The design of passive buildings starts with the climate. Different climatic regions have diverse requirements for heating in winters and cooling in summers.
In cold climates, passive buildings aim to achieve heating of indoor environment without excessive reliance on active heating measures. They need to capture solar energy through large glass openings on southern and northern faces of building envelope.
Insulation
Insulation prevents heat loss through roof and wall surfaces, reducing heating costs in winter and cooling costs in summer. It may be made from natural or man-made materials. Eco-friendly choices include recycled denim and sheep’s wool, cellulose and Aerogel (a material that contains more than 90 percent air). Some insulating materials have health risks or are non-biodegradable.
Blanket insulation is available in a range of thicknesses and R-values. It comes in rolls or sheets that are cut to size and fitted between studs or joists. It’s a relatively quick and easy option for homebuilders or DIYers who follow manufacturers’ instructions and safety precautions.
Blown-in loose-fill insulation is installed in enclosed cavities, such as walls, or unenclosed spaces like attics. It’s blown in by experienced installers who are skilled at achieving the correct density and R-value. It’s available in a wide variety of materials, including cellulose, fiberglass and mineral (rock or slag) wool, with some products containing more recycled content than others.
Structural insulated panels are prefabricated structural elements that build walls and ceilings, offering superior and more uniform insulation than conventional stud construction. They also reduce construction time and can help with energy efficiency.
Ventilation
A well-designed passive design minimizes air exchange with the outside, which reduces heating and cooling costs. It also minimises heat loss through the building envelope, especially where gaps and leakage occur.
Insulation is a key component in this, but it is best implemented as continuous insulation (which eliminates thermal bridging) rather than cavity insulation. This reduces the risk of draughts and cold spots as air moves through a space, and it prevents heated or cooled air from moving to unheated spaces.
The most efficient passive strategies are based on local climatic conditions and include a site orientated design, shading and cross-ventilation for natural cooling. The LS1 House in Sarasota, for example, uses a breezeway with slatted wood shutters to harness cooling breezes that circulate the whole house. In tropical climates, it is important to ensure that the location and orientation of a home can make use of cooling breezes. In addition, sloping roofs that allow for evaporative cooling and large overhangs to reduce solar gain are essential. The design must also incorporate ventilation systems that can control incoming air speed so that a minimum fresh air requirement is met without excessive energy consumption.
Shading
As energy prices rise and climate change impacts entire ecosystems, the Passive House standard is a more compelling choice than ever. Its rigorous environmental, comfort and quality standards provide real financial and sustainability benefits for homeowners.
Passive buildings take advantage of free passive solar heating in winter and shade strategies to reduce overheating in summer. This is achieved by balancing the amount of heat and sun that is allowed in through appropriate windows, and ensuring that any unwanted solar radiation is blocked.
This is usually done by orienting the aperture to face within 30 degrees of true south during the winter and using awnings, trellises, shutters and vegetation to shade this area during summer. It is also important to consider the thermal mass of a building when designing the shade and ventilation systems.
Passive homes can be built in any style of architecture and with any materials, as long as they are well positioned and shaded according to the climate zone. The best way to maximize the passive design benefits is to incorporate them in the initial planning phase and ideally with the help of computer simulation tools.
Lightweight Materials
The use of lighter materials such as timber, concrete and masonry allows these building materials to reflect heat away from the building rather than absorb it. Light-colored surfaces also have the ability to reflect sunlight, which can significantly lower temperatures inside the building.
Passive design strategies seek to optimise the use of free, renewable energy sources and natural environmental conditions to provide heating, ventilation and lighting for buildings, thereby eliminating the need for mechanical systems. This primarily involves a strategic siting and arrangement of the building, allowing daylight to penetrate into living spaces and connecting occupants with the outdoors.
In addition to thermal mass, insulation and shading, passive designs may include energy efficiency measures such as water efficient appliances and evaporative cooling. These strategies can reduce both energy consumption and operational costs.
The increasing interest in employing passive strategies is largely due to the fact that they provide real solutions to global issues such as energy crisis and environmental pollution. However, a key factor limiting the adoption of passive designs is their initial cost. Hence, it is vital that a thorough evaluation of the economic feasibility of passive construction be carried out.
Energy Efficiency
Passive design strategies can help architects achieve energy efficient, climate-controlled spaces without the need for electricity, thereby reducing greenhouse gas emissions. These measures, while best incorporated during new construction periods, can also be retrofitted to existing buildings.
Optimal insulation, an airtight thermal envelope and the use of efficient windows are key to keeping a house warm in winter and cool in summer. Moreover, the use of high-density materials with good thermal mass, such as concrete, brick and rammed earth, helps slow indoor temperature fluctuations and improve thermal performance.
Moreover, the use of natural light and providing occupants with control over ventilation (when site conditions permit) are also highly preferred passive design features for their ability to provide health benefits, including the regulation of circadian rhythms. Similarly, a building’s siting, orientation and material selection are dictated by its location and climate. New-age technologies like parametric and generative modeling softwares as well as building performance simulation tools can help architects to integrate passive design into their projects. This is a key to achieving higher ratings across standards such as PassivHaus, BREEAM and the Code for Sustainable Homes.