How to Design an Energy-Efficient House
Traditionally, the best way to stop a house from losing heat is to add several inches of insulation into the roof cavity to keep the heat in. Add some double glazing, and that's good enough, right? It all seems a bit like an afterthought, and that's pretty much what it is. It happened at the end of the build.
Taking a step back, it's now easy to see where improvements to this process can be made. If the whole building is taken into consideration—slab, walls, roof, windows, doors—the energy efficiency of a new property can be improved immeasurably. There is therefore much to consider when designing that energy efficient house.
The areas where buildings lose most energy are windows, doors, chimneys, and roofs. These are the areas that have an interface with the outdoors. However, walls still leak energy and so an approach that considers all aspects of the building needs to be taken.
If you have free reign on the design of the property, then the first thing to consider is how to build it while making the most of the natural elements for energy conservation. At its basic level, this means ensuring that the building is exposed to the sun as much as possible so that it can use the solar gain in the winter. In North America or anywhere in the Northern hemisphere, this means facing the property towards the south where it will get the most sun and, therefore, heat.
In order to minimize overheating in a hot climate, the roof design should incorporate large overhangs and cool roofs to bounce the heat back into the sky. In turn, this will reduce the amount of energy that the heating, ventilation, and air conditioning (HVAC) system uses in order to maintain a cool indoor temperature.
The choice of construction method is a big factor too, along with the amount of insulation that can be built into the fabric of the property, such as the walls and ceilings. This is why insulation needs to be considered at the early stages of the build and be integrated as soon as the slab is laid.
Insulating concrete forms is now popular for creating energy efficient walls. Concrete is poured into a polystyrene sandwich. Concrete is a good insulator and adding the polystyrene increases the thermal efficiency of the house.
SIPS, or Structural Insulated Panels, also use the sandwich as a basis. This time, it's a hard foam insulation between two timber sheets. These are bought as a ready-made product, rather than building the sandwich on site, like the insulating concrete forms.
A slightly left field building technique uses straw bales, as they're cheap and very thermally efficient. Treatments are required to prevent fires and rodent infestations, however. Some people are also just not happy with using straw as a building material, even though it's been used for thousands of years.
Air sealing is a relatively recent development in construction. House wrap, air barriers, Airtight Drywall Approach (ADA) and Simple Caulk and Seal (SCS) are now part of the house building process. House wrap is the most common as it effectively insulates all of the walls around the house, thus keeping the heat in. Any joints are then taped, increasing the efficiency further. It's a basic concept that works well.
Air barriers are a physical way of stopping the escape of warm/cool air. Caulking gaps, using filler to close up holes, and taping joints in walls prior to plastering all increase the property's efficiency.
Of course, if the air is sealed in, then there isn't an exchange of fresh air from outside with the stale, indoor air. Hence, the need for an HVAC system to provide air circulation and remove the moisture from inside the property. Since the HVAC system is such an important aspect of the finished property, its design and integration needs to be considered at the design phase of the build. This way, ducting can be hidden away as best as possible and any holes created as a result can be sealed to better insulate the house. Up to 30% of conditioned air can be lost due to gaps or holes in the system, so this needs to be minimized as much as possible. It's far easier to do this as the build is continuing rather than after the event.
Once the build is almost complete, a blower door test should be undertaken so that any air leaks can be found and addressed. The aim is to keep the comfortable indoor temperature constant and this means keeping it inside the property.