Insulation

Insulative materials are used to give the required thermal properties to the building, and are available as part of a built-up system or within composite panels.

Mineral and glass fibres are made from sand, limestone or refined borax in the case of glass fibre and volcanic rock or dolomite in the case of rock fibre. The fibres are relatively stable and durable, and, when combined with small amounts of resin added as a binding agent, can be formed into mats, quilts and semi-rigid slabs. The relevant standard for the production of glass mineral fibre is BS 3533:1981. There are hazards, however as mineral fibres are classed as irritants. To deal with them safely, workers are advised to wear protective clothing, including gloves, eyeglasses and disposable respirators. The density of mineral fibres varies, depending on its form and can be up to 150 kg/m3 for dense slab.

Both mineral and glass fibre contain some recycled material, although at present only manufacturing waste is recycled, as impurities can affect the quality of the product. However, mineral fibre can be reused if it is extracted carefully. Thin paper or other film facings reduce irritation and installation time. Mineral fibres are non-corrosive, fungus and insect resistant, flame retardant, and used for fire resistance.

Polyurethane/Polyisocyanurate foams (PUR/PIR) can be found in a rigid form or, alternatively, can be foamed insitu. Foams which are CFC/HCFC-free (using pentane, water or carbon dioxide) are now widely used. They are manufactured from petrochemical products. The main difference between PUR and PIR is that PIR has superior thermal stability and performance in fire. PIR products are commonly used because they char more easily than PUR products. With the correct chemical formulation, char can be stable and is therefore advantageous with regard to fire protection.

Extruded polystyrene (XPS) and expanded polystyrene (EPS) are carbon (oil or natural gas) based synthetic polymers. XPS has a skin and is therefore ‘closed-cell’ and does not absorb water. Typical K values of XPS are better than EPS. XPS has about twice the compressive strength of EPS at a reduced density. CFCs and HCFCs have been phased out, and alternative blowing agents are now used.

Built-up systems use mainly mineral fibre or glass fibre insulation quilt, supplied in roll form. Systems also exist which use profiled mineral fibre slabs, profiled polyurethane (PUR) and polystyrene slab. Insulation thickness depends on the U-value specified for the application and mineral fibre and glass fibre have higher thermal conductivities but have better fire performance than plastic insulants. The two pre-finished steel sheets are held apart by a spacer system, which must allow the quilting to loft fully and not lead to excessive localised cold bridging.

Composite panels comprise an external sheet, a rigid insulation core and liner sheet, which are bonded together. The panels may be formed from separate elements, which are adhesively bonded together, or produced on a composite panel line, where the expanding foam core material bonds to both prefinished steel sheets. Two main types of foams are used – PIR and PUR, both of which provide excellent thermal insulation. Composite panels are also available with a mineral fibre core adhesively bonded to the metal sheets.

The main physical properties of the commonly available insulation materials are detailed in the table below.

Insulation thermal properties are normally expressed as thermal conductivities. This can be translated as a thickness of insulation, which is required to meet the correct U-value as specified in the Building Regulations. The table below shows the different thickness of the most common insulation with typical K-values, required to meet these requirements.

*Bar and bracket spacer depth is 10 mm greater than insulation thickness, based on a 19 mm deep lining panel. If a 32 mm deep liner is used, then spacer depth should be increased by 10 mm.