The benefits of a green home extend far beyond one’s own front door. Learn what a passive house is and why you might want to think about buying one. —-
Even if television shows like The Jetsons aired well before your time, we can all appreciate the science-fiction fantasy of a house that costs very little to heat or cool, repurposes its own energy and resources in sustainable ways … and cleans itself with a robot. You’ll need a Roomba to make that final part of the dream come (partially) true, but there’s a type of home that’s practically Jetsons-like in its attention to conservation and efficiency. It’s called a passive house.
As sustainable living continues to be an important topic of discussion in the United States, homeowners are increasingly looking for ways to make their homes more energy efficient. Saving money on utility bills and enjoying a more comfortable living environment are rewarding personal advantages, but the benefits of a green home extend far beyond one’s own front door.
If you’ve not yet heard of a passive house, you’ll be forgiven. This type of home — built to a rigorous standard of construction to maximize energy efficiency — is widely embraced in Europe, though awareness is still growing in the United States. In this article, we’re going to explore what a passive house is, and speak with experts to understand the principles of passive house design and what it’s like to live in one.
Let’s jump in.
What is a passive house?
As defined by Passipedia, a passive house is “a building standard that is truly energy efficient, comfortable, and affordable at the same time.”
The history of passive homes is traceable to the 1980s. A German physicist and a Swedish scientist later developed the metrics for what would become the gold standard of passive buildings; and the Passive House Institute, founded in 1996 in Darmstadt, Germany, remains the authority on passive construction principles.
These principles, which we’ll elaborate on shortly, include:
- An airtight building envelope
- A ventilation system that balances heat and moisture management
- High-performance windows and doors
- Continuous insulation throughout the envelope, with no thermal bridging
- A minimal space conditioning system
Because passive homes are achieved through construction technique, the term “passive house” is arguably limiting — nearly any type of building can be passive, from single-family homes to skyscrapers.
What’s more, passive is an open-source concept, not a brand. There are no requirements for certification or permission from any one organization to build a house to passive standards; the approach is beautifully generic.
Passive construction principles
The objective of a passive house is to optimize efficiency, which is why the criteria for construction are so important.
“It’s a set of principles that puts conservation first to reduce the amount of energy it takes to heat and cool a building to measurable comfort levels,” explains Michael Knezovich, the Communications Director at Passive House Institute U.S. (PHIUS).
“Passive construction focuses on heating and cooling, but as it has evolved, it’s become sort of a tool in the toolbox of people who are trying to achieve net-zero buildings,” explains Knezovich.
“It lowers the baseline of how much energy is needed from renewables to a point where it’s much more practical to hit zero.”
The design of a new passive home begins with consideration for how the building should be positioned in order to capitalize on natural sun and shade exposure, and the attention to detail only strengthens from there.
The most crucial element of a passive house is its airtight construction. A truly passive building will have fewer than 0.6 air changes per hour (ACH), meaning that there are no air leaks and no drafts near windows or doors.
Passive houses are so thoroughly insulated and well-sealed that they’re able to make use of internal heat sources, including the warmth emitted from appliances. (Bet you’ve never thought of your refrigerator as a way to warm your kitchen’s tile floors!)
An airtight building needs proper ventilation to ensure air quality and protect against moisture damage. Passive homes use a heat recovery ventilator (HRV) to continuously circulate fresh, filtered air while capturing and retaining at least 75% of heat from the exhaust air.
“Ventilation in a passive building is very intentionally executed,” says Knezovich. “There is a low level of ventilation running continuously, with fresh air circulating and equal amounts of air leaving and coming in.”
The result of this mechanical ventilation is efficient heat retention and excellent indoor air quality year-round.
Passive houses use ultra-high-performance glazing systems to ensure an airtight seal. Windows are double- or even triple-paned, are framed in nonconductive materials, and may be filled with an insulating gas.
Quality window construction allows passive homes to optimize solar energy. Since it is, however, possible to have too much of a good thing, passive buildings are often equipped with exterior rolling blinds, which lower and raise at the flip of a switch to block out heat and excess light.
No thermal bridging
Knezovich explains a thermal bridge as “anything that protrudes from the inside to the outside and can conduct energy.”
Examples of thermal bridging can include anything from a window-mounted air conditioning unit to insulation-breaching anchor bolts.
Thermal bridges allow warm air to escape, effectively breaking the seal of a building’s envelope and making it less efficient.
“It’s relatively easy to avoid thermal bridging when designing a new building; it’s harder to mitigate on a retrofit,” says Knezovich.
Minimal space conditioning
Because passive houses are so efficient, it’s easy to maintain a comfortable indoor temperature no matter the season. Savings on heating and cooling costs can be as high as 90% compared to conventionally built homes, since passive buildings use just 15 kWh of heating energy per 10 square feet per year.
This means that a 2,000 square-foot house will only use about 3,000 kWh of heating energy in a year — compare that to the U.S. average of 12,000 kWh per year!
Passive house living
Life in a passive building is nothing short of pleasant. Air quality is high, temperature variation is minimal, and because they’re so well-insulated, passive homes tend to be very quiet.
Plus, there’s that nice little perk of saving cash on heating and cooling costs. Utility bills are more stable and predictable, and so are your day-to-day living conditions.
“In an older house, heat escapes from joints in the building, so you often get colder places near the windows, you may have certain rooms that are colder than others; in a passive house that is very airtight with mechanical ventilation, you’re getting that air continuously moved around, and the house remains at a more constant temperature,” says Isabel Beattie, director of strategy and development for Beattie Passive, a passive building company based in Norwich, England.
“You can walk around in shorts and a T-shirt in winter because you’re at a comfortable temperature, but you’re not actually heating the house any hotter; it’s just that it doesn’t lose heat so quickly and that heat is being recirculated,” Beattie explains.
Less carbon, less maintenance
Another undeniable advantage of living in a passive home is the reduced need for ongoing maintenance and eventual upgrades.
“With a shift toward achieving zero carbon, it’s about getting the fabric of building right,” says Beattie.
Passive homes make use of high-quality, eco-friendly materials. The buildings are designed for longevity and sustainability, which means that your list of would-be renovation projects during the years is kept to an absolute minimum. There’s no need for upgrades or retrofitting to improve comfort or efficiency.
In fact, passive houses perform best when you simply leave them alone.
“People shouldn’t fiddle or turn off the mechanical ventilation system,” Beattie advises.
“Passive houses perform very well if you don’t mess with them; they’re set up to do their job very well.”
The only real required maintenance is changing the filters in the ventilation system, which is an easy task since most systems used in passive homes will tell you when the filter is due for cleaning or replacing. How often this is required will vary — if you’re a heavy indoor smoker, you’ll likely need to change the filter every three months — but under average living conditions, once every six to eight months is realistic.
If you’re intrigued by the benefits of passive house living but aren’t so keen on the idea of giving up your existing home to build something completely new … well, that’s understandable.
The good news is that it is possible to retrofit most buildings to bring them up to passive standards. Doing so requires:
- Improving — or possibly replacing — a home’s envelope to remove thermal bridges
- Installing a suitable ventilation system
- Replacing the windows (and maybe doors)
- Potentially upgrading or removing current heating and cooling systems
Due to the need for an airtight envelope, passive retrofitting works best when the whole building is involved. This is no problem for a single-family home, but if you live in a townhouse, condominium, or another type of multi-unit space, you’ll be faced with the task of getting the other property owner(s) on board with the idea.
If your home is part of a homeowner’s association, you may also need to seek approval to complete your passive retrofit project, as the exterior of the home will likely have visual changes.
Passive retrofitting can be expensive, but the efforts can add to your home’s value, in addition to giving you the great lifestyle and environmental benefits we’ve discussed. If you’re interested in learning more about what it would take to retrofit your home, PHIUS has a comprehensive list of passive builders to help you get started.
Buying a passive — or closer-to-passive — house
If you’re in the market for a new home, this is a great opportunity to pursue a passive house. Particularly if your timeline allows for the construction of a new-build, you can experience the ground-up design process and make your passive home truly your own.
Again, PHIUS is a great resource for finding a passive contractor in your state, and websites like GreenHomesforSale.com specialize in listing environmentally friendly properties around the United States and beyond.
New construction isn’t always feasible, and finding a truly passive house for sale may be tricky depending on your location, but you can still make the most of your search and seek out an eco-friendly home. Working with an experienced agent who can help you find sustainable properties in your city is a great strategy.
Homes built within the past few years will often have sustainability at the forefront of their planning, and older homes will likely have undergone upgrades and renovations to keep up with buyer preferences.
“We don’t see any new construction here in the Bay Area that is not focused on energy efficiency,” says Rick Fuller, a top agent in the San Francisco, California area; he works with 74% more single-family homes than the average agent in his area.
Fuller has seen the demand for efficient homes increase dramatically — and with it, home values.
“One home that’s not energy-efficient might require upgrading the windows, might require replacing an old pool pump with a variable speed pump, or replacing old appliances with newer, more efficient models. A property that has those things already done provides value to that buyer, and they are typically more interested in proceeding with the home that has those amenities,” he explains.
Homeowners — and the real estate agents helping them prepare their homes for market — are more aware than ever of the importance of components like proper insulation and high-quality windows for effective temperature regulation.
Passive buildings may not be a fixture of U.S. neighborhoods just yet, but minor upgrades like low-flush toilets and LED light bulbs are no longer enough for a home to be considered energy-efficient. This is good news for buyers, as you’ll likely have less work to do on your newly purchased home to make it more comfortable and carbon-friendly.
Alternatively, you could purchase an existing home that is ripe for renovation and move forward with a passive retrofit. As with most things in real estate, it all comes down to your time, budget, and personal preferences.
A comfortable conclusion
Whether you live in one, dream of owning one, or have never heard of a passive house until reading this article, there’s no denying that real estate has a green future.
“Doing what’s right for the community and the environment is a high priority today,” says Fuller. “Most buyers want to have a small footprint, they want to be energy-efficient, they want to use their utilities wisely. They don’t want to waste money, and they don’t want to contribute to climate change or impact their community adversely.”
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