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I am looking at designing a covered outdoor area using timber. I assume LVL is the correct product to span circa 20m.
The timber is external but undercover. It will not be exposed to the rain.
My client wants minimal maintentance.
What treatment is appropriate to the LVL and how long until first maintenance?

Woodsolutions Answer +

For a 20m span some kind of ‘engineered’ product would be needed since sawn timber is not available in such long lengths. Of course shorter spans could be supported with posts. For a clear span, LVL will be fine although for a higher quality appearance you could consider glued laminated timber (‘glulam’). LVL is produced with a structural grade face and is not generally used in appearance applications unless a rustic look is desired. While a 20m beam is theoretically possible to produce, it’s beyond the usual range of sizes used in domestic construction and likely to require a special order. We suggest you discuss lead times and transport considerations with an LVL producer. If the timber is shielded so it won’t get wet when it rains, preservative treatment is not necessary and the usual range of paints and exterior wood stains can be used. Maintenance will not be an issue if the timber is not exposed to the weather.


We are looking to use a timber portal frame for a building we are currently designing. The building is quite simple, rectangular with metal sheet cladding. The portals are required to offer a clear span of 25m. Can you please advise what a rough lead time may be for such a product, and additionally could you provide some advice or reference to the fire resistance properties of these sort of portal frame products?

Woodsolutions Answer +

You will have to contact a company that produces timber portal frames to discuss lead times, for example Timberbuilt Solutions could advise you. They have a website here: www.timberbuilt.com.au. Regarding fire resistance, this can be calculated by reference to Australian Standard 1720, ‘Timber Structures’, Part 4: Fire resistance for structural adequacy of timber members. Possibly Timberbuilt can also advise on this point.


I am building a pergola that has no roof on it so the timber beams are open to the elements. The design also has beams that over hang so are not constrained. Because of the cost of recycled spotted gum, I am looking at Vic Ash Glulam. My concern is whether Glulam will bow or not in these type of application.

Woodsolutions Answer +

Glulam is a very stable product and is unlikely to bow even in an external application. However, we would be concerned about the durability of untreated Vic ash glulam in the long term. It’s not a highly durable timber under full weather exposure. Preservative treated Vic ash is now available, known as ‘IronAsh’, so if the glulam you are considering is made from preservative-treated material it should give satisfactory performance. Otherwise it would be a good idea to consider a more durable species.

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