Passive House Details

Solutions for High-Performance Design

Donald Corner, Jan Fillinger, Alison Kwok

• Verlag: Routledge
• Jahr: 2017
• ISBN:
  9781317339649
• Auflage: 1
• Thema: Architektur
• Thema: Nachhaltigkeit in der Architektur

Passive House Details introduces the concepts, principles, and design processes of building ultralow-energy buildings. The objective of this book is to provide design goals, research, analysis, systems, details, and inspiring images of some of the most energy-efficient, carbon-neutral, healthy, and satisfying buildings currently built in the region. Other topics included: heat transfer, moisture management, performance targets, and climatic zones. Illustrated with more than 375 color images, the book is a visual catalog of construction details, materials, and systems drawn from projects contributed from forty firms. Fourteen in-depth case studies demonstrate the most energy-efficient systems for foundations, walls, floors, roofs, windows, doors, and more.

CHAPTER 1

Design Process for an Optimized Enclosure

Architectural design is a complex and subtle process. It requires full intellectual engagement and is deeply satisfying when good solutions emerge. Design involves a combination of experience and insight. It is driven by precedent, springing from the accumulated knowledge of architects, owners, and builders in a particular culture or community. Creative insight allows that knowledge to be captured and transformed to serve new purposes.

Many of the best designs are those grounded in the sense of a region. There are characteristic architectures, for example, in New England and in the Pacific Northwest. They each have a set of recurring themes that are based on long-term performance in use and in place. These working traditions are the building blocks for higher-performance designs going forward. Early settlers in New England were challenged by the harsh climate. They responded with tight, concentric plans, carefully chosen openings, and attention to the surface–volume ratio of the building. New England traditions lend themselves directly to successful passive house designs in that region. Buildings in the Pacific Northwest are recognized for significant overhanging roof forms that shelter walls and windows from the rain. Overhangs remain a logical, cost-effective means to extend the longevity of a structure. Northwest houses were once heated with forest by-products, such as sawdust, burning virtually all day. Heat that was allowed to escape through the envelope prevented the accumulation of moisture inside the walls. Contemporary low-energy homes do not waste heat and strive to block airflows that carry water through any gaps in the weather shell. Drying outcomes are greatly improved by overhangs that deflect water away from the walls in the first place.

Good design is of great ecological significance. Buildings that work well, that are loved and cared for, stay in service longer. There is a tremendous amount of energy embodied in a building, locked into the materials and in the work that was done to process and assemble them. The longer a building stays in use, the greater the opportunity to recover that environmental investment. Life cycle cost analysis reflects favorably on sound investments in primary structure, elements that remain undisturbed through extended periods of use. A more critical analysis must be made regarding the weather shell and interior finishes—systems that are frequently replaced, at great expense of energy, because they have either degraded or simply fallen out of fashion. At the residential scale, primary structure, weather shell, and interior finish are largely provided in a single, integrated system. To control the long-term environmental footprint of a residential building requires thoughtful and appropriate investments in a durable, high-performance envelope.

Defining an effective building envelope is an essential part of the design process. The envelope is not a generic treatment wrapped around the building at the end of design, but something that evolves continuously along the way. The building envelope passes through all phases of design investigation. There must be careful analysis of precedent and the identification of performance goals and aesthetic objectives. There is schematic design—balancing solids and voids, attending to the placement and proportion of the openings. There is design development—selecting from alternative materials and systems while integrating them into a smoothly functioning whole. Finally, there are construction documents—the vehicle used to transfer this long, collaborative effort from the design studio to the project site.

The focus of this book is on the details, with recognition that they are specific products of the broad and inclusive process required to make good architecture. In order to provide this focus, this chapter presents a discussion of the design process that is limited to themes that are fundamental to high performance, measured by passive house standards; this is followed by a discussion of design development considerations, technical analyses for the envelope, and useful tools.

The design of a project—whether residential or non-residential—to passive house performance standards involves progressive definition and refinement in four major areas:

1. activity program and organization;

2. site and climate response;

3. performance of the building enclosure as a whole;

4. selection, integration, and refinement of the component parts.

The design process treats these considerations, not sequentially, but interactively, visiting and revisiting each set of issues in turn. Underlying all are considerations of project budget, as well as the materials and skills that are available and appropriate to the location. Passive house standards do not apply just to single-family residences, but the majority of passive house activity in North America to date has involved residential buildings. The majority of the projects featured in this book are also residential. Thus, the following discussion of the design process has a residential focus. This should not be interpreted as a bias toward residential design, but rather as a reflection of the wide diversity of design considerations encountered in non-residential projects.

ACTIVITIES

So that the performance of a passive house project can be optimized, and its costs controlled, the spaces within should accommodate the intended uses as efficiently as possible. Generally, the smaller the building, the smaller its environmental impacts. Accordingly, spaces should be of a size that is truly productive. Activity settings should be rehearsed using comparable furnishings and mapped to reveal what is needed to support the recurring events of daily life. Attention must be given to body measures, proximity, arrangement, clearances, and movement. The dining table, in its size and shape, is inextricably bound to the quality of the experience at a meal. Extra steps, taken repeatedly across an expanse of empty floor between the table and the kitchen, will consume energy on a variety of levels. There must also be adequate space for special occasions. Flexibility must be provided, so that a few everyday things can be moved aside when it is necessary to expand the table for Thanksgiving dinner.

The organization of parts within the whole must also be efficient. Circulation through a dwelling should pass along the edges of an activity setting rather than cutting a swath right through it. This requires careful attention to the relative position of rooms and the location of doors that join them. The shape and position of staircases have a tremendous influence on the efficiency of a plan. Good stairs depart from the social center of the public level and deliver residents to the logistical center of the private one. The gathering of bedrooms logically around this point of arrival eliminates the need for a long corridor. Privacy, in close proximity, can be enhanced by placing storage closets as thickened walls between the rooms.

Within the thermal envelope of a building, priority must be given to activity settings that really will receive year-round use. Expanded living areas that serve a special event or a particular season can be provided in buffer spaces that do not require continuous, active conditioning. Porches or readily accessible decks add to the generosity and spontaneity of a home while reducing the volume that must be fully controlled. Outside the building shell, design considerations for activity must include analysis of the comfort zone and the microclimate produced by adjacent structures.

There are many references that support and inform a human-centered approach to building design. As a framework and a starting point, the best single source remains A Pattern Language, by Christopher Alexander and his co-authors, Ishikawa, Silverstein, Jacobson, Fiksdahl-King, and Angel (1977). Liberally illustrated building examples have followed in publications by some of the co-authors, by their academic colleagues, and by the generations of students they have collectively influenced. There is an extensive behavior-based literature for multifamily housing design as well.

SITE AND CLIMATE

One of the first activities in building design is a thorough analysis of the potential site. The attributes of particular importance to a passive house project include:

• climate and microclimate:

– seasonal temperature and humidity patterns;

– diurnal temperature ranges;

– solar incidence on the site;

– wind patterns;

• physical structure:

– topography: advantageous but manageable slopes;

– water flows: surface and subsurface;

– vegetation: tree canopies;

– opportunities for access: construction and thereafter;

• regulatory context:

– property size and boundaries;

– buildable area: setbacks;

– height limits;

– permitted uses: zoning;

• architectural context:

– adjacent buildings: size and type;

– characteristic materials: sense of place.

When fortune smiles, a preliminary inventory of desirable characteristics can be used to select the best fit from a number of potential site options. It is clearly advantageous if a site supports the design preferences for a high-performance building. A site that faces south on the private side will allow major rooms to open to the sun and the outdoor space. Access from the north allows garages, car parking, entry vestibules, and service spaces to be clustered on that side. A passive house does not depend on these conditions, but they are frequently present in successful projects. Ultimately, buildings should develop a reciprocal relationship with the site. Site attributes should help to reduce the environmental stress on the building. The building, in turn, should improve the ecology and microclimate of the site.

Larger sites offer the opportunity to focus on the ideal position for the building. Can the approach and access be arranged so that the public and private sides of the house face in the preferred directions? Can the house be built above or against a slope? Each degree of tilt toward the sun acts like a change in latitude. Can the house be placed among deciduous trees that will admit sun in the winter and offer shade in the summer? Are there evergreen trees that block the winter winds? If such trees are not available initially, is there room to plant them? Do the principal vistas from the site align with the preferred orientation of the major rooms, or must there be a differentiation of on-site and off-site views?

As sites get smaller, and regulatory limits take effect, the choice of position may be severely limited. The critical question may become one of orientation. Is the preferred orientation possible? There are many neighborhoods in which the ends of the houses face the street, so that the longer edges can face the sun and a private garden. Zero-lot-line zoning may help to make this work. Solar access on smaller sites might be shaped by trees or buildings on adjacent parcels and, therefore, be out of the designer’s control. A skyline plot of obstacles can help determine if the shadows cast and solar access allowed are helpful or harmful, by season.

Finally, there may be the opportunity to consider the building configuration. Passive solar design techniques suggest that buildings be oriented toward the sun and elongated in the east–west direction to maximize solar gain through the illuminated façade. The elongated plan allows glass in the principal rooms to act as a passive collector of the sun’s energy. If the building has significant mass, the benefits of that gain can be extended throughout the day. By contrast, the narrow ends of the building receive less of the low sun from the east and the west, which is much more difficult to control. Frank Lloyd Wright’s iconic Solar Hemicycle House near Madison, Wisconsin, vividly demonstrates early passive solar design. South-facing windows provide for direct solar gain and daylighting of most activity areas. An earth berm against the curving north wall provides winter protection. The stone in that wall and the concrete floors provide mass for thermal storage. The entire house celebrates access to the sunny terrace surrounded by the signature curve. However, with little insulation in the walls and roof, and without night shutters on the windows, the house gives back much of what it gains from the sun.

A passive house design, as distinguished from a passive solar design, does not imply a house that is heated by the sun. A passive house relies on a high-performance envelope to reduce energy demands for heating and cooling. Guidelines for the shape of the building encourage compact, non-elongated forms with a low surface-to-volume ratio, so that there is less area through which heat losses can occur. These principles extend beyond single-family houses to retail, office, civic, and education buildings. Multifamily apartments in which the units shelter each other offer a particular opportunity for passive house design. Site and orientation still come into play in a passive house, but the building does not rely on them to deliver a high level of energy harvest. Well-placed windows provide useful gains during the winter, in addition to daylight, views, and a temporal connection to the outdoors. Solar gains cannot be allowed to create a demand for cooling energy. Whether by deciduous trees or adjustable building components, there must be external shading during the overheated periods.

The advice to “insulate before you insolate” applies to both passive solar and passive house design. These principles and practices can work together. The key is to drive down total demand by constructing a well-insulated, airtight envelope in both cases. The principal activities of the interior must be arranged so that as many as possible enjoy a preferred exposure within the limits of a compact form. In climates with a high diurnal temperature range, flushing the building with cool air at night may bring passive cooling. Passive house designers are cautious about the size and location of windows, but, with careful study, it may be possible to shift window positions slightly to take advantage of prevailing breezes for cross ventilation. The building may have a positive influence on the wind patterns, as in the classic case of a screened porch placed in the path of cooling air that accelerates in its journey around the corner of a building.

Elongation of a passive house may apply best to that larger set of activity spaces that are not contained inside the thermally isolated core. Transitional space, shaded terraces, and outdoor rooms can enhance the appreciation of the site. If they are stretched out to the east and the west, they can help to protect the building from over heating and not interfere with winter sun. Seasonal migration to extended living spaces across the site is a valuable alternative to overglazing as a means to connect to nature.

PERFORMANCE OF THE WHOLE

The design of a passive house represents a paradigm shift in architectural design. Previously, the typical process was driven by considerations of human activity, the site, and the formal intentions of...