Is Passivhaus the next step in the evolution of sustainable design?
14 October 2019

Australia's Guide to sustainable homes and Construction Cost Guide on plans and specifications

 

Awareness of our individual impact on the environment, and what we can do about it, has led to an emergence in the adoption of solar passive principles when designing sustainable homes. The adoption of a common-sense approach to design allows us to achieve much with little or no extra cost. 

A custom designed home links the geographic and environmental aspects of your site with modern materials and sensible construction techniques to save reduce the operational costs of you home; you will enjoy a more comfortable home to live in and have the satisfaction of knowing that you are making a positive contribution towards combating global warming. 

 

Sustainable design – what exactly is it?

Sustainable design originated from research of North American builders during the 1970s, who—in response to the oil embargo—sought to build homes that used very little or no energy. These designs utilised the sun as a heat source and this led to the development of “Solar Passive Design”.

Sustainable design has continued to evolve and is now based on understanding the environment at the regional, local and site levels, taking into account the site’s unique geographical characteristics and combining these to develop an appropriate building form. From these design considerations materials and construction techniques are selected  to create an intuitive, location-sensitive home. To date the most important elements are the home’s orientation, insulation and natural ventilation.

  1. The northern orientation makes the most of sun angles to help maintain a constant temperature; preventing overheating in summer and in winter, taking advantage of the lower sun angles to heat the thermal mass of the home. 

  2. Good insulation to ensure that the thermal mass of the home is maintained at a relatively constant temperature. This includes sealing the home to ensure that warm and cool air is not uncontrollably lost to the environment or altered.

  3. Cross Ventilation considers the effects of natural and induced breezes to provide good air flow that will cool or heat the home.

There is a newcomer to sustainable design that is creating discussion among custom sustainable home designers: “Passivhaus”

Passivhaus

Passivhaus is a German approach to home design that uses a combination of high-performance glazing, insulation and an airtight building envelope to regulate a home’s internal temperature without relying on artificial heating or cooling.

The Passivhaus standard originated 1988 from a discussion between Bo Adamson of Lund University, Sweden, and Wolfgang Feist of the Institut für Wohnen und Umwelt (Institute for Housing and the Environment) in Darmstadt, Germany.  Their concept was further developed through a number of research projects, aided by financial assistance from the German state of Hessen

Passivehaus is a new way of looking at how we live. The aim being to dramatically reduce power costs through design. The Passivhaus methodology is underpinned by five key components relating to how the home is designed and constructed. Let’s take a look at how it all works.

What is Passivhaus?

Passivhaus, which literally translates as “Passive House”, is a voluntary housing performance standard. In short it is physics for buildings. While we have understood the need for natural light and big windows and ventilation and these sorts concepts when we construct using solar passive design principles there is a general lack of specific physics in the design process. Passivhaus, on the other hand,  is very rigorous and scientific.

The first official passive house was constructed in Germany in 1990. During its first year of operation, the energy used for heating was just 8 per cent of a standard home at the time. Continued monitoring over subsequent years saw this figure fall to less than 5.5 per cent of the energy consumption in comparable homes.

The concept gathered momentum, and 27 years later some 50,000 certified passive houses have been built – mostly in European countries. The technology continues to be developed and improved at the Passivhaus Institut in Germany, which oversees the Passivhaus building performance standard worldwide.

Certified passive houses must be built to particular design and construction standards and, once completed, must meet the Institute’s rigorous performance requirements regarding energy use.

The Principles of a Passive House

While a passive house won’t necessarily look any different from a “normal” home, there are five key differences in the way it’s constructed.

Insulation

Passive houses are well insulated; in the walls, floor and ceiling. This can be in the form of a conventional insulation blanket but is incorporated into the building envelope where practicable. This could be in the form of insulating materials, such as aerated autoclaved concrete (AAC) blocks, prefabricated foam panels, or even straw bale. Adequate insulation is the first step in minimising heat gain in summer and heat loss in winter.

Insulated windows and doors

There is little use creating an insulated blanket and losing all of your energy through the windows and doors. The Passivhaus Institut stipulates that window frames must be well insulated, and fitted with double glazing or low-emissivity glass.

Note: Low-emissivity or low-e glass has a very thin coating that reflects heat. This is great if you want to block hot western sun, for example, but may compromise winter heat gain if used on north-facing windows.

Eliminate thermal bridges

The next requirement is to address “thermal bridging”. Thermal bridging refers to points in the building shell that conduct heat or cold more quickly than the rest of the structure, for example where metal wall framing “bridges” between interior and exterior wall linings. Heat or cold will transfer along this point, and it compromises the overall performance of your insulation.

Air-tightness

The fourth principle is the air-tightness: the building envelope is airtight and so you don’t get draughts coming in or air leaking out. This is where most Australian designed homes fail. In Australia we have inherently built leaky homes. To achieve Passivhaus standards every joint must be sealed; no gaps can exist within the “skin” of the building.

An airtight, insulated building will successfully retain any warmth or coolness generated within, which is, essentially, why these houses require so little energy to heat or cool.

Heat recovery ventilation

Because the building is airtight, and all draughts and air leakages are precluded, the flow of air in and out of a passive house must be  controlled with a heat recovery ventilation (HRV) system, which is the fifth design component.  

The HRV is essential for a passive house to function; the stale and oxygen depleted air must be replaced with a constant supply of fresh, temperature-controlled, filtered air. It stops the house from getting stuffy, improves air quality, and, in cold weather, prevents the build-up of condensation.

The incorporation of a heat exchanger in the HRV system keeps the incoming air as close as possible to the exhausted air temperature. 85 to 90 per cent of the energy that is in the house stays in the house. Once the home achieves its optimal temperature of 22 to 23°C, it wants to maintain the equilibrium. 

Advantages and Disadvantages of Passivhaus

The advantages of a passive house include:

  • higher air quality and consistent interior temperatures. 

  • Long-term cost savings using energy efficiency.

  • Systems need minimal space in the design construction.

  • Integrates with hot water heating system.

Disadvantages of passive house construction

The lack of consumer knowledge is a major drawback for green building as a whole, and passive house construction is no exception. That’s the sad news, since so many owners struggle to maximize a home’s use of energy. The big disadvantages of passive house construction are:

  • Initial costs can be 10%-30% higher.

  • Poor design can lead to condensation problems

  • Redundant ventilation systems may be required.

Is Passivhaus an evolutionary step in sustainable design?

To use a classic Australianism “Yeah nah”.  Depending on the climatic circumstances Passivhaus, or a derivative of it may become the design standard. I do not think this will apply in most parts of Australia due to our temperate climate. I tend to take a golf bag approach to developing sustainable homes. Passivhaus is a big club in that golf bag and can be to meet specific needs and requirements.  Probably not the most used club – but well worth carrying and considering.

Until next time

Craig