Custom designed energy efficient two story house

Energy Efficient House Design

An energy efficient house is one which uses energy or power efficiently.

Here in Tasmania we use a lot of energy keeping our houses warm in winter. This makes building an energy efficient house design in Tasmania vital if you want to reduce your carbon foot print, keep your power bills low and live in a comfortable house.

An energy efficient house design can be broken down into three main design principles: Power Efficiency, Passive Design & Water Efficiency. These design principles can work together creating a much more efficient house than if only one of these principles is used. For example, using efficient appliances and lights reduces the amount of energy generation and storage needed. Likewise a passive house design can reduce energy requirements for heating and cooling.

Power Efficient Design

Efficient Appliances

Appliances such as fridges, freezers, dryers, washing machines and dishwashers can make up a large percentage of a home’s energy use. Choosing high efficiency rated appliances will help to reduce your homes energy requirements. The governments rating system makes it easy to choose the right appliances for your energy efficient home. Check out www.energyrating.gov.au for more information on energy ratings for appliances.

Efficient Lighting

Specifying energy efficient lights for your new house can make a considerable difference to your energy needs. LED down-lights which are very energy efficient have come down in price in recent years and are now a very cost effective and commonly used option in Tasmania. Other feature lights are also available with LED globes allowing you to use LED’s for most situations.

In addition to using energy efficient artificial lighting it’s also important to ensure your design includes adequate natural lighting. The National Construction Codes (NCC) require that natural lighting is provided to all habitable rooms which are used for extended periods. This includes living areas and bedrooms but does not include utility rooms such as bathrooms, laundries, pantries, storage rooms or garages. Providing utility rooms with natural lighting can reduce artificial lighting use. In bathrooms and laundries, a window which provides natural light can also provide natural ventilation making windows in these rooms desirable for most people.

Power Generation & Storage

Generating your own renewable power, most commonly with a solar PV (Photovoltaic) system provides energy that you can use in your home and feed back to the grid when not needed. The cost of solar PV systems is becoming more and more affordable. Government rebates may also be available which help to make a solar PV system an even more viable option.

Before deciding to install a Solar PV system it important to find out what your rebates are and what your feed in tariff is. A feed in tariff is the money you get back or deducted from your power bill for feeding power back to the grid. This is generally less than the cost to use power from the grid. If your feed in tariff is very low, it might be worth considering using energy storage with your Solar PV system. Storing energy, you generate during the day to use at night instead of feeding it back into the grid can make a big difference to the energy savings of your Solar PV system.

Passive House Design

A passive house design considers the climate and site conditions of a house to make it more energy efficient. In Tasmania using passive heating and appropriate levels of insulation can drastically reduce winter heating costs and make your home more comfortable

Energy and water efficient design is also important but can easily be upgraded or changed over time. Many principles of passive design need to be applied at the very start of planning a new home as they can be difficult and costly to change later.

Solar Passive Design and Orientation

A solar passive design considers the direction of the sun at different times of the day and year. This allows you to use the sun to warm your house naturally in winter while keeping windows and external walls protected from direct sun light in summer. Here are some details about different window orientations (this also applies to walls but to a much lesser extent if they’re well insulated):

  • North windows – North facing windows allow direct sunlight to enter the home during the day. In winter this can help to warm the house. North facing windows can also be protected from the sun in summer reducing cooling costs. As the sun’s angle is lower in winter than in summer a fixed eave over a window can block the summer sun while allowing the winter sun in. This is one of the most important considerations in designing a solar passive house.
  • South windows – South facing windows let in very little direct sunlight, but they do allow heat to escape. In cooler climates like Tasmania’s it is important to minimise the size of south facing windows.
  • East windows – East facing windows receive direct sun in the mornings but are shaded from the sun in the afternoon. In Tasmania it is better to reduce east facing windows as they do not generate much heat gain in winter and can also cause overheating in summer.
  • West windows – West facing windows get direct sun in the afternoon when it is the hottest. This can be beneficial particularly in colder parts of Tasmania when the warmth can heat the house, however being able to protect west facing windows is crucial in summer. West facing windows can be protected with external shutters, louvers, adjustable awnings or deciduous trees.

Shape and Orientation

The shape and orientation of a building can have a big impact on energy efficiency. Square or short rectangular shaped houses have a smaller perimeter than one with a complex shape. This means there is less external wall area for heat to enter or escape. The orientation of the house also has a big impact as west facing walls receive direct sunlight in the afternoon which can cause overheating in summer.

Generally, the most efficient shape and orientation for a house in Tasmania is a short rectangular shape that faces north with the shorter sides facing east and west. This also makes it much easier to reduce east and west facing windows and provide plenty of north facing windows.

Thermal Mass

Solid building materials like brick, stone, tile and concrete have a high thermal mass and can be used to store thermal energy. This is an important part of designing an energy efficient house as thermal mass can regulate fluctuations or changes in temperature over a short period (day and night temperature changes).

Materials with high thermal mass use a lot of energy to change temperature. They also release energy slowly. Direct sunlight can be used to heat thermal mass. This heat will then be slowly released over night when there is no sunlight available to warm the house.

Thermal mass is less effective or can even have a negative effect if optimal window orientations are not used. For house designs with lots of west or south facing windows it may be beneficial to reduce thermal mass and use light weight construction instead.

Shading

Adding external shading can protect exposed windows from direct sunlight that can cause unwanted summer heating. It can also be used to protect walls that can heat up and radiate heat into the house.

Louvered awnings or pergolas are particularly useful as they can shade a house from the summer sun but still allow direct winter sunlight though. These can be fixed at an angle that will block the higher angle of the summer sun or they can be adjustable, so they can be opened or closed as needed. Other shading options that are useful are eaves, verandahs and screens.

Insulation

Insulation prevents heat escaping a house in winter and keeps heat out in summer. A material’s insulating ability can be determined by the R-value (thermal resistance value) the higher the R-value the more resistance it has for preventing heat from pass through it. Heat is lost or gained through a home’s roof, walls, windows and floor so it is important to allow for insulation to all these areas. All building materials have an R-value, but most are very low which is why added insulation is needed.

Insulation is available in two main types: reflective & bulk. Bulk insulation contains small air pockets that reduce heat transfer. Reflective insulation, which is normally aluminium foil over a paper or plastic sheet, has a shiny surface that reflects heat. Composite materials that combine the two types of insulation are also available.

The minimum insulation requirements for new homes are determined when an energy rating is completed. Most new houses in Tasmania require an R-value of 4.0 for the roof or ceilings, 2.5 for the walls and 2.5 for the floors.

Air Sealing

In Tasmania’s cool climate preventing the leakage of warm air in winter can play a big part in creating an energy efficient house design. Air can escape through gaps around walls, ceilings, floors, doors, windows as well as fire places, fans and vents. Sealing these gaps can increase energy efficiency but can also cause moisture and condensation problems. When a house is well sealed it is important to provide ventilation particularly in bathrooms, kitchens and laundries where moisture and condensation can cause air quality problems. Providing moisture and condensation control in the roof space and insulation should also be considered and detailed by your building designer.

Self-closing extractor fans can provide ventilation when needed but close to reduce unwanted air leakage.

Another good option for very well sealed homes is a “Heat Recovery System” which works by using the heat from extracted air to warm cool external air being drawn into the house. A heat recovery system can also reduce condensation problems and improve indoor air quality as it replaces stale moist air inside the house with fresh air from outside. Heat recovery systems should always be designed by a specialist supplier or installer who can advise on a system suitable for your home.

My Tips for a Passive House Design in Tasmania

  • Keep your living areas on the north side of the house and bedrooms on the south.
  • Use lots of north facing windows protected by an eave or awning (a good building designer should be able to calculate the optimal size of your eaves or awnings)
  • Reduce the size of east, west and south facing windows
  • Protect any east or west facing windows with a larger eave, verandah or awning.
  • Use concrete or brickwork internally for thermal mass when optimal window orientations have been used. Concrete slabs on the ground should also include edge and under slab insulation.
  • Include high levels of insulation in walls, ceilings and elevated floors.
  • Use double glazed windows, preferably with timber, UPVC or thermally broken frames.

Water Efficient House Design

Reducing a home’s water use contributes to creating an energy efficient home. To create a highly water efficient home collecting and storing rainwater and reusing grey water should also be considered. This is great for the environment and can save money off your water bills.

Water Use

Choosing water efficient appliances like choosing energy efficient appliances will help to reduce a home’s water usage. Showers and toilets are two of the biggest water users in a home so choosing a water saving shower head and toilet will make a big difference. Efficient washing machines and dishwashers also offer a good amount of water savings and are well worth the investment. While some of these water saving features can easily be upgraded or added at any time, including these in your new homes specifications when it’s built can save on making upgrades later.

Rainwater

Collecting and storing rainwater from your roof either for use in your home or garden is a great way to increase your homes water efficiency. Many rural properties throughout Tasmania do not have water mains and instead rely on rainwater harvesting for their homes water supplies. However even with mains water available collecting and storing rainwater can help reduce your water bills.

As Tasmania’s annual rainfall is quite consistent throughout the year, large volumes of rainwater storage are not normally needed. For most two to four-person households around 30,0000 litres should be enough.

While many people use rainwater for drinking, showering and cooking it is important to ensure your system is properly maintained and regularly cleaned. Where mains water is also available it may be worth considering using rainwater for flushing toilets and in the laundry only. This makes cleaning your rainwater storage, gutters and roof less important, so you can do this less often. Flushing toilets and laundry use generally accounts for a large percentage of a home water use so using rainwater can save a considerable amount.

Grey Water

Another water saving measure that can be worth considering particularly if you’re having large areas of lawn or gardens is to reuse grey water. Grey water is water other than sewerage that’s been used in the house, often collected from showers, baths, hand basins and washing machines (but not toilets or the kitchen sink). This grey water can be treated in a specially designed treatment system or piped directly into the garden. If grey water is being used above ground or to water fruit trees, it’s important to use a good treatment system to reduce the amount of chemicals and bacteria in the water.