Thermal & Sound Insulation

The use of insulation and prevention of sound transmission.

How Heat Is Transmitted

Conduction: the transmission of heat from one molecule to another within a material or from one material to another when they are held in direct contact.

Insert 14-4 conduction

Convection: the transfer of heat by another agent, such as air or water.

Convection Currents: the flow of air that is created within the space.

Insert fig. 14-4 convection

Radiation: the transmission of heat through a wave motion, similar to the way light is transmitted.

Insert fig. 14-4 radiation

Thermal Insulation Facts

Fibrous materials are generally good insulators Commercial insulation materials are made of:

Glass fibers Glass foam Mineral fibers Organic fibers Foamed plastic

Characteristics of a good insulation material: fireproof vermin proof moisture proof resistant to any

physical change that would reduce its effectiveness against heat flow

Selection of insulation is based on: Initial cost Effectiveness Durability Adaptation of its form

to that of the construction and installation methods

Heat Loss Coefficients

British Thermal Unit: Btu, the amount of heat needed to raise the temperature of 1 pound of water to 1 degree Fahrenheit.

Coefficient of Thermal Conductivity: k, the amount of heat, in Btu’s, transferred in one hour through 1 sq. ft. of a given material that is 1” thick and has a temperature difference between its surfaces of 1 degree Fahrenheit.

Conductance: C, the amount of heat that will flow through the material in 1 hour / sq. ft. of surface with a 1 degree Fahrenheit of temperature difference.

Resistance: R, the opposite of conductivity or conductance. A good insulation material will have a high R- value.

Total Heat Transmission: U, represents in Btu / sq. ft. / hour with 1 degree temperature difference for a structure which may consist of several materials or spaces.

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Map insulation zones for different parts of the U.S. R-values that are recommended by the U.S. Department

of Energy.

Types of InsulationInsert fig. 14-10

Flexible Insulation 2 types

Blanket: made of loosely felted mats of mineral or vegetable fibers. Generally furnished in rolls or strips of convenient lengths and various widths. Thicknesses vary from ¾” to 12”.

Batt: Thicknesses range from 3 ½” to 12”. Generally available in widths of 15”, 23”, 24” or 48”. Available with a single flanged cover or with both sides uncovered.

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Loose Fill Insulation: Composed of various materials in bulk form and supplied in bags or bales. It may be poured or blown.

Rigid Insulation: Used mostly in residential construction. Made by reducing fibers to a pulp and then made into a low density board.

Reflective Insulation: Usually a metal foil or foil-surfaced material. The # of reflecting surfaces determines its insulating value.

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Where to Insulate

Heated areas, especially in cold climates should be surrounded with insulation. Attics Crawl spaces Basements

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Condensation

Water Vapor Always present in the air Penetrates wood, stone,

concrete Warm, moisture laden air

within a heated building forms a vapor pressure which constantly seeks to escape and mix with the colder, drier outside air

Comes from cooking, bathing, clothes washing and drying and by humidifiers

Dew Point The temperature at which

the air is completely saturated with moisture

Any lowering of the air temperature will cause condensation

Moisture can cause deterioration of siding and paint and can also make surfaces wet

Vapor Barriers

A membrane through which water vapor cannot readily pass Protects ceilings,

walls, and floors 3 types: asphalt-

coated paper, aluminum foil, and polyethylene films

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Safety with Insulation

The Occupational Safety and Health Act (OSHA) does not have specific recommendations for working with fiberglass. Installing insulation is not particularly hazardous. However, it has proposed a permissible exposure limit (PEL). The American Conference of Governmental Hygienists has suggested limits. They recommend the following practices:

Wear loose clothing. Long sleeved shirts or blouses loose at the neck and wrists, caps and long trousers will prevent most fibers from coming in contact with the skin. Loose clothing will prevent chafing where fibers do contact skin. Gloves may be recommended in some circumstances.

Protect eyes. Use goggles or safety glasses with side shields when applying fiberglass materials overhead or where loose particles or fibers may get into the eyes.

Wear a mask covering the nose and mouth. Don’t rub or scratch the skin Wash work clothes separately Dispose of scrap materials

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Acoustical Terms

Sound: a vibration or wave motion that can be heard, reaches the ear through air, the air vibrates back and forth in tiny molecular motions of high and low pressure

Decibel: the unit of measurement used to indicate the loudness or intensity of sound; comparable to the “degree” as a measurement of heat or cold

Reverberation Sounds: airborne sounds which continue after the actual source has ceased, caused by reflections from floors, walls and ceilings

Frequency: rate at which sound energized air molecules vibrate Impact Sounds: sounds that are carried through the building by the

vibrations of the structural materials themselves Masking Sounds: normal sounds within habitable rooms which

tend to “mask” some of the external sounds entering the room

Decibels Reduction: expression used to indicate the sound insulating properties of a wall or floor panel

Sound Transmission Loss: STL, the number of decibels which sound loses when transmitted through a wall or floor

Sound Absorption: capacity of a material or object to reduce sound waves by absorbing them, these sounds are otherwise reflected and cause excessive reverberation and build up of intensity within that area

Noise Reduction Coefficient: NRC, the sound absorption of acoustical materials is expressed as the average percentage absorption at the four frequencies which are representative of most household noises, these frequencies are 250, 500, 1000, and 2000 cycles/second

Sound Transmission Class: STC, single number which represents the minimum performance of a wall or floor at all frequencies, the higher the STC number, the more efficient the wall or floor will be in reducing sound transmission.

Sound Intensity

Threshold of Audibility Threshold of Pain

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Wall Constructions

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