Design Affordable Passive Homes

In some markets, Passive Houses can be built for the same price tag as a conventional custom home

By Molly Merriman

As the cost of construction trends upward, the idea of building a new Passive Home can seem especially out of reach for those on a tight budget.

Our focus as a residential design firm is to develop cost-effective building techniques that make achieving Net-Zero a possibility for everyday homeowners across North America.

However, building green on a budget relies on more than just construction methods – there are also many design strategies that can drastically bring cost down. Here are seven design tips to consider during the planning stage that can help make your Passive Home both energy efficient and affordable:

Efficient Building Shape

Keeping your structural elements, such as load bearing walls, vertically stacked will go a long way in simplifying construction, minimizing complicated air sealing details, and saving on materials. Design elements like cantilevers or staggered bearing walls may sometimes be integral to an impactful design – just bear in mind those can create thermal bridging, which results in energy loss. If you can avoid the need for a structural engineer, you also save costs. It’s all about balance!

Spaces like garages and screened-in porches are a great way to maximize space that doesn’t require the same airtightness, degree of insulation and level of finish as conditioned space. In many climates, there are several months of the year where a semi-outdoor, screened-in living space is ideal, and garage space can easily be expanded to provide much-needed storage as an alternative to a basement. These spaces can add architectural interest to a simple building shape and be built at a lower cost.

From Inside, To Outside

A long run between hot water heater and plumbing fixture means more construction expense and less efficiency. The energy lost in the plumbing runs in a Passive House are calculated with the sum of all the individual pipe lengths from the tank to the fixtures. Even if the pipe is branched off a main, the loss is calculated using the entire pipe length. Keeping this in mind during design can pay off by keeping plumbing runs short, and fixtures as grouped together as possible.

Windows and doors are expensive components that require a higher degree of maintenance, and even a triple-glazed window or well-insulated door is a source of air leakage in a Passive Home. However, windows also play a key role in passive solar heating and with the right size, orientation, and relationship with shading elements, can provide your home with free heating and cooling, not to mention beautiful views and connection to nature.

In the Northern Hemisphere, here are some guidelines:
  • Use fewer, larger windows. The frames are less energy efficient than the glass with today’s advanced glazing technology, so we want to have more glass and less frame for the best performance.
  • Try to maximize the glazing on the south side with some overhead shading to block the summer sun.
  • Minimize glazing to the north where it is not needed. Placing spaces like mechanical rooms and closets to the north helps, as these are typically rooms that don’t require windows.
  • Carefully consider the windows to the west to mitigate afternoon overheating in the summer months.
  • Designing for cross-ventilation is crucial during the shoulder seasons. It’s important to know your prevailing wind directions to ensure that operable windows are placed on opposing windward and leeward sides. This will facilitate good air flow and natural ventilation.
Locally Available Materials

The Passive House model originated in Germany, but that doesn’t mean the materials used to build one have to be expensive European imports. It is possible to achieve Passive House performance using assemblies that are built from conventional, readily available North American building materials. Windows, doors, and mechanical equipment that are locally available are more likely to have good warranty and maintenance services, which reduces repair and replacement headaches. Not only that, but using local materials typically lowers the embodied carbon of the building.

Energy modeling demonstrates the positive impact smart design can have on energy efficiency, 50% of which stems from good design, and the other 50% from how you build. By following the above tips, a Passive House can be achieved with minimal increase in construction; in fact, in some markets, Passive Houses can be built for the same price tag as a conventional custom home.

Molly Merriman (OAA, MRAIC) is a licensed architect with Passive Design Solutions, a residential architecture firm dedicated to Net Zero, Passive House design, consulting, and construction. www.passivedesign.ca