What is an Energy Rating?

When building a house, commercial building or renovating there is a requirement that it complies with the Building Regulation's requirements for energy efficiency and that it achieves the required energy rating.

For houses this is usually done by an external consultant who uses computer software to model the house and produce a report. In Victoria there is a requirement for a 6 star rating for new houses and an equivalent rating for renovations that takes into account the percentage of new area.

Energy rating goes beyond just a requirement of the Building Regulations and based in good design principles. It is a regulation that ensures that the house not only uses less energy, but is also more pleasant to live in. The rating takes into account orientation, area and location of windows, shading, building materials and their thermal values, artificial lighting power consumption and heating and cooling equipment efficiency.

In regards to the orientation and windows, the principles of passive solar design play a large part. Refer to our article on Passive Solar Design. One of the factors that plays a major part is the size and location of windows. Generally our clients, as well as us, like large full height windows that take in the view and add light to the houses interior, blurring the divide between the outside and inside. However they are the major contributor to heat loss and gain. You only have to put your hand against a single glazed window in winter or stand next to it to feel the heat literally flowing out through the glass. Windows on the North are best suited to contributing to energy efficiency - allowing passive solar heat gain in winter. Windows on the South only loose heat and don't have the benefit of winter heat gain. As a rule of thumb once a design has an area of double glazed windows that is about 30% of the floor area extra measures are needed to be taken to get to the 6 star rating, such as higher insulation values and performance glass. Traditional houses have been able to achieve the 6 star rating by having a lesser number and smaller windows, this of course reduces light and views.

We design our buildings taking into carefully taking into account the placement and size of windows. They are placed to orient to the views, let in light to minimise the use of artificial light during the day and sized based on their location. Most of this is common sense, small windows in the laundry and bathroom areas, medium sized windows with higher sills in bedrooms to allow for furniture placement under them and to provide privacy, larger windows in lounge and common areas. As the windows get towards the limit of what is allowed there is a requirement to increase their performance with double glazing, performance low-e glazing and insulated frames.

A building's materials are also important. Insulation plays an important role as well as the use of thermal mass, this is most usually in the form of a concrete slab. These help regulate the internal temperature, and stop rapid internal temperature changes when the external temperature fluctuates.

Other factors that have recently been taken into consideration are the use of LED lighting, and the reduction of recessed downlights that allow heat to flow into the roof cavity.

An energy rating is usually conducted at the end of sketch design to ensure that the number and size of windows can be achieved before we start documenting the house and make the required changes if any. The report is a minimal cost - usually around $500.

At the end of the day the requirements of the rating make the house a much more pleasant environment to live in. You have to heat and cool your house less and this is especially noticeable during Spring and Autumn where you can rely on the heat of the day to keep your house warm at night.

What is passive solar design?

We all may have heard this term bandied around, but really, what is passive solar design and how is it implemented?

Passive solar design is an essential part of the architect's tool kit. For us, it is one of the core factors that influence how a building is designed. Different buildings have different requirements for solar access based on their use. Houses benefit from direct sunlight, whereas office buildings, classrooms and studios are better off with indirect light, mostly to reduce glare. Today we are going to focus on passive solar design for houses.

The basic definition of passive solar design is "the design of a building's components including its orientation, location of windows, materials and shading devices to distribute the sun's heat during the winter and exclude it during the summer without the use of mechanical heating or cooling".

It is the architect's role to look at all of these factors when designing a house and use them to create an internal environment that does not fluctuate greatly with external temperature changes, maintaining thermal comfort. Being in the unique Australian environment, at SLAP Architects, we design with these following factors in mind and will discuss with you, our client, during the design process:

Orientation

In the Southern hemisphere, the sun travels across the North. Ideally the house will be oriented with the living areas and back yard to the North. This way you can benefit from full sun during the day - especially in winter. If you are looking at a house block, and have a choice, it should be on the North side of the street with the road to the south. Both Eastern and western light have their own effects, as the both have the sun low in the sky at these orientations and can cause glare. I like to have kitchen areas on the East as they capture the sunrise and morning sun and it is a nice way to start the day. Western sun can be particularly glary and hot, especially in summer, and so Western windows are generally avoided where possible. Rooms that do not need too much natural light like garages, laundries, service areas are best located on the South, where there is indirect light. Artists' studios are also often located on the South for their indirect light.

Although these are the ideals, we know that not everyone's new building can be oriented like this, otherwise we would be able to take a one-design-suits-all approach and our jobs would be a lot easier!

Often there are other factors that influence the design, such as blocks with different orientations, on slopes, or with a view to the South. This situation that occurs quite often with our clients as we are located on the south coast of Australia, many of our clients are lucky enough to have water views to the South and so the living areas are oriented to the South to take full advantage of the views. It is our job as architects to produce a design that still makes use of the opportunities to maximise daylight and solar gain while orienting views to the South.

Windows

Windows have three main functions; to provide views to the outside, to let light in and to allow ventilation for heat gain or loss. These three factors must be balanced to produce the best outcome for a house design. Again depending on the house and its orientation, the size and number of windows is one of the greatest factors that ultimately affect thermal comfort.

Ideally to make use of a correctly-oriented house as mentioned before, the main bulk of windows should be to the North and arranged to allow the sun into the house in winter and to be excluded in summer. A large amount of windows on the South should be generally avoided as they only cause heat loss because the South side of the house doesn't receive any direct sunlight. Windows on the West need external shading to keep the low, hot summer sun out.

Correct window design is the basis of good passive solar design; it allows the winter sun to come through the windows and cause heat gain in the house, and excludes summer sun to keep the house cool. There are several ways to achieve this, such as angled louvres that allow the lower winter sun in and exclude the higher summer sun, external blinds and screens in summer, a pergola with deciduous vine on it or again deciduous planting.

On a sunny winter's day with the temperature at about 10 degrees outside, with good solar gain you can have your heating off most of the day and still maintain a comfortable temperature inside.

Materials

Another important factor in maintaining interior thermal comfort is the building materials. These materials have two important tasks, to keep the heat/cold out - this is usually in the form of insulation, and to keep the internal temperature moderated. This last one is usually achieved by including "thermal mass" in the design.

Thermal mass is a mass of material that is usually very dense and absorbs heat during the day in winter and slowly releases it during the night. In summer the thermal mass cools at night and absorbs the higher internal temperatures from the day, keeping the internal air cool.

The simplest use of thermal mass in a building is to use concrete floors and concrete or brick internal walls (often used as reverse brick veneer). In winter the low sun shines through the windows and heats up the floor. In addition the thermal mass of the slab and walls absorb and radiate heat regulating the internal environment. The most noticeable effect of this is that the internal temperature does not dramatically fluctuate with the external temperature but maintains a reasonably constant, moderate temperature: it takes a lot longer for the house to heat up on hot days in summer and to cool down in winter.

Of course this the use of passive solar is just part of the equation in terms of efficient environment management for a house. Carefully planned ventilation, heating, cooling and insulation all have a part to play as well, but used in conjunction your house can be comfortable all year round without total reliance on your air-conditioning and heating. With this environmentally friendly approach of course comes the benefit of reduced services bills.

More information can be found here and here.