Engineered timber products: LVL, Glulam, CLT, and I-joists

TL;DR

Engineered timber products (LVL, Glulam, CLT, I-joists, finger-jointed pine) outperform sawn solid timber on span, dimensional stability, and consistency. The trade-off: they sit outside AS 1684 span tables and must be sized from manufacturer-published span tables or by an engineer under AS 1720.1. LVL handles concealed structural work (lintels, floor beams, roof beams) at F17, F22, or F27. Glulam suits exposed feature beams and curved sections in GL8 to GL17. CLT is mass-timber wall and floor panels, used predominantly in Class 2 and commercial; in Australia CLT design is a performance solution because AS 1720.1 doesn’t yet cover it. I-joists are the lightweight floor and roof joist alternative to deep solid sections. The two most common builder errors are notching engineered sections in the field (kills the published capacity) and leaving unsealed LVL or I-joists exposed to weather (irreversible delamination).

What it is

Engineered timber product (ETP) is the umbrella term for structural timber sections built up from smaller graded pieces, veneers, or strands bonded together with structural adhesive. Each product has a different geometry and intended use, but all share three properties solid timber lacks: predictable strength (every beam of a given grade behaves the same), longer available lengths (12+ m off the truck), and sections deeper or wider than any tree the log came from.

The five products a residential builder will typically meet:

LVL (Laminated Veneer Lumber): thin rotary-peeled veneers (typically 3 mm) glued with grain parallel to length. Rectangular only. Brand examples: Wesbeam SmartLVL, Carter Holt Harvey hySPAN, Tilling SmartLVL.
Glulam (Glued-Laminated Timber): thicker laminations (35 to 45 mm) of solid graded timber glued grain-parallel. Straight or curved. Brand examples: Hyne, Wesbeam, Dindas.
CLT (Cross-Laminated Timber): layers (lamellae) glued at 90-degree alternating orientation, producing a panel that spans in both directions. Brand examples: XLam (Australian, plantation pine), Stora Enso (imported).
I-joists: a top and bottom flange (LVL or solid timber) connected by a thin OSB or plywood web. Profile looks like a steel I-beam. Brand examples: smartLAM iLevel, Lumin8 iLevel, Boise BCI.
Finger-jointed pine (FJP): short pieces of solid pine end-jointed with interlocking fingers and adhesive into long, straight sections. Used for studs, plates, and architraves where solid pine bows too much.

Properties

Product	Cross-section	Typical lengths	Sized from
LVL	Rectangular, fixed widths 35-90 mm, depths 95-600 mm	Up to 13.5 m	AS/NZS 4357, manufacturer span tables, AS 1720.1
Glulam	Rectangular or curved, custom widths and depths	Up to 24 m straight	AS/NZS 1328, AS 1720.1 Section 7
CLT	Panels 1.2 to 3.5 m wide, 60 to 320 mm thick	Up to 16 m	Manufacturer engineering, performance solution
I-joist	Fixed flange/web combos, depths 200-600 mm	Up to 12 m	Manufacturer span tables only
FJP	Standard stud and plate sizes (90x35, 90x45, 140x45)	Up to 6 m	AS 1684 (treated as solid sawn)

Grades / variants

Product	Common grades	Notes
LVL	F17, F22, F27	F17 is the residential workhorse; F22 / F27 for high-load lintels
Glulam	GL8, GL10, GL12, GL13, GL17	GL10 standard structural; GL17 for feature and heavy spans
CLT	CL12, CL16, CL20, CL24	Designation reflects characteristic bending strength
I-joist	Manufacturer-specific (e.g. iLevel TJI 110, 210, 360)	Span depends on flange size + web thickness, not a single grade
FJP	F5, F7, MGP10, MGP12	Same grades as solid pine framing

Where to use

LVL: lintels, floor beams, roof beams, ridge beams concealed in framing. The sweet spot is a span solid pine cannot reach with the same depth.
Glulam: feature beams in cathedral ceilings, exposed pergolas, post-and-beam, curved arches.
CLT: prefabricated walls and floors in Class 2 apartments, education, commercial. Rare on Class 1 detached unless the architect has chosen mass-timber as a feature.
I-joists: long-span floor joists where deep solid sections would be wasteful, and trussed roof bottom-chord runs.
FJP: any place where solid pine bowing or twist would defeat the install: long architraves, tall studs, wall plates over 4.8 m.

Where NOT to use

LVL exposed to weather, even briefly without a sealed end or wax coating. Rapid moisture intake delaminates the veneer adhesive. The product is intended for concealed dry-in-service use unless specifically rated H3 / H4.
Glulam in unprotected exterior, unless it is H3-treated softwood or naturally durable hardwood specified for exterior. Standard Radiata Pine glulam is interior-only.
CLT in fire-exposed Class 1a residential: the BCA fire-rating pathway for CLT in detached housing is unfamiliar to most certifiers. Check the certifier accepts the design before specifying.
I-joists notched or drilled outside the manufacturer’s web layout. Holes are permitted only in the marked zones and at marked sizes; cutting elsewhere collapses the published capacity.
FJP for visible exposed timber. The finger joints telegraph through paint over time and are unacceptable in feature finishes.

Fixing / installation

Each product has a manufacturer install guide that overrides general timber framing rules. Common rules across the family:

Use structural screws sized per the manufacturer’s table. Generic nails into LVL or I-joist flanges void the published capacity.
Flange-mount hangers (Pryda, Mitek) sized for the section depth. Top-flange and face-mount differ; reading the wrong column on the hanger catalogue is a common defect.
Bearings: minimum bearing length per the manufacturer table (typically 45 mm for LVL, 90 mm for I-joist). Squashed-fibre bearing failures are visible as crushed end grain at supports.
Connections at hard points (steel posts, masonry corbels) typically need an engineer’s detail; generic AS 1684 connections do not apply.

Tolerances and acceptance

Manufacturer-stamped grade and length legible on every section delivered. Reject sections without legible stamps.
Bow, spring, twist within the manufacturer’s published tolerances (typically tighter than AS 1684 for solid pine).
No delamination at any glue line. Glue-line failure is a reject defect at delivery, not something to remediate on site.
End-sealed on LVL ordered for outdoor or wet-area use (paint or wax visible).
Engineer’s certification required for all CLT panel design and for any LVL or Glulam application outside published manufacturer span tables.

Working with other trades

Chippy / framer: the trade actually fixing engineered timber. Must work to the manufacturer install guide, not site-rule-of-thumb.
Engineer: stamps the design where the application sits outside manufacturer tables (CLT always; LVL and Glulam for non-standard spans, holes, or connections).
Sparky and plumber: must coordinate service runs through the marked zones in I-joist webs only. Site re-cutting holes elsewhere is a defect.
Building surveyor / certifier: needs to see manufacturer span-table calc OR engineer’s certificate for any engineered-timber member during framing inspection.

Health & safety

Lifting weight: Glulam beams and CLT panels regularly exceed safe two-person lift limits. Plan crane or telehandler lifts before delivery.
Adhesive dust: cutting LVL, I-joist webs, or CLT releases bonded-resin dust. Wear P2 respirator; use dust extraction on circular saws.
Sharp edges on I-joist OSB webs: gloves when handling.
Site moisture during install: wrap or cover sections at end of day until the structure is dried-in. A weekend in the rain on bare LVL will cost a beam.

Suppliers

Major Australian suppliers (alphabetical):

Boise Cascade (BCI I-joists)
Carter Holt Harvey (hySPAN LVL, hyJOIST I-joists)
Dindas (Glulam)
Hyne (Glulam, LVL)
Lumin8 (LVL, I-joists)
Tilling (SmartLVL)
Wesbeam (LVL, Glulam)
XLam (CLT, Australian-made plantation pine)

What can go wrong

Notching or holing on site outside the published zone. The most common cause of structural reject at framing inspection. Cut zones are printed on the section; cut elsewhere and the beam is scrap.
Wrong-grade substitution at delivery. F17 vs F22 LVL at the same nominal depth looks identical. The supplier docket plus the stamp on the section must match the engineer’s spec.
Weather exposure of unsealed LVL. Site-stored LVL left uncovered in rain for as little as 48 hours can swell and delaminate. Cost: replace, not remediate.
I-joist flange overload from point loads (a column landing on the flange instead of through to a support). Always block under point loads to the bottom flange or to the wall plate below.
Glulam beam orientation flipped during install. Tension and compression faces are graded differently in some Glulam grades; the stamp shows which face is up. Installing upside-down halves the published capacity.
CLT panel edges left unsealed at site cuts. Field-cut edges expose the unprotected core and need re-sealing per the manufacturer guide.

References

AS 1720.1:2010, Timber structures, Part 1: Design methods (verified 2026-05-14, Standards Australia).
AS/NZS 4357.0:2022, Structural laminated veneer lumber (verified 2026-05-14, Standards Australia).
AS/NZS 1328.1:1998 and AS/NZS 1328.2:1998, Glued laminated structural timber (verified 2026-05-14, Standards Australia).
AS 1684.2:2021, Residential timber-framed construction (verified 2026-05-14, ABCB).
WoodSolutions Cross-Laminated Timber (CLT) Guide (verified 2026-05-14).
XLam Structural Design Guide Australia & New Zealand, June 2020 (verified 2026-05-14).