Engineered Timber is enjoying a new lease of life. Glulam is perhaps the first form to be widely adopted and remains the most versatile. LVL (Laminated Veneer Lumber) and its derivatives have been developed more recently and have special qualities. This page comments on structural forms with rules of thumb for initial sizing.

Glulam has been developed over many years but improvements in manufacturing techniques have reduced costs and increased its viable range. It is the original engineered form of wood and is made by bonding together readily available section sizes - maximum 45mm thick.

Glue laminated timber is available in straight or curved profiles. Size is limited only by transport considerations and custom made shapes offer unparalleled versatility. Appearance is an important attribute. Continental manufacturers dominate the market but a few specialist British companies have limited capacity mainly used for unusual species (or shapes). Whitewood (Spruce) is the preferred material but Redwood is available at a premium. Most beams have 45mm laminae but some 33.3mm multiples are supplied.

For curved profiles lamination thicknesses are reduced to facilitate bending - say approx R/180.

Laminated Veneer Lumber is made from 3mm veneers with the grain parallel to the span. Kerto is made from Whitewood in Finland in blanks 26000 long x 1800 wide and up to 75mm thick.

It is then divided into standard sizes for ease of specification and handling but conversion can be to suit particular projects. Strength properties are higher than Glulam but its appearance is not normally considered as attractive.

The cost is generally lower than Glulam.

Hand-made ply-web beams enjoyed popularity in the 50's & 60's and were largely eclipsed by the demise of flat roofed buildings.

A significant revival is being experienced led by exponential growth in North America. Automated manufacturing methods have reduced the costs of a neater product. They form close centre (400 & 600mm) joist and rafter systems and are particularly suitable for floors. They are stable, uniform and in greater lengths and depths than solid timber. This can save intermediate wall and foundation costs. Installation is faster and more accurate. The finished floor is free from squeaks and other shrinking related problems. As rafters the improved spans create more usable roof space with higher levels of insulation.

Simply supported straight beams are widely used for purlins, lintels, flat roof joists and similar applications. Relatively light weight combined with ease of fixing make the use of timber popular with contractors and visually attractive.

Simply supported beams are usually deflection governed in design. It follows that beams which are continuous over multiple supports are more efficient with consequent cost savings. Care will, however, be needed to allow for the changed distribution of loading on the support structure.

Some alternative locations for local trimming or longer span support.

For roofs that are nominally flat a generous fall is strongly recommended. Timber beams can be tapered from one end or both ways from centre.

This can be done with or without a camber which can considerably enhance the appearence of beams which might otherwise look quite deep mid span.

It is easy to taper Glulam & LVL. Balconies, canopies and larger roofs will look better trimmed to a structurally efficient profile.

Depth ratios are approximate to assist preliminary assessment of proportions. For breadth (thickness) assume approx H/5.