Insulation is a key component of sustainable building design. A well insulated home reduces energy bills by keeping warm in the winter and cool in the summer, and this in turn cuts down carbon emissions linked to global climate change.
In terms of energy efficiency, investing in high levels of insulation materials for your home is more cost-effective than investing in expensive heating technologies. It is worth taking the time to choose the right materials in the context of whole building design.
Insulation materials are used in roofs, walls and floors. Solid wall structures such as stone, cob and adobe cannot be insulated, but they have good thermal mass to compensate. Timber frame homes need wall insulation in the form of batts (pre-cut sections that are designed to fit between stud walls), rolls or boards. Other types of construction such as brick or concrete insulate with spray foam, loose fill or rolls. It is far easier and cheaper to install insulation in the walls and floors of a new build home, than to retrofit an existing home. However, insulating roofs is easily achieved in any home using rolls or bags of loose fill.
Insulation materials work by resisting heat flow, measured by an R-value (the higher the R-value, the greater the insulation). This R-value varies according to material type, density and thickness, and is affected by thermal bridging, unwanted heat flow that occurs at joists, studs and rafter beams.
Conventional InsulationConventional insulation materials are made from petrochemicals and include: fibreglass, mineral wool, polystyrene, polyurethane foam, and multi-foils. These materials are widely used because not only are they inexpensive to buy and install, but there is an assumption from the building industry that their performance ability is higher than the natural alternatives. On the downside, almost all conventional insulation materials contain a wide range of chemical fire retardants, adhesives and other additives, and the embodied energy in the manufacturing process is very high.
Natural Insulation MaterialsThe green alternative to synthetic insulation is natural insulation. There are many different types available, including:
Sheep's WoolThis material usually needs to be treated with chemicals to prevent mite infestation and reduce fire risk, although some natural builders use it untreated with success. It has very low embodied energy (unless it is imported) and performs exceptionally well as an insulation material. Thermafleece is the most common commercial brand available.
Flax and HempNatural plant fibres that are available in batts and rolls, and typically contain borates that act as a fungicide, insecticide and fire retardant. Potato starch is added to flax as a binder. Both materials have low embodied energy and are often combined in the same product. Examples include Isonat and Flax 100.
CelluloseA recycled product made from newsprint and other cellulose fibre. It is one of the most favoured materials of natural builders because it can be blown into cavity walls, floors and roofs; used as a loose fill; and is also available in quilts, boards and batts. Like hemp and flax it contains borate as an additive. Products include: Warmcell and Ecocel.
Wood FibreMade from wood chips that have been compressed into boards or batts using water or natural resins as a binder. It has very low embodied energy and uses by-products from the forestry industry. Examples include: Pavatex, Thermowall and Homatherm.
Expanded Clay AggregateThese are small fired clay pellets that expand at very high temperatures to become lightweight, porous and weight-bearing. They can be used in foundations as both an insulator and aggregate. They have excellent thermal insulation properties, but high embodied energy.
Insulating for a Better EnvironmentNatural insulation products have many advantages over conventional materials. They are low impact, made from renewable, organic resources and have low embodied energy. They can be reused and recycled, and are fully biodegradable. They are non-toxic, allergen-free and can be safely handled and installed. They also allow for a buildings to breathe by regulating humidity through their absorbent properties, and reducing problems of condensation. This keeps the indoor environment comfortable and protects any timber structures from rot. Unfortunately, natural insulation materials are currently up to four times more expensive than conventional materials, which can be prohibitive to builders, architects and developers. But the environmental and health benefits of natural insulation materials far outweigh their costs, and growing consumer demand combined with government regulation, and rising oil prices will inevitably drive prices down. Despite the high price, natural insulation is an energy-efficient, healthy and sustainable choice for a better indoor and outdoor environment.