American white oak, which is native only to the eastern US and south-east Canada, is a group of about eight Quercus species, mainly Quercus alba, which are sold together either as northern white oak or southern white oak. However, the white oaks occur less frequently than American red oak, which is more dominant and a favourite of US domestic consumers.
In the US, white oak accounts for about 13.5% of the hardwood forest resource, making it one of the most available species, especially for export. In fact, latest statistics show oaks (red and white) accounting for about half American sawn timber production.
Oaks vary in grain characteristic and colours due to many factors, including site growing conditions and methods of sawmilling, along with the intrinsic differences between the various sub-species. European oaks, for example, tend to be darker in colour and less available in straight grain. American oaks, which grow to greater heights, offer longer lengths. They are also dried to a lower moisture content (mc) (around 6-8% as against 10-12%).
The colour of white oak may also vary from north to south. The sapwood is light or almost white and the heartwood is light to brown. The heartwood is durable and naturally resists insect attack and rot from humid conditions. Under the US’s National Hardwood Lumber Association grading rules, sapwood is not a defect and, in many interior applications, it can be used as a feature. White oak, being hard, is particularly suitable for flooring in high traffic areas. The wood is mostly straight grained with a medium to coarse texture and the wood rays are longer than in red oak, which produce a more pronounced figure.
Architect Ciaran O'Connor chose white oak for the Marine Institute in Galway
White oak machines, nails and screws well, although pre-boring is advised. Its adhesive properties are variable, but it stains and polishes to a good finish. The wood dries slowly and care is needed to avoid splitting and checking and, due to its high shrinkage, it can be susceptible to movement in performance. The wood is hard and heavy, with medium bending and crushing strength and is low in stiffness, but very good in steam bending. It can vary in texture, characteristics and properties according to the growing region. Southern white oak is faster grown, with wide growth rings, and tends to be harder and heavier.
The price of white oak is generally more affected by export markets than red oak because a higher percentage is exported around the world. American white oak is the leading hardwood species imported from North America by many European markets such as Spain and the UK. Sawn lumber and veneer of white oak are both readily available, which is an important issue for specifiers or manufacturers wishing to match solid wood with veneer. Most US exporters offer white oak sawn lumber, and all UK temperate hardwood importers carry it in stock.
Furniture and joinery markets around the world are still showing a preference for oak above any other single temperate hardwood species and American white oak is one of the most sought after and readily available. As a consequence there has been a tendency by oak producers in other regions to cash in and re-name theirs as “white” oak.
End uses for the species range from the esoteric to the spectacular. Its imperviousness to moisture makes it a barrel material of choice among American whisky and wine producers and it has been used in flagship construction projects worldwide.
In the Portcullis House parliamentary building in London, Michael Hopkins and Partners, with engineers Arup, solved a technical problem in a dramatic way by exploiting the strength to weight ratio of American white oak.
The central courtyard atrium was originally conceived as a steel structure set on six columns. However, the architects switched to “traditional” oak to satisfy their desire to reflect the character of the nearby Palace of Westminster, and to keep the individual struts of the lattice roof to a minimum mass, allowing maximum penetration of natural light. The result, which is one of the most complex timber roofs in Europe, is based on a system of stainless steel node joints and glass panels with a consistent curvature, and set a standard for oak in architecture.
Also in the UK, architect Simon Conder used American white oak, which he “learned to trust for its consistency in grain and tremendous warmth”, in his 2005 Wood Award-winning Pinions Barn (Timber Building Spring 2006).
White oak was chosen for the upper storey floors of Pinions Barn
Abroad, Spanish architects have long appreciated oak as a material that works well in the arid climate of the Iberian Peninsular and 80% of all American hardwood exported to Spain is white oak. In Ireland, Ciaran O’Connor at the Office of Public Works chose white oak for two signature buildings in recent years – the Marine Institute in Galway (Timber Building Summer 2006) and the EU Veterinary headquarters outside Dublin. And in Scandinavia, Danish architect Henning Larsen specified white oak for its uniform texture and colour for the flooring in his mammoth opera house of 41,000m2 in Copenhagen.
Information on white oak and all American hardwood species is available at www.ahec-europe.org
Keywords: American white oak AHEC
