We look at the types of home insulation available to Australians, and how to know which is right for your home. We will then explain what R-values and U-values are, what they mean and how you can calculate them.
The temperature at which the majority of humans are comfortable when they are at rest is between 18 and 24 degrees Celsius. While this average range of temperatures can sometimes occur without any help, in most parts of Australia, the outside air temperature will often be well outside this range. Inside the home, we use various climate controlling devices to alter the temperature to suit our comfort, either heating or cooling it depending on the location and time of year.
The energy required to heat and cool the inside of a home varies according to a range of influences including:
- The construction materials used to build the house initially
- The use of insulation materials of different types
- The method of heating or cooling used to change the temperature
- How much the temperature needs to be changed to maintain a comfortable environment for people indoors.
Insulation can be relatively simple to change in many building types, so we’ve decided to look at the various options available to Australians, and where they could work best.
Gains and losses with no insulation
In Victoria, over 50% of a household energy budget can be spent on heating and cooling the home according to this SEAV report from 2002. The cost of heating and cooling an uninsulated house is likely to be much higher than in a home with appropriate insulation, though some building materials are better at maintaining a stable inside temperature than others.
Houses with no insulation can lose up to 35% of their heat through the roof in winter, and gain a similar amount of heat in the summer months. Heat loss through windows is about 10-20%, but heat gain in summer can be as high as 35%. Both heat gain and loss through walls is up to 25%, and heat loss through the floor can be as high as 20% according to the figures from the SEAV report. This can add up to a large proportion of energy bills heating and cooling the peripheral environment rather than the areas where people are living.
For free-standing houses, the type of construction used will have a major impact on the energy efficiency of the building without any additional insulation. In units, apartments or flats with shared walls, floors and ceilings are generally more energy-efficient than free-standing houses. However, there are differences between the major house types in efficiency as well.
Wooden weatherboard homes are cheap to construct, but generally very inefficient when it comes to heat loss and gain. They heat up and cool down very quickly, and this is magnified by the typical roofing material of choice for weatherboard homes – predominantly lightweight metal sheeting.
By insulating floors, walls and ceilings of weatherboard homes, a potential saving of $1,120 per year on heating and cooling costs can be achieved over a similar house with no insulation. For an average weatherboard house, this kind of insulation will cost a little less than $8,000 according to the figures in this article from Sustainability Victoria, which means the changes will pay themselves off in less than seven years.
Double brick houses are an older type of house, though they have a lot in common with more modern cast-concrete buildings. The thermal mass provided by the thick masonry walls means they heat up and cool down slowly. Accordingly, they retain heat in the winter very well, and transfer it slowly in the summer, so the inside stays relatively stable throughout the year. During extended heat wave conditions, they can absorb and retain a lot of excess heat which can make them uncomfortable during those periods.
The naturally insulating properties of the building materials in these houses make extra insulation less effective at cutting costs. While improving ceiling, floor and wall insulation costs about the same as for a weatherboard house, the savings are only about $500 per year in energy costs, which means they take almost 14 years to pay back. In these houses, draft reduction may be a more effective way to spend money on energy efficiency.
The two common types of brick veneer home in Australia are the older style double-fronted version built in the 1950s to 1970s, and the post-1980s style. The major difference is in the flooring material, with the older houses having timber floors, while more recent constructions are based on a concrete slab floor. The flooring can make a big difference to heating and cooling, with many concrete slab floors containing hydronic underfloor heating which is highly efficient.
Improving wall and ceiling insulation in both types of brick veneer house can cost between $3,000-$4,000, and will pay itself off in about 10 years. In timber floored brick veneer homes, insulating the floors will cost around $2,000, and will pay itself off in about 6 years from the energy savings. On top of timber floors, carpeting and other floor coverings may be a quick way to partially insulate floors and stop drafts quickly without any renovations required.
Types of insulation
There are a number of different types of insulation materials that can be considered for improving the thermal properties of a building. Some are suitable for multiple applications, while others are only of benefit for specific parts of the house, such as floors, or roofs.
These insulate by reflecting heat, either back into the house or away from it. They are double-sided, so work in summer or winter, and are generally useful for roofs and walls. Some of the options are metal-based, and therefore may be capable of conducting electricity, making DIY installation unadvisable. The functional reflectivity can be reduced over time by dust build-up on the reflective surface, and they generally work best with sealed air gaps between the reflective surface and the roof or wall outer shell.
Probably more familiar to most people, bulk insulation can be used for ceilings, floors, and walls, and provides a physical barrier to heat transfer. Effectively they function in much the same way as a blanket, slowing the movement of warm air. In winter, these materials retain warm air inside the house, and in summer they prevent it from getting in. There are a huge number of materials that are readily available for bulk insulation, and most of them can be installed by non-professionals with good results. Glass wool (fibreglass) or rockwool batts are very common, but also actual wool, paper based and polystyrene materials are commonly used and effective. There are also composite materials which combine the benefits of reflective and bulk insulation.
Measuring insulation effectiveness
Insulation works by slowing the exchange of heat between the inside and the outside of a house or building. There are two commonly used measures of how well a material works in this capacity, the R-value and the U-value.
The R value measures how much resistance a material has in allowing heat to be transferred from one side of it to the other. It takes into account the thickness of the material and how much heat passes through it in a given amount of time. R-values are a quick way to compare insulation materials; the higher the R-value given, the better insulation it is. The R-value is calculated by dividing the thickness of the material (l) by its thermal conductivity (?), or how quickly heat moves through it. R = l
The U value is a bit more complex , and is a measure of heat loss through a material. The higher the U-value of a material, the less effective it is as insulation (in contrast to the R-value – don’t confuse the two when comparing materials!). It takes into account the three ways heat can be exchanged: convection, conduction and radiation. It is better used for working out the existing insulation capacity of parts of a building. The U-value is calculated by dividing 1 by the R-value of the material, then adding the convection and radiation losses of the material. Due to the complicated nature of the calculation, it’s best to rely on U-value calculators such as this one, or just speak with an expert.
Gains and losses with no insulation
Most homes built before 1990 will not have insulation as standard features. Those that do may focus on the ceiling, but as the figures show, wall and floor insulation can significantly reduce household energy spending on heating and cooling the home. In almost all situations, improving insulation in the home will save money, no matter where in Australia a house is built.
If your goal is solely to save on energy use for environmental reasons, then the best, most expensive set-up will fulfil that goal. If you’d simply like to reap the financial benefits while you create a more comfortable living environment, you’ll have more careful decisions to ponder. The more research you do and the more quotes you have, the more likely you’ll be to end up a satisfied customer.