With the increasing emphasis on energy-conscious design and the broader environmental impact of buildings, greater attention is necessarily being focused upon the appropriate use of thermal and sound insulation materials.
Thermal and Sound Insulation Materials
The Approved Document of the Building Construction Regulations gives guidance on minimum thermal performance criteria for buildings (Piping and Duct Works) based on standards for their individual elements, or the overall energy efficiency of the whole building. To consider the relative efficiency of insulating materials, the thermal conductivities (W/m K) are quoted at the standard 10°C to allow direct comparisons. U-values would not illustrate direct comparability owing to the varying thicknesses used, and the wide variety of combinations of materials such as Polyethylene Rolls and Sheets Insulation typically used in construction.
In considering acoustic control, distinction is made between the reduction of sound transmitted directly through the building components and the attenuation of reflected sound by the surfaces within a particular enclosure. Furthermore, transmitted sound is considered in terms of both impact and airborne sound. Impact sound is caused by direct impact onto the building fabric which then vibrates, transmitting the sound through the structure; it is particularly significant in the case of intermediate floors. Airborne sound waves, from the human voice and sound generating equipment, cause the building fabric to vibrate, thus transmitting the sound. Airborne sound is particularly critical in relation to separating walls and is significantly increased by leakage at discontinuities within the building fabric, particularly around unsealed openings. This phenomenon works in the same way as in Thermal Insulation The reduction in sound energy passing through a building element is expressed in decibels (dB). The doubling of the mass of a building component reduces the sound transmission by approximately 5 dB, thus sound insulating materials are generally heavy structural elements. However, the judicious use of dissipative absorbers within walls can reduce the reliance for sound absorption on mass alone. Noise may be transmitted through services installations, so consideration should be given to the use of acoustic sleeves and linings as appropriate.
The absorption of sound at surfaces is related to the porosity of the material. Generally, light materials with fibrous or open surfaces are good absorbers, reducing ambient noise levels and reverberation times, whereas smooth hard surfaces are highly reflective to sound (Table 13.1). Sound absorption is measured on a 0 to 1 scale with 1 representing total absorption of the sound.
Forms of Thermal/Sound Insulation Materials
Thermal and sound insulation materials may be categorized variously according to their appropriate uses in construction, their physical forms or their material origin. Many thermal insulating materials are available in different physical forms each with their appropriate uses in building. Broadly, the key forms of material could be divided into:
1) Structural roof insulation materials;
2) Rigid and semi rigid sheets and slabs;
3) Loose fill, blanket materials and applied finishes;
4) Aluminum foil.
However, within this grouping, it is clear that certain materials spread over two or three categories. Insulation materials are therefore categorized according to their composition, with descriptions of their various forms, typical uses in construction and, where appropriate, fire protection properties. Thermal Insulation Materials are initially divided into those of inorganic and organic origin respectively.
The broad range of non-combustible insulating materials is manufactured from ceramics and inorganic minerals including natural rock, glass, calcium silicate and cements. Some organic products are manufactured from natural cork or wood fibers but materials developed by the plastics industry predominate. In some cases these organic materials offer the higher thermal insulation properties but many are either inflammable or decompose within fire. Cellular plastics include open and closed-cell materials. Generally the closed-cell products are more rigid and have better thermal insulation properties and resistance to moisture, whereas the open-cell materials are more flexible and permeable. Aluminum foil is considered as a particular case as its thermal insulation properties relate to the transmission of radiant rather than conducted heat.