why should you build a Passivhaus?

Passivhaus is one of those things that sounds great, but what does it actually mean? What is the standard, how do you achieve it, and why should you work with an architect to design you one? Interested, then Read on…..

Yew Tree House, Swindon, Wiltshire. A New Self-Build Passivhaus.

What is the Passivhaus Standard?

Passivhaus, literally passive house in English, refers to buildings created to rigorous energy efficient design standards so that they maintain an almost constant temperature.

Passivhaus buildings are so well constructed, insulated and ventilated that they retain heat from the sun and the activities of their occupants, requiring very little additional heating or cooling.

For a building to be considered a Passive House, it must meet the following criteria:

1. The Space Heating Energy Demand is not to exceed 15 kWh per square meter of net living space (treated floor area) per year or 10 W per square meter peak demand.

This means you need VERY little heat input to your home, and therefore your heating bills will be extremely low.

2. The Renewable Primary Energy Demand (PER, according to PHI method), the total energy to be used for all domestic applications (heating, hot water and domestic electricity) must not exceed 60 kWh per square meter of treated floor area per year for Passive House Classic.

This means that the energy required to power your home will be very low, and therefore your electricity bills will be extremely low.

3. In terms of Airtightness, a maximum of 0.6 air changes per hour at 50 Pascals pressure (ACH50), as verified with an onsite pressure test (in both pressurized and depressurized states).

This means that you are not losing heat by leaking through drafty walls, floors, roofs and windows! It DOES NOT mean that you can’t open your windows.

4. Thermal comfort must be met for all living areas during winter as well as in summer, with not more than 10 % of the hours in a given year over 25 °C.

This means that your house will not overheat or be uncomfortably hot very often.

Cross Section Diagram of a Passivhaus Timber Frame with Continuous Insulation.

How do you achieve the Passivhaus Standard?

Achieving the Passivhaus Standard means committing to a range of things, ideally from the outset of your project. To make life easier for yourself, prioritise the following principles of good Passivhaus design:

• Siting and Orientation: Try to ensure, as far as practically possible, that your home faces South. Make the most of south and east facing windows and minimise north and west facing windows which cause heat loss and overheating respectively.

• Simple Building Shape: The so called ‘form factor’ describes the relationship between the living area that you create and the total external surface area of your home that heat can escape from. A simple building form helps keep u-values to easily achievable levels using a range of materials.  

• Continuous Insulation: High levels of insulation are required (achieving low u-values), in a continuous, ‘thermal bridge’ free/reduced construction. Thermal bridges are weak points in the junctions of your walls, floors, and roofs and need to be carefully avoided with well thought through details.

  Triple Glazed Windows: Windows that are certified for use by the Passivhaus institute are usually required. There are a range of suppliers for these, and they tend to have larger frames which can be partially covered by additional insulation. Unlike other windows, the surface temperature remains warmer – preventing the feeling of being cold next to them.  

• Mechanical Ventilation with Heat Recovery: MVHR systems control ventilation and fresh air to your home. A fan brings fresh air in and passes it over a heat exchanger that takes over 90% of the heat energy from air being extracted from bathrooms, kitchens and utility spaces. Filters remove dust and irritants from your air, improving your health.

• Airtight Construction: Not to be confused, or thought of as living in a sealed box, airtight construction means that you are not losing precious heat through gaps in your home! This saves energy and minimises the amount of heat input required. Of course, you can open your windows and doors in a Passivhaus, you just won’t rely on doing so to feel comfortable!

Initial Sketch Layout Considering Solar Orientation, Form Factor, Views and Access.

Working with Barefoot Architects to achieve the Passivhaus Standard:

• We aren’t wedded to any particular construction system to achieve the standard. (We’re not trying to sell you anything)!

• We have excellent market awareness of a range of construction systems that can be used to achieve Passivhaus.

• We often propose using a certified / tested system is generally easier (cheaper), because it does not require as much technical design checking.

• Several of our team have completed the Passivhaus Designer course and have in depth knowledge of low energy sustainable design.

• We can design you a bespoke home which meets the standard and guide you through the process step by step.

• We can deal with the planning process, technical design, and oversee construction on site to ensure that what you paid us to design gets built.

  We can optimise your brief, budget, site, and design to ensure that you have a warm, healthy, sustainable home that is affordable to run - a Passive house.

If your priorities aren’t to have a certified Passivhaus, but you do want a very low energy home then its fine with us! We’re not dogmatic about it and can still apply the principles! Get in touch, wherever you are on your journey to design and build a new home, and let us help you to take the next steps.