What is PassivHaus?

The benefits and methods of the PassivHaus low-energy building standard.


PassivHaus is a completely voluntary building standard which is aimed towards those interested in constructing a low-energy home. As a method of building, PassivHaus is currently enjoying a great lot of interest in the UK, and is based around the concept of reducing heating demands as opposed to relying on renewable sources. The standards set by PassivHaus far outreach those of the current Building Regulations, and its popularity is down to the many ways in which it is possible to meet the criteria, with designers able to use software to predict the eventual energy demand of the building being designed.

How is PassivHaus different?

The concept began its life as a research project which aimed to determine exactly why so many of the previous attempts at building low-energy homes could not deliver on their promises. The lessons taken from from this were then used to draw up  set of guidelines on how to get such projects done properly. The PassivHaus method is very thorough, and it has been shown numerous times to work perfectly.

How does PassivHaus achieve this?

In order to work properly, the house has to be designed from the very beginning using the PassivHaus method. It is important that you use a detailed spreadsheet known as the PassivHaus Planning Package (PHPP), which you will use to feed all of the relevant details of the construction. This includes the insulation depths, the size and orientation of all windows, junction details, and more. This will give you a predicted space heating demand (expressed as kWh/m2/yr). The design is adjusted continually until the outcome meets the standard. A PassivHaus can be constructed using almost any method of construction, but some features are universal. These include mass insulation at an average depth of 300mm, triple glazing with insulated frames, excellent airtightness levels of better than 0.6 air changes per hour, mechanical ventilation systems with heat recovery, and more.

passkeyprinciplewithtags What is PassivHaus?

1. Uses 90% less energy to heat than the average home, with heating costs of around just £75 per year.

2. Optimises the sun’s heat.

3. Uses only minimal micro-renewables.

4. Mechanical ventilation with heat recovery (MVHR) gives constant fresh air and keeps heat within the house.

5. Triple glazed windows with insulated frames.

6. The Tea Cosy Effect (also known as ‘minimising thermal bridging’), whereby the building is wrapped in insulation to keep any breaks or cold spots to a minimum.

7. Super-Insulation.

8. The house retains heat from the sun and the day-to-day activities of its occupants.

9. First cavity wall PassivHaus in the UK.

10. 20 times greater airtightness than a standard home.

Are PassivHaus homes Unheated?

Quite simply, no. The standard aims to reduce the space heating requirements to the point at which conventional heating is not required. The level is set at 15kWh/m2/yr, and this is the key target. What it means is that if you build a 160m&sups house to a PassivHaus standard, you will need only 2,400kWh of energy over the course of a year. That is roughly just 1/10th of what the typical UK home would use, and only a third of the energy used by so-called ‘eco-homes’. However, this is not no heating whatsoever, which would be expressed quite simply as 0kWh/m2/yr.

So, How is a PassivHaus Heated?

There is no set method for heating under the standard, and there are many ways in existence and many ways emerging of providing space heating. The most popular is to add a small heating element into the ventilation system, therefore turning it into a warm-air heating system too. The units are normally no more than 3kW, and will only become active when the outside temperature is nearing zero degrees Celsius. You will also need to consider your domestic hot water supply, so some kind of boiler is beneficial.

How is a PassivHaus Certified?

The PassivHaus Institute is the body which acts as both the training and certification centre for the low-energy standard. The Institute charges a fee of roughly £1,500 to certify a PassivHaus home. The certification is not compulsory, and in fact most of the 20,000 homes build according to the standard are not actually certified by the institute. However, there are advantages to being properly certified. The advantages of certification are mainly to do with obtaining a real measure of quality control for your new home. The certification means that the design is checked over thoroughly to make sure that it truly meets the standards, and the house itself is put to the test to make sure it properly follows the design.

The Key Points

- Low heating demand of less than 15kWh/m2/yr (about one tenth of the typical home’s usage)

- Super insulation means exterior walls achieve a U-value of less than 0.15

- Windows under the standard have U-values of less than 0.8

- The airtightness of a PassivHaus is less than 0.6 air changes per hour at 50Pa (Pascals)

- Heat recovery is at over 80% from Ventilation exhaust air.

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