An Up-Close Look at Passive Homes
My parents have always been massive tree-huggers. Growing up, they’d take my sisters and I on birding outings, camping adventures, and road trips to explore the natural beauty of the Pacific Northwest. So, when they informed me that they were going to design and build an off-grid, passive home for their retirement, I wasn’t the least bit surprised.
It wasn’t until recently that I began to fully understand how big of a project this was. Building a passive home – especially off-grid in remote Southern Oregon – presents many challenges both financially and architecturally. But the benefits of retiring in a beautiful, secluded location while living sustainably off of renewable resources far outweigh the costs of planning a passive house.
The term “passive” home alludes to the energy efficiency of a building; the design and construction of a passive house includes extreme insulation so that very little technology and energy is needed to heat and cool the building. My parents’ house, for example, will be extremely energy efficient so that their ecological footprint is minimal. Outlined below are the elements and principles that one would use in the design of a passive home to create their own sustainable living.
Structural Elements of Passive Homes
The main element of a passive home, that which makes it sustainable, is not some trendy green device or renewable energy technology – it’s actually the quality of extreme insulation within the building. The design of a passive home revolves around the thermal envelop; one-foot thick walls create an extremely air-tight space with no “thermal bridges,” a minimal number of entry doors, and no penetrations through the walls or roof (thus no vents or stovepipes). The windows must also be designed to minimize any heat migration, therefore they must be triple-paned. Doors as well are specially engineered to ensure no air leakage.
The goal of the thermal envelop is to minimize the need for technology in heating the home, and to allow solar heat to be utilized instead. Passive homes are usually seven times more air-tight than conventionally built homes, but surprisingly, the cost is actually not too outrageous. For instance, my parents’ high performance house was estimated to be only 10% more expensive than a conventional house – this also means their home will have no cold air drafts and will not require a furnace.
Sunny Southern Oregon is a prime location for exploiting the sun’s bountiful heat energy, and that’s exactly what my parents plan to do: install a large array of solar panels to power their passive home. Batteries will be charged by these roof-mounted solar panels and will be their primary source of electricity. Realistically, however, the kitchen range will be fueled by propane, and if the sun is hidden for several days, there will be a backup generator fueled by diesel. The goal, though, is to power the passive home with as much renewable energy as possible to shrink the carbon footprint.
Another important factor in planning a passive home is the actual house site. To maximize solar gain, the house will be situated on a sun-soaked hill facing south or southeast. As for ventilation, a Heat Recovery Ventilator (HRV) will be needed to bring fresh air into the house, while also warming it with vented hot air.
A two-in-one heating and cooling system called “ductless, mini-split heat pumps” (also powered by the batteries) will provide heating and air conditioning as well. This system continually circulates the air so it’s distributed throughout the house without the need for ducts in each room.
To bring efficiency to all aspects of the home, one should plan to employ extremely efficient and water-wise appliances as well as LED and fluorescent lighting.
Because the home is off-grid, my parents decided to utilize rainwater harvesting as their primary water source. In many cases, rainwater harvesting can be used as a substitute for well water because it’s much more sustainable and efficient, it’s renewable, and most importantly, it’s extremely pure and safe (when collected properly).
For my parent’s passive home, rainwater will be harvested from the garage and roof gutters. A pipe will run from the gutters to four large water tanks where it will then be purified using a UV storage system. Of course, droughts occur often in southern Oregon, therefore if the tanks run dry, potable water would be purchased from a local water company. Rainwater harvesting is a smart alternative to well water or other potable municipal water – it can be used for a variety of purposes including irrigation, toilet flushing, grey-water uses, and drinking water.
To reduce the need for an irrigation system, a passive home will likely have no lawn, but rather a garden filled with native plants and herbs that are adapted to the environmental conditions of the region. Natural landscaping requires little water, is extremely easy to grow (thus requires very little maintenance), is less susceptible to diseases. It also attracts native pollinators and wildlife. A small herb garden will be planted at my parents’ retirement home, and a variety of other potted plants will also be maintained.
Maximize Your Gains, Minimize Your Losses
A passive home cuts energy consumption by 60 to 80 percent compared to conventional buildings, while still remaining cost-effective. It’s a practical, yet comfortable design that should go further than just being a green trend – it should become a popular option for many residential and commercial building models.Feature Image: An array of solar panels. Image via Mike Lewinski.