The Basics of Eco-House Construction
There are many different ways to build an eco-house, just as there are many different structures for most modern conventional houses. Determining which is the best (and greenest) option is a matter for debate, but architectural and personal preference, geographic location, current trends and, of course, cost all play an important part. Some of the most traditional materials and methods are outlined here, along with more recent developments.
Mixing Green and Conventional Materials
Building an entirely green house or renovating an existing structure to completely green specifications is rarely a practical option. Instead, it is more likely that a green solution is reached by combining green and conventional methods. When considering a green new-build, such as a straw-bale house for example, using a solid concrete foundation could be the best option because the risk of subsidence and egress of moisture is greatly reduced. Equally, with a renovation project, using thermally efficient blocks for an extension will improve the green credentials of a house, even though much of the existing structure may be made from less green alternatives.
An Ungreen Means to a Green End
There is often a conflict of interest when it comes to determining what is and what isn't "green." While the structural elements of an eco-house may ultimately perform in an energy efficient way, their initial production may involve the use of materials or techniques that are far from ecologically sound. A house constructed entirely from poured concrete, for example, with thick, well-insulated walls, is a green option in the long term. However, the initial outlay of energy to produce the concrete in the first place is high—and consequently very ungreen.
Types of Foundation
Many green homes are built on conventional foundations, predominantly because they offer a sound defense against subsidence and damp. However, it is still possible to use less conventional foundations for a green home. The two examples shown here have been used successfully in straw-bale constructions. The use of rammed earth held in place by old car tires, and compacted rubble reinforced with steel rods, clearly demonstrate that concrete is by no means the only material capable of providing a solid foundation for a house structure.
Rammed-earth foundations consist of compacted subsoil. For the rammed earth to form a solid base for the structure's walls, it needs to be contained within an effective mold. A modern example of a type of mold is shown here — the compacted earth is being contained within old car tires. Image 2 shows the cross section of a rammed-earth tire foundation.
In this example, a trench is filled with compacted rubble or stone. Some blockwork or natural stone is required above ground level to provide a solid base for the structure. Rubble foundations form an ideal base for a straw-bale home, as reinforced steel bars can be buried into the rubble for extra strength and support. Image 2 shows the cross section of a rubble foundation.
Types of Roofing
In a structural sense, most green roofs follow the same design as conventional roofs, with the main difference being that any materials must be obtained from sustainable sources. Wood is the most common component and should be sourced from responsibly managed forests. Equally, roof coverings must be green—wooden shingles are a clear green alternative to concrete tiles, and thatch is a roofing material with excellent green credentials.
Green Living Roof
A green living roof is a truly "green" option as the covered surface consists of plant matter. A living roof offers good insulation, retains a high percentage of rainwater (reducing stormwater run-off), and provides a habitat for wildlife. However, the main roof structure must be strong enough to support its weight — a key concern, especially if considering a retrospective fit.
Extensive Green Living Roof
A green living roof may be described as "extensive" (shown here) or "intensive." An extensive roof is typically planted with sedum, which requires a low-level of maintenance for use on often inaccessible roofs. An intensive roof is similar in nature to a roof garden: it has good access and a greater variety of plants. Higher maintenance, however, is usually required.
Types of Walls
A green structure must score highly in terms of sustainability and performance — the materials should come from a sustainable source and the building should be well-insulated. Some conventional structures, such as modern timber-framed houses, can be considered green as long as they conform to these principles. The alternative methods described here, however, arguably come closest to the ideal of a truly green construction.
Wood Post and Beam
Large wooden timbers are used to create the loadbearing structure of the house. Wooden post and beam differs from a conventional timber-framed house in that the size of the timbers often means they form an integral part of the aesthetic finish of the house, and may be visible from the inside, outside, or both. Straw bales may be used as infill.
After wood, earth- or soil-based structures make up the next biggest category of green structures. Compressed soil, usually in the form of blocks, is used to build the structural walls of the home. Although modern building standards question the integrity of such structures, history has shown that they can easily withstand a variety of climates.
Bales can be used as either loadbearing blocks or infill for a timber-framed house. Although straw-bale constructions have been built around the globe, climate is an important consideration as it is vital that water is kept out of the structure. Straw bales are a perfect example of what is essentially a waste product being used in major construction.
Structural Insulated Panel
This type of eco-house construction is an example of green building at its most developed. Highly efficient insulation is integrated into building boards to form large panels. These panels can then be clipped together in a custom-made design. Structural insulated panels may be used to form the roof structure as well as the walls of a house.
Copyright 2009 Dorling Kindersley Limited
Text copyright 2009 Julian Cassell and Peter Parham