You may already be familiar with the Passive House movement. Homes built to that standard are entirely concerned with energy consumption from heating, cooling and plug load. The standard requires that homes be so well insulated that there is no need for a conventional furnace, but rather a pellet stove, baseboard heating or a heat pump will do. Because the standard focuses entirely on heating, builders attempting passive house certification will also sometimes combine it with other environmental certifications, such as LEED, which is concerned with overall building and occupant health. Now, however, there is a new building philosophy called Active House that was developed by several representatives, among others, those from Denmark and Holland. It has three main tenets: Occupants’ indoor comfort be maximized, Energy Consumption minimized and Environmental Conservation be considered at each building phase from design through use through end-of-life.
Instead of evaluating homes on a “points” basis the way LEED does, Active Houses are evaluated in a web on a scale from 1 to 4. “1” being the best and “4” the lowest. The idea is to achieve as many of the specific category demands as possible to create a broad web – 1s and 2s, the outer rings of the web, being preferable to 3s and 4s, the inner rings.
Comfort: The first category considered is indoor comfort. This is a broad and somewhat open-ended term and covers daylight, indoor temperature and indoor air quality.
- Thermal Environment: One occupant might be more interested in keeping a room warmer or cooler than another and that’s exactly what the creators of the Active House had in mind — individual desires of the occupants. To achieve this and to conserve energy, zoned heating and cooling are used for different floors and rooms. Further, through the use of low to no energy features including orientation of the building, heat stack design, operable windows and the maximizing cross breezes, the use of natural ventilation is optimized and mechanical ventilation (and therefore electricity consumption) is limited. Building envelopes are well-insulated, so the addition of a Heat Recovery Ventilator is usually necessary to allow fresh air to enter and moist, stale air to leave the building even on excessively cold or hot days when windows aren’t opened. HRVs also improve energy efficiency as they transfer the heat from the stale air leaving to the fresh air entering.
- Daylight: Of critical importance to a person’s mental and physical well-being is the amount and quality of daylight a building is designed to receive. With the fairly recent discovery of Seasonal Affective Disorder (SAD), most of us living in the Northern Hemisphere don’t receive enough natural daylight during the winter months, one of the consequences for some people being depression. Architects working to Active House philosophy are required to design homes with high quality daylight reaching as many lived-in rooms as possible (storage and utility rooms aren’t counted). The recommended daylight factor is 2% or higher, while the lowest score of evaluated rooms must be greater than 1% on average.
- Indoor Air Quality: The Active House standard requires a constant supply of fresh air into the building, whether through operable windows or an HRV or a combination of the two. The HRV also can be used to control indoor humidity levels ensuring a dry environment to prevent mould growth.
Energy: Since the operation of buildings worldwide consumes about 40% of all fossil fuels, an Active House aims to be light on the use of carbon-based fuels and nuclear energy. For example, a house that uses 100% renewable energy scores a “1”, while a house using 25% or more renewable energy would score a “4”.
- Energy Demand: This is the amount of energy required by the house, including space heating and cooling, water heating, lighting, ventilation, technical installations, plug load and appliances. In the design phase, architects will focus on designing a house that maximizes energy conservation and efficiency by taking advantage of passive solar gains for both lighting and heat, as well as designing tight building envelopes. Other features include the addition of renewable energy systems and demand-control ventilation, which also contribute to the energy savings. Use of dynamic building envelope with solar shadings and natural ventilations reduces the need for
mechanical cooling and air conditioning during summer period. Finally, the type of construction is very important to successful implementation of this phase.
- Energy Supply: The type and quality of energy supplied to the house is another important facet of the Active House philosophy. Homes that use 100% renewable energy produced on site or nearby receive a “1”. Homes that use 25% or more renewable energy receive a “4”. Note that not using any renewable energy isn’t even an option, regardless of how efficient you are.
- Primary Energy Performance: This value is the calculation of (total energy consumption – renewable energy supply) x national primary energy factors. What they are looking for here,, in principle, is your CO2 output based on the national, or in our case, provincial, energy production mix. If your home uses 100% renewable energy, either from the grid or produced all on-site your score would be “1”.
Environment: This is the area that focuses on building materials, waste and life cycle. The Active House is concerned not only with the functioning of the building, but how it got there and what will happen to it when its useful life is over.
- Environmental Load: Building a house is a disruptive process to the global environment. The Active House takes into account how damaging construction can be by considering a house’s Global Warming Potential, Primary Energy consumption, ozone depletion, smog potential, water acidification potential and eutrophication of the soil. The environmental load is all encompassing, and considers the whole Life Cycle, including the production and transportation of the materials used to build the house, the maintenance and operation of the house, and disposal of the house at end of life.
- Fresh water consumption: Minimizing consumption of freshwater by occupants’ also plays an important role in the Active House. A “1” is achieved by reducing water consumption by 50% versus the national average, while a “4” is graded for a house that conserves 10% or more. Devices and techniques used can be items such as a cistern to catch rain water or a gray water system, which captures used water from baths and showers and recirculates it to toilets. Low-flow fixtures can also be installed.
- Sustainable Construction: As many renewable and recycled/recyclable products are used in the construction of the house as possible. A house containing a minimum of 5% recyclable content will receive a “4” while a house that uses over 50% recycled content receives a 1. Regarding wood, the standard is more demanding. At least 50% of all wood used in construction of the house must be certified either by PEFC or FSC. 25-80% of new material needs to be EMS certified. If you’re not familiar with this requirement, EMS stands for Environmental Management System, usually referring to ISO 14001 standard which is a voluntary guideline outlining the criteria a company would have to go through to get ISO 14001 certification. A company with an EMS in place tends to have a greater responsibility with how its products are made, including taking steps towards responsible sourcing and improving its overall energy and water efficiency.
Qualitative parameters: In addition to the evaluative web used to rate an Active House, there is a long list of other considerations that are used to make this house a lower impact, thoughtfully designed house, which architects, designers and other building professionals can use as a guide. Other issues such as noise and acoustics, accessibility, visual transmittance and glare management among the factors considered.
The philosophy behind the design process is thorough, thoughtful and addresses gaps in the Passive House built house and even the LEED for Homes designation. It does not go as far as Living Building Challenge, which requires that most, if not all energy and water used by the house be produced or captured by the house. Perhaps though, it is a more realistic approach for urban dwellers. The developers of the Active House philosophy consider it a work in progress, not dissimilar to LEED. They evaluate houses already built to the standard to see how it can be improved. Homes are evaluated before and during occupancy and compared so that professionals involved in Active House design-build can learn from the results.
The first Canadian built Active House has just been completed in Thorold, Ontario by Great Gulf Homes. It provides an excellent example of the philosophy being put into practice. Stay tuned as I will discuss the features of that house in the next post.
For more information on the Active House philosophy, visit the website: http://www.activehouse.info/
The Active House Alliance is now in process of developing concept guidelines and classification for Active House projects, with an expected launch by the end of the year.
For two Active homes already built, see the following articles:
La Maison Aire et Lumiere (in French)