There are usually many factors and conditions which contribute to the selection of the appropriate type of wood for an interior architectural design project. This might include the intended use of the space, cost, hardwood or softwood, relative stability, local and environmental factors, and legislation.
The Architectural Woodwork Standards provides comprehensive guidance and information on the characteristics of wood, and in this article we’ll look specifically at the types of wood to consider for your architectural woodwork project.
About Lumber in Architectural Woodwork
Lumber used in architectural woodwork is either:
- Hardwood – i.e. lumber from angiosperms (flowering plants with broad leaves). Of the 200,000 species of angiosperm on earth, around 900 species are commonly used for lumber or veneer.
- Softwood – i.e. lumber from gymnosperms (seed-producing plants with needle-like leaves), about 600 of which are coniferous trees such as pine, spruce and fir. Around 80% of the world’s lumber comes from gymnosperms.
The hardwood/softwood classification can seem like a misnomer as the names don’t refer to how hard or soft the wood is. For example, balsa is a hardwood that is softer than many softwoods, and yew is a softwood that is harder than many hardwoods. Hardness also varies greatly between species within each group. Both hardwood and softwood are graded. Hardwood is graded on the percentage of usable material, and softwood is graded on strength and appearance.
Biological and Aesthetic Characteristics of Different Types of Wood
With so many types of wood to choose from, it’s important to understand the main differences, both aesthetic and biological, between them. This knowledge will help you choose the right type of wood for your interior woodwork project.
- Annual growth rings – Most wood species grown in temperate climates produce well-defined annual growth rings. These rings are created by the difference in density and color between wood formed early and wood formed late in the growing season, and provide the grain or characteristic pattern of the wood when it’s sawed. Distinguishing features between wood species are enhanced by the differences in growth ring formation. Some tropical species experience year-long, even growth which may result in less obvious growth rings.
- Heartwood – Heartwood consists of inactive cells formed by changes in the living cells of the inner sapwood rings. Material deposited in these cells usually result in lumber which is more durable when exposed to weather.
- Medullary rays – Medullary rays extend radially from the center of a log toward the circumference, and serve mainly to store and transport food. They vary in height and produce the fleck effect.
- Photodegradation – Photodegradation affects the pigment of the wood caused by exposure to either sun or artificial light. If an entire face is exposed, it will normally photodegrade uniformly, whereas partially exposed surfaces might result in non-uniform photodegradation. Some woods, such as cherry and walnut, are more susceptible to photodegradation than others, and extra care should be taken to protect against the effects of non-uniform photodegradation.
- Oxidation – Oxidation is the effect on the appearance of the woods outer surface caused by exposure to atmosphere, similar to the browning of freshly cut fruit. For example, hardwoods can develop deep yellow to reddish-brown discolorations on the surface of the wood when exposed to air immediately after sawing or peeling, and some species develop these discolorations during air-seasoning. Proper selection, sanding, and finishing can minimize the effects of oxidation.
Related: A Guide to Wood Veneers
There is clearly a lot of choice when it comes to the different aesthetic characteristics of wood. Different wood species vary, different logs from the same tree vary, and even different boards from the same log vary. Aesthetic considerations when it comes to specifying wood for your interior woodwork project are normally influenced by:
- Color – not just the basic color of the species, but also how it might be enhanced during finishing.
- Heartwood and sapwood – the color of wood within a tree varies between the lighter “sapwood” (the outer layers of the tree that transport sap) and the “heartwood” (the inner layers filled with natural deposits). Sapwood can be stained to blend with the heartwood.
- Grain – the appearance produced by the arrangement of wood fibers and pores of the species. Lumber grain may not match veneer grain.
- Open grain and closed grain – open grain woods usually have a distinct grain pattern, while closed-grain woods have a more even grain. The size and distribution of the cellular structure of the wood influences the appearance and uniformity.
- Grain patterns – different species of wood produce different grain patterns, and there are variations of grain patterns within a species. It isn’t possible to select solid lumber cuttings within a species by grain and color in the same way that you would select veneers.
- Finishing characteristics – wood varies considerably in how it reacts to different finishing processes. For example, some woods will accept fillers when some won’t, and some will show greater contrast between the “early wood” and the “late wood” when stained than others. It’s important to take the required finish into consideration when selecting your wood. Lumber doesn’t normally accept transparent finishes in the same way that veneer does, and may require special finishing techniques.
What to Consider When Choosing Wood for Your Interior Woodwork Project
There are a few things to consider when it comes to choosing the right type of wood for your architectural woodwork project, including:
- Cost – The cost of lumber is influenced by supply and demand, both of which are constantly changing.
- Hardness – Consider the ability of the wood species to sustain stress; resist indentation, abuse and wear; and carry its anticipated load in applications such as shelving and structural members.
- Dimensional stability – In areas where humidity conditions vary widely and where design or fabrication of a wood product does not allow free movement or the use of sheet products, dimensional stability should be strongly considered.
In order to simplify things, the AWI section on lumber contains a Comparative Table of Wood Species, showing relevant characteristics of the main species of domestic and foreign woods used by the architectural woodwork industry.
This table will help you make an informed selection of the type of wood you need.
Specifying Lumber Using the Architectural Woodwork Standards
As shown, a design professional has a wide variety of foreign and domestic species of wood to choose from. The unique quality that wood imparts is that each type of wood has its own distinguishing characteristics. Once the species is chosen, its effectiveness can vary according to the manner in which it is sawn, sliced as veneer, treated, and finished. The Architectural Woodwork Standards aims to advise you on the comparisons, considerations, and species which should be evaluated before decisions are made and specifications are written. An informed choice will reward your client with the best possible performance by a natural building material.
You’ll find all the information and guidance you need about lumber in the Architectural Woodwork Standards. This section covers lumber in detail, as well as compliance requirements.
Contact us to find out more about how you can join the American Woodwork Institute’s Quality Certification Program and build your reputation for high-quality woodwork.