Using the generic term ‘wood’ is analogous to using the word ‘food’. Wood covers an estimated global diversity of over 20,000 woody species of plant. A few thousand of these are commercially used and these are as diverse as the cultures that use them. Wherever we look, the use of wood is deeply rooted in human history and indeed in everything we do today.
When I think of ‘wood’ I think of an ingredient that can be transformed from a renewable material resource into a gourmet feast of colour, texture, and pattern or used simply as a mass-produced component that we order from the builders’ merchant. The designs we dream up sometimes rely on individual trees where we want something special, but we are most likely to rely on standard sawn or Planed All Round Timber (PAR) sizes harvested and converted from forest trees and readily connectable using metal fixings like a Meccano set. Whichever way we use wood we must only specify sustainably sourced timber from schemes such as the Forest Stewardship Council (FSC) or Forest Law Enforcement, Governance and Trade (FLEGT) to help protect them as a regenerative resource. Thankfully most timber suppliers now endorse these schemes and provide a range of timber products with trusted certification.
There is no other material like wood and it is so easy to use once you have familiarized yourself with its properties and available sizes, which do vary considerably from softwood to hardwood and across the available species. As an architect, this is what makes designing, specifying, making joinery and furniture and especially working with those skilled in the art of woodwork in all its forms, so rewarding.
The versatility of the material is as diverse as its applications. The relative lightness of this material is balanced by its strength and for some species, the ratio of these is better than steel. When exposed as a finish there are exquisite tactile qualities to choose from as well as a softness in light which is so appealing in exposed CLT construction. There are now multi-occupancy buildings where CLT has been used as a wall or ceiling finish – even the stairs and furniture can be made from this material. These advantages of using the wood stem from the connections to the forest that is then recreated itself in the home.
Cutting edge zero-carbon houses need to incorporate as much wood as possible to sequester carbon. This is important as it is the most practical way to reduce or even produce a negative carbon footprint. But the mindset for sustainable thinking starts with choosing the right materials. Foundations can be minimised using light timber framing and by making the most of the engineered timber products available which now play a significant role in MMC. I also see more interest in systems that are hybrid in nature and incorporate steel connections and consider thermal mass to assist with mitigating overheating now that the new Approved Document O must be met. Meeting the overall building physics strategy is essential to futureproof the asset so that it is insurable, mortgageable and comfortable to live in.
Moving up the scale, multi-occupancy mid-rise apartments can be constructed in timber frames or CLT but architects and engineers must understand the material and its possibilities and limitations. A decade ago, when low U-values became central to developers’ sustainability ambitions and Approved Document L of the Building Regulations cranked up demands for lower U-values, the Structural Timber Association (STA) began to develop new high performance-tested wall, floor and roof types to address this. These now form pattern books available for download on their website.
Architects’ demands on timber frame-based building systems must now change to align with the requirements of the Building Safety Bill. Design teams are now expected to demonstrate that they have the relevant experience and expertise to design buildings and are expected to use comprehensively tested systems and to pass Gateway 2. No home should be built unless it is constructed safely and competently and, of course, can be maintained as such thereafter. This is foremost for the protection of life enshrined in the Approved Documents or Building Regulations but also – and of rising importance for insurers – is the robustness of fire protection for the building as an asset.
For structural timber or any other MMC system for that matter, the complete assembly of parts and systems forming a multi-occupancy building must meet the performance requirements for fire, airtightness and acoustic performance as a whole. This must be done within the context of changing guidance like the impending changes to BS EN 9991, the forthcoming updates to Approved Documents B and L of the Building Regulations, updated Future Homes Standards and other guidance which is generally becoming more prescriptive.
The insurance industry has raised concerns about the protection of timber structures from fire and water ingress and the STA has done much to put the timber frame industry at the forefront of addressing these issues. However, it is worth reflecting that the principles of fire safety also apply to other MMC construction systems like those that use cold or hot rolled steel framing or those built as volumetric units. Architects are very reliant on the technical know-how and expertise of manufacturers who design and test their own systems or on fire engineering specialists who form part of the design team. Encouragingly the STA has pooled much of the test information from timber frame manufacturers into one place on their website to add to their own.
We cannot live without healthy forests and perhaps many of us cannot live without wood in our lives, whether that be a timber-framed house or everyday furniture. We must make sure that these homes are constructed to the very highest technical standards and as buildings that must also play a big part in the fight against climate change.