An Introduction To Passive House Standard – Part 1
In recent years the term “Passive House” has become more commonly used in the UK, largely as a result of increased media coverage on the radio and television programmes, such as Channel 4’s “Grand Designs”. There is now mounting pressure to reduce our CO² emissions and to become more sustainable and energy efficient in line with Government objectives. Could this rigorous German energy standard help us to reach our ambitious targets for the following years?
At the beginning of the year, our team was strengthened by Steff Bell, a certified Passive House Designer. ACA can now offer full Passive House design and certification services. In order to give you a sense of what Passive House (Passivhaus – as it is in German) standard is, Steff wrote this two-piece article presenting all the important information on this concept. The first part introduces the concept of Passive House and its fundamental features. The second one will present a more detailed description of the principles required of this building standard such as preventing heat loss and maximising solar gains. If you are considering building a passive house, this article is a perfect start.
The Passive House Concept
A Passive House is a building that is designed and constructed to a strict set of criteria to ensure maximum comfort with minimum overall energy consumption. The building fabric is detailed in such a way that heat loss is reduced to an absolute minimum, whilst internal heat gains are maximised. As a result, conventional heating systems can be removed and space heating can sufficiently be supplied through passive sources such as body heat and the sun.
The Passive House approach is tried and tested and is widespread in both Germany and Austria. The first Passive House project was built in Germany in 1990 and there are now an estimated 40,000 Passive Houses across Europe.
The Passive House Institute
The Passive House Institute (PHI) was founded in 1996 by the concept’s co-creator Professor Wolfgang Feist. Based in Darmstadt, Germany the institute have developed the Passive House Standard through extensive research and monitoring of thousands of Passive House projects.
The success of the Passive House Standard in Europe has been, in part, due to the expert guidance and certification schemes led by the PHI, and also, thanks to the backing of the EU and respected professional institutions that have embraced the standard. European projects such as CEPHEUS (Cost Efficient Passive Houses as European Standards) and PEP (Promotion of European Passive Houses) have been launched to assess the potential of the Passive House Standard with regards to providing affordable low energy homes, as standard, across Europe. These projects have been very successful and have played a large role in the development and progression of Passive House.
Passive House Certification
It is important to note from the outset that “Passive House” (and/or “Passivhaus”) is not a legally protected concept, therefore anyone can claim that their building is a Passive House. However, the true proof of a building being a Passive House is certification by the PHI or an independently recognised representative of the PHI. Anything else is merely built “towards” Passive House Standard, using Passive House products, or simply taking advantage of the Passive House reputation for quality and comfort.
The provision of certified Passive House products is a further service offered by the PHI aimed at making Passive House certification more achievable. The PHI have compiled a list of Passive House approved products, such as MVHR units, windows and doors etc. that have been independently tested and proven to adhere to the Passive House criteria and sub-criteria. These products are made by, and available from, a large range of suppliers and manufacturers. They are manufactured in line with the PHI’s “four eyes principle” to ensure that the technical values are reliable for accurate calculations in the PHPP.
Self-Build Project Aiming at PH Standard
The intention to build a Passive House and seek certification must be established and agreed upon at the outset of a self-build project. The process of planning and detailing a building to Passive House Standard demands consideration of the Passive House requirements at every stage of the design. Achieving a certified Passive House building after a project has been designed or after construction has begun can be extremely difficult, and in many cases, impossible. It is therefore imperative that the decision to “go passive” is clear from the beginning.
Passive House Design
After an introduction presenting general information about the Passive House concept, it is time to describe the criteria and main features this standard represent. A building designed to Passive House Standard will provide a number of benefits for its owners and/or tenants. Such benefits will include excellent indoor air quality with reduced internal pollutants and a constant supply of fresh air and a reduction in maintenance and running costs as well as a drastic reduction in energy consumption and CO² emissions.
Passive House Criteria & the PHPP
The basic principles upon which the Passive House Standard has been developed, centre around a set of strict criteria that every Passive House project must adhere to in order to become a certified Passive House. The criteria are outlined below:
- Space Heating Demand ≤ 15 kWh/(m²a)
- Building Heating Load ≤ 10 W/m²
- Useful Cooling Demand ≤ 15kWh/(m²a)
- Primary Energy Demand ≤ 120 kWh/(m²a)
- Building Air-tightness ≤ 0.6 ac/h־¹
- Overheating Frequency ≤ 10%
Compliance with the criteria is verified using the Passive House Planning Package (PHPP) throughout the design and construction process. The PHPP is a sophisticated design tool specifically developed by the PHI for the accurate planning and calculation of Passive House buildings. The PHPP is similar to SAP however, PHPP is considerably more advanced, with the ability to provide accurate results that have been proven through extensive monitoring of existing Passive House buildings across Europe.
In addition to the PHPP calculations, there are a number of sub-criteria that are intended to make certification easier and more achievable. These are discussed below along with a number of design considerations to be taken into account when planning a Passive House project.
As with any project the site and surrounding area will play a major role in what is, ultimately, possible. However, there are a number of constant factors that can improve a buildings performance with regards to becoming a Passive House. Provided a design meets the performance criteria, and is modelled in the PHPP, the designer has a high degree of flexibility in designing a Passive House as they wish.
Self Build’s Orientation and Form
A compact building form, with minimum surface to volume ratios, ensures a reduction in thermal bridging and heat loss, whilst a south facing orientation with large areas of glazing maximises solar gains and provides a passive heat source for the building.
Natural shading methods such as roof overhangs, free standing balconies and deep window recesses should be considered in the design to avoid overheating in the summer. Other forms of shading, popular in both Germany and Austria, include concealed roller shutters and exposed manual shutters.
Construction and Energy Costs
Through the use of rigorous planning and precise execution of construction and site management, it is possible to build a Passive House to the same price as a house built to current building standards in the UK. Generally, it is observed that a Passive House can cost from 8-15% more than a conventional house. The additional costs come through the upgraded building envelope and the mechanical ventilation system. However, over the life cycle of the Passive House this increase in capital costs is eclipsed by the dramatic savings made due to reduced energy consumption and the almost non-existent heating bills.
Improved thermal comfort levels are another of the major benefits to building a Passive house, together with the reduced energy costs and CO² emissions. The reduction in the energy consumption of a Passive House leads to a situation where renewable technologies become a better and more economical option for a project. Not only they can now provide sufficient energy for the building’s needs, but in many cases the building creates more energy than needed, which results in a situation where the house owner can sell this energy back to the grid, for a profit.
Passive Houses in the UK So Far
Passive House development is beginning to take shape in the UK with interest and knowledge developing at a fast pace in recent years. The first UK Passive House projects were built in Wales in the form of a community centre and a detached family house. In November 2009, Scotland had its first certified Passive House project confirmed. The affordable housing project Tigh-Na-Cladach in Bethania, Dunoon was certified having met the relevant criteria. Channel 4’s programme, “Grand Designs” filmed the development of England’s first Passive House project. There is also a project of 14 Passive Houses recently finished in Essex for Hastoe housing association by Parsons and Whittley as well as a Passive House call centre awaiting certification in Dover. In addition to these examples, there are a number of other projects stretching across the UK awaiting certification, or currently under construction, as the Passive House Standard continues to grow in popularity and reputation. For more examples read our guest blog article with Ben Adam-Smith.
This is the first part of our ‘Introduction to Passive House Standard’ article. If you want to find out more about preventing heat loss and maximising solar gains of Passive Houses, you will find all the information you need in the second part of our article.