Grand Designs Extras Kevin's Column: Wood

Date Published:

09/03/2009

In his first column in a new series exploring building materials, Kevin McCloud looks at the ways in which the wood we know and love is becoming ever stronger and more versatile

Wood. Now there’s a healthy product. Grown in the quiet solitude of a forest with no fertilizers or added colourants; a carbon store that locks up CO2 for as long as the wood remains in use as something helpful, such as a book or a chair or this magazine. You would have thought the tree had been invented by God to help get us out of the environmental mess we’re in.

Ever since man discovered how to club something to death, wood has proved useful. Men have built temples, ships and siege engines from minimally processed bits of tree. So what are we up to taking this perfectly serviceable and abundant material and messing around with it to produce something called ‘engineered timber’? What’s wrong with the real thing? After all, Ben Law, he of the house in the woods featured on Grand Designs, established with the University of Sussex that the moment you saw up a round pole of tree into planks or square-section lengths, the timber begins to lose its strength. A wavy branch will always be stronger than the nice square-edged beam that can be cut from it, simply because the grain in the branch, which gives it flex and strength, follows the eccentric shape of the branch, not the beam.

This fact, the wonkiness of wood if you like, its desire to twist as it dries, for the fibres to deform, has bedeviled carpenters ever since that first caveman’s club had a slight kink. It is the reason why oak-framed buildings look the way they do, braced, pegged and jointed in all manner of clever ways to counter the twisting and shrinking – and why we have plywood. We generally like our buildings square and upright and our floors to be flat and level, not made from a raft of round poles strapped together. We want conformity and we want wood to do what it’s told.

Depending on the glues and sealants used, plywood can be bog-standard (shuttering ply for example, which has missing bits here and there), furniture grade (fine layers with no missing bits), WBP (water and boil proof for construction use) or marine-grade (which means you could build a submarine from it, should you be so inclined).

In fact plywood is the most familiar form of engineered timber. There aren’t that many trees around that are large enough to provide us with planks four feet wide and eight feet long, and just one inch thick. And if there were, such a plank would split, curve and weigh an eighth of a ton. The magic of plywood lies in its construction: if you look at it edge-on it’s a bit like a wafer biscuit; layer upon layer of wood, each just a couple of millimetres thick, each ‘peeled’ as a thin sheet from the trunk of a tree. These sheets are then laminated – the woodman’s word for ‘stuck together with glue.’ The genius of the design of plywood is that the grain of each layer runs in a different direction. The temptation of any particular layer to warp or bend is always countered by the inclinations of the other layers. So your bathroom floor and shelves stay more or less level.

And more sophisticated engineered timbers use the same principles and materials enshrined in plywood. In a metre thick laminated timber beam – such as the ones used in Andrew and Meryl Ainslie’s house shown on page 68 – the layers are organised to work against each other’s weaknesses and form a stable, weatherproof and super-strong structural member with, theoretically, infinite length and capable of supporting enormous loads. Think of it as equivalent to a steel beam of about a third or quarter of the thickness.

But the most sensible reason I can think of for using laminated timber is its beauty. It looks prettier than steel. Wood is also inherently a good insulator. If a window is made from wood cleverly glued to form a composite, it won’t deform and the draught won’t get in and it will quietly contribute to the insulation of the building.

And it’s sustainable. Engineered timber often uses bits of tree that are useless for conventional timber products other than newsprint. It locks up carbon dioxide, has a low environmental footprint and is glued together using either formaldehyde phenol or resorcinol adhesive. Ah, yes. They’re not particularly human friendly and of the two, formaldehyde-based compounds are the most pernicious. Products such as MDF, particleboard and OS board (the cheap stranded board often sold as Stirling board) can contain significant quantities of formaldehyde that is known to ‘off-gas’ and is known to cause irritation, asthma and allergic responses. The gas does, however, degrade quickly. Resorcinol-based products have fewer healthcare and environmental implications.

Admittedly, you can buy formaldehyde-free MDF, panels of fibreboard that are held together by dog-lick and beams made from the incredible Parallam, which is more like a timber filou pastry than organised laminated layers and which uses only steam to soften the lignin in the wood and rebind the strands together. It’s the equivalent of mechanically retrieved meat, only a lot more healthy for you.

And you can ensure the quality and sustainability of the product you buy by looking for the FSC or other accredited body’s marking. Do I need to tell you that? Yes, I think I do. Britain is the largest importer of illegal timber in Europe.

Do you agree with Kevin? Let us know your thoughts by emailing info@granddesignsmagazine.com

This edition of Kevin's Column is taken from the April issue of Grand Designs magazine. If you would like to subscribe for as little as £9 then head here to find out more.

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