Firstly, to understand thermal performance, we must understand thermal mass, insulation and the roles they play in reducing temperature extremes that are often experienced in the home.
Thermal Performance refers to how well a home or building structure responds to changes in external temperature during daily and seasonal cycles.
Thermal Mass is the ability of a material to absorb and store heat energy in order to release it later.
Thermal Insulation reduces the flow of heat or heat transfer within the home.
Climatic conditions influence the appropriate level and type of thermal mass and insulation required in a home; therefore, we must firstly establish whether it is predominantly needed to keep heat out or in (or both). Thermal mass and insulation must cater for seasonal as well as daily variations in temperature.
Understanding Thermal Mass
Thermal mass, correctly used, moderates internal temperatures by averaging out diurnal (day−night) extremes. During summer it absorbs heat during the day and releases it by night to cooling breezes or clear night skies, keeping the house comfortable. In winter the same thermal mass can store the heat from the sun or internal heaters to release it at night, helping the home stay warm.
Thermal mass is not a substitute for insulation. Thermal mass stores and re-releases heat; insulation stops heat flowing into or out of the building.
Poor use of thermal mass can exacerbate the worst extremes of the climate and can be a huge energy and comfort liability. It can radiate heat to you all night as you attempt to sleep during a summer heatwave or absorb all the heat you produce on a winter night.
In winter, thermal mass will ideally absorb heat during the day from direct sunlight or from radiant heaters. It re-radiates this warmth back into the home throughout the night. In summer, cool night breezes and/or convection currents pass over the thermal mass, drawing out all the stored heat. During the day in summer it is important to protect the thermal mass from excess sun with the use of shading (eg, overhanging eaves, window awnings) and insulation (eg, double glazed windows or wall insulation) if required.
Types of insulation
Insulation is a layer (or layers) of material in the walls, ceiling, floor, and roof that moderates the temperature inside the home. It makes it easier to keep your house cool in summer and warm in winter. Most heat transfer happens through the roof and ceiling, so insulation is essential in these locations. Essentially, the amount and level of insulation needed depends on your home’s design, location, site orientation and climate zone.
Ceilings and Roof Insulation
If a home’s ceiling or roof has no insulation, the occupant can lose around 40% of their cooling and heating energy. For example, insulating the veranda or alfresco roof in hot climates reduces heat, which affects the area directly below it.
Wall insulation is important in any climate and can save up to 25% of cooling and heating energy. There are countless types of wall insulation products and building materials available within Australia. Your builder will be able to offer suitable recommendations based on your home’s thermal performance requirements.
As a general rule, carpet is a good insulator for cooler climates, trapping heat which can save around 20% of cooling and heating energy. In hotter climates, the use of light weight timber flooring or tiles with no thermal insulation may be best. This is because insulation may affect the natural ground cooling from under the house.
As a bonus, floor insulation can minimise the transfer of impact noises such as footsteps across the floor and reduce vibrations from appliances such as the washer or dryer, giving the floor a more solid ‘underfoot feel’.
Bulk insulation is typically used in cooler climates because it creates a barrier between the inside and outside of your home. Bulk insulation is available in rolls, batts, and boards, and can be made from polyester, glass wool, recycled paper, or natural wood. Bulk insulation keeps heat inside in winter and outside in summer.
Reflective insulation is typically used in warmer climates. It keeps the home cool in hot weather by deflecting heat. One of the best ways to learn how reflective insulation works, or to gain an understanding of its effectiveness, is to crawl up into the roof or loft space of a house which doesn’t have reflective roof sarking installed. If the temperature outside is warm, and the sun is shining onto the roof tiles, unobstructed by cloud cover or any shady trees, then chances are the temperature inside the roof space will be uncomfortably, if not unbearably hot. Why? The main reason is “radiant heat”, and the absence of reflective roof insulation.
Reflective insulation can be used together with bulk insulation in areas which experience both hot and cold climates.
Choosing the right insulation
Insulation’s ability to resist heat leaking in or out is called its ‘R-value’. Matching the R-value of insulation products and installing it properly provides the same insulation level. The amount and level of insulation needed depends on your home’s design, location, site orientation and climate zone. Therefore, in order to determine what’s best for your home, it’s imperative to obtain a Thermal Performance Assessment which measures the heating and cooling loads of each conditioned zone within the home.
These heating and cooling loads are calculated once all relevant building materials and design information have been entered into our accredited software program. At Stellar Thermal Assessments, we provide expert advice and options to suit your needs enabling you to make more informed and educated decisions when talking with your builder.