A Passive House is a very well insulated, virtually air tight building that is primarily heated by passive solar gain and by internal gains from people, electrical equipment, lighting, etc. Energy losses are minimized dramatically.” Passive House Certified Homes meet today’s highest energy standards in the world. This is a third party certification that is tested, inspected, and verified by Passive House Institute US.
Passive homes are built to the highest level of building science, and is the most stringent certification for actual home performance based on construction and craftsmanship.
Some of the key approaches and technologies for passive house design and construction include…
- Building Science = Durability & Longevity. While a home is being schematically designed, strict modeling is done to ensure a high quality structure that is designed to handle moisture risks as well as know how the building will operate from a physics perspective. WUFI modeling is a hygrothermal model that is done to ensure there is no risks of moisture or mold in the wall sections of these homes. This model simulates the performance of a home over several years using site specific historical weather data. It helps to show any risk of condensation planes, and the drying potential of a wall. Therm is another tool that is used to model a wall and building intersections to ensure that there a re no thermal bridges in the buildings. Utilizing these design phase modeling techniques help to ensure a project team is headed down the right path before construction begins. This is why it is key to assemble a team prior to design for construction projects.On top of that construction methods with a high level of craftsmanship must be used to ensure performance. This goes from everything from bulk water management, flashings, and weather barriers; to framing and transitioning materials.
- Air Tightness. The first aspect of passive house design is an airtight structure that is very well insulated. The air leakage on a Passive House, as tested with a blower door, can not have more than .6 Air Changes per Hour at 50 pascal (ACH@50 as it is commonly known). This helps to create a very efficient home with superior air quality. An ERV is used to help mix the air in the home, bring it fresh air while exhausting stale air through a heat / energy recovery unit, clean the air, and draw moist air out of bathrooms, the kitchen, and laundry room. Currently, this Passive House is at .45 ACH@50 prior to drywall. This number is expected to drop even further by completion of the home.
- Insulation. Passive House’s take insulation to the next level. After achieving an airtight home, the walls are insulated with R-60, below the slab gets insulated to R-40, and the ceiling receives about an R-100. This limits heat transfer through the walls, floors, and ceiling, and keeps the conditioned air you have paid to condition, in the building envelope. The windows used in a Passive house have well insulated frames, with triple glazing, argon gas insulation, and Low E coatings.
- Thermal Bridge Free. Thermal bridging is conductive heat transfer through the studs or framing of a structure, and are rigorously avoided in Passive House. Conductive heat loss (thermal bridging) is a major loss of heat in the winter in most buildings. Passive Houses have to run all exterior framing connection and section details through a software program that shows temperature in a wall and the structural component’s of a wall to determine whether or not there is conductive heat flow.
- Super Comfort. Due to the fact that a Passive House is extremely air tight, well insulated, and has balanced ventilation, there are consistent temperatures throughout the home. You do not get cold rooms and hot rooms in a Passive house, nor do you get stack effect or varying stratospheres in the home.
- Air Quality. A Passive House must have balanced ventilation through an ERV (Energy Recovery Ventilator) or HRV (Heat Recovery Ventilator). These units help to bring fresh air into a home while recovering the heat (or cooling – depending on the season) and humidity of the outgoing air. The incoming air is exactly equal to the amount of outgoing air, thus completely balanced. These units also have MERV filters in them to help clean the air. Another benefit is that they run all day everyday at low speeds, but enough that dust does not have a chance to settle in the ducts. Some of the high efficiency units that are popular in Passive House cost about $30 a month to operate continuously. These units give you a houseful of fresh air every 3 hours (.3ACH).On top of the Passive House ventilation requirement, we add our stringent studies of product and ingredient makeup of all our materials. This ensures that we have sourced only healthy materials to go into the home. Although not yet required by Passive House, we add our third party lab indoor air quality testing to assure a healthy indoor air environment.
- Low Heating and Cooling Costs. Due to the air tightness, lack of thermal bridges, and great insulation values, Passive House’s do not need a traditional furnace or air conditioning system. They can operate efficiently and comfortably with a ductless mini split heat pump (26 SEER), and use the ERV or HRV to mix that conditioning in with the rest of the house. Because the efficiency and details in the thermal envelope of the home, as well as the extremely low heat demand on the home, a Passive House uses 90% less energy to heat and cool a home as compared to a code built home. A Passive House must have less than 4.75 kBTU/sq ft. / yr in annual heating demand.
- Low Primary Energy Demand. Passive House energy modeling software, called PHPP, goes into extreme detail on energy consumption of a home. It factors in the exact consumption of every appliance, uses the number of occupants to model lifestyle consumption, and factors in all other electronics in a home. Because of this you get a very detailed analysis of how energy will be used in a home. In order to reach Passive House Certification, a home must use less than 38.1kBTU / sq ft / yr.
- Passive Solar Design. Passive Homes are designed to maximize solar heat gain in the winter months and shade solar heat gain in the summer months. This is achieved through site orientation, as well as window design. A large percentage of the windows should be on the south side of the home, while the north side should have minimal windows. The larger the windows the more efficient they are, so the south side windows tend to be larger windows, while the north side windows have reduced quantity and size. The home in River Forest was moved further north from the previous home that was on the site, to maximize the solar gain on the south. This was a city infill lot, so we wanted to move the home as far away from the house to the south to maximize our solar heat gain in the winter.
Passive House is not only a healthy, energy efficient, and comfortable way to build, but it is also our best route to carbon-neutrality and energy independence. It can also be done on a cash positive basis in many instances. Passive house can be good for your pocketbook, the environment, health, and comfort with no sacrifice needed.