This article is prepared for someone who may not be targeting a wholly certified, plaque-on-the-wall Passive House, but still looking to conserve energy and take smart, functional steps during the design process.
If you are aware of sustainable principles or ‘passive design’ but not yet aware of Passive House, it would be well worth your while to read these additional blog posts:
Air tightness
Try to minimise air leakage throughout the home. This concerns:
Warm internal air out and/or cool air in through the building fabric in winter, and
Warm external air in and/or cool internal air out during summer
The National Construction Code specifies a maximum air-exchange rate of 10/hour under 50 pascals of pressure (equivalent to a 32 km/h wind):
H6V3 Verification of building envelope sealing
(1) Compliance with H6P1 is verified for building envelope sealing when a building envelope is sealed at an air permeability of not more than 10 m3/hr.m2 at 50 Pa reference pressure when tested in accordance with AS/NZS ISO 9972 Method 1.
This means that under 50 pascals of pressure, the air inside will be changed out with new air 10 times an hour. If you think of some current houses with air-exchanges sometimes near 30 an hour, that’s a lot of wastage to air conditioning systems and/or very uncomfortable indoor temperatures.
Be aware that an airtight building is dangerous if other components of Passive House design are not incorporated: ventilation. If the envelope is reduced to less than 5 air changes an hour the BCA requires mechanical ventilation (also under clause H6V3).
Upgrade your glazing specification
Please don’t use single glazed, aluminium framing. The amount of energy lost through the glazing is one item, but the frame itself is likely the poorest conductor of energy transfer from inside to outside.
Double glazing is not double the cost. The most expensive component of window and door components is usually the frame, so double glazing is often around 15% more than the initial quote. This is typically several thousand dollars, amongst a much bigger total project cost, to significantly alter your building's performance. This can also mean that you may be able to use clear glazing in a double system instead of tinted single glazing so you can maximise a clearer outlook to the outside world, whether that’s blue sky, your garden or panoramic Sydney Harbour/ocean views.
Insulation
Insulation as a building material is relatively cheap. Similar to the jump to double glazing, it will not astronomically blow out construction costs. Typically, we aim at a minimum standard of R2.7 in the walls (ideally R4.0 in a 140mm frame) and R 6 in the ceiling or amongst pitched roofs.
Jump here to test insulation prices for, let’s say, 200 sqm of insulation:
90mm R1.5 Wall Batts: $73.20 for 8 sqm or $1,850 for 200 sqm
90mm R2.7 High Performance Wall Batts: $59.80 for 3.3 m2 or $3,642 for 200 sqm
Or
185mm R3.5 Ceiling Batts: $54.75 for 6.7 sqm or $1,634 for 200 sqm
260mm R6.0 High Performance Ceiling Batts: $66.70 for 4.0 sqm or $3,335 for 200 sqm
These numbers are arbitrary, but in this scenario an extra $1,800 for walls and $1,700 for the ceiling completely transforms your home’s performance. This is a fraction of a percent of the total project cost and will save you money on each and every energy bill (assuming you’re at least partially on the grid).
We have no affiliation with the above website, simply using it as a demonstrative tool for this article on how to conserve energy.
Energy production
Air conditioning is not a dirty word if the energy can be produced on site. Solar panels should be considered on every project. Have a look at another website I regularly follow (again, no affiliation).
Orientation
If your site primarily faces social and entertaining spaces (living, kitchen, dining, alfresco etc) to the south, consider breaking up the façade and building envelope geometry to utilise courtyards for natural light. Skylights are generally not the answer for heating cool, south facing spaces because during winter the sun is at such a low angle that it’s not really penetrating into the spaces and heating thermal masses, rather the regularly horizontal planes of skylights is perfect (bad for us) for hot, high and direct summer sun to smash into the internal spaces. If you’re lucky enough to be house and/or land hunting, consider orientation!
Orientation is only as useful as the design that follows. You don’t want to have a north-facing backyard and then put a long alfresco roof across the entire rear as this will not only remove the summer sun, but the winter sun will have no chance to improve internal spaces in winter. Locate all rooms, roof structures and building elements intelligently.
Don’t forget about any existing or new trees, deciduous or not, when assessing solar orientation.
Window Location and Sizes
Utilise larger windows facing the sun (north in the southern hemisphere) and utilise effective shading to block it out in summer and let it in during winter. The 0.45:1 projection:height ratio works best for northern windows. This means that if the window is 1 m tall, the awning or shading device should be 450 mm deep. This is assuming the device is directly above the head of the window. If a typical roof eave or other shading device is used then you have to account for the dimension from the sill to the shading device.
Thermal Mass
Use where it can be maximised. A masonry slab and wall that doesn’t receive any direct sun in winter is not providing the benefit. Also a concrete slab that gets pounded with summer sun is doing the opposite of what it’s intended to do. Be smart with structural material selection as it can significantly alter performance and help conserve energy.
Cross Ventilation
This isn’t necessarily a critical factor in Passive Houses as, realistically, you don’t need to open the windows in a Passive House as the fresh air is constantly pumped throughout the home without ideal outdoor temperatures and a suitable cross-breeze. However, suppose you are targeting night purges (i.e., opening windows in cooler summer evenings) or your fresh air intake coming from for non-mechanically ventilated homes then it’s wise to locate your openings to provide an entry and exit point for the flow of air to two sides of as many rooms as possible. This may not be possible in ‘landlocked’ rooms, but the ability for air to enter one window and flush out another will increase the health benefits of the home. Items you must be aware of when focusing on a cross-ventilated design is to ensure the window sizes correlate to the orientation of the rooms. Don’t have significant southern (loss of heat in winter) and western (afternoon heat-gain in summer) windows placed to meet cross-ventilation targets, as these windows will be considerable leakers of energy.
Overall, these steps to conserve energy should be viewed as a starting point for any project. It doesn’t need to blow out construction costs, and some design changes can be cost neutral, especially when considering the year on year expenditure of energy bills. In the sample project explored here, moving to double glazing and increasing the insulation specification has moved the needle a fraction of a percent in cost, but a significant way in energy conservation and efficiency.
If you want to push your efforts to conserve energy even further we can discuss completing a certified Passive House which aims to reduce energy consumption by 90% compared to a traditional build. Please get in contact with Shore Architects if you wish to discuss any upcoming developments with a sustainable target.