“Air” itself is poor at conducting heat. When held still, it is a good insulator. Most forms of bulk insulation utilise this. They trap air within a ‘mesh’ of material. Typically the thicker and more dense these products are the better the insulation qualities they have. Note that different product types will be different thicknesses to achieve the same rating. Be sure to assess products by their R-Value rather than thickness. For example Glass Wool (otherwise known as fiberglass) can be thinner than polyester to achieve the same thermal performance. The main types of bulk fill are fibreglass, polystyrene, polyester and wool. Fibreglass is the cheapest but least pleasant to work with, polyester sits mid range on price and like wool is safe and non irritant to work with.
Polyester and wool are generally better for wall insulation as they can be stapled into place hence will never slump or sag but you will pay a little more for these products.
Fibre forms of insulation work in much the same way as a jersey you wear. Generally the thicker the product the better in works. The most popular form of fibre underfloor insulation is polyester. The key advantage of fibre types of insulation is that they allow the floor to ‘breathe’ while still offering excellent thermal qualities. Pre-cut products are available for fitting between your joists or alternatively blanket format is also available for attaching underneath the joists. They are not particularly suitable for high wind zones or where you have a rising dampness issue but they do offer very good performance and very long life.
Polystyrene Underfloor insulation is a well known product on the market. It works in your home just like it does as a coffee cup or chilly bin. There are different forms of polystrene products available on the market, each with a small differences. We prefer Retrotherm as it is the more simple and effective products to install. Polystyrene is great for dampening sound reverberation in wooden floor boards and also acts as a partial vapour barrier. Available in wide variety of widths (360mm, 410mm, 440mm, 470mm and 560mm) it is always installed between your joists and each piece is cut to size and friction fit up in place.
Reflective forms of insulation (ie. foils such as Silverzone) work to reflect radiant heat. Some more sophisticated forms of foils utilise an air gap between layers of aluminium sheets to boost performance.
In July 2016 the NZ Government banned the installation or repair of foil insulation in homes with an existing power supply connection.
Foil can still be used in new commercial building and buildings with no live power system
Foil insulation works as a convectional and radiant barrier. It has been difficult to get the best performance out of traditional foils due to building construction methods and strength of products, however newer more advanced types on the market offer some fantastic performance features. The primary advantage of foil is that it acts as a complete vapour barrier stopping rising dampness coming into the home and they are also great for working in tighter areas. Foils are installed in blanket format making them quick and easy to install but there is risk of electrocution in using them so please read and watch the installation instructions carefully.