Home Insulation

Things You Should Know

Good home insulation makes economical sense. Lets face it buying a new house or having one built is possibly the largest investment that you will make in your lifetime.

You and your family will fill your home with all the things that you all cherish and love because everything in your home is important to you, and rightly so.

However, there is something in your home that is very important which you wouldn't normally see when you are living there, and that is the insulation.

Below is a list of what's on this page:

For more information on the thermal heat loss from a house see the Thermal Heat Loss page.

Why is Home Insulation So Important?

Home insulation is without doubt an important aspect of your home that has a direct influence on your energy consumptions relating to your home heating needs.

This is because of cold air attraction and heat transfer:

  • Insulation is designed to inhibit this transfer of outward flow of heat and the inward flow of cold air attraction.

So, home insulation is important to keep the heat in and limit heat loss from your home.


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What is Cold Air Attraction?

Cold air is naturally attracted to warmer air just as cold objects attract the heat from warmer objects. So when heating a poorly insulated house all that's happening is a continued use of energy to heat your home over and over again.

You could compare good home insulation to a good warm glove, and your hand inside that glove represents a nice warm house. Wearing this glove you could place your hand next to a block of ice and feel no chill in your hand as the heat is retained inside the glove keeping your hand warm.

If you placed your bare hand next to a block of ice you would soon feel the tingling chill as the heat from your hand is drawn out by the cold, this is exactly the same thing that occurs with a poorly insulated house.

Good insulation reduces unwanted cold air infiltration into the building and heat loss from the fabric/structure of the building.

Therefore, when you're thinking about installing a home heating system the proper home insulation must be achieved first. This will save you heaps of cash as your home heating system will not have to supply high heating loads to off-set the excessive heat loss due to poor or inadequate insulation.

Remember if the 'form' of your building isn't simple then you will be spending more on home insulation compared to a building that has simple 'form'.

Note: All buildings must be adequatly ventilated for good air quality, the removal of water vapours and the prevention of bacterial growth such as mould and fungi.


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What Are The Types of Insulation?

There are two main categories of thermal home insulation - bulk and reflective. For example, fibre, polyester, polystyrene and mineral wool are of the 'bulk' category while aluminium/aluminum foil is in the 'reflective' category. These are sometimes combined into a composite material fibre and aluminium/aluminum for underfloor installations.

  • Bulk insulation mainly resists the transfer of conducted and convected heat, which is achieved by trapping air within its structure. Because of these numerous air pockets it is able to thermally resist heat transfer regardless of the direction of heat flow, like an excellent ski-jacket.

  • Reflective insulation acts by resisting the radiant heat flow by its high reflectivity (its ability to reflect light-waves) and its low emissivity (this means the ability of a material to emit heat, for example, iron has high emissivity, while aluminum foil has a low emissivity) which means that foil is great at reflecting radiant energy.

    The thermal resistance of foil will however vary depending on the direction of heat flow. The greatest resistance is below the heat source which is why this is such a good underfloor insulator.


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What Insulation Products Are Available?

Perimeter Slab Insulation reduces heat loss like all home insulation adding to energy savings.

Perimeter slab insulation can be constructed from:

  • Polystyrene Sheets
  • Foam Boards
  • Styrofoam
    • Polystyrene Sheets can be laid below or above the slab. The polystyrene sheet and slab are separated with a plastic membrane
    • Foam Board insulation come in a variety of types - the most common are polystyrene, polyisocyanurate or polyiso, and polyurethane (polyisocyanurate or polyiso is a thermosetting type of plastic. Thermosetting plastics can only be heated once to form a shape if heated again it will just melt). Foam boards are rigid panels of insulation that can be used to insulate almost any part of your home, from the foundation right up to the roof. They provide good thermal resistance in your home.
    • Styrofoam is used in roofs or slab insulation because of its long term performance, and when this type of insulation is buried the moisture resistance and long term compressive resistance of this product is fully utilized.

If you contact your local weather bureau or agency for your area's 'Heating Degree Days' (HDD) you will be able to get the annual (historic) HDD data for your area. You can then use that data in the table below to work out the 'R' value of your slab insulation based on foundation depth

('R' means the ability the material has to resist the transfer of heat through it - the higher the 'R' value the better the insulation).

Heating Degree Days
Depth mm
R Value
0 - 2499
not required
not required
2499 - 4500
4500 - 6000
6000 - 7200
7200 - 8700
8700 - 10000
10000 - 12400
12400 - 14000

Note: The temperature inside of an unheated building is usually around 2.78ᵒC higher than the outside air temperature, so when the outside air temperature is at 15.6ᵒC the inside temperature will be 18.3oC and this is close to the average internal design temperature.

The 'Degree Day' is the difference between 15.6ᵒC and the daily 'mean' outside temperature when it is below 15.6ᵒC. However, if you prefer to be warmer use 18 instead of 15.6ᵒC as the base temperature.

A heating degree day represents how cold a particular day has been.

For example, if the mean outside temperature on a particular day was 8ᵒC then the number of 'degree Days for that day would be; 15.6 - 8 = 7.6 , or 18 - 8 = 10 (Degree Days).

The degree day values in the table above represents the annual total heating degree days, the foundation depth and thickness of slab insulation Heating degree days are also used to estimate annual fuel heating bills.

Celsius to Fahrenheit conversions
Enter Celsius
Value in Fahrenheit

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Fibre or polyester 'batt & roll' home insulation is constructed to slow the movement of air through it the same as a wooly jumper/jersey, or those string vests that kept you amazingly warm.

Generally used in roof cavities, walls and floors.

Also available is the combination of aluminum foil and fibre, for underfloor insulation.

Polystyrene is used to insulate a number of things from insulation of crash helmets and chilly bins to disposable coffee cups. The reason for this is because polystyrene is a very poor conductor of energy (force) and heat. This insulation is 'friction fitted' meaning it fits 'tightly between the floor joists with or without an air-gap.

Generally used under floors. Also available are 'Structural Insulating Panels' (SIP's) for walls. Some wall insulation products can be installed on the inside or outside of solid walls.

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Aluminum/Aluminum foil works by reflecting heat back into your home, just like a thermos/flask and the life saving survival blanket.

Generally used in floors.

Polyurethane Foam insulates and air-seals, it sound proofs and it is water resistant. You should confirm that the foam only contains environmentally friendly (safe) fire retardants.

Generally used in walls and roofs.

Mineral wool home insulation has excellent thermal resistance. The fibres in this product are non-combustible and used to prevent the spread of fires.

Generally used in walls, roof and ceiling space, and also used as pipe lagging/insulation.

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Well fitted Double Glazing can cut heat loss through it by as much as 50%, and if you had double glazing with 'low emissivity' then you can reduce heat loss by a further 30%. You will lose around 20% of total heat loss through single glazing even when there are draught proofed.

Door Seals for insulation against draughts.

Hot water cylinders should be insulated to conserve the heat in stored hot water cylinder. Insulation comes in wraps/jackets. Some cylinders are factory insulated with a polystyrene coat.

Pipe insulation (lagging) on hot water pipes will save you money in energy costs. The lagging of cold water pipes prevents freezing in adverse winter temperatures.

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Where Do I Insulate?

Installing insulation in these areas will prevent heat loss and reduce your energy costs:

  • Roofs and ceilings
  • Verandah roofs - insulation will prevent heat gain allowing for comfortable external use in summer
  • Bulkheads - wall sections between ceilings of different heights
  • External walls
  • Floors
  • The underside of suspended floors
  • Under or above ground slabs

Note: The 'R' value (resistance) of a product represents the ability of that product to resist the transfer of heat (temperature) through it. The higher the 'R' value the better the insulation. Make sure that the product is energy rated for your geographical region (different regions - different external temperatures). Also, depending on the particular situation, some forms of home insulation can double as a vapour or moisture barrier.

Good home insulation can seriously reduce your energy needs for heating and domestic hot water.

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