The Passivhaus Handbook: A practical guide to constructing and retrofitting buildings for ultra-low energy performance (Sustainable Building) - Softcover

Cotterell, Janet; Dadeby, Adam

Softcover

ISBN 10: 0857840193 ISBN 13: 9780857840196

Verlag: Green Books, 2012

Inhaltsangabe

An essential guide to making a supremely comfortable, healthy and durable home with exceptionally low energy costs. Covers both retrofitting and new-build.

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Über die Autorinnen und Autoren

Janet Cotterell is a chartered architect with more than 20 years' experience working in sensitive settings (conservation areas, listed buildings, historic parks), so is familiar with the use of traditional and natural materials. Her focus is on the importance of sustainable building practices and low-energy design principles. She is also a Certified Passivhaus Designer and holds an MSc in Architecture: Advanced Environmental & Energy Studies.

Adam Dadeby is one of the UK's leading experts in Passivhaus and residential heat recovery ventilation (MVHR). A Certified Passivhaus Consultant and a member of the AECB (the Sustainable Building Association), Adam also holds a postgraduate diploma in Architecture: Advanced Environmental & Energy Studies from the Centre for Alternative Technology (CAT), where he became passionate about the ways 'sustainability' and 'resilience' affect building practice. He and his wife Erica ran the UK's first and only Passivhaus bed and breakfast for a number of years. He has presented talks nationally on Passivhaus and MVHR to built-environment professionals and aspiring self-builders.

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The Passivhaus Handbook

A Practical Guide to Constructing and Retrofitting Buildings for Ultra-Low Energy Performance

By Janet Cotterell, Adam Dadeby

UIT Cambridge Ltd

Copyright © 2012 Janet Cotterell and Adam Dadeby
All rights reserved.

ISBN: 978-0-85784-019-6

Contents

Foreword by Wolfgang Feist, 
Introduction, 
How to use this book, 
Part One: The how and why of Passivhaus, 
Chapter 1 What is a Passivhaus?, 
Chapter 2 The economics of a Passivhaus, 
Chapter 3 Passivhaus Certification, 
Chapter 4 Challenges of meeting the Passivhaus standard, 
Chapter 5 Natural materials, zero carbon and resilience, 
Chapter 6 Setting up a Passivhaus project, 
Part Two: Passivhaus projects: a practical guide, 
Chapter 7 Using the Passivhaus Planning Package (PHPP), 
Chapter 8 Thermal bridges, 
Chapter 9 Airtightness and sequencing, 
Chapter 10 Moisture, 
Chapter 11 Windows, 
Chapter 12 Ventilation, 
Chapter 13 Living in a Passivhaus, 
Chapter 14 Policy change in the UK, 
Appendix A: Space heating and hot water, 
Appendix B: Thermal conductivity values, 
Appendix C: US units – metric conversions, 
Appendix D: Certified Passivhaus projects in the UK, 
Glossary of terms, 
Glossary of units, 
Notes, 
Resources, 
Index, 

CHAPTER 1

What is a Passivhaus?

The Passivhaus energy standard, the Passivhaus concept, common misconceptions, retrofitting and the EnerPHit energy standard

A Passivhaus building is designed to be very comfortable and healthy, and to use vastly less energy than conventional buildings, irrespective of the climate. This is achieved by careful design informed by building physics and, crucially, by thoughtful and careful construction by a properly skilled and motivated team.

Passivhaus originates in Germany; the German word Passivhaus literally translates as 'passive house or building', since Haus refers to a building as well as a house. The word is being incorporated into English, although the concept is still often referred to as 'passive house', particularly in the United States. When people hear the term 'passive', they sometimes assume that this means no heating system or that the design relies on 'passive solar design', i.e. utilising heat from the sun. There is some truth in these assumptions. A Passivhaus does require a trickle of heat to maintain 20°C, although not nearly enough to justify a central heating system. It relies on high levels of uninterrupted, all-round insulation, airtight design and heat gained from the winter sun through the windows (solar gain); however, solar gain is not in itself sufficient to heat a Passivhaus. A Passivhaus is also more comfortable and healthier than a standard build, as there are no draughts, no condensation or mould in cold spots, and the air is fresher. We will see later in the book how and why this is the case.

The thermographic images below, in which surface temperatures are represented with colours, show how high levels of insulation transform a building's energy performance. A well-insulated building in winter has cold external surface temperatures (shown in blue). Thermographic imaging also highlights any 'thermal bridges' – gaps in insulation that allow heat to bypass it.

The Passivhaus energy standard

A building is a Passivhaus if it meets a voluntary technical standard that, being international, has to be met regardless of the local climate. It was developed by the Passivhaus Institut (PHI), an independent research institute founded in Germany in 1996. The Passivhaus standard is defined by the core technical requirements listed in Table 1.1 opposite. However, understanding Passivhaus is about a lot more than these numbers. It is a process informed by some key principles, which we will briefly explore next (and in more detail in the rest of the book).

Any building that meets the standards in the second column of Table 1.1 is a Passivhaus. If you don't understand the entire table now, you should become familiar with the ideas as you read the rest of this book. Each requirement is also discussed in the sections that follow. Definitions of terms and units are given in the box below the table, and are also explained in the glossary.

To be sure that a building designed as a Passivhaus genuinely meets the Passivhaus standard and to have independent verification that the design will work as intended, it helps to be certified. Chapter 3 explains what Passivhaus Certification involves and what benefits it brings.

Passivhaus and other building standards

Different standards are not, for the most part, quantitatively comparable, either because they do not measure the same things or, often, because the conventions and assumptions on which they are based are different, making direct comparison impossible. Some are country-specific and stem from government initiatives. Others, such as Passivhaus, originate from non-governmental organisations and are therefore voluntary. Some standards have a narrow focus, while others, such as the UK's Code for Sustainable Homes (CSH), attempt to cover a broad range of sustainability goals. The CSH was originally conceived as an assessment system. By contrast, Passivhaus is not only an energy performance standard but, critically, is also intended to be a design process – which, if applied intelligently, will get you to your low-energy goal.

To some extent, it is possible to mix and match standards. For example, there is no reason why water usage targets from one code cannot be mixed with energy usage standards from another. Some projects are required to meet statutory assessment-based targets, but you can still choose to work to a tougher, voluntary standard. Similarly, there is no reason why other areas of sustainable building not covered by standards or codes cannot be addressed in the design. For example, Passivhaus does not address the properties of building materials – such as embodied energy (the energy used in the sourcing, manufacture and transport of a material), breathability and recycle-ability – but clearly there is nothing to stop you choosing to address these independently of any standard, while still achieving the Passivhaus energy-inuse standard. These issues are discussed further in Chapter 5.

The Passivhaus concept

Underlying the Passivhaus concept are several key ideas, discussed on the following pages. While some are 'common sense', others are less obvious and more technical in nature.

Getting the fabric right

The Passivhaus approach concentrates above all on 'getting the fabric right'; in other words, on designing, specifying and constructing the foundation/floor, walls, roof and windows correctly to achieve the Passivhaus standard. Money spent on the building fabric should be seen as an investment for the life of a building (normally a minimum of 60 years), as production of the building materials can consume considerable energy. Designing the fabric to last means that the invested money, energy and carbon provide enduring benefit. In contrast, money spent on 'bolt-on' technologies, such as those needed to provide hot water or space heating (e.g. a boiler or a hot water tank), is a shorter-term investment – 20 or perhaps 30 years at the very most. Those systems may well be replaced several times during a building's lifespan. The smaller the energy burden needed to heat (or, in hot climates, to cool) the building, the less hard the bolt-on technologies have to work, and the smaller and potentially simpler to manufacture, maintain and use they can be.

Optimising the design from day one

The architect's initial designs are modelled for energy performance using the Passivhaus Planning Package (PHPP), specialist software developed by the PHI (see Chapter 7). The PHPP makes it possible to test whether the design will achieve the Passivhaus energy and comfort standard. Once the design has been entered into the PHPP, it is possible to vary elements of it to measure the effect on energy performance. This is an iterative process where client preference, aesthetics, planning considerations, costs and any other practical constraints can be balanced against the design's energy performance. Such an approach brings multiple benefits. Rather than over-engineering the design to make sure it reaches the Passivhaus standard, the design can be optimised. It also means that the client, architect and builder can make informed decisions about the design, that money is not wasted, and that everyone understands the significance of the design and why certain choices were made. Depending on the project, this preliminary detailed work helps to reduce the risk of unexpected cost overruns later in the project.

There is no doubt that this approach is good for the project and makes it easier to reach the Passivhaus standard. However, it is difficult for many to accept the risk of paying for more detailed design work than is typical in a standard build before planning permission has been given. The planning system is discussed in Chapters 4 and 14.

Solar gain and shading

Wintertime solar gain (heat gain from the sun through glazing) is an important part of how a Passivhaus stays warm. However, when a building is designed to minimise heat loss in winter, it is especially important to ensure that summertime solar gain is avoided as far as practicable. This can be achieved by the use of shading devices, which are discussed in Chapter 11.

Insulation and avoidance of thermal bridges

A Passivhaus needs more insulation than other buildings, and that insulation must wrap continuously around the building so that thermal bridges are eliminated (or, in a retrofit, minimised). A thermal bridge, commonly known as a cold bridge, is a gap in insulation that allows heat to 'short-circuit' it. This happens when a material with relatively high conductivity interrupts the insulation layer.

Form factor

The term 'form factor' essentially refers to the shape of the building: it is the ratio of the external surface area to the internal usable floor area, known as the treated floor area (TFA), and is a measure of how compact or spread-out the design is. A more compact design makes it easier and cheaper to achieve the Passivhaus standard because the walls, roof and floor can be a little thinner (have a higher U-value) than would be needed in a more spread-out design. Table 1.2 below demonstrates this.

Thermal comfort

Most discussion of Passivhaus tends to focus on saving energy, but just as central to Passivhaus methodology is the concept of thermal comfort, defined as the "condition of mind which expresses satisfaction with the thermal environment". More simply, this means not feeling too hot or too cold. In designing a building, the effort to improve thermal comfort needs to be directed at reducing all cold surfaces and draughts. In Passivhaus, there are comfort design criteria (see Table 1.3 overleaf) intended to eliminate all draughts and cold surfaces, and to provide sufficient fresh air. Improving thermal comfort has an added benefit. In a conventional building, we often turn up the heating in cold weather to compensate for draughts and the chilly feeling (known as 'cold radiant') we experience when near cold surfaces. The occupants' need to overcome the effects of draughts and cold radiant often adds to a conventional build's real-world energy consumption. In a Passivhaus, this does not happen, allowing thermostats to be set lower for the same level of thermal comfort.

Airtightness and indoor air quality (IAQ)

Making a building less 'leaky' is important because air escaping in an uncontrolled way through the building fabric wastes energy, risks reducing the building's lifespan (as a result of air carrying moisture into the fabric) and also makes it feel less comfortable during cold or windy weather. As statutory energy standards improve, there is a trend towards greater airtightness. The problem is that as buildings are made more airtight, indoor air quality (IAQ) almost always deteriorates. In some countries, the practice of opening windows daily to ventilate can help a little, but some research (see Chapter 12, page 192) has shown that opening windows provides only a brief improvement of IAQ. In the UK, where buildings were traditionally very draughty, there is no similar custom of regularly purging stale air. New windows often have trickle vents in an attempt to address this problem, but these are arguably ineffective because people are quite often unaware of their existence or significance and they simply remain closed. Even if they are used correctly, the rate at which air is changed is dependent on how windy the conditions are.

A Passivhaus is many times more airtight than typical new builds, so a reliable and consistent method must be used to keep the indoor air fresh and healthy when the windows are closed. Passivhaus uses a carefully designed, highly efficient and quiet heat recovery ventilation system, known as mechanical ventilation with heat recovery (MVHR). In an MVHR system, no air is recirculated, only the heat is recovered and recirculated; and, if correctly designed and installed, there should be no noise or perceptible draught from the movement of air. The result is that IAQ in winter is maintained at a very good level. In the summertime, ventilation can be achieved by leaving windows tilted open and/or using the ventilation system. Chapter 12 explores in more detail how heat recovery ventilation works in a Passivhaus.

Designing correctly for airtightness, or minimal air leakage, is part of the Passivhaus architect's job (see Chapter 9). However, the Passivhaus airtightness standard is a particular challenge for contractors because once the airtightness layer has been created, it is very easy to damage it accidentally later in the build. To avoid this, everyone in the construction team, including subcontractors, needs to understand exactly what the airtightness layer is, why it is important, and what changes in working practice are needed to reliably create and protect it. Chapter 9 explores the challenges contractors face in delivering the airtightness standard onsite.

Annual space heat demand / heat load

These terms refer to the energy and the maximum power needed to heat your home. Achieving either the 15kWh/m2.aannual [specific] space heat (or cooling) demand – which represents around 90 per cent less space heating energy than in a typical UK building – or the 10W/m2 [specific] heat load is one of the key requirements for a Passivhaus (see Table 1.1, page 18). (Note that, unlike the heat load, the 'cooling load' requirement for a Passivhaus in a hot climate is not yet fully specified as part of the Passivhaus standard.) Some people ask why these requirements aren't made even lower. Why not completely design out the need for any space heating or cooling? While this is technically possible, it significantly increases the build costs for relatively little additional energy saving. The choice of 15kWh/m2.a represents an optimum point where the need for conventional central heating (or, in hot climates, air conditioning) is eliminated. Space heating options in a Passivhaus are discussed overleaf.

Annual primary energy demand

The 120kWh/m2.a annual [specific] primary energy demand requirement (see Table 1.1) is designed to ensure that consumption of energy for hot water, cooking, appliances, lighting and all other uses is efficient. It effectively makes it impossible to use internal heat gains from inefficient appliances or poorly designed hot-water pipework as a tactic to get around the 15kWh/m2.a space heating requirement. It also discourages the use of electricity for direct water heating (for instance, an immersion heater) and encourages the use of solar hot water where practicable. Eliminating excess heat gain from inefficient domestic hot water systems and appliances also has the benefit of reducing the risk of your house overheating in summer.

Working as a team – building trust between architect, builder and client

Working as a team may well sound like a clichéd aspiration, but it is an ideal we fall short of in many real-world builds. Being able to achieve an effective, trusting and cooperative working relationship between architect, builder and client is critical to the success of a Passivhaus build. In the same way that a Passivhaus build demands much attention to technical details, this 'human' detail is one that must also be addressed.

Typically, architects work on their designs with minimal input from those who will be tasked with building them. While this approach does not preclude a close, trusting relationship between the key parties, it does make it harder to achieve in practice. If the builder is involved in the initial stages of the project and has a meaningful input into the construction details, he or she should be able to help reduce the complexity of the build without affecting the aesthetic or the function. More importantly, early involvement of the builder will help to build trust and mutual respect with the architect. The builder is more likely to accept the design and to have a deeper understanding of its rationale.

Common misconceptions about Passivhaus buildings

While it is fairly easy to grasp what a Passivhaus is about, it remains an abstract matter for those of us who have never experienced one, and so most people find it hard to predict how they would feel about living in such a place. We have long experience of buildings that are draughty and hard to heat, or stuffy and tricky or expensive to keep cool. Many of the misconceptions about Passivhaus reflect this. Here are a few of the most common.

(Continues...)

Excerpted from The Passivhaus Handbook by Janet Cotterell, Adam Dadeby. Copyright © 2012 Janet Cotterell and Adam Dadeby. Excerpted by permission of UIT Cambridge Ltd.
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Details zur Ausgabe

• Verlag: Green Books
• Erscheinungsdatum: 2012
• Sprache: Englisch
• ISBN 10: 0857840193
• ISBN 13: 9780857840196
• Einband: Tapa blanda
• Anzahl der Seiten: 256
• Kontakt zum Hersteller: Nicht verfügbar
• Verantwortliche Person: Nicht verfügbar