PASSIVE HOUSE STANDARD - DOMESTIC, NON-DOMESTIC AND RETROFIT (Part 1 of 2)
Steff Bell, BSC (Hons) Certified Passive House Designer
The Passive House Standard has been growing in popularity in the UK over the past few years with a large variety of buildings achieving certifi cation. The standard has also become popular in other European countries and across the world. With this in mind we ask how easy is the Passive House Standard to understand, can our construction industry implement this and can it be used to upgrade the UK’s aging housing stock?
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 a minimum, whilst internal heat gains are maximised. As a result, conventional heating systems can be removed and space heating can be supplied through passive sources such as body heat and the sun. This saves up to 90 percent of the building’s overall energy consumption when compared to a standard house constructed to current building regulations.
Underhill House, the first certified Passive House in England
THE PASSIVE HOUSE INSTITUTE
The tried and tested Passive House approach is widespread in Germany and Austria. The first Passive House project was built in Germany in 1990 and there are now an estimated 30,000 Passive Houses across Europe.
The Passive House Institute (PHI) was founded in 1996 by the concepts cocreator, Professor Wolfgang Feist. Based in Darmstadt, Germany the Institute has developed the Passive House Standard through extensive research and monitoring of thousands of Passive House projects.
PASSIVE HOUSE DESIGN
A building designed to Passive House Standards will provide a number of benefits for its owners and/or tenants. Such as excellent indoor air quality with reduced internal pollutants and a constant supply of fresh air, a reduction in maintenance and running costs and a drastic reduction in energy consumption and CO2 emissions.
These benefits are produced through simple means such as orientating the building to the south where you will have large glazing for solar gains and reducing the amount of glazing to the north, east and west to avoid overheating and heat losses at night. Enhancing the building envelope through super insulation, superior air-tightness and reduced thermal bridge detailing, as well as the incorporation of Passive House approved products such as triple glazed windows with insulated frames and mechanical ventilation with heat recovery systems (MVHR). The Passive House Standard can be applied to all types of buildings including new-build, commercial and retro fit. All construction types can also be used as long as they have the sufficient U-values.
PASSIVE HOUSE CRITERIA AND THE PASSIVE HOUSE PLANNING PACKAGE (PHPP)
The basic principles, upon which the Passive House Standard has been developed, centre on a set of strict criteria that every Passive House project must adhere to in order to become a certified Passive House. (The main 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
- Excess Temperature Frequency ≤ 10%
The criteria for a retro fit Passive House is the same as above with one important difference - the space heating demand has been relaxed to ≤ 25 kWh/(m²a). This is because it can be very difficult, but not impossible, to achieve certification with a retro fit project due to issues with the existing structure and achieving appropriate insulation and air-tightness levels. Regardless of difficulties with achieving certification the use of the Passive House Standard on an old building has the potential to improve its performance by a factor of 10 if not better.
Compliance with the Passive House 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.
In addition to the PHPP calculations, there are a number of sub-criteria and design considerations to be taken into account when planning a Passive House Project that are intended to make certification easier and more achievable. (These are shown briefly in the Passive House diagram and whilst they are displayed here in a domestic example the same criteria are applied to all types of the standard).
This Passive House diagram is purely intended as an illustration of principles,it is not representative of housing layouts or product sizes
It is important to note 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 intention to build a Passive House and seek certification must be established and agreed upon at the outset of a 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 often impossible. It is therefore imperative that the decision to “go passive” is clear from the beginning.
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 though, it is observed that a Passive House can cost from 8-15 percent 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 nonexistent heating bills.
Dunoon Project, the first certified Passive House in Scotland
PASSIVE HOUSES IN THE UK
Passive House development is beginning to take shape in the UK with interest and knowledge now increasing at a fast pace. Many of the first building types relating to the Passive House standard have now been built including the first certified domestic Passive House in Scotland, England, Wales and Northern Ireland. Beyond this there has also been the first non-domestic building, the first Passive House School and the first Passive House retro fit project all successfully certified.
Current numbers of Passive House buildings are thought to be around 150 although it is difficult to be accurate. The majority of these buildings are new build residential properties although the numbers of other types of Passive House buildings are rising rapidly.
It is clear from the rapid growth of the Passive House standard in the UK that the simplicity of the concepts and the strictness of the criteria make it an easy standard to understand and implement. It has been observed that many projects incur extra costs in some cases due to lack of experience from architects and contractors alike although in many cases this is easily overcome and rarely repeated.
As already mentioned, the majority of current Passive House buildings are new build residential properties but interest is growing in the retro fit market and with new and innovative products and materials coming onto the market all the time it is now becoming easier than ever to overcome previous issues with these types of renovation project. We envisage that the retro fit market could be a large growth sector for the Passive House standard and would provide a realistic solution for achieving our Government’s ambitious energy and zero carbon targets, certified or not.
For more information, contact: Steff Bell, email: email@example.com
Scottish Passive House Centre, 24 Fairykirk Road, Rosyth, Fife, KY11 2QQ. Tel: 0845 3883 716 8 www.sphc.co.uk