Warmth is a valuable commodity and it will seek every possible means to escape from our homes. Walls, roofs, floors, chimneys and windows are all escape routes, and in most homes escape is easy. The answer is to wrap the home in a thermal blanket which involves
• insulation; and
• draught sealing.
Space heating usually makes the greatest demand on energy. The procedures described below could reduce energy bills by up to 50 per cent and more in the most substandard properties. Starting with insulation, it is necessary to outline the range of insulants currently available and to summarize their characteristics. When we come to consider the elements of a house in detail, there will be further advice regarding the insulants appropriate to a particular situation since it is important to know that some insulants carry risks.
The range of options
There are numerous alternatives when it comes to choosing insulation materials.They differ in thermal efficiency and certain important properties, such as resistance to fire and avoidance of ozone-depleting chemicals. Some also lose much of their insulating efficiency if affected by moisture. So, at the outset it is advisable to understand something about the most readily available insulants. The thermal efficiency of an insulant is denoted by its thermal conductivity termed Lambda value measured in W/mK. The thermal conductivity of a material ‘is the amount of heat transfer per unit of thickness for a given temperature difference’ (Thomas, 1996: 10). Technically it is a measure of the rate of heat conduction through 1 m3 of a material with a 1°C temperature difference across the two opposite faces. The lower the value the more efficient the material.
It is important to select insulants which have zero ozone-depleting potential (ZODP). There are three main categories of insulation material.
• Inorganic, mineral based
• Organic synthetic, derived from oil
• Natural organic, derived from animals and plants.
Mineral-based insulants come in two forms, fibre or cellular structure.
Produced by melting a base substance at high temperature and spinning it into fibres with a binder added to provide rigidity. It is vapour and air permeable due to its structure. Moisture can build up in the insulant reducing its insulating value. May degrade over time. Lambda value 0.033-0.040 W/mK.
As for rock wool.
Health and safety
There is a health issue with fibrous materials. Some cause skin irritation and it is advisable to wear protective gear during installation. Loose fill fibre insulants should not be ventilated to internal habitable spaces. There has been the suggestion that fibrous materials constitute a cancer risk. However they are currently listed as ‘not classifiable as to carcinogenicity in humans’.
Manufactured from natural materials and over 40 per cent recycled glass. It is impervious to water vapour and waterproof, dimensionally stable, noncombustible, vermin-proof and has high compressive strength as well as CFC and HCFC free. Lambda value 0.037-0.047 depending on particular application. Typical proprietary brand: Foamglas by Pittsburgh Corning (UK) Ltd.
Vermiculite is the name given to a group of geological materials that resemble mica. When subject to high temperature the flakes of vermiculite expand due to their water content to many times their original size to become ‘exfoliated vermiculite’. It has a high insulation value, resistant to decay, odourless, and non-irritant.
Organic/synthetic insulants are confined to cellular structure: EPS (expanded polystyrene)
Rigid, flame retardant cellular, non-toxic, vapour resistant plastic insulation CFC and HCFC free. Lambda value 0.032-0.040 W/mK XPS (extruded polystyrene)
Closed cell insulant water and vapour tight, free from CFCs and HCFCs, Lambda value 0.027-0.036 W/mK PIR (polyisocyanurate)
Cellular plastic foam, vapour tight, available CFC and HCFC free Lambda value 0.025-0.028
Rigid cellular foam very low Lambda value, vapour tight, good fire resistance, available CFC and HCFC free. Lambda value 0.018-0.019 W/mK
In general, cellular materials do not pose a health risk and there are no special installation requirements.
Fibre structure: Cellulose
Mainly manufactured from recycled newspapers. Manufactured into fibres, batts or boards. Treated with fire retardant and pesticides. Lambda value 0.038-0.040 W/mK
Must be treated with boron and a fire retardant. Disposal may have to be at specified sites. Lambda value 0.040 W/mK
Treated with polyester and boron Lambda value 0.037 W/mK
Heat-treated and compressed into fibre boards. Treated with fire retardant and pesticide. It can be used as a wall material with a high thermal efficiency. Hopefully in its present day form it will be much more reliable than the strawboard of the 1960s. Lambda value 0.037 W/mK
Under development as a compressed insulation board. A highly eco-friendly material, grows without needing pesticides and produces no toxins. Initial tests have used hemp as a building material mixed with lime and placed like concrete. Test houses have proved as thermally efficient as identical well-insulated brick built houses built alongside the hemp examples.
Insulation materials should be free from HFCs and HCFCs,
• The choice of insulation material is governed primarily by two factors: thermal conductivity and location in the home. These points are considered further in topics 3 and 4.
• The ecological preference is for materials derived from organic or recycled sources and which do not use high levels of energy during production. However, there are certain overriding factors which will be described below.