What is Passivhaus?
Passivhaus is an entirely voluntary building performance standard that anyone setting out to build a low-energy home might be interested in. It’s gaining lots of attention in the UK and is based around the principle of reducing heating demand to a very low level rather than relying on renewables.
The standards far exceed those of the current Building Regulations, and it is popular because there are many different ways to meet the criteria. Designers use a software package to predict the home’s future energy demand.
What is Different About Passivhaus?
It started life as a research project to find out just why so many previous attempts at building low-energy houses failed to deliver what they promised. The lessons learnt from this were then distilled into a set of guidelines about how to get it right. It’s very thorough and exacting to build this way, and numerous studies have shown that it works.
How Does a Passivhaus do This?
The house must be designed from the ground up as a Passivhaus. There is a complex spreadsheet known as the Passivhaus Planning Package (PHPP) into which you feed all the relevant construction details, including:
- the insulation depths
- the window sizes and orientations
- the junction details.
This gives you a predicted space heating demand (expressed in kWh/m²/yr).
You keep adjusting the design until your outcome meets the standard. Passivhaus can be built using almost any construction method. However, there are some universal features, including:
- massive insulation (average depth 300mm)
- triple glazing with insulated frames
- fantastic airtightness levels (must score better than 0.6 air changes per hour)
- mechanical ventilation with heat recovery.