In an age where we are constantly told that climate change is real and poised to wreak havoc, there is one form of construction which doesn’t just reduce our future environmental impact, it eliminates it.
The term “passive house” has been known in the US for a few years, but it never really ended up catching on. After all, it is not a very catchy term. Perhaps this is why most Americans associate the passive house standard with environmentally friendly and green energy initiatives. Yes, you can build such a house in the US, even if you are not committed to a 100% renewable energy source.
How to build a passive house
The key to a passive house is the insulation. The minimum insulation requirement for the walls, roof and floor is 1.5 times that required by code in most climates. For example, if your code requires R-19 insulation in your walls, you need to install R-38 in a passive house. In other words, you will use more material than building a typical home but it will be worth it because you won’t have to run your heating system as much throughout the year.
Passive house requirements
For passive houses, the minimum window area is 5% of total floor area plus 1% for each inch of wall over 18 inches (3% for 19″-21″ and 4% for 22″ or more). You also need some form or thermal storage — either an insulated slab or an earthen floor. The rest is standard HVAC work: ducts and fans with heat recovery ventilators (HRVs) and air-to-air heat exchangers (AAHUs).
Passive house examples
One of the first successful passive houses was built by Mike Holmes in Toronto in 2001 as part of his show Holmes on Homes. It had an AECB energy report showing that it used only 10
Passive house construction details
The most important detail when building a passive house is the insulation. Typically, walls are insulated with thick layers of rock wool or cellulose, and windows are triple-glazed to minimize heat loss.
The Passive House Institute U.S. (PHIUS) has established standards for passive houses in the United States. The minimum standard is an energy use of 15 kWh/m2/year and no more than 0.6 air changes per hour (ACH). There are three levels of certification: certified, certified plus, and net zero ready.
There are over 100 passive houses in the U.S., mostly in New York City and California, but also in states such as Massachusetts and Minnesota. Examples include:
Passive House construction details are very stringent. The airtightness must be greater than 0.6 ach and be verified with a blower door test. In addition, there must be no thermal bridging through the building envelope. All windows should be triple glazed and have low emissivity coatings to reduce heat loss through the glass. The walls and roof should have insulation values of R-30 or higher. All ductwork must be sealed or located inside the building envelope. The HVAC system is designed to bring in fresh air from outside, heat it up, then exhaust stale air back outside. This can be accomplished with a heat recovery ventilator (HRV) or an energy recovery ventilator (ERV). Both devices recover heat from stale air being exhausted and use it to help preheat fresh air being brought into the house by the HVAC system. Energy recovery ventilators also remove moisture from the incoming fresh air before heating it up for distribution throughout the house. Because all of these components are required to meet very strict standards in order for a home to qualify as a passive house, they are often more expensive than comparable systems used in conventional homes
Passive houses are designed to be energy efficient, comfortable and affordable. They’re also built to a high standard of quality and durability.
In a passive house, it’s important to make sure that your home is airtight by using the proper insulation, airtight windows and doors, and good weather-stripping. This ensures your home uses less energy to keep it comfortable inside.
If you’re building a passive house retrofit, you’ll need to add insulation around pipes and wiring that run through the walls of your house. You’ll also need to add extra insulation around windows where they contact the exterior wall surface. Passive houses are typically built with an insulated foundation as well.
The International Passive House Institute (IPHI) has created standards for passive house construction that help ensure homes meet their high efficiency goals. The IPHI sets requirements for:
Building shell – The building shell must have an air leakage rate of less than 0.6 air changes per hour at 50 pascals pressure differential at normal room temperature (20 degrees C). The building shell must also include double-glazed windows with low-e coating on both sides.
Heating system – Passive houses use an energy source such as
Passive house construction details
Passive houses are built to the highest standards of airtightness, insulation and ventilation. They are designed to use as little energy as possible to heat and cool. The following are some of the key elements that make a passive house so energy efficient:
– High-performance windows with triple glazing or even better (thermal break)
– Airtightness so that cold air cannot escape through gaps in the building envelope
– Very high levels of insulation (up to 10 inches thick on exterior walls, 20 inches on floors and ceilings)
– An extremely efficient building envelope that keeps heat in during cold weather and out during warm weather
– A heat recovery ventilator (HRV) that captures stale indoor air, heats it with fresh outdoor air before distributing it throughout the home
– A ground source heat pump for heating water and space heating