Confused about insulation
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Why insulate? Energy savings, health, comfort. Insulating your home will save energy and provide a healthier and more comfortable indoor environment. Insulated surfaces are warmer. Condensation is less likely to form on them so there is less mould and mildew. In summer insulation will keep the heat out, making your home cooler. Insulation will provide a more even temperature all year round.
The initial investment of installing higher insulation than the Building Code prescribes will pay off over time because you save money in energy bills. Older homes often have little or no insulation but they can be retrofitted, making them much more comfortable and saving energy for heating. The payback period for installing ceiling insulation, for example, is about 5 years. However the main motivation behind installing insulation is often the added comfort and warmth, rather than financial savings.
How does it work?
Most insulation works by trapping air in cavities. The smaller the cavities of trapped air, the better the insulation material will work.
Where to insulate
The main heat loss in an un-insulated home is through the ceiling (42%). Walls also loose a significant amount of heat, but they are difficult to retrofit with insulation, without removing the internal lining. Floors only loose 10% of heat, but they are easy and cheap to insulate with floor coverings. Windows are the biggest heat drain for their area. They can be fitted with thermal drapes, but it is important that the curtains are well fitted and that pelmets are provided. Double-glazing is relatively expensive and is not generally economical unless the heat loss is extreme - as with skylights, conservatories, and large south-facing windows built to take advantage of views.
To what level (R-values)?
The ability of a material to insulate is measured as thermal resistance, or R-value. The higher the R-value the better is the insulation. The R-value increases with the thickness of a material. Installing higher ceiling insulation lets you compensate for lower wall insulation.
Keep in mind that it is much easier to fit insulation while building than to retrofit it later. Increasing the R-value at the time of construction is relatively cheap.
When retrofitting, choose a product of at least 2.0 R-value for your ceiling - the higher the R-value the better.
The best insulation material can be ineffective if it is installed poorly. How well your insulation is fitted is important, because heat can escape through small gaps or by thermal bridging. Thermal bridging occurs, when a material with lower thermal resistance allows the heat to by-pass the insulation. One example is stud framing, which has a lower thermal resistance than insulation. Heat passes through the framing at a faster rate than it does through the batts in the spaces between.
To avoid air gaps batts fitted into walls or ceilings should be slightly larger than the size of the cavity for a friction fit.
What material to choose
There are several insulation materials on the market - all have their pros and cons.
Polyester (approximately R 2 for 100mm batt)
The performance of polyester is good. It is a non-renewable resource (made from mineral oil) and is more expensive than fibreglass. However the health concerns raised about fibreglass do not apply to polyester insulation. Polyester will not burn easily, but it will give off dense smoke.
Fibreglass (and Rockwool) (approximately R 2.4 for 100mm thickness)
This is the most commonly used insulation material. Its technical performance is well proven and it outperforms most other materials in R-values. Fibreglass does not burn, but it can melt in the intense heat of a house fire. It tends to be cheaper than alternative options.
However, fibreglass is a non-renewable resource and concerns have been raised about health impacts on installers and occupants. It is the size of the fibres that causes concern to some scientists, and comparisons to asbestos have been made. The World Health Organisation, has recently removed glass wool insulation from its list of possible carcinogens into the category labelled as "not classifiable as to its carcinogenicity to humans".
Fibreglass can cause irritation of the skin and respiratory tract. If you do choose fibreglass or Rockwool wear gloves, full shirtsleeves, long trousers, and a mask while installing it. Fibreglass and Rockwool are available as batts, blankets and loose fill insulation.
Wool and wool blends approximately R 2.5 for 100 mm of loose fill - less for batts and blankets*)
Wool is a natural resource and it is pleasant to handle, making it a good choice for DIY installation. However current wool products do not perform as well as fibreglass technically (as highlighted in a recent Consumer magazine article). Wool products are also currently 10-20% more expensive. Manufacturers claim that wool will balance the moisture content in the air by absorbing moisture and giving it off later. Some also say that wool has the ability to absorb indoor pollutants, such as those resulting from furniture or flooring glues. A lot of research and development is now taking place in the wool insulation industry and products are likely to keep improving.
All wool products on the market have been treated to discourage mould and pests. Wool will burn if it comes into direct contact with a flame, but will not ignite through heat or aid a fire to spread.
There are two different types of wool products available. Some are sprayed with a resin to bind the fibres and provide strength, while others are blended with polyester. Wool is cheaper as loose fill insulation – comparable to fibreglass.
Recycled paper (approximately R 2.2 for 100mm loose fill)
Generally loose fill insulation is cheaper than batts. It has to be installed by a contractor, and is best suited for ceilings, where it should fill all small gaps and cover the framing. Loose fill insulation can settle over time reducing its effectiveness. It can also be blown to one end of the ceiling cavity if there are strong drafts. Get the contractor to give you a guarantee of the R-value and the thickness.
Recycled paper treated with a fire retardant can be used as loose fill insulation in ceilings. Like all loose fill materials its performance depends on the quality of the installation, so ask to see test results and request a written guarantee. The ceiling cavity has to be dry, because wet paper will sink and the R-value will be reduced.
Polystyrene (approximately R 1.4 for 50 mm sheet)
Polystyrene is used increasingly in new buildings. It can be used in sheets on framing and then plastered, or under concrete floors. Hollow polystyrene blocks that are filled with reinforced concrete give very good R-values. Polystyrene is a product of the petro-chemical industry and therefore a non-sustainable resource. It gives off toxic fumes in a fire, though not if it is sealed under a concrete floor slab. Its insulation properties are excellent.
Foam products (R value varies but similar to polystyrene)
These are products that are injected into cavities and expand. Many are propelled by CFCs and HCFCs, which deplete the ozone layer. Foams, such as urea formaldehyde and polyurethane foams, can release small amounts of toxic substances over time contributing to indoor air pollution.
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