temperature by damping, evening out nighttime and daytime lows and highs. If a house has an attic, indications that it is poorly insulated and poorly ventilated include the attic being extremely hot in the summer, and dew and frost forming on cold surfaces in the attic, such as on the underside of the roof sheathing, during the winter.
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[edit] Architectural engineering
- Planning the proper placement of building elements (e.g. windows, doors, heaters) is a significant part of insulating and lowering energy consumption for heating and cooling.
- Execution of insulation is an important part of ensuring that the insulation performs as expected.
See insulated glass for discussion of windows.
[edit] Airtight envelope
A thermal envelope encloses conditioned or living space in a house. To prevent heat loss or gain, the envelope must be airtight within a range of tolerance not easy to achieve. Airtightness must be built in. The attic and basement can be unconditioned space, but either, or both, can be part of the conditioned space.
Stopping air infiltration is a necessary step in insulating a building. Depending on climate, up to 40% of a building's heat loss or gain is due to air leaks to the outdoors. Source: http://www.ornl.gov/sci/roofs+walls/whole_wall/airtight.html . Quality of work is key. Gaps in taped seams, and cracks in materials in walls, are too deep to be considered a function of weatherproofing, or weatherization.
Once airtight, a building needs an active air exchange system, or a passive system to manage air, in order to prevent humidity buildup. If not, then the building rots from the inside over many years, as moisture (or invisible humidity) accumulates in or near these insulating materials, thus harbouring conditions enabling mold, bacteria and other microorganisms to thrive inside walls. Moisture control depends totally on the choices made for thermal insulation, and a buildup of moisture can reduce the effectiveness of insulation drastically. Airtightness prevents inside air from escaping to the exterior. This traps water vapour (a gas lighter than air) in the inside portion of walls and especially attic and roof structures inside the envelope. This reduces the effectiveness of materials used as insulation. Thus the need to manage humidity and exchange outside and indoor air.
[edit] Insulation materials
There are many different building insulation materials used to provide thermal insulation. For details, see building insulation materials. Due to this variety and the various building elements that may require insulation, there are a number of ways of installing building insulation.
[edit] Isolating to prevent heat bridging
Heat flows through the path of least resistance. A thermal bridge is created when materials that are poor insulators come in contact. Wood and rubber are poor insulators compared to other materials known as insulators; thus heat flows through joists and studs unless insulated. Therefore, loose-fill insulation such as cellulose & granulated glass wool that are installed over the timbers joists and studs, achieve superior insulation performance at higher insulation levels.
In low-energy buildings measures are taken to reduce or eliminate thermal bridging, which becomes an increasingly important source of heat loss as the thermal performance of the other elements of the building envelope is improved.
- See also thermal conductivity
[edit] Thickness and effectiveness of insulation
The R (Resistance) value of a material indicates its resistance to heat flow, and therefore its effectiveness as an insulator against conduction. R-values are measured at 75 °F (22 °C) and are calculated from the thermal conductivity, k, and the thickness, d, of materials: R = d/k.
The thickness of the materials must be considered when comparing R-values. For instance, the R-value of a 14-inch adobe brick is about R-4, while that of an equal thickness of cellulose, at R-3 per inch, is about R-42.
How much insulation a house should have depends on building design, climate, energy costs, budget, and personal preference. Regional climates make for different requirements as to R-values of each component of a building. Building codes specify only the bare minimum; insulating beyond what code requires is often recommended.
Insulating as tightly and completely as one can while building a house is much easier than retrofitting. For example, if a closed-cell foam gasket is not installed to the sill plate when a house is under construction, there is no way to install it afterwards.
[edit] Obtaining advice
In a home energy audit, professionals evaluate the energy efficiency of the home, using blower doors, infrared cameras, and other air leakage measuring equipment. They identify the greatest leaks and recommend the best ways to improve the energy efficiency of your house. They tell you what you should do first for the best bang for the buck.
Who to call for a home energy audit:
- Public utility companies, or their energy conservation department.
- Independent, private-sector companies such as energy services company, insulation contractor, or air sealing specialist.
- State energy office.
- Websites for any of the above.
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.
Where to look for insulation recommendations:
- Local building inspector’s office.
- Local or state building codes.
- US Department of Energy.
- Websites for any of the above.
[edit] See also
- Installing building insulation
- Building insulation materials
- Superinsulation
- R-value (insulation)
- Passive house
- Zero energy building
- Wool insulation
- Building construction
- Building Envelope
- Weatherization
- Condensation
- Thermal mass
- Thermal insulation
- Low-energy building
