Energy Efficient Window Design


The total radiation received per window varies according to the time of the year and the orientation. In summer, all windows receive heat gains, in particular those facing east and west. Whereas in winter, only windows facing north, north-west and north-east have a net heat gain, with heat gains outweighing heat losses. Windows facing all other directions will affectively lose more heat than they can gain. However, in the absence of northern solar access, windows to the east and west can provide some winter heat gains.
The most appropriate size of windows in terms of energy efficiency depends on many factors, such as glazing type, orientation of a building and thermal mass located inside the building materials. It is important to consider every room separately, as each room may have different acceptable limits and therefore may need different sized windows. Thinking about the windows early in the design process can save time and money otherwise needed later in the progress, to chase after the required stars to obtain a valid energy rating. We can help determine the effect of variations to window orientations, window sizes, internal glazing, double glazing versus single glazing, shading and internal coverings by using the FirstRate House Energy Rating software. Below are some clues on how and where to place windows.

How to orientate and size windows

Windows should be orientated to the north where possible. If solar access is good, north-facing windows should be large, but the size also depends on the amount of thermal mass in the building. South and east-facing windows should be kept pretty small, and windows to the south need to be positioned to enable cooling summer breezes to pass easily through the rooms. Whereas west-facing windows should be avoided where possible, if needed they should be relatively small and well shaded.
Appropriate window sizing, combined with double glazing, and/or close-fitting internal coverings such as drapes with pelmets, can minimise heat loss in winter. Furthermore, it is important not to overshadow windows in winter by the structure of the building itself, as it will reduce the solar access.

How to respond to poor solar access

Innovative design can overcome problems of poor solar access and overshadowing, especially in renovations, infill developments, higher density or small allotments with bad orientation, which can cause problems. In these cases, it’s important to use better performing insulation, protect windows, minimise overshadowing and courtyards, and reduce air leakage as much as possible. To compensate for poor solar access, the total window area of a building should be reduced.

Where solar access to north-facing windows is obstructed, clearstory windows are a good option to get solar energy into the building. Another option in responding to bad solar access is raising the sill height, as it will minimise permanent shaded glass areas, as these aren’t able to gain heat in winter and will lose heat instead.
Skylights and roof lights are also a good way to bring light into rooms, if obstructions from other buildings and structures prevent good solar access. Furthermore it’s a great opportunity to overcome overlooking into neighbouring properties, as windows above 1.7m don’t need to be screened. However, it is vital to protect the windows against harsh summer sun. Double glazing is mandatory as well as shading (a combination of external as well as internal shading would be the ideal solution).

The 20/20 House Part 6 – Why the 20/20 House?

The 20/20 House Part 6

The Gruen Eco Design blog about how to convert your dream from an energy efficient home into a reality.

Why the 20/20 House?

You may ask yourself: Why the 20/20 House? What does it mean?

I guess if you have studied architecture and even more so if you design houses for a living, it is only natural that all that you are dreaming of is designing and building your own dream home one day. For us as a couple with 2 architexxx (no, hold on, I’m not allowed to say that, since I’m not registered as one) with 2 that have studied architecture, it was a real mission.

Several years ago, while we were still looking for our first home, that turned out to be our 8.4 Star renovation in Vermont, we started to make plans for our future home. Our goal was to be in our very own home by 2020. Also, especially when coming to Australia, we were really shocked about the quality of the homes and how cold they felt and how difficult it was to feel comfortable in them. The mission was to create the perfect family home. Nice and comfortable, not too big, not too small. Architecturally appealing, energy efficient, sustainable and most importantly affordable.

This was the 20/20 Vision for our Future.

There you go. And now finally, many, many years after we started dreaming about it, we bought a block of land!!! Our journey has started.

The plan is to rent out the existing house for 1 – 1,5 years while we design our new family home and prepare all required plans and permits. And then hopefully start building end of 2018. Which will bring us into our new home in  mid 2019 if all goes well. Happy times ahead.

We bought ourselves a little challenge. A very wide easement and stringent setback restrictions, combined with a bit of a slope will call for some compromises and creativity. But well, where is the fun without a challenge 🙂

In the next blog I will talk some more about the actual site, its constraints and opportunities.

Why Is Good Window Design So Important?

Windows are essential for a house and the comfort and well-being of its habitants, as they let natural light and fresh air into the building and enable views.

Appropriate window design, size, location and glazing treatment, combined with shading and internal covers, can significantly reduce the energy required for heating and cooling. Maximum solar access for north-facing windows can reduce winter heating bills up to 25%. External shading can block up to 80% of summer heat gain through windows. Double glazing and internal coverings can reduce heat loss in winter up to 40%.

Glass is the potential weak point of a building in terms of energy efficiency. A single glazed window can gain or lose up to ten times more heat than an insulated wall. The main heat gain through windows is due to thermal radiation. Windows receive direct solar radiation when the sun strikes the glass, but also diffuse radiation reflected from the sky and the ground. Between 30-40% of total radiation to north windows is diffuse, depending on the weather conditions. Radiation from the sun travels through glass to the inside of a house. This radiant heat is absorbed by thermal mass, building elements and furniture, which when warmed up, re-radiates heat to the room air. This re-radiated heat is trapped inside, resulting in convective heat build-up within the room. This process is called ‘glasshouse effect’. In order to hinder direct rays from the sun entering the building in summer, glass needs to be shaded appropriately. On the other hand it is also important to ensure valuable winter sun can shine into the house, as heat gains in winter can reduce the requirements for mechanical heating.

Read more about how to design and orientate your windows and the importance of avoiding thermal bridges in our other articles.

The 20/20 House Part 5 – What else to look for?

What else to look for when selection the ideal site to build your energy efficient and sustainable home?

The Gruen Eco Design blog about how to convert your dream from an energy efficient home into a reality.


Something important to look out for are trees on your site as well as on your neighbouring sites. Especially when it comes to large trees and even more so indigenous trees, like any kind of gumtree. A permit if often required to remove large trees and in many cases council does not support the removal of these trees at all. Therefore be mindful if there are any trees that might hinder your project.

Also, when it comes to trees there is something called a Tree Protection Zone. Meaning depending on the size of the tree and the circumference of the trunk there is an area – a radius around the tree -where you can’t build in. Or to be more precise, you can build into this area to a certain percentage, but special construction techniques may need to get applied. You will also often need an arborist to examine and document the trees and determine the tree protection zone. This also applies to trees on your neighbouring properties or the nature strip. The bigger the tree the bigger the tree protection zone. Just one tree in the wrong location can make or break a site.

Even more so when the site has a Significant Landscape Overlay, or a Vegetation Protection Overlay. If such an overlay is present it might not be possible at all to remove trees. So you will need to investigate and discuss with council and or our architect/designer first before getting seriously invested.

Speaking of overlays, zoning and council in general. It is really important to check the planning regulations, the zoning and more so the schedule to the zone and any restrictions this may pose on your dream home. Planning regulations can control an almost endless list of things, like setbacks, building heights, site coverage, materials, ground floor to first floor ratios and so on. You also have to check if a planning permit is needed for what you want to do.

In most cases a planning permit can take anywhere from 6-12 months. Even longer when the neighbours object, especially when they take you to VCAT.

One other thing that needs to be taken into consideration is that once you lodge a planning permit, council will try to force their ideal image of a house on to you. For instance, council usually does not support so called sheer walls, first floor walls sitting on top of ground floor walls. Just because they do want articulation and they think such walls are ugly. If you have a look around at the typical subdivision, you can see this sort of wedding cake style everywhere, where the first floor walls step in. This articulation poses quite a few issues. For once, since the first floor walls are not supported by walls below you need steel beams and posts to pick up the load, which makes the construction more expensive. But the bigger issue is that it is contra productive when it comes to energy efficiency and sustainability. You need way more material, more insulation. Due to the articulation there is more external wall area and roof area, which increases the area to volume ratio of your home. The larger wall and roof area leads to more potential heat loss or gain.

As a general rule I would always say try to find a side where you don’t need a planning permit to build your house. This means a lot less problems. Obviously this does not always work. And if you have to get a planning permit make sure you budget in for the time the project can sit with council and consider getting a private planner to help you navigate the council maze.

The 20/20 House Part 4 – How should a site be oriented when you want to build your energy efficient and sustainable home?

The Gruen Eco Design blog about how to convert your dream from an energy efficient home into a reality.

Now that you have narrowed down the area you want to build in. It’s time to check out what’s on the market and to observe. Go to a few inspections and maybe a few auctions and keep an eye on for how much houses or land is getting listed and for how much it has been sold. This will give you a better idea about what you will be able to afford. Also see if you can get hold of RP Data from the area and a market analysis from a real estate agent.
What to look for on your ideal block depends also on what kind of house you are after. Ideally the site should be facing east-west. With the road either on the west or east side. This allows you to place your new home close to the southern boundary and have the long side of the house facing north. To get all the passive solar gains you want and need. (of course, you have to be careful not to overglaze and need shading, but we will talk about this in a later blog). However, this set out only works if the side is wide enough, so that you still have enough room between the north wall of your house and the fence. Ideally you should have 5.5m or close to that. This scenario will only work if you are happy to live in a relatively compact home, as opposed to a big mansion.
If you do want a rather large house with a large number of bedrooms and several living areas, or if the side is fairly narrow, you will most likely not be able to setback the walls enough from the northern boundary and therefore north should be orientated towards the rear, so that at least the living areas can open up to the garden and face north.
Of course, you can also make the house work if north is not straight out the side or the back, but I would advice on having north on the side of the road. Although a clever design can often overcome a poor orientation to some degree, this will make the layout and the design of your home much more restricted and might increase your construction cost.

In the next blog I will talk about council regulations and trees and how they can have a big impact on your project.

Insulation: How are they doing it Overseas?

Thermal bridges

When I started working in Australia in 2007,I was puzzled how thin walls can be. For example, an external wall can 110mm, 90mm for the timber studs, 10mm plasterboard on one side ,10mm fc sheeting on the outside and insulation just between the studs. This construction in general 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 studs in the wall 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


insulation 2



  AUSTRALIA (Melbourne 2015) GERMANY (2010)
External Wall R-value: 2.8 R-value: 5.0
Roof Not required R-value: 6.6
Ceiling R-value: 4.1 R-value: 3.3
Internal Walls                                         (to garage, bathroom, staircase etc.) Not required R-value: 3.3
Floor R-value: NIL for slab on ground

R-value: 2.25 for suspended floor

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.


The 20/20 House Part 3 – How to decide where you want to build?

The Gruen Eco Design blog about how to convert your dream from an energy efficient home into a reality.


When looking for a site to build your new energy efficient home there are many things you have to consider and seemingly endless obstacles to manoeuvre around.

Ideally the site should be located close to your work, the school, family, or anything else that is important for you. Unfortunately the reality is often that living close to work is for most families not affordable. So you should at least look in areas that have a good connection to wherever your work place is.

When selecting a site and thinking about your future home you should analyse your needs and lifestyle. And consider the current situation as well as the future.

What type of home do you need?
(single, double storey, room for parents etc; is a large garden required, lifestyle options and access to facilities)

Does the location suit your lifestyle and can it accommodate potential changes in the future?(family addition, retirement, old age, health and so on)

Is the site close to public transport, work, school, family members or other social activities?
(Proximity may reduce the need of a second car. It will reduce car trips, travel time and carbon footprint, consequently protecting the environment, and saving money)

Determine the true cost of the location.
(A site/ home in the outer suburbs may be cheaper, but will this compensate the higher transport cost and the additional times spend on the road or on public transport?)

You also have to keep your budget in mind. In which areas can you afford to buy and build. Unfortunately in most build up areas it is hard or almost impossible to buy vacant land. You have to buy a house and demolish it. Therefore you should look at houses that are really run down, as it would be too much of a shame to tear down a nice home. Having said this, when demolishing a home make sure to salvage and or sell what ever you can from the home. So that it does not end up being land fill.

We as a family have decided that we want our kids to go into the public German-English bilingual primary school in Bayswater. Luckily being German natives we don’t have to live in the actual school zone. But we still want to live close to the school. So that is where we have concentrated our search on.

In the next blog I will write about what to look out for when house/site hunting.

The 20/20 House – Part 2: How much money can you borrow from the bank to build your dream home?

The 20/20 House – part 2

The Gruen Eco Design blog about how to convert your dream from an energy efficient home into a reality.



How much money can you borrow from the bank to build your dream home?

The question how much money you can borrow depends on many factors.

For instance, how much money are you and your partner earning per year? Do you have any debts, investment properties? How many credit cards do you have?

As a first step. If you do want to live in your own home you do have to speak with your bank or mortgage broker, to find out how much you can borrow. This amount will determine if and where you will be able to buy or build. And also what kind of build it can be. For most of us money is sitting tight. So the high end mansion in Toorak is just not an option.

We personally have opted for a mortgage broker, rather than a bank. As our needs are quite unique and this way we were able to compare many different scenarios.

In order to get a mortgage pre-approval and to know how much money we could potentially borrow we had to provide the following documents.

  • 2 most recent payslips (if employed)
  • Tax returns for 2 years
  • If you have investment properties you will also need rental appraisals and a valuation of the property
  • Information about any personal loans you might have (in our case a car loan)
  • Information about any credit cards you have and what the limit on each card is
  • Proof of identity (like drivers licence and passport)
  • Some banks also want a list of the general expenses you have

In our case, we have 3 credit cards, of which we only use one. The other ones are just for emergency. However, when it comes to the banks they assume the worst case scenario, hence assume all cards would be maxed out. Which is deducted from your income and hence reduces how much money you could potentially repay. Same goes for any other personal loans. They influence negatively your borrowing capacity.

I personally think the most important thing is to keep in mind that it’s not all about how much money you can borrow. The more important question is “how much money can you afford to pay back monthly”? Do you have to make sacrifices in order to repay the mortgage? And are you willing to make these sacrifices?

For us as a family we have decided that we don’t want to be slaves to our repayments. All our family is in Germany and Italy, so we still want to visit them sometimes. And we do want to see the world and travel with our 2 girls. Therefore we have decided to move away from the city a bit further, like 10 minutes further from where we live now. Which means we are still close enough to our current group of friends. But land is a bit more affordable.

In our case this also means for now we can only borrow enough money to buy a block of land to build on. But we are not able to borrow enough money yet to build our dream home. In order to be able to build our house we will need to pay off our car in the next year and also need to cancel 2 of our credit cards. We also want to sell our current unit.

We now have the banks approval and are officially house hunting. Wish us luck!


In the next blog I will talk about the process of looking for the perfect side to build on.

The 20/20 House – Part 1

The Gruen Eco Design blog about how to convert your dream from an energy efficient home into a reality.

My partner and I are planning to build an affordable energy efficient house for our family. So I thought I take this opportunity to write about all the things we will have to go through to get into our home. And hopefully this can give some guidance or help to others in the same position.

I do want to talk about the whole process. Starting on how we get the finance sorted, finding the right side. How to determine what rooms we need and how the house has to function for us. But also what things we have to consider during the design phase, how to find and deal with a builder. Through to the construction process and then hopefully a happy ever after move into our new dream home.

But for now, we are just at the start. So in my first blog I will talk about finance. And what you need in order to get a pre approval from the bank, so that you can start actively looking for the right site.

Stay tuned and follow our journey.

How to Install Insulation

How to Install Insulation


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.

Neither good performing insulation or a 6 or 7-star energy rating are a guarantee for real 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.

Affordable, energy efficient & sustainable architecture