Tag Archives: Insulation

101 Building Physics & Condensation or why is it important to open your windows?

Have you ever wondered why there is water running down your window? Or why you have damp spots or even mould in your bathroom or behind the robe? No, it does not come from the outside. (except of course if there is some sort of water leakage somewhere).

The main sources of moisture in a home are cooking, baking, but also all other processes where water is used, like having a shower or a bath, using the toilet, washing your hands or the dishes, using the dishwasher or the washing machine, indoor planting and open water features, like aquariums or indoor ponds and pools. But did you know that one of the main contributors to the moisture in the air and in your home are we humans ourselves?

You might be asking: why, it can’t be that bad. How much moisture, water can there be? Here a little example.

Let’s take a small 3-person household, living in a 100square metres home (While this sounds tiny for most Australians, this is the average home size in Germany!) The indoor temperature is 20° C and 65% relative humidity (which is kind of average). This means there is about 2,8 litres water in the air. In average, this household will produce about 12 litres of water every day.

Between 2-3 litres by breathing, 4 l by showering and washing, about 4 litres for cooking and about 2-3 litres for indoor plants and the like. This 12 litres does not include any extra humidity due to drying clothes inside , which would increase the amount even further.

Summarising this means each household produces each month between 300 and 600 litres of water that is converted into steam. Only a portion of this water will be extracted through ventilation directly. (This is if you open the windows). The rest will be stored initially in the construction elements (walls, ceiling and floor) and furnishings and then later on extracted indirectly. Sufficient fresh air must be provided to exchange the ‘used’ air to allow for the required direct and indirect extraction of the moisture content in the air.

Let’s go one step back. Why is there moisture in the air?

Air is a mixture of different gases. From our school days, we know the air consisting of nitrogen (N), oxygen (O ²) and carbon dioxide (CO ²) as the main constituents.

The absorption of water (H ² O) depends on the temperature of the air. Warm air can hold more water than cold air.

Condensation occurs when air with accumulated moisture content through climate and occupancy cools down.

If the temperature drops, the moisture content of the air remains the same initially, but the maximum capacity to hold water will be reduced. As a consequence the relative humidity is increased. Once it has cooled down to a point where the existing humidity reaches the saturation value condensation takes place. The relative humidity is 100%.

The temperature at which this condition occurs is called the dew point temperature; this depends on the moisture content as well as the temperature of the air.

If temperatures on glazing, walls, ceilings, floors, windows are colder than the room temperature this can lead to condensation on the surface of the materials, which, if not tried out, can lead to mould and fungees. But it is also possible that condensation occurs within the construction, for instance within the insulation. This condensation within the wall components can also be harmful in certain circumstances to the structural integrity of the entire home.

In Europe homes are sealed so tightly that we are taught how important it is to open the windows at least a couple of times a day to exchange the used air. Well, here in Australia most people haven’t heard about it. But when you live in an old ‘typical’ Australian home, this might not be an issue, as there are so many gaps and openings everywhere, that fresh air might get in anyway. But if you live in a new home, or you are thinking about renovating and making your home more energy efficient by sealing your house, this is an entirely different story. Condensation and hence mould can occur internally which can lead to several health issues, like asthma, eczemas, etc., if you do not ventilate your home properly.

However, keeping the rising energy prices in mind and our environment in general, there is nothing more important than making our homes more energy efficient. At least that’s my opinion. In order to do this we have to insulate our houses better, seal it as air tight as possible and also avoid thermal bridges. (I will explain more about thermal bridges in another article).

The better insulated and the more air-tight our homes get, the more we have to convert our thinking. The temperature inside the house, the air’s moisture content as well as the temperature on the surfaces inside the house is fluctuating constantly and depends largely on the usage by its occupants, as well as heating and cooling habits.

It will not be enough anymore to open the window every now and then. You have to exchange the air inside by opening the windows regularly, ideally twice a day for let’s say 5 minutes and create a proper cross-ventilation. Just opening one awning window won’t do it.


Humidity levels for typical household processes can be specified as follows:

Emitted amount of water vapour in the household (per person/per day)

Human body – light to medium activity –                   1 to 1,5 litres

Human body – while sleeping –                                     1 litres

Shower                                                                                 1 – 1,5 litres

Bathing                                                                               0.5 – 1 litres

Cooking                                                                              0.5 – 1 litres

Dishwasher (one load)                                                    0,2 litres

Washing machine (one load)                                         from 0.2 to 0.3 litres

Drying tumble dry washing inside (4.5 kg)                 from 1 to 1.5 litres

Drying wet washing/clothing inside (4.5 kg)            2 to 3.5 litres

Flowers                                                                             from 0.5 to 1 litres

Indoor plants from                                                        1 to 1.5 litres

Water features (eg pond, aquarium)                          from 0.8 to 1.3 litres.


If you have a really air tight home it is actually recommendable to ventilate the house 4 – 5 times a day properly and perform a complete air exchange.

Now you might think, gosh, that will just increase my heating bills. But, consider this. It’s actually the other way around. Firstly, the higher the humidity inside your house, and inside the wall, the higher the thermal conductivity of the wall, meaning the more heat can the wall store and detract from the room, meaning you have to heat more. But even more critical is, that the insulative properties of the insulation will get reduced significantly. As a rule of thumb you can say that for each 1% moisture increase inside the insulation  value drops by 5%. That’s actually quite a lot, isn’t it?


It can be stated that a dwelling with insufficient ventilation will most likely have higher heating bills due to the poorer performance of the thermal insulation. It is not recommended to open for instance one awning window the entire day. This will in fact just cool down the house constantly and not exchange the indoor air. Ideally you should open one casement window or door on either side of the house to create a good cross ventilation for about 5 minutes.

Having said all this, this applies for highly energy efficient, highly insulated and well-sealed homes. However, keep in mind even if you home is not that air tight, the humidity is there, even when you can’t see it, and opening the windows should become a daily habit of yours.

Adequate Insulation

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
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
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

Thermal bridges
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.

Thermal Comfort

Nowadays, you can see sustainable buildings and green design solutions everywhere. But what does it actually mean?  Is a so called sustainable home automatically environmentally friendly?  How to distinguish between real sustainable design and one that claims to be?


What IsThermal Comfort And Why Is It So Important For The Well-Being?

What is thermal comfort?

Human thermal comfort describes the state of mind that expresses satisfaction with the surrounding environment and refers to several conditions in which the majority of people feel comfortable. The human body produces heat depending on the level of activity, and expels heat according to the surrounding environmental conditions.

The body loses heat in three main ways:  radiation, convection and evaporation. An unpleasant sensation of being too hot or too cold (thermal discomfort) can distract people from their activities and disturb their well being. This may reduce the ability to concentrate and decrease motivation to work. Thermal comfort is affected by six variable factors which are needed to maintain a healthy balance in order to sustain satisfaction with the surrounding environment.

1) Air Temperature is the most common measure of thermal comfort and can easily be influenced with passive and mechanical heating and cooling.

2) Mean Radiant Temperature is the weighted average temperature of all exposed surfaces in a room. The greater the difference between air temperature and exposed surfaces, the greater the Relative Air Velocity.

3) Relative Air Velocity (‘wind chill factor’) is the apparent temperature felt on exposed skin due to wind.  For example, if cold air is leaking in from a window, the air temperature feels lower than the actual air temperature, hence the increased likelihood of feeling cold, even when the heater is on.

4) Humidity or relative humidity is the moisture content of the air. If the humidity is above 70% or below 30% it may cause discomfort.

5) Activity Levels can reduce the heating needs, as lower air temperature is acceptable when occupants have higher activity levels.

6) Thermal Resistance of clothing or warm blankets in a bedroom can reduce the need of heating.

Building design is affected by the first four of these thermal comfort variables. The last two depend on the action and behaviour of the occupants.

What factors are influencing  thermal comfort ?
If the insulation applied is faulty or insufficient, the exposed surfaces in a room will stay significantly colder in winter or hotter in summer than the room temperature. Although the heater pumps hot air into a room, or the air-conditioning blows cool air, the thermal radiation will affect the equilibrium. The Mean Radiant Temperature is affected negatively and the occupants won’t feel comfortable.

  • The ceiling isn’t insulated or the insulation is penetrated for example because of the installation of down light. As warm air is always moving upwards, heat is lost to the cooler air in the roof space.
  • Air leakage around doors, windows, down lights, pipes, and other wall penetrations are exceeding the acceptable Relative Air Velocity.
  • Wrong application of thermal mass can influence the Mean Radiant Temperature and can therefore increase the need of mechanic heating and cooling.
  • Under- performing windows and doors (when air is able to leak in/out of poor fitting doors and windows) are also influencing the Mean Radiant Temperature and the Relative Air Velocity.

When it comes to comfort, the perception of temperature is more important than the temperature itself. For a person to feel comfortable, the difference of temperature between the head and the feet should not exceed 2.5 degrees. This demonstrates the importance of floor insulation and this explains why we usually feel more comfortable standing barefoot on carpet than on tiles.

Energy Ratings In Australia And Overseas
In Australia, energy rating assessments are done pre-construction, assuming competent application of all insulation and building materials. However, common construction practices often demonstrate misapplications and air leakages. In Europe, energy efficiency is most often assessed or checked post construction, with special attention to the prevention of thermal bridges. Some countries require airtight buildings, and amongst other things, double glazing, solar energy for hot water and heating systems, the usage of storm water, greywater recycling, recycled materials and product life cycle considerations to minimise energy demand and carbon footprint.

Well performing insulation and building materials is not a guarantee for well performing homes. The building envelope needs to be treated as a delicate continuous shell. Each small gap and leakage will impair the energy efficiency and the well being of the occupants. It is essential to consider the end product in order to determine how energy efficient a building really is.

Energy Cost Calculator

How can a renovation help to save money?

Imagine the house’s external walls as a continuous shell, and every little gap you have in this shell will result in heat loss, or the other way around in summer.
Hence, every time you stop this unwanted heat transfer, you can reduce your energy bill.

Energy Cost Calculator

With the FirstRate5 energy rating assessment tool, we can determine the Total Energy Usage per year of the different Star Rated versions of our home.
Once we have the annual energy costs, we can factor in the effects of inflation to understand how much  money the renovation can save us over a period of 7 years.

The existing house, with 0.8 Stars, will cost us more than $33.500 over the 7 years.

Insulating our house, sealing all wall and ceiling vents, putting in self-closing exhaust fans and weather-stripping windows and doors brings us to 3.6 Stars and we will use 38% of the energy – saving approximately $20,000.

Putting in an air-lock and replacing some single glazing aluminium windows with good performing double glazing windows will increase the energy rating to 5.6 Stars. We will use 19% of the energy – a saving of more than $27,000.

5.6 Stars: It’s not that hard

Now, after we have retrofitted the insulation and sealed all the gaps,  it’s time to look into other options on how to improve the energy efficiency. But also we want to optimise the floor plan.
We think there is potential to utilise the floor area more efficient. We decided to reorganise the kitchen/living/dining area and also that an European laundry would be enough for us. That means we will be able to transform the 2 bedroom unit into a 3 bedroom unit. But that’s not all, we will even manage to fit in an extra ensuite for the new master bedroom.

But what are we planning to do to that will improve the energy efficiency?



One of the first things you should do is to put in an air-lock. With the extra door you can close of the entry area. This is especially important in Winter, then
the moment you open the front door the warm air gets sucked out and you have to start afresh. In summer it can be open all the time, but there should be a way in winter to close it off.

Replace Windows/Doors

Many might think, there is no point replacing one or 2 windows, it won’t make a difference. But you would be surprised what you can achieve. Especially big windows lead to unwanted heat gains or losses. Even just replacing some windows can make a massive difference.
We want to put in a new french door towards the new deck, also we will put in a new door and new windows in the new master bedroom. So altogether we will put in 2 new windows and 2 new doors. Keep in mind, the lower the U-value the better performing the window. In our case, we will try to get the best windows/doors we can get; double glazed, uPVC or timber windows, with a  U-value of 1.99 or lower.

Energy Savings

Just putting in the air-lock and a few new windows/doors increases our energy rating to 5.6 Stars. This means the renovated house will need 81% less energy, meaning instead of $4,300, we will just pay $829 per year.

Imagine how much energy you could save!!!

3.6 Stars: How to make an existing home more energy efficient without spending a lot of money

There are a few simple things you can do that will make a huge difference to your energy bill, without spending a lot of money.
In our case, it brings us already up to 3.6 stars. This means that we will need 62% less energy than before the renovation. Instead of paying more than $4,300 per year, we can reduce our energy bill to approximately $1,600.

So what did we do?

Seal your house

Every little gap causes unwanted heat losses and heat gains, therefore, one of the first things you can do to make your house more energy efficient are:

– Close off wall and ceiling vents

– Replace existing exhaust fans with self-closing ones

– Weather-stripe existing windows and doors

– Don’t use standard down lights in the ceiling as they leave gaps/holes in the insulation

Insulate your home as much as possible

The more insulation the better. Put in as much insulation as you can
In our case, we’re going to install insulation to the ceiling and to the roof, with a combined overall R-value of  R6.0 and insulation to the timber sub-floor of R2.0.

– Insulate the sub floor using waterproof rigid insulation and ensure there are no gaps around the insulation – for example, use expandable foam.

– Update roof/ceiling insulation using both reflective and bulk insulation, the higher the R-value the better. Aim for a combined R-value for the roof and the ceiling insulation of min. R.5.0

Retrofitting an existing brick veneer wall is a bit more tricky.  It is a pretty time intense and messy job. Therefore we decided not to insulate the walls, at least not at this stage.
Taking off the plasterboard to install bulk insulation may be the most obvious way, but you can also bore holes in between studs and pump in cellulose fibre. But if you do this you have to ensure that the walls are closed at the bottom and that the insulation can’t fall though.

3.6 stars is a good start, but we can do better.