Frequent Terms Click on to see explanations
Glued laminated timber – glulam – is manufactured by bonding together prepared laminations of solid timber so that all have their grain arranged in an essentially parallel, longitudinal direction. This produces straight or curved members that are larger and longer than may be obtained simply by sawing a normal log. Further information is provided in Introducing Glulam.
BS EN 14080 addresses adhesives, and your standard production will automatically use one of those included in the standard, so actually it is unnecessary to specify the adhesives separately. Special products, including those for Service Class 3 (external), require careful consideration and possibly different adhesive types, still covered by various BS EN Standards. For more information on glulam adhesives generally, see Principal choices - Adhesives
Much larger section sizes than those available as standard stock, as well as a range of built-up sections e.g. I. H. T. X, are available in bespoke glulam. Special milling can even provide curved cross-sections e.g. aerofoils. See - Principal choices – Available dimensional ranges
Curves and complex shapes are a valuable feature. It is usually necessary to reduce the thickness of the individual laminations so these are non-standards, meaning that potential manufacturers need to be contacted at the preliminary design stages. Avoiding a great variety of shapes in the project will reduce the cost of setting up jigs. See Principal choices – curved glulam for more information
Design – Architectural concepts
Some hints and general guidance are given in More about glulam – Concept design.
It should also be helpful to view our Case Studies
– these are subdivided into seven broad categories of structural form. Individual GLTA Members’ websites also carry useful case studies of their own projects. At www.TRADA.co.uk
there is a very wide range of timber building case studies, involving both glulam and other woo-based materials. These are free-to-view after a simple registration process.
Design – Structural aspects
This should be according to BS EN 1995-1-1, its Normative Annexes, its BS National Annex and the BS PD 6693 Support Document. These standards are highly recommended for UK projects both for ease of supply and also for implementation of the most up-to-date design theories and test data. Fire resistance, if required, is structurally designed according to BS EN 1995-1-2 whilst timber bridges are designed to BS EN 1995-2 taken in conjunction with BS EN 1995-1-1. For more information see More about glulam – Design data
For the structural design of glulam, the essential harmonised standard for use with Eurocode 5 is Timber structures – Glued laminated timber – Requirements – BS EN 14080. This in turn contains a number of “Normative references” (references to other BS EN’s) that should be consulted as appropriate. For more advice on structural design in general, see More about glulam – Design data
Longevity – what is the track record for glulam?
The longevity of glulam is well-established. There are documented examples of its use around two hundred years ago and a number of structures more than 150 years old are still standing, some in the UK. In its modern format, using waterproof synthetic resin adhesives, many examples remain in use from dates shortly after the Second World War when waterproof synthetic resin adhesives became available for civilian applications.
Marking and certification
In the UK and the Republic of Ireland, compliance with the Construction Products Directive may be demonstrated via third party certification from Notified Bodies, with suitable schemes already prepared for glulam. Elsewhere in the CEN zone there are comparable systems whereby “CE” marking on components and/or on the certificates accompanying deliveries is established. Further information on marking and certification is given in More about glulam – Design data
. Notified bodies include BM TRADA Certification. Where for architectural reasons the finished elements remain visible during the service of the building, paper-based certification rather than marking on the product is acceptable.
Ready-made columns and posts
Standard stock round columns are available for immediate delivery in a limited rage of dimensions and lengths. Some manufacturers also offer a “cut-to-length” service based on these. For built-up columns/posts/stanchions etc. See - Principal choices – Available dimensional ranges
. For round-section columns – hollow, including octagonal, tapered and double tapered along length, as bespoke items. For more information see - More about glulam – Concept design
Sections and lengths greater than standard stock beams
Much larger cross-section sizes as well as a range of built-up sections e.g. I. H. T. X, are available in bespoke glulam. Special milling can even provide curved cross-sections e.g. aerofoils. See - Principal choices – Available dimensional ranges.
What are the principal timber species used in the glulam that is supplied in the UK? Common softwood alternatives include European redwood (pine); Larch; Douglas fir. Hardwood choices include temperate species, especially European oak, and tropical species such as Iroko. For more information see Principal choices – Timber species
Standard stock items
How may I specify these and what are the size limits? See Specification hints
. Please do not dismiss the idea of using glulam if standard stock does not meet your needs, since bespoke glulam may be manufactured and supplied quite quickly.
Strength class suffixes “h” and “c”
see More about glulam – Design data
for discussion of BS EN 1194 Strength Class number affixes “h” and “c” e.g. GL28 c. The “c” sub-class utilises forest products more efficiently than the “h” sub-class, so it should be preferred when strength and stiffness values permit.
GL24 is most readily available strtength class. GL28 and GL32 are also commonly available, particularly for bespoke glulam. More about glulam – Design data
includes explanations and additional options for Strength classes.
A wide range of surface finishes is readily available. Colours may be translucent or opaque, and in natural wood tones or other tints. Consider whether, simply because it is laminated timber, it has to be “wood shades”? Darker tones generally tend to be less affected by weathering and by degradation from sunlight. Manufacturers offer finishing services that are much more effectively applied in the factory or workshop, prior to delivery. The stages at which further decorative and water-repellent coats are to be added depends upon the construction sequence. See Principal choices – Appearance and surface finishes
Transport and delivery
Members of up to 42 m are transported by road in the UK. Vehicle regulations are the same as for structural steel. Dependent upon site location, other delivery possibilities may include water transport. See More about glulam – Supplying your glulam
. After delivery, it is important to maintain the carefully-produced even moisture content until the project is enclosed. The same section of this web gives further advice.