CONVERSATIONS WITH THE DESIGNERS - Passivhaus. The principals and benefits.

Uncategorized Apr 22, 2021

Whether you've heard of Passivhaus (Passive House) or not, the chances are you may not fully understand what it is and how it's of benefit, to not only those living in a passive house environment but also it's benefits to our planet.

A simple way to define Passivhaus would be; A standard of building that uses various principles of insulation, passive solar climate control, and low-energy construction methods. This creates a building that requires very little in the way of fuel or electricity input in order to meet cooling and heating  requirements. It's thermal comfort can be achieved solely by post-heating or post-cooling the fresh air flow required for a good indoor air quality.

Buildings are responsible for producing 40% of Australia's total greenhouse gas emissions. And that around 23% of these emissions are associated with the energy used to run machinery to heat and cool buildings due to the inefficiencies in the way we currently build houses. Heat escapes our homes through gaps resulting from badly sealed windows & poorly insulated wall & roof spaces. We then spend a lot of money on putting heat back into our homes that leaks straight back out again. These same gaps in the fabric of our homes, allow the outside heat to enter during the hotter months too, so we spend even more money on machines that cool & take that heat out of our homes, all while the outside heat continues to re-enter our homes through the gaps in our walls and windows. 

Let's take a look at the fundamental principals that make the Passivhaus building so much more energy efficient while at the same time, a much healthier environment to live in.

1. A super-insulated envelope;

This is to separate the inside from the outside. This includes the walls, roof & floors and the use of material and construction methods that increases the thermal insulation of the building compared to standard practice & codes. This creates a comfortable & consistent internal temperature all year round, despite the temperature outside. It also improves on sound proofing, has greater building resiliency and increased durability.

 2. Minimisation of thermal bridging;

Unfortunately, there are going to be weak spots within the thermal envelope such as Struts for walls & frames for doors and windows. Any physical component that can transfer heat & cold through the insulated envelop to the interior, is called a 'thermal bridge'. The idea is to minimise the amount of thermal bridging where possible. Some thermal bridges are difficult to avoid as they are structurally necessary, however there are ways to insulate and greatly minimise the transference of heat across these components.

3. Airtight Construction; 

The envelope seal is further enhanced by the airtight construction. Special membranes, tapes and seals are carefully fitted to minimise the volume of uncontrolled air exchange between the interior and exterior of the building. This in turn reduces the need for energy use to reheat or cool the air, discomfort from draughts near the walls as well as localised moisture damage, condensation and mould problems. A pressure test is required in order to certify a house as fully passive.

4. Heat Recovery Ventilation ;

Because of the airtight principal of the Passivhaus, we need to install an efficient mechanical air exchange system. It delivers fresh air (filtered of odours, dust, pollen and other pollutants) and extracts stale, moist air, all at a carefully calibrated level. In areas of high pollution or where the occupants suffer allergies such as hay fever or asthma, the filters in the mechanical ventilation system can be upgraded. Specialist filters will even remove very small particulate matter, such as is found in bushfire haze. While the airtightness is important, it doesn't mean you can't open a window and enjoy the the outdoors on those mild & pleasant days.

5. High performance Glazing;

By their very nature, windows and glazed doors are there to provide light and visibility therefore can't be insulated to the same degree as a wall. This is why high-quality, highly energy-efficient doors and windows are used in a Passivhaus. Double glazing is standard however triple glazing is sometimes used due to specific climate or comfort requirements. Glazing performance is typically improved in a Passivhaus by using high quality spacers between the glass panes, glass coatings and argon (gasses) fill. The window and door frames must also be high-performance. They stay at the same temperature as the interior of the house meaning condensation and mould are avoided. Heat loss is reduced by about three quarters compared to that of standard (thermally-conductive) frames.

You may ask; Is Passivhaus relevant in Australia, considering we love alfresco living and our climate is relatively mild compared to that of Europe? Our climate may not be as extreme as parts of Europe but we too have seasons of extreme temperatures, mainly in the way of heat, tropical rains & in some parts of Australia, cold. We consume a lot of energy to keep our homes cool, dry and comfortable, so it makes sense that a climate controlled environment would be of great benefit on those days of extreme heat & cold. Passivhaus design, not only greatly reduces energy expenditure, which is great for the environment (as well as your hip pocket!) because it is way more cost-effective in the long term. It is quiet and provides a much healthier environment for those occupying the space.

Passivhaus used to be considered an expensive indulgence but 30 years on, a well planned Passivhaus is relatively comparative in price to traditional construction. You would be looking at around a 10-20% increase in costs to build. So I guess it comes down to what is important to you & the world we live in!


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