Laminated Veneer Lumber (LVL)

Laminated Veneer Lumber is a high-strength engineered wood product made from veneers bonded together under heat and pressure. It is used for permanent structural applications including beams and rafters.

Overview

Laminated Veneer Lumber (LVL) is a high-strength engineered wood product used primarily for structural applications. It is comparable in strength to solid timber, concrete and steel and is manufactured by bonding together rotary peeled or sliced thin wood veneers under heat and pressure. LVL was developed in the 1970s and is today used for permanent structural applications including beams, lintels, purlins, truss chords and formwork. LVL can be used wherever sawn timber is used however one of the main advantages is that it can be manufactured to almost any length, restricted only by transportation to site.

Prior to lamination, the veneers are dried and the grains of each veneer are oriented in the same direction. This makes LVL stronger, straighter and more uniform than solid timber and overcomes some of timber's natural limitations such as strength-reducing knots. This gives orthotropic properties (different mechanical properties against different axes) in a similar way to the properties of sawn timber, rather than the isotropic properties (the same mechanical properties in each direction) in the plane of plywood. The added durability of being an engineered wood product means LVL is less prone to shrinking or warping. LVL can also support heavier loads and span longer distances than normal timber.

Section sizes are then cut from 1200 m wide sheets or "billets". The ability to cut different shapes from the LVL sheets allows for structural innovation using angular and curved shapes.

LVL provides a cost-effective and sustainable building material, delivering high structural reliability and strength.

Note: Some LVL members can be made with a few laminations laid up at right angles to enhance the shear strength of the member. These are known as Cross-Banded LVLs and may need to be specially ordered, as it is not a commonly stocked item.

The structure of an LVL member

Properties

Durability

Durability will be in part based on the species used for LVL. Although LVL is manufactured using a fully weatherproof glue, it is not recommended for use in permanent exposure to weather. If ongoing exposure is planned, products can be specially manufactured with a preservative treatment for the particular application. Members should also be painted or stained, with the coating maintained as required. Particular attention should be paid to sealing of end grain and in joints.

LVL may be subject to decay if there is a high moisture content or used in an unventilated area. If used for in-ground applications, LVL should be treated to protect against decay and termites.

Termite resistance
LVL is generally manufactured from Durability Class 4 (non-durable) softwood but needs to also be preservative treated to be termite resistant. Treatment to H2 level with a Light Organic Solvent Preservative would usually be sufficient.

Termite infestation should not be a problem for above-ground applications in Australia.

Sizes

LVL sizes will vary between manufacturers. Manufactured sheets or billets are usually 1200 m and 2400 m wide and in standard thicknesses of 35, 36, 39, 45 and 63 mm.

Lengths of up to 12 m are available from some manufacturers.

Beam depths are available of 1200 mm deep.

Check with individual manufacturers for the range of sizes they produce.

Grades

There are no generic grades for LVL. Each LVL or LSL manufacturer has designed and tested their products in accordance with AS/NZS 4063 Timber - Stress-graded - In-grade strength and stiffness evaluation to determine their design properties. This engineering data is available from the relevant manufacturer, together with span tables for common applications.

Appearance Grades

While there are no generic grades for LVL, it is generally not used for appearance-based applications. One reason is that gluelines are often visible. LVL can be sanded and painted if required.

LVL veneer grades are as per manufacturer's specifications.

Regulations / Standards & Codes

The Engineered Wood Products Association of Australasia (EWPAA), formerly Plywood Association of Australia, has operated a quality assurance program since 1963. This ensures that the LVL manufactured by mills participating in the scheme conforms to the relevant Australian Standard.

EWPAA members manufacture LVL to the following Australian Standards under an industry wide total product certification scheme:

AS/NZS 4357 Structural Laminated Veneer Lumber

The following standards are used in relation to sampling and testing:

AS/NZS 2097 Methods of Sampling Veneer and Plywood
AS/NZS 2098 Parts 1 to 8 Methods of test for Veneer and Plywood

The following standard is also applicable to LVL:

AS 1720.1 Timber Structures Code
AS 1604.4 Specification for Preservative Treatment, Part 4: LVL


*Disclaimer : The species mentioned here are just a guide and for specific information refer to Suppliers Section

Description

Material Sub Type

LSL (Laminated Strand Lumber)
Rather than being manufactured from veneers, as the name suggests LSL is produced from timber strands.

There is currently no Australian product standard or design rules for LSL, however manufacturers will have their own engineering data for the products they manufacture.

Cross-banded LVL
Cross-banded LVL is manufactured by including one or two laminations in the cross section with the grain running perpendicular to the longitudinal axis of the sheet.

This product has advantages when used in specific applications:

  • Short span deep beams produce very high shear stresses compared with the flexural stresses. The cross-banding removes some of the wood fibre that contributes to bending strength and stiffness and substitutes it with fibre that contributes to shear strength.
  • Elements that are curve or taper cut from sheets have slope of grain that is at an angle to the flexural stresses. This would normally tend to cause splitting along the grain lines, but the cross-bands provide fibre with strength in the direction that will minimise those splits.
  • Elements that are used in an environment that may have changeable moisture content may tend to split on wetting and drying. The cross-banding will reduce the tendency of these elements to split.

Cross-banded LVL has a different set of properties to LVL with all plies parallel to the longitudinal axis. The shear strength is higher and the tensile strength perpendicular to the grain is also considerably higher. The flexural strength is marginally lower and the Modulus of Elasticity parallel to grain is also a little lower.

Fire Resistance

Fire resistance of LVL and LSL depends on the section size of the member.

LVL and LSL acts similarly to solid timber during exposure to fire, and has a slow and predictable charring rate, dependent on the timber species.

When members are required to have a fire resistance rating, this can be calculated by subtracting a charred thickness from the original member size. Higher stresses can be used in combination with the reduced cross section. The fire resistance requirements can be calculated using the procedure given in AS 1720.4 Timber Structures: Fire Resistance of Structural Timber Members. Depending on the fire performance requirement, metal connectors may need special fire protection.

For more information about fire resistance regulations please refer to C1.10 Fire Hazard Properties within the Building Code of Australia (BCA).

Adhesives

As LVL is primarily used for permanent structural applications it is manufactured with a Type A bond using a phenolic resin-based adhesive (phenol formaldehyde) and is recognisable by its black gluelines. A Type A bond will not deteriorate under wet conditions, heat or cold.

It is important to remember that while the Type A bond is fully durable, the species may not always be in exposed weather situations.

Treatments

Depending on the timber species used, treatment may be required to ensure durability where LVL is subject to exposed weather situations. Timber laminate members that are to be fully exposed to the weather need to be protected against UV and moisture. LVL can be preservative treated, however some chemical treatments may not be suitable so it is always best to check with manufacturers.

As with plywood, LVL can be treated with a range of preservative treatments including CCA (copper chrome arsenate), LOSPs (light organic solvent preservatives) and for veneers, Ruply and ACQ (Alkaline Copper Quaternary Compounds).

For building construction the most suitable treatments are Copper Chromium Arsenic (CCA) and Light Organic Solvent Preservative (LOSP)

Most softwood species can be treated with non-leachable preservative salts, which will impart decay resistance. The level of preservative treatment specified for softwood laminated beams used in Service Class 3 applications should be H3. Similarly LOSP envelope treatment can be used satisfactorily. It is always recommended that you check with individual manufacturers for recommended use.

Treatment methods
LVL can be treated during manufacture by impregnating veneers or surface treated after manufacture. Preservative treating after manufacture or surface treating with 'brush on' preservatives should be done only after machining, sawing and boring has been completed.

Preservative treated LVL can be painted as per manufacturers' recommendations.

Design/Engineering Considerations

As LVL is a proprietary product, engineering properties, including span tables, are published by individual manufacturers. The following information provides a general overview of the engineering characteristics of LVL.

Engineering characteristics
The properties of LVL show much less variation than those of both sawn timber and glulam. In fact, LVL has a coefficient of variation in structural properties that is similar to Australian-produced hot rolled steel sections.

Like other timbers, LVL offers good chemical resistance. It is resistant to most acids, rust and other corrosive agents. If exposed to strong oxidising agents, sulphides and alkalis, ‘pulping' action (timber becomes very fibrous) may occur, so specialist advice should be sought regarding the choice of timber species and adhesive for specific applications.

LVL beams

The veneers that make up LVL are oriented in the same direction, which makes it an excellent material for beams, with spanning in one direction. Due to the long length, large depth and reliable strength with uniform stiffness that LVL offers, it is very effective for carrying loads over long spans.

LVL beams are normally straight, as the most cost-effective production is to cut a number of straight members out of one sheet; curved or tapered members can also be cut out of a single sheet although this will likely be more expensive. Care with sloping grain is needed in determining performance with curved or tapered members.

LVL can be used as primary roof members such as strutting beams, hanging beams, valley or hip rafters and ridge beams. It can also be used for long span joists and floor bearers.

When combined with stiff connections at the knee and ridge, LVL can be used in portal frames. LVL sections can be quite slender (a high depth to breadth ratio), so care should be made to provide torsional stability to the member at its supports. This can be achieved with blocking pieces between members or a strap over the top of the beam. Deep members may need fly bracing to prevent lateral torsional buckling of beams under wind uplift loading. Where large shear forces need to be carried (particularly in the connections), then it may be necessary to use cross-banded LVL.

LVL truss members
LVL has high tensile strength relative to sawn timber and high reliability. This makes it ideal for use in trusses.

Truss members can be made from single pieces of LVL, but for very large loads, LVL can be glue-laminated to make large cross-section square or nearly square members. In all truss applications, the limiting factor is the connection, so for very large loads, complex high capacity connections will be required. This may require testing of prototypes of the joints to verify the capacity.

Note: Not all LVL is the same. Where a design is based on a particular size and brand of LVL or LSL, substitution with another brand should not be made without engineering advice.

Handling, Storage & Protection

Generally LVL and LSL should be handled as you would solid seasoned timber. While some light handling damage may be acceptable for non-appearance structural applications, care should be taken to prevent damage to exposed edges or corners where the member is to be visually exposed.

For on-site storage of LVL, it should be supported on level bearers to keep it flat, well clear of the ground for good ventilation and stored undercover to keep it dry prior to installation, and protected from the sun to prevent cupping.

LVL is not suitable for long term weather exposure unless preservative treated and finished with a protective coating. However, short-term exposure during the construction process does not affect LVL's performance.

Cutting Holes & Notches

LVL can be sawn, and drilled using regular carpenter's tools.

LVL beams can easily have holes cut in the web of the beam through which services can be installed.

Each manufacturer or the Engineered Wood Panel Association of Australasia (EWPAA) can provide further advice for the location and size of holes.

Maintenance

Ongoing maintenance and inspections will help to make sure rot and infestation does not occur in structural above-ground applications.

Workability

LVL can be sawn, drilled, screwed, nailed with ordinary woodworking tools.

Joints & Connectors

Joining LVL and LSL are the same as joining solid timber. Traditional fasteners such as nails, screws and bolts can be used as well as proprietary metal connectors such as framing anchors, joist hangers etc.

Concealed or exposed plates can also be used to secure butt connections such as in portal knee joints and joins in curved members.

At supports it is essential that minimum bearing requirements be achieved. This may vary between different manufacturers.

Finishes

LVL would rarely be used as an appearance product. The surface finish is usually of low architectural quality - similar in appearance to lower grade plywood, except that it does not have its veneers laid at right angles - with rough glue lines often visible. However, where required, products can be fine sanded and painted to give a similar finish to solid painted timber, creating a more visually appealing finish.

Applications

  • Architectural Roof Trusses

    Architectural timber roof trusses create strong visual impact. Often used as part of ‘cathedral ceiling’ systems, timber can be specified light or heavy to suit the chosen theme and style. On finish, they can be left natural or may be oiled, stained, painted or highly decorated. Choice is limited only by individual style and design preferences.

  • Framing

    Since people began building simple shelters, wooden framing has played an important role in shaping structures of many kinds. One of the most popular types of wooden framing is known as lightweight timber construction.

  • Timber Portal Frames

    For buildings that require large spans and column free interiors, timber portal frames provide one of the most aesthetically pleasing solutions. Utilising modern engineering technology, portal frame design transforms timber into a highly effective, efficient and economical structural product. This application guide provides a comprehensive overview of the process of using timber in the specification, fabrication and erection of portal frame structures.

Case Studies

  • Lewis St House, Thornbury

    A stunning residential renovation and addition that uses timber and timber products throughout with a commitment to sustainable design.

    Applications : Architectural Roof Trusses, Doors, External Cladding, Flooring, Framing, Interior Stairs, Windows,

  • Mingara One Fitness Centre

    A breathtaking addition to the Mingara Recreation Club campus on the NSW central coast, covering 2000sqm of commercial gymnasium over two levels.

    Applications : Doors, External Cladding, Flooring, Interior Stairs, Internal Paneling,

  • Narrabeen House

    Narrabeen House – an innovative use of timber and timber products creates a private paradise in the suburbs.

    Applications : Doors, External Cladding, Fencing, Framing, Interior Stairs, Internal Paneling, Structural Timber Poles, Windows,

  • NMIT Arts & Media Building, New Zealand

    A world first for its innovative use of LVL in the structure of a multi‐storey building, the NMIT building also incorporates a new generation of earthquake-­resistant engineering technology.

    Applications : Doors, Framing, Interior Stairs, Internal Paneling, Shear walls, Structural Timber Poles,

  • Peninsula Hot Springs

    At the Peninsula Hot Springs Gregory Burgess Architects use timber to create environments that enhance the spirit.

    Applications : Decking, External Cladding, Flooring, Framing, Interior Stairs, Structural Timber Poles,

  • Svarmisk Resort Centre, Mt Beauty

    A striking eco-resort that embodies the essence of new and recycled timber working together to form a unique, innovative and sustainable development.

    Applications : External Cladding, Flooring, Framing, Interior Rails and Balustrades, Interior Stairs, Internal Paneling, Pergolas, Shear walls, Structural Timber Poles,

  • The Dickson Apartments, Little Bay

    An innovative coastal refurbishment where the use of timber contributed to an environmentally sustainable development while respecting the site's heritage significance.

    Applications : Doors, Exterior Rails and Balustrades, Exterior Stairs, External Cladding, Fencing, Framing, Interior Rails and Balustrades, Interior Stairs, Internal Paneling, Retaining Walls (Landscaping), Timber Portal Frames, Windows,

  • tvzeb experimental zero energy building

    The goal of the project was to develop a low-impact building that blended seamlessly into the surrounding natural setting and showcased the visual, renewable energy and user well-being resources.

  • Yuille Park Community College

    A school becomes an integrated community hub where the versatile qualities of timber are used throughout to create an award-winning learning environment.

    Applications : Flooring, Framing, Internal Paneling, Shear walls,

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