You’ve heard again and again that south-facing is the optimal orientation for a passive home. What if this isn’t possible?
Southern or Northern Exposure?
A key feature in any passive home is the orientation. In northern latitudes, it’s ideal to have the largest bank of windows (usually in the main living areas) south facing, or within 15 degrees of true south. In southern latitudes, the reverse will be true.
This orientation, along with strategic window placement and use of overhangs for shading, will optimize the home’s comfort and low energy footprint.
When optimal passive home design is possible, the home is naturally kept cooler in the hottest months, and warmer in the coldest months, reducing the need for additional energy input.
The fact is, most of us will be faced with limitations on our home’s orientation, depending on where we are building.
A home in an urban neighbourhood, like the one shown here, has a pre-defined orientation that can’t be changed and will be affected by shade elements such as neighboring homes and buildings, as well as trees.
Anyone building on waterfront will naturally want to maximize the home’s relationship to the water and may have heavy tree coverage to factor into the equation.
The truth is, a passive home built in the middle of a dense forest with very little natural light would still require far less energy to heat and cool compared to any other type of home. This is because of its tight building envelope.
Running the numbers
A passive home with optimal orientation won’t use more than 15 kilowatt hours per square metre of the home (15 kWh/m²) per year for its heating and cooling.
If certification isn’t what’s driving your project, and you simply want to benefit from the superior building method, then a passive home with worst case scenario orientation would use roughly 50% more energy on heating and cooling than in the optimal scenario.
Our net zero model home is 1,634 sq ft, with a treated floor area of 1,250 sq ft or 115 sq m (this is calculated by removing the total wall thicknesses).
The home’s total treated floor area, which does not use more than 15 kWh/m² per year means the home, based on $0.10 per kWh, costs approximately $173 per year to heat and cool. A passive built home with terrible orientation would cost more like $260 per year. This is still astoundingly low energy and low cost.
A comparable 1,600 sq ft code built home heated with natural gas would use roughly 7.68 cubic metres per day, for a total of 85.94 kWh per day during the winter (based on four months of heating). This heating energy requirement is nearly six times more than the passive home. The contrast is even greater when you consider that conventionally built homes often need heating in the shoulder months too.
The natural gas bill for one month for the 1,600 sq ft code built home used as an example here would run approximately $182. We compare with actual homes to be sure our figures are current.
Site placement and orientation factors
Planning your passive home or net zero home (passive is the best way to achieve net zero) is going to happen according to these key factors:
- Design limitations based on property: your access to the property, whether the ground is sloped, soil composition, etc. These factors will determine whether the home can have or requires a basement (versus slab on grade), driveway placement, and ultimately will factor into orientation.
- Design limitations from shading obstacles: neighboring buildings or natural features (trees, mountains, etc.) that introduce shading beyond your control will need to be considered.
- Opportunities for strategic window placement and general orientation.
The home’s layout and design should be driven by all of these factors, resulting in the most comfortable, low energy home possible.
Siting your passive home
Depending on the many factors affecting your property and options for siting your passive home, we’ll work with you to determine the home’s orientation and the optimal design for that orientation, including strategic window placement.
East or west facing windows are difficult to shade because of the low angle of the sun, particularly early and late in the day when it’s low in the sky. Large windows in this case will run the risk of overheating the home. We tend to avoid windows or reduce them dramatically for these orientations.
As we ship our passive house kit across North America, we rely on Google Earth for a site assessment, but we can also work with a site survey or even a sketch for a site that might not be easily viewed this way.