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You can design an energy efficient home to be naturally warm in winter and cool in summer. A comfortable home that saves money and is better for the environment. This detailed article explains how.

The sun and its path

Each square meter of sunlight provides us with up to a thousand watts of energy on a summer’s day. That’s the equivalent heat to what a standard radiator provides each square meter. By following some straightforward rules when designing and building your energy efficient home, we can capture this free energy in winter when we need it and block it out in summer when we don’t. The position of the sun varies throughout the seasons. In winter, the sun moves across the northern sky at a relatively low angle of elevation. In summer, the sun is high in the sky and almost directly overhead of midday but at a low angle in the east and west in the morning and afternoon. So what should we do to make the most of the changing position of the sun to obtain an energy efficient home? let’s look at glazing, shading and building layout.

Glazing

Normal glass allows up to 90% of the sun’s heat directly into the house. As a result, the location, size, and type of glass is a critical aspect of design. As a general rule, install more glass on the north facade where it is easy to let in the winter sun and less on the eastern westward is difficult to block out the hot Summer Sun in the morning and in the afternoon. The solar heat gain coefficient or SHGC is a measure of the amount of solar heat that passes through the glass. The higher the SHGC, the greater the heat that passes through. So, in temperate climates, install glazing with a high SHGC on the northern side of the house to allow the winter sun in. In summer, it is the glazing on the east and west which is exposed to the sun. So install shading, and if that’s not possible, use low SHGC glazing to keep the solar heat out.

Check the words label to help select the right glazing. It contains the SHGC at the bottom of the label. As well as other measures such as U value.

Shading

High-performance glazing is important for an energy efficient home. But especially in the east and west, external shading will be even more effective. On the east and west, horizontal shadings such as eaves do not block any summer sun at lower angles. So shading must be vertical with good options being shutters, pulldown awnings, shade cloth, and vegetation.

On the northern side, horizontal shading will sufficiently block the direct summer sunlight, whilst allow the low angled winter sun to get in.

As a rule of thumb, shading should extend out no more than half the height of the window. Adjustable shading is a good option, allowing occupants to control solar heat gain depending on comfort at any time of the day in any season.

Deciduous vegetation is also useful as it shades well in summer but lets the winter sun. Such options may be used to block summer glare which is bounced off outside objects. The sun also heats up roofs and walls which will eventually transfer heat into the house. Shading of east and west sides of the building using vegetation can be very effective at keeping the house cool in summer months.

Colors of the roofs and walls affect how much of the sun’s energy that is reflected or absorbed. So in cold climates, choose darker colors to absorb solar heat and choose lighter colors in warmer climates to reflect solar heat.

Building layout

The building shape and orientation will have a big impact on the design of an energy efficient home. If you have any role in the design, here are some tips:

North facing areas are a good spot for living areas. Locating the garage or laundry on the western side will create a heat barrier to the rest of the house and summer afternoons. A longer northern layout allows a more solar gain in winter than summer.

If the block has a narrow northern aspect, other solutions exist. For example, you can split the house into two sections providing every room with north facing glazing.

So, to build with the sun in mind, allow sunshine through glazing in winter shade glazing in summer, and plan the building layout to take advantage of the northern aspect.

The Building Envelope of An Energy Efficient Home

In this section, we look at how to design and build building envelope to resist variations in outdoor temperature and to get an energy efficient home.

Houses in temperate Australia must deal with a wide range of temperatures. When there is a difference between the indoor and outdoor temperature, it will flow through the building envelope. The greater the temperature difference, the greater the heat flow. In winter, heat will be lost from the building and in summer it will be ganked.

Insulation

To reduce the heat transfer, it’s crucial to have insulation in the roof and walls. And also beneficial to insulate timber floors. Insulation keeps heat inside in winter and stops heat getting inside in summer.

The R-value is a measure of how well the insulation will reduce heat flow. The higher the R-value, the better the performance. The regs might ask for a system R-value or an added R-value. So you need to know the difference. The timber brick and plasterboard also have an R-value which can be added to the R-value of the insulation to give a system R-value. The r-value of the installation itself is called the added R-value. Only system R-values are quoted for reflective insulation, as it depends on how and where it is installed.

Glazing

Getting the glazing right is critical for ensuring indoor comfort and energy efficiency for the home. The words label contains all the information to make an informed choice. Look not only at the star ratings but at the u-value, which tells you the level of the installation. The lower the u-value, the better the installation. This is the opposite way around to r-value of insulation. Standard three mil glazing has a u-value of about six, which allows up to ten times more heat through than an insulated wall.  Higher performance glazing such as low E double glazing has even lower u-values. Other measures on the labels such as SHGC are also important. So do not base your decision on u-value alone.

To successfully build your energy efficient home, it’s crucial you install glazing that complies with the building code and planning approval. Frames are an important consideration. Choose only timber frames or aluminum frames with the thermal break which is a layer of insulation to reduce heat transfer through the frame.

Draft Proofing

Our well-insulated energy efficient home envelope is of little use if it’s not well sealed. A leaky house might have 20 air changes per hour. The air inside gets replaced every few minutes. Drafts are a problem in cold weather and also in hot weather. Make sure you’ve got good seals on doors, windows, chimneys, exhaust fans and recessed downlights. There will be still enough fresh air to keep people healthy.

Ventilation

Ventilation can provide effective cooling when the outside temperature is cooler than the inside. Allow cross ventilation by locating openings on opposite sides with minimal obstructions in between. This will allow in breezes on cool summer nights to flush out the trap. Design and orientate your energy efficient home to capture prevailing breezes and choose windows with a large open herbal area.

But ventilation can’t cool a building on hot days. So it’s good to have insulation and draft proofing they let you seal the building and keep heat out. This avoids or reduces the energy needed for air conditioning and lets your home energy efficient.

Thermal mass

With a well insulated, sealed and ventilated home, thermal mass can even out maximum and minimum temperatures inside a building over 24 hours. Mass doesn’t create heat, it just stores and then releases. In winter, you need mass exposed to sunlight, which will warm up through the day and then release warm in the evening once the sun is gone. In summer, mass absorbs heat from the air to keep the temperature down during the day and it releases it at night when it can be flushed out by cool breezes.

A concrete slab or internal masonry walls are the easiest ways to provide effective thermal mass. A slab on the ground takes advantages of the Earth’s mass to even out indoor temperatures throughout the year.

So to design and build an energy efficient home, insulate to reduce heat gain and loss, use seals to prevent drafts, provide openings for cross ventilation and use mass to even out the temperatures.

As you can see, it doesn’t have to cost more to build a lower energy home. Just a little bit of know-how.