Last edited 09 May 2016

Laminated veneer lumber LVL


[edit] Introduction

Laminated veneer lumber (LVL) is a type of high-strength engineered timber that can be used as an alternative to solid timber, concrete and steel for structural applications. It is manufactured by bonding rotary peeled or wood veneers that have been sliced thinly under heat and pressure.

First developed in the 1970s, LVL is used as a cost-effective and sustainable building material that provides high structural reliability and strength. By reducing solid timber’s natural flaws, such as strength-reducing knots, LVL has good strength, uniformity and durability. As an engineered product, LVL is also less prone to shrinkage or warping and is able to span longer distances and support heavier loads than regular timber.

The veneers that make up LVL are oriented in the same direction, making it particularly suitable for beams, and its length, depth and strength make it effective at carrying loads over long spans. Its high tensile strength relative to sawn timber means it is also commonly used for trusses.

Structural applications include:

LVL is covered by British Standard BS EN 14279:2004+A1:2009 – Definitions, classification and specifications.

[edit] Manufacture

Once logs have been debarked, they are conditioned in hot water for 24 hours. A lathe then peels the logs into veneers – thin slices of wood, usually thinner than 3 mm. The veneer is scanned by camera for defects, analysed for moisture content and then clipped to a width of approximately 1.4 m by a rotary clipper. Veneers are then dried to a target moisture content of between 8-10%.

Before being laminated, the veneers are dried and then oriented in the same direction. Once dried, the edge of the veneer is scarfed for a uniform thickness at the joints. Veneers are then coated with an adhesive (such as phenol formaldehyde), and heated in a continuous press. They can then be cut to the required sizes.

LVL beams are usually straight as the most cost-effective production method is to cut a number of straight members from one sheet. Curved or tapered members can be cut although these are more expensive.

LVL may be subject to decay if there is a high moisture content or if it is used in an unventilated area. If used for in-ground applications, LVL should be treated with preservatives to protect against decay and infestation. See, Timber preservatives for more information.

LVL can be treated during manufacture by impregnating veneers or surface-treated post-manufacture.

LVL can be sawn, nailed, screwed and drilled using normal tools. Holes can be cut in the web of a beam for services installation.

[edit] Sizes

One of the main advantages of LVL is that it can be manufactured to almost any length, although available sizes will vary between manufacturers. Sheets, or billets, are usually manufactured to thicknesses of 35-63 mm, and to lengths of up to 12 m.

[edit] Fire resistance

The fire resistance of LVL is similar to solid timber, with a slow and predictable charring rate, dependent on the timber species and the size of the member.

[edit] Handling and storage

LVL should be handled in the same way as solid seasoned timber. Care should be taken to avoid damage to exposed corners or edges where the member is to be visually exposed.

On site, LVL members should be stored flat, off the ground and kept dry prior to installation. While short-term weather exposure will not unduly affect its performance, long-term exposure will require preservative treatment and finishing with a protective coating.

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