Timber construction allows for a range of design solutions to
achieve environmentally friendly housing in all climate zones.
Wooden structures have been used in all kinds of building types for many years. lightweight timber construction has a long history and it is the most common house construction type. When it comes from genuinely sustainable sources, timber has the potential to provide a renewable building material that stores carbon in its production.
One of the key advantages of timber is that it provides an adaptive material for use in all climatic zones. This fact sheet deals with lightweight timber constructions that are climatically appropriate for Australia.
The lightweight timber house can provide cost effective and flexible design options. Just as the high mass construction materials are most effectively employed when used as part of appropriate design strategies, so there are many situations where a lightweight building may result in a low lifecycle energy use (eg. hot, humid climates, sloping or shaded sites).
Timber frames can support internal and external walls, floors and roofs. A variety of non-structural claddings, linings and finishes can be used such as weatherboards, timber fiber products, or non timber products such as brick veneer, fiber cement sheet or metal.
Lightweight timber houses are well suited to stilt construction and similar design approaches intended to minimize site disruption. Framed structures lend themselves to making houses with diverse openings that provide light and natural ventilation by careful window, door and ventilator placement. Timber provides an adaptive material for use in all climatic zones.
Thermal mass
In general timber has low thermal mass. There are hardwoods that have similar densities to concrete but these are not common building materials. Thermal mass can be built into lightweight timber constructions if a particular design requires it using elements such as:
> Concrete slabs
> Masonry features
> Water tanks integrated into walls or floors.
Sound insulation
The sound insulation of walls is usually obtained by providing a barrier of sufficient mass to absorb the sound energy. In lightweight timber constructions the wall cavities provide
a cushion of air that absorbs some of the sound energy, and as long as here are no rigid bridging’s to transmit the energy this can be a reasonably effective barrier. Acoustic barriers can be supplemented by placing insulation materials in the wall cavity and this also helps to reduce the drumming effect of large sheets of lining material.
Environmental impacts
Timber is a renewable building resource that absorbs carbon it its production. A lightweight timber construction can be built for deconstruction or easy dismantling, and timbers from the construction re-used or recycled at the end of its use in the building. [See: 5.3 Waste Minimization]
Timber is completely biodegradable and can even be composted if no re-use application can be found. Timber building products offer an opportunity to sequester carbon in the built environment, complementing efforts to mitigate global warming with carbon abatement schemes using timber plantations (typically, pine) to absorb carbon from the atmosphere.
Although it is a low greenhouse emission product in principle, transport and manufacturing processes can add significantly to the overall emissions associated with typical modern timber construction. Fundamentally, timber construction has very low greenhouse gas emissions but the more highly engineered and processed it is the more there is potential for significant emissions. Nevertheless, lightweight timber construction is often a sustainable option for housing.
Appearance
Like most natural materials that have not undergone a lot of industrial processing timber possesses an attractiveness that people readily relate to. Its range of colour, grain and texture make it a material with qualities that people generally find visually pleasing and enjoyable to touch.
Timber houses can range in appearance from the ultra modern to the traditional weatherboard house. Depending on the cladding used, the appearance may express the timber construction or disguise it (most timber framed houses in Australia are finished in brick veneer).
Timber construction allows for a range of design solutions to achieve environmentally friendly housing in all climatic zones. Timber framed houses can be found in very cold climates such as Scandinavia and Canada through to the very hot tropical climates of South East Asia, and their appearance will vary according to the climate.
Buildability, availability and cost
Lightweight timber construction is relatively simple to build. The typical interpretation of lightweight construction mostly encompasses the use of stud frames. Contractors are familiar with timber in this context and are comfortable using it. They find it easy to handle, easy to nail and easy to adjust. This contributes to affordable labour costs, and means that construction is quicker.
Less typical uses of timber for lightweight construction may carry a cost premium but on the whole timber structures are affordable to build in the short-term and with good design can provide a dwelling with low operational
Structural capability
Timber has good compressive strength but is strongest in tension. Structural design techniques exploit this characteristic that can be clearly seen in the design of roof trusses.
As well as solid timber there are many products that are composites or made of components that can be used in lightweight construction. These include plywood, particle board, fibreboard and engineered products such as glue laminated timber (Glulam) and Laminated Veneer Lumber (LVL). Particularly when used internally, care should be taken to ensure that composite timber products do not contain adhesives that compromise indoor air quality.
There is a timber product to meet most structural requirements, and engineered timber products can be manufactured to meet specified structural requirements.
Joints and connections
There are many types of traditional joints and a professional joiner or carpenter will use the most appropriate for a specific construction.
Timber frames and trusses can also be purchased ready fabricated. A common joining system is a nail plate that is a metal plate with integral nail shapes, or holes for nails, designed to join the timbers together.
Durability and moisture resistance
Timber is an organic material and deteriorates due to weathering. The main way of preventing weathering is protection of the timber surface. This may be achieved by appropriate design detailing, so that the timber remains dry or sheds water quickly. It may be achieved by treatment with an appropriate surface coating of oil, varnish or paint. Such coatings on external timber components of buildings generally need replacing every 5-7 years.
Weathering can be reduced by the selection of durable timber species in the first instance. Over a forty year life a fully maintained timber clad building will require less embodied energy than common alternatives, see table below.
A lightweight timber construction can have a very long life, making the dwelling more valuable both from an economic and environmental perspective. This can be achieved using appropriate design, building practices and detailing.
Toxicity and breathability
Timber is generally non-toxic. Provided it is not sealed with material that is impervious to air it maintains its breathability. The durability of the timbers used in the lightweight construction can be improved by treatments. Very low VOC treatments are readily available nowadays and most are water rather than solvent based.
Finishes
Finishes can be applied to increase timber’s resilience: to make it more durable in external applications, to protect it from the elements, or to increase wear resistance
for internal applications (such as varnish on floors). There are a wide range of finishing products on the market with a number of environmentally friendly water based finishes emerging that make timber more durable whilst complementing its aesthetic beauty.
