Some insulations use a combination of bulk insulation and reflective foil to achieve their insulating effect.
Bulk Insulations, such as fibreglass or cellulose fibre, reduce the rate of heat transfer due to conduction, convection, and radiation. The small air pockets which are trapped by the fibres or foam in the insulation help to reduce the rate of heat conduction and convection. The physical barrier provided by insulation reduces the radiant heat transfer.
Bulk insulations come in a variety of forms:
Insulation Batts, Blankets or Boards
Loose Fill Insulations - which are pumped or blown into a roof space
Foam - which can be pumped or sprayed into a roof or wall space.
Reflective Foil Insulation provides little resistance to conducted heat transfer, but it reduces the rate of heat transfer due to radiation. With a double sided foil, the front highly reflective surface reflects up to 95% of the radiant heat, and the other side emits only around 5%. To work effectively, the reflective surfaces must stay shiny, and there should be a still air gap of greater than 25 mm.
Reflective Foil Insulations come in two main types:
Reflective Foil Laminate (RFL) - available in double and single sided forms
Foil Batts, which are made up of 2 to 4 layers of foil separated by spacers.
If the reflective foil is installed horizontally or sloping, the top layer will become covered in dust, and this reduces the effectiveness of the insulation. If the reflective foil is installed with an air gap of less than 25mm, its effectiveness will also decrease.
Due to their ability to reduce radiant heat transfer, reflective foil insulations are better at reducing heat gains in summer than they are at reducing heat losses in winter.
Types of Insulation
Bulk insulation: traps pockets of still air within it structure, providing a barrier or resistance to heat flow.
Reflective insulation: reflects large amounts of heat away from its polished metallic surface (must face a sealed airspace at least 25 mm wide).
How is Insulation Measured?
When choosing insulation, the most important factor to consider is its R value.
The R value is a measure of the material's resistance to heat flow, and therefore its performance. The higher the R value, the greater the resistance to heat transfer, and the greater the energy savings.
Where to Insulate
Ceilings: saving 20-40% on heating and cooling costs
External walls: saving an additional 10-60% on energy costs
Floor: saving another 5-10% on energy costs
Existing homes can easily have insulation installed in the ceiling and under timber floors if crawl space is available. Walls can be insulated during recladding or replastering. Specialised products are also available to insulate existing walls.
Tips for good insulation performance
Do not compress bulk insulation. It must retain its normal thickness wherever possible.
Make sure corners of ceilings, walls and floors are properly insulated.
Keep bulk insulation dry at all times.
Make sure your wiring is appropriately rated. Have it inspected by an electrician to ensure it can be safely covered by insulation.
Caution! Do not install insulation within 90mm or hot flues or exhaust fans.
Do not put insulation over or around recessed light fittings " leave a 25 mm gap around their perimeters.
Avoid gaps in the insulation. Even if only 5% of the area is left uninsulated, up to 50% of the potential benefits may be lost.
The R value of loose-fill insulation depends on its density, not simply the depth to which it is installed.
Avoid loose-fill insulation if your roof space is excessively draughty, unless a sealant can be added to bond its top surface. Loose-fill insulation should not be installed on steeply sloping ceilings.
Reflective foil should be installed with a still air gap of at least 25 mm width next to the reflective surface.
Insulation
