Lintel Size Requirements Over Windows and Doors

What This Requirement Covers

Lintels are horizontal structural members placed over openings - such as windows and doors - to transfer loads from the wall or roof above around the opening and into adjacent supports. The requirement covers minimum sizes, bearing lengths, material grades, installation orientation and corrosion protection so the lintel can safely support masonry, roof and floor loads without excessive deflection or failure. These rules exist to protect structural performance, weatherproofing and, where relevant, fire resistance of the building fabric.

This guidance applies to designers, builders, certifiers and homeowners involved with new work, alterations or repairs to openings in masonry and framed walls across Australian building classes. It draws on the National Construction Code (NCC) provisions (including the ABCB Housing Provisions where applicable) and applicable Australian Standards such as AS 4100 for steel and AS 1684 for timber framed lintel design where relevant.

Key Requirements

1. Minimum bearing length: For masonry lintels the minimum bearing at each end is 100 mm for clear spans up to 1 m, and 150 mm for clear spans greater than 1 m (ABCB Housing Provisions Standard 2022, H1D/5.6.7(a)(v)).
2. Minimum masonry above lintel: A lintel must have a minimum of three courses of masonry above it (ABCB Housing Provisions Standard 2022, 5.6.7(a)(vi)).
3. Masonry overhang on lintel: Lintels must be wide enough so masonry does not overhang the horizontal leg by more than 25 mm (ABCB Housing Provisions Standard 2022, 5.6.7(a)(iii)).
4. Maximum masonry supported: A lintel must not support masonry more than 3 m in height when measured above the opening (ABCB Housing Provisions Standard 2022, 5.6.7(a)(iv)).
5. Steel lintel sizing: Steel lintels must be sized in accordance with tabulated lintel sizes in the ABCB Housing Provisions (Table 5.6.7a). Examples from that table include:
6. Flat 75 x 8 for certain spans and masonry heights
7. Flat 100 x 10 for larger spans
8. Angle 90 x 90 x 6EA for spans up to 3,000 mm (some entries vary with the amount of masonry above the opening) (ABCB Housing Provisions Standard 2022, Table 5.6.7a).
9. Steel grade: Lintels described in the ABCB tables must be a minimum of 300 MPa grade steel in accordance with AS 4100 (ABCB Housing Provisions Standard 2022, table notes to 5.6.7a).
10. Corrosion protection: Lintels must comply with the corrosion protection requirements set out in Table 5.6.7b of the ABCB Housing Provisions; AS 2699.3 is referenced for corrosivity categories and coating thickness (ABCB Housing Provisions Standard 2022, Table 5.6.7b notes).
11. Installation orientation: Where angles are used as lintels, the long leg of the lintel angle must be vertical (ABCB Housing Provisions Standard 2022, 5.6.7(a)(ii)).
12. Fire resistance - FRL: Lintels must have the fire-resistance level (FRL) required for the part of the building in which they are situated (NCC 2022 Volume One, S5C4(1)). However, concessions apply where the lintel does not support a fire door/window/shutter and other specific conditions (NCC 2022 Volume One, S5C4(2)).
13. Structural lintels supporting roofs/floors: Structural steel lintels that support roofs, framed floors or timber floors must have spans and effective load widths determined by the relevant NCC / ABCB Housing Provision tables (e.g., Tables 6.3.5a-f and Figure 6.3.5) and meet installation requirements including even load distribution and lateral restraint of the top flange (ABCB Housing Provisions Standard 2022, Section 6.3.5).
14. Design standards:
15. Steel lintels and their design should be in accordance with AS 4100 where noted.
16. Timber lintels, strutting beams and associated framing loads follow the ABCB framing tables and are consistent with AS 1684 framing practices where relevant (ABCB Housing Provisions Standard 2022, Section 6.3 notes).
17. Attachment and finishes: The method of attaching finishes or ancillary elements must not reduce the fire resistance of building elements (NCC 2022 Volume One, S5C5).

Residential vs Commercial

1. Residential (Class 1 and 10, covered by the ABCB Housing Provisions):
2. The Housing Provisions provide prescriptive lintel tables and clear installation rules suitable for typical domestic masonry and framed construction, including the specific lintel sizes in Table 5.6.7a, minimum bearings (100 mm / 150 mm), three courses of masonry above the lintel and corrosion protection details (ABCB Housing Provisions Standard 2022, 5.6.7 and Table 5.6.7b).
3. Structural steel lintels supporting roof or floor framing in housing are sized from the ABCB framing lintel tables (Section 6.3.5) so a prescriptive solution is often available for common spans and loadings.
4. Commercial (Class 2-9, covered by NCC Volume One and relevant standards):
5. Commercial buildings typically require project-specific structural design. NCC Volume One requires lintels to achieve the FRL of the building part where applicable (NCC 2022 Volume One, S5C4). Where fire protection, larger spans, unusual loads or loadbearing cavity walls apply, engineered lintel design in accordance with AS 4100 (steel) or relevant design standards is normally required rather than relying solely on prescriptive tables.
6. For non-loadbearing internal walls in Class 2 or 3 buildings, some concessions apply where lintels need not meet full FRL if they do not support fire doors/windows (NCC 2022 Volume One, S5C4(2)(a)(ii)).

Exceptions and Exemptions

1. Fire-resistance concession: A lintel need not have the full FRL for the part of the building where it is situated if it does not contribute to the support of a fire door, fire window or fire shutter and it spans an opening in a single-storey building or a non-loadbearing wall of a Class 2 or 3 building, or meets the alternative masonry thickness/span conditions (NCC 2022 Volume One, S5C4(2)).
2. Small masonry openings: For masonry not more than 150 mm thick, smaller maximum clear opening widths apply before an FRL is required - not more than 3.0 m for non-loadbearing masonry or not more than 1.8 m for loadbearing masonry leaf of a cavity wall (NCC 2022 Volume One, S5C4(2)(b)).
3. Alternate engineered solutions: Project-specific design in accordance with structural standards such as AS 4100 (steel) or relevant engineering practice may be used as an alternative to prescriptive ABCB table sizes, provided calculations and details demonstrate compliance with the NCC.

State and Territory Variations

1. The NCC is a national document but each State and Territory may include schedules or local amendments that affect lintel or corrosion requirements. The ABCB Housing Provisions note that corrosion categories should be determined using AS 2699.3, and some jurisdictions apply local interpretations or additional requirements for coastal or highly corrosive environments.
2. Notable practice points:
3. Check the state schedule in NCC Volume One (Schedules 4-12) for any modifications that affect FRL or material protection in your jurisdiction.
4. Local councils or certifiers in coastal regions commonly require increased corrosion protection beyond the minimums in Table 5.6.7b; verify with the relevant state schedule or local authority.

Practical Compliance Tips

1. Verify span and loading first - always check the clear span (width of opening) and the masonry height/load above the opening. Many prescribed lintel sizes and bearing requirements depend on these two measurements (ABCB Housing Provisions, Table 5.6.7a; 5.6.7(a)(v)).
2. Use the ABCB lintel tables for dwellings - for Class 1/10 work the ABCB Housing Provisions provide prescriptive lintel sizes and installation details which avoid the need for bespoke structural design for common spans.
3. Observe minimum bearings - provide 100 mm bearing for spans up to 1 m and 150 mm for spans over 1 m to avoid local crushing or failure (ABCB Housing Provisions, 5.6.7(a)(v)).
4. Protect against corrosion - select lintels with the required corrosion protection and restore any coating damaged by cutting or welding, referring to Table 5.6.7b and AS 2699.3 for coastal exposures (ABCB Housing Provisions Standard 2022, Table 5.6.7b notes).
5. Keep at least three courses of masonry above lintels where prescribed - this is a simple check often missed on renovations (ABCB Housing Provisions Standard 2022, 5.6.7(a)(vi)).
6. Consider FRL early - if the lintel is part of an element that must achieve an FRL (e.g., fire walls, openings with fire doors/windows) confirm FRL requirements from NCC Volume One, S5C4 and design the lintel and its supports to meet that FRL or use an alternative compliant solution.
7. Engage an engineer for atypical conditions - for large spans, heavy roof/floor loads, unusual lintel arrangements or when working on commercial Class 2-9 buildings, obtain certified structural design in accordance with AS 4100 (steel) or relevant standards rather than relying on prescriptive tables.

References:

1. ABCB Housing Provisions Standard 2022 - Lintels and Masonry rules (Sections 5.6.7, Table 5.6.7a, Table 5.6.7b; Section 6.3.5)
2. NCC 2022 Volume One - Building Code of Australia (S5C4 Lintels; S5C5 Method of attachment)
3. AS 4100 (Steel Structures) - referenced for lintel steel grade and design
4. AS 1684 - timber framing practices relevant where timber lintels or framing affect lintel loads
5. AS 2699.3 - guidance on corrosivity categories and coating thickness for steel lintels

Could not locate jurisdiction-specific schedule text in this search output - always check the relevant state schedule in NCC Volume One and local authority requirements for any additional variations.