This blog entry looks to take you through the benefits and limitations of applying the Passivhaus Standard to homes both as new builds and retrofits. In this article we refer to Passivhaus as the performance standard and Passive House as a building that has been designed and constructed to the Passivhaus Standard.
© Passive House Institute
What is Passivhaus?
Backed by over 30 years of international evidence, the Passivhaus standard is a tried & tested solution that provides a range of proven approaches to deliver net-zero-ready new and existing buildings optimised for a decarbonised grid. Passivhaus buildings provide higher levels of occupant comfort whilst using minimal energy for heating and cooling.
Passivhaus adopts a whole-building approach with clear, measured targets, focused on high-quality construction.
For a building to be considered a Passive House, it must meet the following criteria:
The Space Heating Energy Demand must not exceed 15 kWh per square meter of ‘treated floor area’ per year or 10W per square meter peak demand.
The Renewable Primary Energy Demand (PER, according to PHI method), sets the total energy consumption for domestic applications (heating, hot water and domestic electricity) at no more than 60 kWh per square meter annually (for the Passive House Classic standard).
Airtightness targets must meet a maximum of 0.6 air changes per hour at 50 Pascals pressure difference (both in positive and negative pressure), as verified with an onsite pressure test.
All living areas must meet thermal comfort during winter as well as in summer, with no more than 10% of the total hours in a given year reaching over 25°C.
How much does it cost to build a Passive House?
In 2018 the Passivhaus Trust reported that the total extra cost of building a house to Passivhaus standards was approximately 8% more than that of a traditional build. This difference continues to drop to around 4% as the standard grows in uptake.
Increased cost, when compared to a traditional build, also facilitate additional site supervision required in order to ensure the build is constructed to the highest possible standard.
Passivhaus certification is optional. However, certification verifies compliance with the Passivhaus Standard both during the design stage and construction. This service is carried out by a certified assessor and typically costs approximately £1,500 for a single home.
How much energy do Passive Houses save?
Passive Houses allow for heating and cooling related energy savings of up to 90% compared to the average building stock and approx. 75% when compared with an average new build.
Benefits of Passivhaus
Building Performance
The Passivhaus standard focuses providing buildings with low energy demand, high levels of comfort and healthy effective ventilation. The use of higher performance building components also help to reduce the risk of damage to the building fabric whilst providing a resilient future proofed building that helps to reduce the performance gap.
Climate Emergency
We are all aware of the climate emergency and that we all need to do our part to minimise our impact. Passive Houses lower carbon emissions, reduce the overall demand for renewables, take an approach where it is more economical to save energy then to generate it and enables decarbonisation without increasing fuel bills. Passive Houses are also resilient in the face of short term extremes and long terms climate change and are the best chance we have of achieving net zero in buildings.
Health and Wellbeing
The Passivhaus standard provides a much healthier environment for occupants to live in. A Passive House will eliminate cold homes, guarantee a good level of well distributed ventilation, reduce internal and external pollutants, eliminate the risk of condensation and mould, reduce the risk of airborne infection and impact of external noise.
Financial
The financial benefits of a Passive House come in many form. Most notable are lower energy bills, reduced extend of fuel poverty, higher capital cost of approx. 5-7%, lower whole life costs, lower borrowing costs (green mortgages or finance) and lower risk of repetitive damage or defects due to quality issues.
Common misconceptions of Passive Houses
The standard restricts design choice often resulting in boxy looking houses
Whilst the standard has a 'form factor' to bear in mind it does not limit creativity. With careful consideration, Passive Houses can be designed as creatively as any other.
You can't open windows
This is a myth derived from the misconception of how the concept of airtightness works. Windows can of course be opened, this is not only for occupant comfort, or rather perception of comfort, but also to cater for means of escape. A Passive House integrates a Mechanical Ventilation System with Heat Recovery (MVHR) often coupled with heating distribution. This system allows for a continuous supply of fresh filtered outdoor air whilst extracting stale indoor air. The filers trap pollutants, pollen and other particles resulting in a healthier more comfortable environment for the occupants.
The airtightness of Passive House make them stuffy and increase moisture
Airtightness plays an important part in controlling the loss of energy and controlling moisture ingress. Spaces are not left stuffy nor do they contain excess moisture due to the ventilation system mentioned above. Airtightness also contributes to a significant reduction of external noise.
Passive Houses are more expensive than traditional houses to build
This is true, however the initial investment is often made back within 5-10 years, during which time you would have enjoyed exceptional comfort. You then begin to make significant savings beyond the payback period.
Passive Houses are too complicated to construct
Whilst this is perceived to be true now it will not be once the construction industry upskills to meet demand. The complexity comes from the high standards of construction required to achieve a high net-zero ready building. This too can be seen as an investment due to the longevity of components and added protection of structure resulting in a building that is highly durable and capable to providing constant energy saving performance for years to come.
Passive Houses are too difficult to maintain
The main area which requires additional maintenance when compared to a traditional home is the ventilation system. These come with air filters that need to be periodically replaced. Good systems have been designed to make this as easy as possible for the occupant to replace. Occupants will however need to think differently about how they live, a Passive House with MVHR combined heating for example does not need heating to be adjusted as you would on traditional radiators or thermostats. Temperature is set and maintained at a consistent level which is more easily achieved in a well insulated airtight building. Furthermore, Passive Houses require very little maintenance due to their high quality construction.
You cannot modify or extend a Passive House
This is not true. Modifications or extensions need to be carefully considered in order to avoid compromising the building’s airtightness and insulation layers. Particular care needs to be taken, when extending in order to minimise thermal bridges as continuing the ventilation system to maintain even air distribution and extraction.