Thermal insulation is a fundamental factor to achieve thermal comfort for occupants. Insulation reduces undesirable heat loss or gain and can lower the energy demand on heating and cooling systems.
The Victorian Government is planning to introduce new regulations for the existing housing market. Originally planned for 2011, then moved to 2012, we’re now in 2016 and it this initiative is still getting postponed further. However, eventually hopefully it will be a requirement to provide information about energy, water and greenhouse performance to buyers and renters.
Assume two homes are for sale in the same street, both are three bedrooms single storey brick veneer buildings with a double garage on a block of approximately the same size. One has a 2-star energy rating and the other one has 5-stars. Which one is more likely to sell for more?
Insulation, Why Is It So Important?
Insulation is the most effective way to improve the energy efficiency of a building, as it acts as a barrier to heat transfer. It will keep the house warm in winter and will help to stay cool in summer, improves thermal comfort and well-being, and minimises condensation on walls and ceilings. Furthermore, insulation needs to be combined with appropriate shading devices to windows and adequate ventilation possibilities, otherwise heat entering a building through windows will be trapped inside by the insulation and lead to overheating.
Older houses in particular pose a problem: inadequate insulation, poor solar access and air leakages amongst other things lead to unwanted heat gain and loss, and consequently higher energy bills.
Adding insulation to a home can save 45-55% of mechanical heating and cooling needs and as a result, save non-renewable resources and reduce greenhouse gas emissions. With the current energy prices, additional insulation usually pays for itself in around five to six years. With the prospect of rising energy prices it’s more than likely that insulation retrofitting will pay off even quicker.
Different Types Of Insulation
The purpose of thermal insulation in a building is to regulate the internal temperature by minimising or stopping heat transfer through radiation, convection and conduction. Generally speaking, there are two different types of insulation that must work together to prevent heat transfer: Bulk insulation and reflective insulation.
Bulk insulation mostly resists the transfer of conducted and convected heat, using millions of tiny pockets filled with still air or other gases within its structure. This air provides the material’s insulating effect, therefore it’s essential not to compress bulk insulation. Bulk insulation is available in different shapes and materials.
-Batts and Blankets (Glasswool/Fibreglass, Rockwool, Natural Wool, Polyester)
-Loose-fill insulation (Cellulose Fibre, Natural Wool, Granulated Rockwool)
-Boards (Extruded Polystyrene, Foil-faced expanded polystyrene, Wood Fibre)
Reflective insulation mainly resists radiant heat flow. It is made of thin sheets of highly reflective aluminium foil, which reflects heat from its polished surfaces. The performance relies on the presence of an air layer of at least 25 mm next to the reflecting surface. Keep in mind that dust will greatly reduce the performance. Some examples include:
– Reflective Foil Laminate
– Multi-Cell Reflective Foil Products
– Expandable Concertina-Style Foil
– Foil Bonded to Bulk Insulation
For information about electrical safety checks for householders with foil insulation go to ‘Home Insulation Program’ webpage from the Australian Government.
Insulation needs to be installed with careful attention to detail, as inappropriate or incorrect application will crucially decrease performance. For instance, failure to butt all ends and edges of batts to give a snug fit could mean that about 5% of the ceiling area is not being covered. This could result in losing up to 50% of the potential insulation benefits.
- Avoid thermal bridges
- Eliminate gaps in insulation
- Do not compress bulk insulation
- Protect insulation from contact with moisture, provide vapour and moisture barriers to prevent condensation
- Provide a sealed air space of 25mm adjacent to reflective insulation
- Allow clearance around appliances and fittings
- All electrical wiring encased in insulation must conform to AS3000: Electrical installations-buildings, structures and premises. It’s best to keep wiring clear of insulation, e.g. to run wiring on top of ceiling joists.
How Much Insulation Is Needed?
The Building Code of Australia (BCA) identifies eight different climate zones for Australia, but within a zone, there are some locations with slightly different temperature ranges. There can be significant differences between maximum and minimum temperatures in summer and winter and in length and intensity of heating and cooling periods. The house design, the insulation and construction must respond to these variations in order to be able to perform energy efficient. But keep in mind, the required R-values in the BCA are minimum requirements and NOT best practice!!!!
For simplicity, Victoria is divided in five climate zones, with winter heating as the predominant concern especially in the Temperate Coastal and Cool Inland Zones. Summer cooling is variable but generally less significant. House design in these zones requires attention to better performing insulation, draught proofing, window protection in winter and shading in summer. Likewise, in warmer cities and areas like Mildura supplementary heating is obligatory for thermal comfort. In these regions, it’s advisable to include extra thermal mass, cross ventilation and summer shading, whereas alpine areas may require constant heating for most of the year and cooling requirements are negligible. Consequently, a 5-star home inMildura wouldn’t comply with the minimum requirements for a 5-star home in Ballarat.
The higher the R-value the better the performance. Consider what insulation is needed in order to build an energy efficient home in a certain climate zone early in the design process. In particular, it’s important to think about the roof insulation. For example, it would be cheaper to use larger rafters in order to fit in sufficient glasswool to fulfil the desired R-value, instead of using thinner expensive extruded polystyrene. Larger rafters would mean that the overall height of the building rises slightly. This is no problem, if the amendments are done early in the design. However, if a town planning permit has already been granted, it’s not that easy any more. It’s necessary to go back to the council with the changes, which can cost a lot of time and money, therefore in most cases, people choose to use the thinner, more expensive insulation instead.
Adding R1.0 insulation can significantly improve the energy efficiency. For example in Melbourne, adding insulation with a R-value of R3.0 to the ceilings and R1.5 insulation to walls can save 12% on energy bills each year and can ensure a higher level of comfort.
Insulation Regulations Overseas
When I started working in Australia, I was puzzled how thin walls can be. For example, a typical timber wall measures 110mm, 90mm for the timber studs, 10mm plasterboard on each side and insulation just between the studs. This construction is not allowed in most European countries, as it creates a structural thermal bridge. The U-value of timber is much higher than the U-value of the insulation, which means that heat can escape through the timber and consequently increases unwanted heat gain or loss. In Europe, the main focus lies on avoiding thermal bridges. A timber construction is usually done as a double stud wall. In this case, there is also a timber stud to the interior, covered with plasterboard and insulation between the studs, but at the outside is another continuous layer of insulation, and then another timber stud, with external plasterboard and again insulation in between. (see diagram below)
In Australia, there are no strict regulations about thermal bridges and also no minimum insulation regulations for concrete slab-on-ground construction, roof or internal walls.
Example for an insulation for a typical Australian home compared to a German home
|External Wall||R-value: 1.3||R-value: 5.0|
|Roof||Not required||R-value: 6.6|
|Ceiling||R-value: 2.2||R-value: 3.3|
|Internal Walls (to garage, bathroom, staircase etc.)||Not required||R-value: 3.3|
|Floor||R-value: 1.0||R-value: 3.3|
Obviously, the average temperature in Germany is much lower than in Australia, therefore it is natural, that the R-values of the insulation need to be higher, but there are also some differences in where the insulation needs to be installed. In Australia, usually just the ceiling gets insulated, although the roof space is ventilated, heat can be trapped inside in summer which can transfer through the ceiling and heat up the rooms below. In Germany, the main focus lies on the roof itself, the whole outside of the building is treated as a continuous shell. Ideally, no heat should be able to transfer into the building at all. There are no wall or roof vents, most of the buildings are even air-tight.
For instance, in winter you can easily distinguish between a good and a bad insulated home in Germany. In a good insulated home snow won’t melt on the roof tiles, as no internal heat can escape the through the insulation which reduces the energy required for heating enormously. Furthermore, it is also a requirement to insulate the ceiling to a roof space and to floors/ceilings between different levels, as well as to place insulation on some internal walls, for instance walls between rooms with different heating requirements, to unheated corridors, garages etc. This is to stop heat ‘traveling’ through a house from room to room.
Furthermore, typical brick veneer constructions, as shown above, are not advisable, as the thermal mass is located on the outside of the building and therefore can’t be used to actively contribute to heating and cooling needs. Brick should be located on the inside. Therefore a better opting would be to use a reverse-brick construction, where the brick is inside the building envelope and consequently is able to store heat and to regulate the indoor temperature.
What can we learn from overseas?
Minimising thermal bridges and heat transfer is mandatory in order to create energy efficient and environmentally friendly buildings. All insulation must be installed snug-fit, there should be no gaps and also thermal bridges should be avoided where possible in order to minimise greenhouse gas emission and to protect the environment.
Neither a 6 or 7-star energy rating nor high R-values are a guarantee for energy efficiency. The building envelope needs to be treated as a delicate continuous shell. Each small gap and leakage will impair the performance of the insulation. It is essential to consider the end product in order to determine how energy efficient a building really is. Even small gaps in the insulation such as around windows or other wall penetrations can halve the potential insulation benefits. Adding good performing and appropriately installed insulation can save a lot on your energy bill and minimise the greenhouse gas emission.