INSULATION MATERIALS

With the increasing importance of energy-conscious design and the broader environmental impact of buildings, greater attention is being focused on the appropriate use of thermal and sound insulation materials.

THERMAL AND SOUND INSULATION MATERIALS

To consider the relative efficiency of insulating materials, the thermal conductivities (λ W/m K) are quoted at the standard 10°C to allow direct comparisons.

λ – Symbol for thermal conductivity of materials, which was in the past denoted as k-value.

Thermal conductivity (λ-value) is a thermal property of a material, of its ability to conduct heat, measured as the rate of heat flow (W) over unit length (m) through that material over a unit area (m²), caused by unit temperature difference K).

W.m/m².K, by cancellation: W/m.K.

The rate of heat flow is the amount of heat transferred per unit of time in some material, usually measured in watts (joules per second).

Metals have high conductivities. Therefore low-conductivity materials are used as thermal insulation.

U-value is the thermal transmittance of a building element, expressed as the rate of heat flow through a unit area for a unit temperature difference between the air on either side of the component.

In considering acoustic control, a distinction is made between the reduction of sound transmitted directly through the building components and the reduction of sound reflected by the surfaces within a particular enclosure.

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 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 critical with separating walls and is increased by leakage at discontinuities within the building fabric, around unsealed openings.

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. Therefore, sound-insulating materials are generally heavy structural elements.

The absorption of sound at surfaces is connected 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 of sound.

Forms of insulation materials

Thermal and sound insulation materials may be categorized according to their appropriate uses in construction, their physical forms, or their material origin.

The key forms of materials may be divided into:

structural insulation materials;
rigid and semi-rigid sheets and slabs;
loose fill, blanket materials, and applied finishes;
aluminum foil;
vacuum and gas-filled panels.

Insulation materials are categorized according to their composition, various forms, uses in construction, and where appropriate, fire protection properties.

Materials are divided into inorganic and organic origin.

Non-combustible insulating materials are manufactured from ceramics and inorganic minerals. (Natural rock, glass, calcium silicate, and cement are some of them).

Organic products are from natural cork or wood fibers. However, materials manufactured by the plastics industry predominate.

Organic materials offer higher thermal insulation properties. However, many are either inflammable or decompose within fire.

Cellular plastics include open and closed-cell materials.

The closed-cell products are more rigid and have better thermal insulation properties and moisture resistance. The open-cell materials are more flexible and permeable.

Aluminum foil has thermal insulation properties related to the transmission of radiant rather than conducted heat.

Inorganic insulation materials

Foamed concrete – Foamed concrete with air content in the range of 30 – 80% is a fire and frost-resistant material. Foamed concrete can be easily placed and is suitable for insulating under floors and on flat roofs and can be laid to a fall of up to 1 in 100. (Thermal conductivity ranges from 0.10 W/m K at a density of 400 kg/m³ to 0.63 W/m K at a density of 1600 kg/m³.)

Lightweight aggregate concrete – Lightweight concrete offers a range of insulating and load-bearing properties, starting from 0.10 W/m K at a crushing strength of 2.8 MPa.

Resistance to airborne sound in masonry walls is closely related to the mass of the wall.

Gypsum plaster – The thermal conductivity of gypsum plaster is typically 0.16 W/m K. Sound transmission through lightweight walls can be reduced by using two layers of gypsum plasterboards with different thicknesses. The addition of an extra layer of plasterboard attached to existing ceilings can reduce sound transmission from upper floors.

Wood wool products – Wood wool products are manufactured from wood fibers and cement. These are both fire and rot-resistant. Wood wool slabs are suitable as a roof decking material, which may be exposed painted or plastered to the exposed lower face.

Wood wool slabs offer good sound absorption properties due to their open textured surface. This is unaffected by the application of sprayed emulsion paint. Acoustic insulation for a pre-screeded 50 mm slab is typically 30 dB. (The thermal conductivity of wood wool is typically 0.077 W/m K.)

Mineral wool – Mineral wool is manufactured from volcanic rock (silica, with alumina and magnesium oxide), and blended with coke and limestone, fused at 1500°C in a furnace. It is non-combustible, water-repellent, and rots-proof and contains no CFCs or HCFCs.

It may be used to reduce transmitted sound. Due to its non-combustible property, it can be used for the manufacture of fire stops to prevent fire spread, giving fire resistance ratings between 30 – 120 minutes.

Glass wool – Glass wool is non-combustible, water-repellent, and rots-proof. It contains no CFCs or HCFCs and is available in a range of products. The thermal conductivity of glass wool products ranges typically between 0.031 – 0.040 W/m K at 10°C. The sound and fire-resistant properties of glass wool are similar to those of mineral wool.

Cellular or foamed glass blocks – Cellular or foamed glass (CG) is manufactured from a mixture of crushed glass and fine carbon powder. The black material is durable, non-combustible, easily worked, and has a high compressive strength. It is water resistant due to its closed-cell structure, impervious to water vapour, and contains no CFCs.

Cellular glass slabs are suitable for roof insulation, including green roofs and roof-top car parks due to their high compressive strength.

The thermal conductivity of cellular glass is within the range of 0.037–0.055 W/m K at 10°C, depending upon the grade.

Organic insulation materials

Cork products – Cork is harvested from the cork oak. It is considered as an environmentally friendly material. For conversion into boards, typically used for roof insulation, cork granules are expanded, and formed under heat and pressure into blocks using the natural resin within the cork.

The thermal conductivity of the corkboard is typically 0.042 W/m K.

Sheep’s wool – Sheep’s wool is a very efficient renewable resource insulation material, with a low conductivity that compares favourably to other fibrous insulating materials. Wool is a hygroscopic material. That means, it reversibly absorbs and releases water vapour. This effect is beneficial when it is used for thermal insulation. The thermal conductivity is 0.039 W/m K.

Cellulose insulation – Cellulose insulation is manufactured from shredded recycled paper and other organic waste. It is treated with borax for flammability and smouldering resistance. This also makes it unattractive to vermin, and resistant to insects, fungus, and dry rot.

Cellulose is a hygroscopic material. Under conditions of high humidity, it absorbs water vapour and then releases it again under dry conditions. Cellulose is an effective absorber of airborne sound. The thermal conductivity = 0.035 W/m K to 0.040 W/m K in walls.

Flax, hemp, and coconut fiber – Due to increased demand for sustainable insulating materials, products originating from renewable flax, hemp, and coconut fibers are now available in the industry. Chopped hemp fibers, treated with borax for fire resistance, are used to produce insulation batts, and also as loose fill for floors and roofs. Coconut fiber thermal and acoustic insulation boards have the advantage of natural rot resistance. Typical uses include ceiling floor insulation.

Expanded polystyrene – Expanded polystyrene (EPS) is a combustible material, which, in fire, produces large quantities of noxious black smoke. Expanded polystyrene, a closed-cell product, is unaffected by water, dilute acids, and alkalis but is readily dissolved by most organic solvents. It is rot and vermin-proof.

Polystyrene beads

Recycled plastic insulation

Aluminum foil – Aluminium foil is used as an insulation material in conjunction with organic foam or insulating gypsum products. It acts by a combination of two physical effects. First, it reflects heat due to its highly reflecting surface. Second, owing to its low emissivity, the re-radiation of any heat that is absorbed is reduced. Thin aluminum reflective foil insulation can be inserted between studs, joists, or rafters, leaving a 25 mm air gap on either side. In addition to insulation, it acts as an air infiltration and vapor barrier.

Multi-layer aluminium foil