The passive house standard is easier to achieve if the building from is kept simple. If the amount of external wall or roof is kept to a minimum there is less exposed surface area for heat to be lost to the outside. So for example a simple rectangular floor plan will be more energy efficient than a “L” shaped plan, which will have more exposed surface area.
Passive house requires a super insulated building shell. A depth of 300mm or more of insulation is required in the roof and external walls to achieve the standard. The advantage of a super insulated building is it stays warm in the winter, but is remains cool in the summer months. A thermal bridge, also known as a cold bridge, is when heat is transferred through a poorly insulated part of the building. In a Passive House it is essential to ensure that thermal bridges do not occur, or are kept to a minimum. This is achieved through careful design, detailing and briefing of the builder.
A passive house requires triple glazed windows, doors and roof-lights with insulated frames to prevent heat loss. Careful consideration needs to be given to ensure that glazing is maximised to the South Elevation for solar gain, and minimised to the North, to reduce heat loss. Shading may also be required to the windows on the South Elevation to prevent over heating in the summer months.
A passive house needs to be built to a much higher standard of air-tight construction then current UK Building Regulation requirements. Passive House envelopes are air-tight and heat loss through the building fabric is controlled. It provides greater comfort for the occupier, with no cold winter drafts. An air tight construction is achieved through a continuous membrane concealed behind the plasterboard, carefully taped to the window and door frames. Any services which puncture through the wall, roof or floor, are carefully sealed. During the construction process pressurisation tests are carried out to check the standard has been achieved.
As a Passive House is a highly sealed air-tight construction it is essential to have a ventilation system to ensure fresh air supply during the winter months, when windows are kept shut. This is achieved by installing a mechanical ventilation heat recovery unit also known as an MVHR. These units are very modest in their power consumption and can provide up to 93% heat recovery efficiency from the extracted warm air, to the cooler incoming fresh air. The cost of a MVHR unit and associated ductwork is similar to the cost of a conventional radiator fed central heating system and boiler.
Interested in finding out more about Passive House? Julie Wilson, Partner at Brennan & Wilson Architects passed the European Certified Passive House Designer course and has experience of the design and construction of passive house projects. Take a look at our project page on the passive house we have designed and built in East Lothian. > Find out more
Passive House is a construction standard developed in Germany more than 20 years ago following the simple principle that a house if built to be very highly insulated, air tight, with windows orientated to the South for solar gain, then virtually no heating is required to keep the building warm. Incidental gains from people, lighting, appliances and sunlight are often sufficient to keep the house comfortable for most of the year. On extremely cold days a small amount of heat input may be required, but this can be achieved from electric towel rails, a small wood burning stove or a heating element in the ventilation system.
No, passive house is not an architectural style, it is purely a construction standard. It can be applied to any type of house, although it is much easier to achieve passive house standard with new build then renovation projects. Because a Passive House requires solar gain as one of the main sources of heat, it does mean that the building will require quite large windows on the South elevation, and as little glazing as possible to the North.
Air quality in a passive house is exceptionally good. This is because it has a mechanical ventilation heat recovery (MVHR) system, which supplies three full fresh air changes per hour to all the main rooms in the house. Stale air is constantly extracted from the kitchen and the bathrooms. The ventilation system transfers the heat from the warm extracted air, to the colder incoming fresh air. This raises the air temperature before it is distributed to all the living and bedrooms. This ensures that very little heat from the house is wasted, allowing it to be re-circulated and re-used. In summer it is no different from a conventional houseand you can open windows without losing heat.
Yes, we find a passive house is approximately 10-15% more expensive to build. However, this extra initial cost is offset by savings of as much as 90% off energy bills. Due to the increasing popularity of passive house, many products, such as triple glazed windows with insulated frames are now being produced by large manufacturers such as Nordan, Velux and Rationel, which is bringing down the cost of what were previously expensive products to obtain.
You can have a wood burning stove in a passive house, but you might find that you don’t need one. As the houses are so well insulated, over heating can become a problem if a wood burning stove is operating at full capacity. If you want to install a wood burning stove we would recommend a very small low kilowatt stove. A room sealed stove also needs to be installed with it’s own separate air supply, as an open grille for through draft cannot be punctured through the air tight passive house construction.
We strongly recommend that you use a trained passive house designer. The Passive House Institute in Germany provides an intensive course and exam for designers, including training in the use of the passive house planning package (phpp) which is a software programme used to calculate and predict how the building will perform in use. Julie Wilson, Partner at Brennan & Wilson Architects passed the European Certified Passive House Designer course and has experience of the design and construction of passive house projects.
Brennan and Wilson Architects
9 Bayswell Park
T: 01368 655004