Lintel & Header Beam Calculator

Every door, window, sliding glass door, and garage opening in an Australian building creates a structural gap in the wall frame. Without a properly engineered beam across that opening, the weight of the roof rafters, ceiling joists, trusses, and upper floor levels will bear directly down onto the door jamb or window reveal.

In Australian residential construction, these horizontal load-bearing members are called lintels or headers. Sizing them correctly is one of the most critical structural tasks for carpenters, builders, and bricklayers. Using an undersized timber or steel lintel results in sagging door heads, sticking sliding panels, cracked external brick mortar, crushed window frames, and automatic failure during mandatory council building certifier frame inspections.

This guide explains how to calculate timber lintel sizes under AS 1684.2 and AS 1684.3 (Residential Timber-Framed Construction) and how to select galvanised steel lintels under AS 4100 and AS 3700 (Masonry Structures).

Sizing Timber Lintels under AS 1684 (MGP10, F17 & LVL)

Timber lintels are the standard choice for internal partitions, external timber-framed walls, and brick veneer cavity construction across Australian residential builds. Sizing a timber lintel requires evaluating three key engineering parameters:

1. Roof Load Width (RLW)

Roof Load Width represents the width of the pitched roof structure that transfers its dead and live weight onto the external wall bearing the lintel. For a standard gable or hip roof with a central ridge, the RLW on each external wall is roughly half of the building’s total span.

• RLW = 1.5m: Small verandahs, narrow lean-tos, or eaves.
• RLW = 3.0m: Standard Australian residential homes (6m to 7m truss spans).
• RLW = 4.5m: Wide residential floor plans (8m to 9m truss spans).
• RLW = 6.0m: Large commercial spans, girder truss landing zones, or cathedral ceilings.

2. Roof Cladding Weight

The material on the roof dramatically affects the allowable lintel span:

• Lightweight Sheet Roof (Colorbond / Zincalume): Generates a dead load of approximately 0.2 kPa (20 kg/m²). This lower mass allows timber members to span significantly further over wide openings. You can calculate your roof pitch and sheet quantities with our Roof Pitch & Rafter Calculator and Roof Area Calculator.
• Heavyweight Tile Roof (Concrete / Terracotta): Generates a dead load of approximately 0.6 kPa (60 kg/m²). Because tiles are three times heavier than sheet metal, allowable timber lintel spans are reduced by 20% to 30%.
• Two-Storey Floor Loads: When upper floor joists bear directly onto the lower ground-floor lintel, the combined dead and live floor load (~1.5 kPa) requires much deeper members such as 240x45mm pine or 63mm thick LVL.

3. Timber Stress Grade Selection

In standard 90mm stud walls, chippies standardly laminate two 45mm members together (e.g. 2/140x45mm or 2/190x45mm) so the lintel matches the 90mm wall cavity perfectly without requiring packers:

• MGP10 (Machine Graded Pine): The most widely available framing pine in Australian timber yards. Economical for door openings up to 1.8m and standard 1.2m–1.8m windows.
• MGP12 (High-Strength Pine): Offers higher stiffness (elastic modulus E = 12,000 MPa) than MGP10, giving an extra 200mm–400mm of allowable clear span.
• F17 Seasoned Hardwood: Dense hardwood (Spotted Gum, Blackbutt, Ironbark) offering superior load capacity for heavy tiled roofs and two-storey applications.
• LVL (Laminated Veneer Lumber — SmartFrame / Hyne / Wesbeam): Engineered timber manufactured with parallel veneers. LVL beams (such as 200x63mm, 240x63mm, 300x63mm, or 360x63mm SmartFrame) do not twist or warp and are required for wide sliding glass doors (2.4m to 3.6m) and double garage openings (4.8m to 5.4m).

AS 1684 Timber Lintel Span Reference Table

The following reference table outlines typical maximum clear opening spans (in metres) for standard double timber lintels and single LVL beams under typical suburban residential loading (Roof Load Width = 3.0m, Wind Class N1/N2):

Steel Lintel Selection for Brick Veneer & Cavity Walls

In brick veneer homes, the internal timber framing supports the roof trusses, while the external 110mm brickwork skin requires a dedicated steel lintel spanning across the window and door openings to support the masonry above.

1. Galvanised Steel Angles (Equal & Unequal Angles)

For standard single-skin brick veneer, hot-dip galvanised angles (such as Galintel Multi-Rib or Traditional Structural Angles) are standard:

• 100x100x6mm EA: Ideal for standard door openings (820mm–920mm) and windows up to 1.8m clear span.
• 100x100x8mm EA: Used for wider openings up to 2.4m (such as standard sliding doors).
• 150x100x10mm UA: Designed with a deep 150mm vertical leg to provide stiffness over spans up to 3.1m without excessive mid-span sag.

2. Galvanised T-Bars (Tee Sections)

In cavity brick (double brick) construction, a single central T-Bar supports both the external 110mm brick skin and the internal 110mm brick skin across a 50mm cavity:

• 200x10mm T-Bar: Standard cavity lintel for openings up to 2.7m.
• 200x12mm T-Bar: Medium spans up to 3.3m for sliding doors.
• 250x10mm / 250x12mm T-Bar: Heavy-duty sections for spans up to 4.5m across large alfresco openings.

3. Heavy Structural Steel (PFC Channels & RHS Box Sections)

When residential architectural designs feature open-plan living areas with 4.8m to 5.4m double garage doors or corner-less stacking bi-folds, standard angles and timber lintels cannot handle the span. Carpenters and builders install structural steel members:

• 180 PFC / 200 PFC (Parallel Flange Channel): Flange channels that fit inside wall frames or bolt alongside timber studs.
• 150x100x5mm / 200x100x6mm RHS (Rectangular Hollow Section): Closed box sections that offer high torsional resistance against wind suction on large garage doors.

4. Masonry Composite Arching Action

Under AS 3700, when there are 6 or more unbroken courses of clay brickwork laid in mortar above a lintel, the masonry forms a natural triangular arch. This arching transfers a substantial portion of the brick weight directly onto the adjacent side piers. However, if the opening is located tight under the roof eave soffit (with only 1 to 4 courses of brick), no arching action occurs, and the full weight of the brickwork rests entirely on the steel lintel, requiring a heavier angle profile.

End Bearing, Jack Studs & King Stud Requirements

Even the strongest lintel will fail if the support framing on either side of the opening is improperly constructed. AS 1684 defines mandatory rules for minimum end bearing length and vertical stud supports:

Timber Wall Framing Rules (AS 1684)

• Minimum End Bearing Length: For openings up to 1.8m under single-storey loads, the lintel must sit at least 35mm on the trimmer stud. For spans between 1.8m and 3.0m, minimum bearing is 45mm. For spans exceeding 3.0m or under multi-storey floor loads, minimum bearing increases to 70mm (achieved with double 90x45mm trimmer studs).
• Trimmer (Jack) Studs: Trimmer studs sit directly underneath the lintel and run full height down to the bottom plate. Never fix a load-bearing lintel solely with nails into the face of a stud without a trimmer underneath.
  • Spans up to 1.8m: 1 trimmer stud on each side.
  • Spans 1.8m to 3.6m: 2 trimmer studs on each side.
  • Spans over 3.6m or high concentrated point loads: 2 to 3 trimmer studs or a solid 90x90mm post.
• King Studs: A full-height king stud must sit directly alongside the trimmer stud, running from the bottom plate continuously up to the double top plate. The king stud provides lateral resistance against wind loads pushing on the window or door frame.

Masonry End Bearing Rules (AS 3700)

• Spans up to 1.8m: Minimum 100mm of solid brickwork bearing on mortar at each end.
• Spans over 1.8m: Minimum 150mm of solid brickwork bearing at each end.
• Heavy Structural Beams (PFC / UB): Minimum 200mm bearing on concrete padstones or steel distribution plates to prevent localized crushing of brickwork.

Step-by-Step Worked On-Site Examples

Example 1: 2.4m External Sliding Glass Door in a Single-Storey Colorbond Home

Project Scenario: Framing a 2400mm clear opening for a powder-coated aluminium sliding door in an external 90mm timber wall. The roof is Colorbond metal sheet with a standard 3.0m Roof Load Width (RLW) in wind region N2.

1. Identify Load Condition: Single Storey — Light Sheet Roof (Colorbond).
2. Check MGP10 Pine Capacity: A 2/190x45mm MGP10 lintel has an allowable clear span of 2.7m under a 3.0m RLW. Since the actual span is 2.4m, the capacity utilisation is 89% (PASS).
3. Alternative Engineered LVL: If vertical ceiling headroom is tight, a 150x63mm LVL SmartFrame has an allowable span of 2.7m, saving 40mm of valuable wall cavity height.
4. Support Framing Specification: The 2.4m span requires 2 × 90x45mm trimmer studs (providing 90mm bearing) and 1 full-height king stud at each side of the opening.
5. Total Cut Length: 2400mm clear opening + (2 × 90mm bearing) = 2580mm total lintel length.

Example 2: 3.6m Open-Plan Stacking Bi-Fold Door under Tile Roof

Project Scenario: Creating a wide 3600mm indoor-outdoor alfresco opening under a heavy concrete tile roof with an RLW of 3.0m.

1. Evaluate Standard Pine: The largest standard double pine member, 2/290x45mm MGP10, has a maximum allowable span of only 3.1m under heavy tile loads. It FAILS for a 3.6m opening.
2. Select Engineered LVL: Upgrading to a 240x63mm LVL (SmartFrame) provides an allowable clear span of 3.3m (still close to the limit). Selecting a 300x63mm LVL provides an allowable span of 4.0m, operating safely at 90% capacity (PASS).
3. Support Framing Specification: Under heavy tile roof loads, the 3.6m opening requires 2 × 90x45mm trimmer studs each side plus double king studs secured to the double top plate.

On-Site Installation Tips & Inspection Traps

Building certifiers regularly issue defect notices for lintel framing. Following these practical on-site trade standards ensures compliance on inspection day:

• Composite Lamination Nailing: Double timber members (e.g. 2/190x45) must act as a single composite beam. Fasten them together with two rows of 75mm framing nails (or 14G construction screws) spaced at maximum 300mm centres along the entire length, with pairs of fixings located within 100mm of each end.
• Damp Proof Course (DPC) Flashing above Steel Angles: In brick veneer construction, always install continuous embossed polythene flashing (DPC) over the horizontal leg of the steel lintel and turn it up the timber stud wall behind the building wrap. Install weep holes in the brick mortar joints directly above the steel angle at maximum 1200mm centres to allow trapped moisture to escape.
• Temporary Propping for Steel Lintels: When bricklayers lay masonry over steel angles and T-bars with spans exceeding 1.5m, install temporary vertical timber props at mid-span. Keep props in place for at least 7 to 10 days until the cement mortar achieves full design compressive strength. Removing props too early causes the wet brickwork to sag and lock into a curved shape permanently.
• Corrosion Protection in Coastal Zones: Within 1km of breaking surf or saltwater estuaries, standard light-duty electroplated zinc is prohibited under the NCC. Ensure all steel lintels are hot-dip galvanised to AS/NZS 4680 with a minimum coating thickness of 600 g/m² (R3 or R4 durability rating).