What is an energy efficient home?
A modern energy efficient home is one that incorporates common sense design principles that makes the building efficient in terms of:
- Reducing the need for expensive heating & cooling appliances/equipment.
- Reducing appliance running costs and therefore energy bills.
- Reducing energy related CO2 emissions at the home and at the electric utility plant.
- Provides a healthy indoor air environment
while providing superior indoor comfort and air quality, an energy efficient home must also be easy to maintain. The additional building costs must have a favorable return on the investment and increase the resale value of the home.
How can I design my house to be Energy Efficient?
General Guidelines
For a house to be really energy efficient and provide a superior indoor environment you need to have a balance of all of the right elements of design. These include a consideration of:
- Orientation & Siting - Taking advantage of supplemental passive solar.
- Layout & Space Utilization - minimizing the building shell surface area.
- Insulation (The Building Shell) - reducing winter heat loss.
- Windows/Blinds/Shading/Landscaping - reducing summer heat gains.
- Ventilation/Draft Proofing - Quality indoor air without infiltration.
- Thermal mass/Earth Sheltering - An energy flywheel to reduce the effect of outdoor temperature swings.
- Foundation Drainage/Damp-proofing - Building dry mold resistant earth sheltered, thermally isolated high mass building shells
- Indoor Air Quality/Filtration/Ventilation - Cleaned air with removal of indoor pollutants.
Orientation & Siting
By carefully considering the position of your home on your chosen building site, you can maximize the passive solar design advantages that can reduce the cost of your alternative energy system. The following points should be considered when selecting a building lot:
- Size and orientation of the lot (having sufficient space for solar siting)
- Solar access to the South side of the house (for winter sun heating)
- Slope of the building lot (to allow adequate drainage)
- Tree coverage and height (to avoid too much winter shading or summer sun)
- Height and proximity of surrounding buildings (to avoid overshadowing)
The orientation and siting of your home can make a huge difference to your energy bills and your comfort. The 'ideal' home is sited with the daytime living areas facing south with the long axis of the house running east-west The good news is that variations on the orientation can be up to 60 degrees to the west and 30 degrees to the east of magnetic north, with no major effects on the solar advantage. Some extra summer sun shading may need to be considered to avoid unnecessary solar gain. Large windows on the South side of the house let the sunshine in during winter and should be shaded from the summer sun. This will make the house warmer in winter and cooler in summer. To prevent over shading from neighbors, allow a set back of at least 25 feet from a single story house to the north, and at least 50 feet from a double story house. If this is not possible, you might be able to use a clearstory (skylight) window or light tube to allow adequate sunlight into the north sides of the home. Note that skylights will require sufficient shading for summer comfort.
Layout & Zoning
Locate the daytime living areas facing south and have south facing windows capture the winter sun. All bedrooms and utility areas should be located on the north side (this assumes that the southern exposure maximises the use of daytime living spaces to benefit from winter sun entry- bedrooms and other rooms can also face south, based on your personal preferences). Following an open plan style of home will also help. Not only does it make the best use of all available space, it should allow light to penetrate easily and air to circulate freely around the home. Design open areas so they can be reduced in size by closing doors, to minimise the areas needing heating and cooling at any one time.
Insulation
The second most important measure to make your house energy efficient is the selection of insulation materials and methods for the walls and roof. (minimum levels of insulation are now mandated by local or State energy codes). Insulation is the material that slows down heat transfer through the external surfaces of your home. In a well insulated house approx. 40% of heat loss takes place through the roof and ceiling, while around 35% of heat is lost through walls and floors.
The performance of insulation materials is specified with an 'R-value'. The greater the `R-value', the more effective the insulation is at resisting conducted heat flow into your house in summer, and out of it in winter. Additionally improtant is the wall construction and framing factor derating for the type of insulation selected. The framing factor is an allowance for the amount of wood in the structure that makes up the wall with a lower R value than the insulation. Some reflective foil type products do not have an 'R-value', but are very effective in minimizing infra-red heat transfer. They do need to have an associated air gap next to them for them to work effectively.
Insulation Materials
Blanket & Batt insulation. There is a range of bulk insulation materials which come in two forms, either in long rolls (called blankets) which must be cut to fit the length of space, or in precut lengths (called batts). Fitting the material snugly is very important. Any gaps left between the insulation and framing will make the insulation less effective.
Loose fill insulation has no backing and is supplied loose. It is simply poured or pumped into a wall cavity or roof space.
Rigid insulation comes in precut boards and are ideal for insulating areas such as raked ceilings, solid brick external walls, under wooden floors and around concrete slabs. These materials eliminate the framing factor associated with batt type insulation.
Spray on materials come in fiberglass, celloulose and expanding foams. The advantage of sprayed on materials is the tighter fit acheived between the insulation and the biulding framing
SIP Panels a newer high tech system of foam insulatin bonded to building sheathing and sheetrock to form a structurally intergrated panel for both insulation and building support.
ICF's, Insulating Concrete Forms consist of insulating foam, commonly expanded polystyrene (EPS) or extruded polystyrene (XPS). The three basic form types are hollow foam blocks, foam planks held together with plastic ties, and 4 x 8 panels with integral foam or plastic ties. ICFs can be used in many various structural configurations, such as a standard bearing wall or post and beam infill. These blocks can also be made of a mineral / cellulose material with no foam from some manufacturers.
Reflective foil insulation works by reflecting radiant heat from its highly polished metallic surface. The key to using these materials is to provide an air space that allows the foil to either reflect heat back into the space or to reflect heat from unwanted solar gain back out of the house.
Windows
Windows are one of the biggest factors in home energy efficiency. The sun's rays pass easily through normal un-tinted windows. This can provide welcomed heat in the winter, but can lead to overheating in summer, as the heating power of sunlight shining directly into windows is around 700 btu/day per square foot (about the same amount of heat from 2 feet of residential baseboard radiator).
Double-glazed windows are essential in reducing conducted heat transfer and do not significantly reduce solar heat gain. They need to be used with effective external shading in summer.
Ideally some south facing windows should be full length, so when the winter sun is low in the sky, the heat will penetrate well into your home. Use less glass on the east and west sides, and minimum or zero glass areas on the north side of the house.
The total window area should be less than 25% of the total floor area of the house (these proportions are a guide only, our computer software for houses considers the solar gains and thermal losses for each home to maximize the benifit of design features when assessing the overall efficiency rating of the house). If windows are made too large they can make the house uncomfortably hot in summer and hard to keep warm on cloudy winter days and cold nights.
| Differing styles of homes have differing amounts of glass area. For passive solar gain optimization, How do I divide up my Window Area? (guide only) | |
| Facing Direction | Recommended % of glass Area |
| South | 50 % |
| West | 30 % |
| East | 15 % |
| North | 5 % |
Glazing
R value or U value
Normal glass in windows has a low 'R' value and can allow relatively large amounts of thermal energy in and out of your house. Advances on glazing technologies now mean that there are options for homeowners to choose from to improve the thermal performance of windows.
The 'R' value of the window (or its inverse 1/R, is called the 'U' value, which measures heat flow, or thermal conductivity), is one part of measuring the performance of the glass / window. Standard double pane windows are about .55µ and the best about .12µ Another factor in attition to insulating value is the window pressure resistance ratingwith a range of 15 to 100 Pa (Pascals), windows of at least a 40 rating should be chosen as a minimum.< /p>
The other way heat gets into a building is from direct solar gain, ie the suns direct rays.
Shading Coefficient or Solar Heat Gain Coefficient (SHGC)
The Shading Coefficient is a measure of how much solar energy is admitted through the glass. The higher the number, the better for passive heat gain. Another way of describing the amount of solar heat gain through a window is the Solar Heat Gain Coefficient (SHGC). The SHGC represents the percentage of the available solar energy that enters the interior of the home. The higher the number the better for passive solar heat gain.
Shading
The shading of sun is vital in keeping your house cool in summer.
Well designed shading greatly reduces heat entry, adding significantly to summer comfort in the home. It can also significantly reduce the need for, and running costs of, airconditioning equipment.
The most effective way to keep summer heat out of the house is to use adequate external shading.
South facing windows can be easily shaded with fixed shading devices, such as an eaves overhang, horizontal shade or awning, and pergolas.
These shading devices must be designed so that they allow sun entry in winter and totally shade the windows in summer. Attention should be paid to adequately shading south facing windows.
While important, internal shading such as curtains and blinds will never be as effective as external shading because the radiant heat from the sun has already passed through the glass. To get the best performance from curtains and blinds you need to ensure that they should be opaque and of light colour, to maximise the reflection of sunlight.
Solar Rebates
A truly energy efficient home harnesses some of it's energy from the sun. Current government rebates for photovoltaic systems (the generation of electricity from the sun) and solar hot water can make these renewable energy technologies more cost effective - enabling significantly lower running costs and reduced greenhouse emissions. More information on these rebates can be found here.
Landscaping
Landscaping can enhance your property and provide benefits to you in maintaining more comfortable conditions in your home.
By carefully planning the landscaping around your home, you can control the entry of heat, as well as the quality and direction of the breezes you allow to blow through it.
Breezes entering your house will be cooler if they have passed through gardens or courtyards that have shade, pools or shrubs and lawns. The layout of your garden can also be used to screen direct breezes.
Ventilation & Draft Proofing
In summer, a cool breeze flowing through the house helps cool down the house and it's occupants at night. The house need not face directly into the prevailing summer breeze, but can be offset at an angle of up to 45° either way.
While adequate controllable ventilation is essential to provide fresh air, prevent condensation, and help cool a house on summer nights, drafts can create discomfort and lead to energy losses in both summer and winter.
In winter, drafts can account for 25% of heat losses or more.
Reducing drafts can be the most cost effective way of reducing heating and cooling costs.
New houses should be built to minimize drafts, by avoiding gaps at construction joints between different wall materials, and where walls join or meet the ceiling and the floor, and by ensuring that doors and windows fit snugly in their frames. Small details can make a big difference. Drafts can be further reduced by:
- Continuous air barrier paper sheeting
- Sealing air barriers with tapes and caulking
- Sealing window flanges with mastic tapes
- Continuous air barrier foam insulation sheeting
- Tight fitting fireplace dampers
- Air tight, insulated recessed light housings
Thermal mass
The term Thermal Mass refers to the ability of building materials to store heat. Building materials that have a high thermal mass, such as internal bricks and masonry, foam/concrete walls and a concrete slabs, can store large amounts of heat without a large temperature change.
In places where the difference between day and night temperatures is 20° or more, there are benefits in using high levels of thermal mass to stabilise internal temperatures in both summer and winter. The correct use of thermal mass inside a house can significantly improve both thermal comfort and energy efficiency.
Floors
Energy efficient homes make good use of concrete, tiled or slate floors, because apart from being easy to clean, they play a big role in absorbing or rejecting heat in winter. The floor must be able to absorb as much heat as possible during the day and then release the stored heat into the room at night. Carpets and rugs act as insulators, so the slab floor can't absorb as or reject as much heat.
Tiles, slate or any other heat absorbing hard surfaces are ideal and work well when situated in rooms that have south facing windows.
FAQ
| Q | If my chosen block does not face the right way, does this mean that I can't build an energy efficient house? |
| A | Correct orientation gives you the best chance to capture winter sun. If this can't be done, more effort is required on the other aspects of the house design to achieve comparable efficiencies. While passive solar gain is a nice thing, it is not everything. There are so many energy saving details that can be incorporated into your home that you don't have to build something funny looking or unusual. |
| Q | My new house plan has all the daytime areas facing north. How can I improve the layout? |
| A | Often it can be as easy as mirroring the floorplan for you. If this cannot be done, we can consider improving the characteristics of the glass, possibly upgrading to high grade of gas filled double glazing, or incorporating a southern facing sklight or light tube to get some winter sunlight into the body of the house. |
| Q | Do open plan houses and two story houses with large stairways need to be zoned? |
| A | Large open plan homes and two story houses allow heat to travel through them easily. This means more energy is required to heat them than if there were smaller areas that can be isolated with lowered thermostat settings when not in use. Since energy efficient homes are so efficient at keeping heat energy in, set back is less benificial that it used to be in a leaky building. Zoned radiant floors can be installed to help spread solar energy around the rest of the home. |
| Q | What is an insulation R-value? |
| A | The level or performance of bulk insulation products is measured by its Thermal Resistance or 'R-value'. The greater the 'R-value', the more effective is the insulation at resisting conducted heat flow into the building in summer, and out of it in winter. Reflective foils work in a different way than bulk insulation, and they do not have an 'R-value' on their own. Like a mirror, they reflect heat energy back where it came from and are very effective at minimising heat flow and have an effectice R value rating. |
| Q | Are batts, loose fill or foam sheet insulation better? |
| A | The important consideration is the R-value of the insulation material and its ability to be installed without gaps and bypasses. For the same R-value, there should be no difference in performance between loose fill insulation and batts (providing both have been installed correctly). Foam sheeting eliminates the framing factor or the stud material and is easier to seal. Note that covering ceiling joists with insulation may create a hazard for anyone who needs to work in the roof space and a walkway will need to be installed for access. |
| Q | Should I consider energy efficient lighting? |
| A | Yes! While fluorescent lighting (compacts and/or tubes) can be relatively expensive to buy, they will last much longer than ordinary incandescent bulbs, with significantly reduced energy consumption. They're great for all areas especially where the light is on for long periods - like kitchens, family rooms and hallways or for outside night security lighting. New low voltage LED lights may also be considered and run off of a solar PV system. |
| Q | Can reflective foil laminate (RFL) be used as an insulator? |
| A | Yes - but its usefullness is in reflecting radiant floor heating back to the space intended. |
| Q | Do louvres and venetian blinds reduce heat loss? |
| A | Yes - Louvres, venetian blinds and vertical blinds are not good insulators, but they can block radiant heat. There are many windo treatments that are very effective in reducing heat loss and unwanted solar gain. Motorized blinds are available for hard to reach areas. |
| Q | Will BTS tell me how much my house will cost to run? |
| A | BTS assess the thermal performance of the housing envelope, ie the need for heating and cooling, and the costs associated with providing domestic hot water, not the costs of running appliances within the house. (This is always tricky, as it is difficult to predict your actual usage of appliances within your home. Appliance running costs are therefore often referred to as averages or as quarterly running costs for specified periods of time). The BTS computer model caluclats the heating and cooling needs for a home on an hourly basis, including domestic hot water heating or swimming pool heating if needed to arrive at a yearly operating cost. |
| Q | What can I get for Federal and State tax credits & incentives for? |
| A | Solar heating equipment and Photo Voltaic Electric, for more info go to... |