Insulation acts in two ways — in winter, it’s like a blanket that keeps buildings warm, and in summer, it’s like the walls of a chilly bin, keeping buildings cool. Heating or cooling an
un-insulated building is like trying to fill a bath with water, but not putting in the plug.
As insulated surfaces are warmer, condensation is less likely to form on them. As a result, an insulated building will have less mould and mildew, and be a less appealing environment for allergy-aggravating dust mites.
The thermal envelope is the insulation barrier between the heated and unheated spaces. It is the invisible wrap which protects the inside of the building from the outside climate. Ideally it should be continuous, have no gaps and have a minimum of weak points around things such as windows, doors, skylights, ceiling fans, downlights and chimneys.
Insulation generally works by trapping air, which is the most effective method, and/or reflecting heat. Materials that provide good heat insulation are lightweight because they contain large amounts of tiny pockets of still air.
The “R-value” measures how good the insulation material is at containing heat. The higher the R-value on an insulation product, the more it slows down the transfer of heat and the more effective it will be.
Generally, the R-value of insulation gets higher as the product gets thicker. For example, an R3.0 product has greater thickness than an R1.0 product of the same type.
However, using R-values helps builders compare the effectiveness of different types of insulation. It should also be noted that insulation needs to be properly installed to reach its R-value and work effectively.
Types of insulation
Glass wool/Fibreglass (eg Pink Batts, Bradford Gold)
Widely available.
A range of R-value products suitable for ceilings, walls and under-floor, including high R-values (“Ultra” type products).
Some products are Environmental Choice- certified and have high rates of recycled glass content.
Suitable for installation in new builds or renovations.
Available as batts and as blankets.
Fibres can irritate installers, and it is not easy to install in ceilings with very low roofs or under floors where access is difficult.
Must be properly installed to perform well, and doesn’t perform when wet.
Early installations (eg those done in the 1970s and 80s) may well have slumped and are of a very thin product — these need topping up or replacing.
Long lasting product — current products have an expected 50-year life.
Wool (eg Eco Fleece, Terra Lana, Latitude, Rockwool, Woolcote)
Widely available.
A range of R-value products suitable for ceilings, walls and under-floor. Slightly lower R-values than fibreglass for same thickness of material. Often available mixed with polyester.
Some products have a high proportion of recycled fibre.
Chemical treatment protects from fire and pests.
Suitable for installation in new builds or renovations.
Available as batts and blankets, or as loose fill.
Not easy to install in ceilings with very low roofs or under floors where access is difficult.
Polyester (eg Autex Greenstuf, Novatherm, Eco Insulation, Cocoon)
Widely available.
A range of R-value products suitable for ceilings, walls and under-floor. Slightly lower R-values than fibreglass for same thickness of material.
Some products are Environmental Choice- certified and have high recycled content.
Suitable for installation in new builds or renovations.
Available as batts and as blankets.
Not easy to install in ceilings with very low roofs or under floors where access is difficult.
Stable, long life product although prone to compression damage if stored inappropriately before installation.
Polystyrene (eg Expol, Retrotherm, Poly Palace, Styrofoam)
Widely available.
A range of R-value products suitable for ceilings, walls and under-floor, although in retrofit situations mainly used under-floor. Slightly higher R-values than fibreglass for same thickness of material.
Available as sheets, beads or less commonly embedded in structural elements.
Current products are CFC-free but some early products used CFCs, so care with their disposal is needed. Some products have high recycled content.
Stable and long life product, although can be vulnerable to damage if exposed. Some shrinkage can occur over time which can affect friction fittings (eg in floors).
Straw
Specialist installation required for straw bale construction — used for wall insulation as a structural element in new homes.
Very high R-values can be achieved.
Renewable product.
Chemical treatment protects from fire and pests.
Durability is affected by extreme sensitivity to moisture, and protection from moisture during construction is critical.
Cellulose/Macerated Paper (eg Insulfluff)
Specialist installation required for blown-in fibre into ceilings.
Has been used in ceilings where access for installation of insulation is difficult. Initial R-values can be similar to fibreglass, but deteriorate over time.
Chemical treatment protects from fire and pests.
Some products contain high recycled content.
Lower cost product than other forms of insulation, but has a shorter life as it is prone to slumpage and moisture penetration over time.
Older installations (eg from 1970s and 80s) are likely to be ineffective now.
Unsafe for use where downlights have been installed as it can create a fire risk.
Hardened U/F foam (eg Airfoam)
Available for installation by specialist installers for retrofits into wall cavities as a blown-in foam.
Unsuitable for brick construction as blocks drainage cavity needed to prevent walls rotting.
Higher R-values than fibreglass.
A 2010 BRANZ study found the installed R-value was less than claimed, the product was prone to cracking, shrinkage and voids, and moisture management could be a problem.
Polymer (eg AirCell, Silverzone)
Available for DIY or for specialist installers.
Used in ceilings and under-floors. Claimed R-values are higher than installations in place. Available as foil-backed rolls for under-floor installations.
Can sometimes be installed in situations where other insulation is difficult (lower under-floors).
Metallic foil (eg Silversark, Sisalation)
Available for DIY or for specialist installers.
Low R-value product.
Used in new homes and retrofitted to suspended floors.
Prone to deterioration and physical damage leading to poor performance over time. Also has risk of electrocution with installation (stapling).
Older installations (more than 5 years old) should be replaced with a better performing product.
Aerated concrete
A specialist installation product mainly used in new installations of walls and floors as blocks and pre-formed panels. A pumped-in product is available for retrofitting under-floors.
Low R-values (0.7 per 100mm).
Expected to be durable for the life of the building.
Insulated concrete
A specialist installation product for walls of new buildings.
R-value depends on the thickness of the insulation — can be higher than fibreglass.
Available as blocks and pre-formed panels, normally with polystyrene as the insulation.
As it is an insulated thermal mass, it can be used for heat storage.
Expected to be durable for the life of the building.
