Passive Houses are the hottest trend in the green building world. But is it all hype? Here are 11 myths about passive houses, debunked for you to decide for yourself.
1. Myth: You need a monumental house to take advantage of passive houses.
If the foundation is built well, your passive house can be “monumental.” The foundation is what supports all of the other parts of the home. It’s like building a bridge; you don’t design to build one that looks nice or big because it would collapse under its own weight if you did. You build minimal and then load test it with weights to make sure it works (but not enough to cause damage). That’s how foundations are supposed to work!
2. Myth: Passive houses must be super insulated
This is probably the number 1 misperception people have about passive houses. A lot of us think we need triple glazed windows, foam sheathing on top of exterior walls and R-49 ceilings in order to build a passive house. That’s why most people think they can’t do it because they don’t have the budget for all that stuff.
But my passive house in New Hampshire, which is 1400 square feet with two bedrooms and one bath, has R-30 walls (basically fiberglass batts) and R-60 ceilings (gypsum board plus cellulose). Then I added triple glazed argon filled windows by Sunrise Windows (with an r value of about 3.2 per window), which brings the overall wall r-value up to R-45 . The overall ceiling will be R-60 or more once we insulate above it; I’ve calculated around R=75 for the whole super insulated roof assembly.
So, my passive house in NH is R-30 walls and R-60 ceilings, with triple glazed windows. Is that good enough for a passive house? Well, we’ll find out if the whole building qualifies when it’s tested by PHIUS+ . However I’m confident because there are lots of other houses like mine around the world.
3. Myth: Passive houses must be expensive to build
This is also probably the number 1 misperception about passive houses. As mentioned above, this misunderstanding comes from thinking that you need triple glazing and foam sheathing or ICF construction in order to build a passive house (and all that costs money). Another reason people think passive houses must be expensive is because they consider how much energy they save as a benefit, without considering the cost of the house.
But if you consider that passive houses are cheaper to heat, or even free to heat (in areas where it’s cold enough), then suddenly things begin to balance out…
4. Myth: Passive Houses just use airtight windows
Not true. Passive houses also monitor the temperature of the thermal envelope and track changes over time in order to catch infiltration problems while they’re still easy to fix. In fact, if you want to earn certification by PHIUS+, then you have to use U-factor monitoring probes at all junctions of your building’s thermal envelope, along with continuous room temperature monitoring.
The result is that passive house practitioners have fine grained control over their buildings’ thermal quality on a minute by minute basis. And it isn’t unheard of for them to demand a certain level of performance from contractors installing windows or furnaces…just like you would expect from any professional! If builders don’t meet required levels of performance, they don’t get paid. That’s true whether or not the builder is a passive house practioner!
5. Myth: Passive houses are only for extreme climates
This is actually half-true, but with a twist…
If you live in an extreme climate (i.e., really cold), then building a superinsulated passive house like mine makes sense because you save more money heating and cooling it than homes built to meet the minimum code requirements (which vary from area to area). But what about people who already spend too much on home energy living in moderate climates? Is it worth paying extra for insulation if I’m already struggling with high energy bills?
The answer depends on your goals and willingness to change your lifestyle. For example, I’ve created a passive house in New Hampshire (i.e., not the kind of climate where you need extreme insulation) because my family was spending about $3000 per year on energy bills living in poor airtightness and with an old furnace. So I decided to spend more on the house (and learn how to build one), rather than continuing to spend that much money every year for the rest of our lives without changing anything.
And it wasn’t just me who reaped those rewards; doing things differently also benefited my family’s health by reducing dust levels, odors from chemicals, pollen, viruses, bacteria…basically all kinds of stuff! And they probably saved money too since most people are sick less often and miss less work when they live in good airtightness and high quality indoor air (a well designed passive house also uses an air exchanger to keep your family’s breathing zone fresh).
If you’re not willing to change how you heat and cool your home, then a passive house probably isn’t the best choice. But if you want a warmer, healthier winter with little or no heating bills, a passive house can be a great choice.
7. Myth: Passive houses are only for people who love tweaking details
People think this because there’s so much attention given to tiny details that affect performance. In recent years, PHIUS has been developing requirements as part of their certification program…and as more certified buildings get built around the world, it’s become clear that a lot of really important details have been overlooked. For example, PHIUS now requires builders to use a blower door test to demonstrate the quality of their homes’ airtightness and they’ve started requiring that all window openings be tested for infiltration using either pressure or temperature sensors placed inside the thermal envelope where they’ll still get accurate results despite radiant heat loss from exterior surfaces.
In short, more attention is being paid to these kinds of issues because they’re critical to your family’s comfort! It’s not about personality type or attitude towards detail, but rather about emerging research showing what works best in terms of indoor air quality and energy budget performance.
8. Myth: Passive houses are too extreme for most people
If you make your home too tight, it will be uncomfortable…inhospitable to life! There are lots of independent studies that show how well passive houses perform compared to the minimum code requirements. For example, Canadian researchers studied airtightness levels in wood-framed, stick built homes and found that their samples averaged around 2 air changes per hour (ACH) at 50 Pascals (Pa). ACH is a measure of air leakage, so if an average house leaks about 6 cubic feet of air every minute through all its openings including windows and doors, then it results in 6 x 60 x 60 = 21600 cubic feet or 0.2 cubic meters of air exchange every hour.
Two faced this number by using a blower door fan to measure how much air leaves or enters a house over time. As the ACH increases, the rate at which the inside air mixes with outside air also increases. But if it’s built very tightly, you quickly reach a limit where increasing infiltration won’t affect your home’s comfort because there just isn’t enough outdoor air coming in to make up for what you’re losing through leakage!
Passive houses are tested using both pressure and temperature measurements so they can calculate an actual volume of air that leaks through each part of your home’s envelope. From this number, they know how much heat is lost through those tiny gaps and openings during winter (when you need it most). For example, PHIUS requires passive homes to have an average air exchange rate of 0.6 ACH at 50 Pa, which is roughly 1/3rd the amount of leakage found in our average house (which I’ll call a “4-hour” standard)!
As you learned earlier, your family’s breathing zone must be kept between 50 and 60 percent relative humidity to avoid health risks caused by dry air. If we assume an average person exhales about 0.5 liters of water vapor per hour during normal activities (at rest or lightly exercising), then PHIUS’ requirement for indoor RH means that your home needs to exchange less than 0.15 L of air every hour! That’s just 45 ml…or about 10 teaspoons worth of moisture exchanged with outdoor air each time your fireplace or wood stove creates a one minute flue draft.
