The Passive House is a new type of home that is designed to be airtight and well insulated, so that the homeowner uses less energy in heating or cooling their home. The idea was invented by Dr. Wolfgang Feist back in 1980s when he found out that there are many people who live in cold climates but still can’t afford to heat their homes during winter. This blog post will review what passive houses are, how they work, why they are so successful, and how you can get one built for your family!
1. What is a Passive House?
A passive house typically has an extremely well insulated exterior, about 10 cm of insulation on the walls and 20 – 30 cm on the roof. This reduces both heat loss from the house in winter, but also decreases cooling needs in summer. In addition to the insulation, there are several design elements that help reduce energy consumption of a passive house:
- Very effective air tightness means no drafts or cold spots inside the home. The airtightness goal for a Passive House is 0.6 ACH @ 50 pascals (ach50). For reference, a normal home will have around 4-7 ACH @ 50 pascals(ach50).
- Sun shading provided by the roof overhangs, awnings or shades on ground-level windows reduces heat from cold winter sun.
- House shape is often more squared off with less exterior wall area to reduce the amount of inside space that needs heating or cooling.
- Windows are triple or quadruple glazed for excellent insulation and an argon gas filled cavity between panes to improve insulation even further. In addition, window shapes are carefully chosen to provide optimal solar heat gain in winter while shading in summer.
Passive house design seems complex at first glance but it is actually a very simple concept: The Passive House approach gives you a home that is highly efficient and easy to live in through proper attention being paid during design, construction and operation. This means a Passive House is a comfortable, healthy house that makes you feel good from the moment you step through the door, effectively doing away with drafts and cold spots, using natural ventilation to allow fresh air inside without having to open windows. It can be heated quickly and easily by your existing heating system(s). In addition, continuous insulation along the underside of the roof allows you to store up surplus heat over summer for use in winter.
A passive house is designed as an ultra-insulated “super tight” home with a whole-house approach to minimizing air leakage—largely through attention to detail during construction utilizing high quality materials….The main difference between a super energy efficient home and a passive home is primarily its construction and its purpose: a super energy efficient home is designed with the primary objective of reducing operating costs for utilities, whereas a passive house design has as its first priority occupant health and comfort, which in turn contributes to reduced operating costs. A passive house thus represents an “envelope first” approach with the building shell demanding optimal attention to air barrier continuity as well as insulation levels. In climate zones where heating or cooling requirements would otherwise make such high levels of envelope efficiency impractical or cost-prohibitive without significant supplemental space conditioning systems, the benefits to occupants from superior indoor air quality and low maintenance costs can outweigh those from utility bill savings—making a passive house a more practical choice compared to an ultra-efficient home.
The term Passive House is being used more often in North America to describe homes that are very energy efficient. The Passive House Development Network defines it as “A building standard requiring very low levels of air leakage, minimal levels of air infiltration, and windows with a very high level of insulation. It is superior to virtually all existing ‘green’ building standards.”
2. How they Work: The Principles
To understand why passive houses require so little heating and cooling we need to take a brief look at how we experience the warmth and coolness around us and what actually controls these processes. By far the most important part of the answer lies in the properties of molecules: their ability to absorb or release heat, their density and the speeds at which they move.
According to basic physics, gases are made up of extremely small particles which fly around at great speed, colliding with each other and any solid object in their paths. As these particles collide with an object’s surface, some of their energy of motion is transferred into the object resulting in a slight rise in temperature. If you hold your hand above a lit candle long enough then this process will eventually cause it to get warm. The higher the temperature and the more rapid the movement of air particles then the greater is its ability to transfer heat or coldness to another surface after contact. This is why we feel cooler when moving air hits our skin than still air—the fast-moving molecules have more energy to impart.
The faster these air particles move, the greater their capacity to carry heat from a warm place to a cold one—and vice versa for cooling. The speed at which they can do this is expressed as their ‘thermal conductivity.’ This value also tells us how densely packed with energy these molecules are and how much impact they will have when colliding with another surface; denser molecules having more capacity for transfer than less-dense ones. As dense molecules hit our skin we feel cooler while less-dense ones make us feel warmer because of their reduced ability to transfer heat after contact. We all know that pure water freezes at 0°C while steam (water in gas form) can be heated above 100°C—the difference being how densely packed with energy these molecules are.
As well as impacting on our sensations of warmth and coolness, air density has a major influence on the natural processes that allow us to ventilate or heat-condition buildings in cold weather. As dense air cools it becomes more dense which causes it to sink towards the ground where it can be warmed by contact with an outside surface (such as soil or brickwork). This brings new, warmer air into contact with the building which then starts to rise. While its ability to transfer heat is relatively low, this process is very effective at cooling hot interiors during warm weather; most of this cooling completely free of any mechanical assistance (a phenomenon known as ‘stack effect’).
The most important difference between a passive house and most other buildings is that they are being specifically designed to have very low levels of air leakage. As the name suggests, these measures will use building materials with high R-values which are less conductive than conventional products. This means they will give up their heat or cold much more slowly via the material through which they are passing—in this case typically air. A second major influence on overall energy performance comes from using glazing with very low U-values in place of usual standard double glazing, resulting in window ‘heat losses’ that are typically half those found in existing houses.
An additional strategy for keeping the building warm involves making it almost continually re-pump its own heating system; this is done by incorporating at least one thermal ‘battery’—a room which has a large mass of material beneath the floor to store heat even if all other rooms are cold. Once it becomes warm, the house can then pump this warmth into other rooms via an underfloor heating system to maintain overall comfort even when outside temperatures drop well below freezing.
A side effect of these measures is that, unlike in traditional buildings where colder air tends to sink towards the lowest occupied part, here it will remain closer to head height because there are so few ways for it to escape. This means that occupants will almost always have their heads in warmer airspace than their feet—a factor which helps explain why they feel so comfortable year round.