665mm Masonry Returns

Understanding Approved Document A, BS 5628-1 and Eurocode 6

What Are 665mm Masonry Returns?

A masonry return is the section of wall that turns through 90 degrees from another wall, creating a corner. This return provides lateral restraint by tying adjoining walls together, increasing the overall stiffness and stability of the structure.

For conventional domestic masonry construction, Approved Document A recognises 665mm masonry returns as a simple means of demonstrating compliance with the structural requirements of Part A of the Building Regulations.

The guidance reflects long-established structural principles that were historically set out in BS 5628-1: Code of Practice for the Structural Use of Masonry. Although BS 5628 has now been superseded by Eurocode 6 (BS EN 1996), the simplified guidance within Approved Document A continues to provide an accepted route to compliance for many low-rise residential buildings.

Why Are Masonry Returns Required?

Masonry performs exceptionally well in compression but is considerably weaker when subjected to bending and lateral loads.

External walls are constantly subjected to forces including:

• Wind pressure and suction
• Thermal movement
• Differential settlement
• Accidental impact
• Structural movement

Without adequate restraint, long masonry panels can become unstable or deflect excessively.

A masonry return acts like a buttress, helping the wall resist these horizontal forces. Rather than relying solely on the strength of the brickwork itself, the return allows adjoining walls to work together as a single structural element.

This improves the wall’s ability to resist wind loading and significantly increases its overall stability.

What Does Approved Document A Require?

Approved Document A provides practical guidance for complying with Part A of the Building Regulations 2010 (as amended), which requires buildings to safely sustain and transfer loads without excessive movement or collapse.

For typical domestic construction, the document includes simplified guidance that avoids the need for detailed structural calculations.

Providing 665mm masonry returns is one recognised method of satisfying these simplified provisions.

However, it is important to understand that Approved Document A does not state that every building must include a 665mm return. Instead, it provides a “deemed-to-satisfy” solution for conventional masonry construction.

Where these recommendations cannot be achieved, designers are free to demonstrate compliance through an engineered structural design.

How Does Eurocode 6 Differ?

One of the biggest misconceptions within the construction industry is that Eurocode 6 contains a mandatory 665mm requirement.

It does not.

Unlike BS 5628-1, which contained prescriptive design guidance, Eurocode 6 adopts a performance-based approach.

Instead of specifying fixed return dimensions, engineers assess factors including:

• Wall slenderness
• Wall height and length
• Masonry strength
• Vertical loading
• Wind loading (determined in accordance with Eurocode 1)
• Boundary conditions and lateral restraint

The question under Eurocode 6 is not whether a wall has a 665mm return, but whether it is structurally stable.

This allows greater flexibility for modern architectural designs while maintaining compliance with the Building Regulations.

What Happens When a 665mm Return Cannot Be Achieved?

Modern homes increasingly feature:

• Large bi-fold doors
• Full-height glazing
• Corner windows
• Open-plan extensions
• Contemporary elevations with minimal brickwork

In these situations, providing a full masonry return is often impractical or conflicts with the architectural vision.

Where the simplified guidance cannot be followed, the structural performance normally provided by the masonry return must instead be achieved by other means.

Common solutions include:

Structural Steel Frames ‘v’ 665mm masonry returns

Goalpost frames and portal frames are widely used around large openings, transferring loads around the opening while providing the lateral stiffness that the masonry return would otherwise deliver.

Steel Wind Posts ‘v’ 665mm masonry returns

Wind posts are frequently incorporated into cavity walls to provide restraint for long masonry panels where returns are limited.

Reinforced Masonry ‘v’ 665mm masonry returns

In certain applications, reinforcement within the masonry itself can improve resistance to lateral forces.

Structural Engineering Design

Where none of the simplified provisions are appropriate, an engineer can undertake calculations in accordance with Eurocode 6 to demonstrate compliance with Part A of the Building Regulations.

This approach is increasingly common for bespoke homes and architect-designed projects.

Why Building Control May Request Further Information

If drawings show returns that are significantly shorter than the guidance contained within Approved Document A, Building Control will usually expect supporting structural justification.

This may take the form of:

• Structural calculations
• An engineer’s design
• Details of steel framing or wind posts
• Alternative restraint methods that demonstrate equivalent structural performance

Provided the wall can be shown to achieve adequate stability, compliance can still be achieved without following the simplified guidance exactly.

Conclusion on 665mm masonry returns

Although 665mm masonry returns remain a widely recognised benchmark for traditional masonry construction, they should be viewed as one route to compliance rather than an absolute requirement.

Approved Document A provides a simplified method suitable for many domestic projects, while the engineering principles that informed the guidance were historically established in BS 5628-1. Today, bespoke structural designs are generally undertaken using Eurocode 6, which focuses on demonstrating structural performance rather than complying with fixed dimensions.

Understanding this distinction allows architects, surveyors, contractors and homeowners to make informed design decisions. Where 665mm returns are not practical, alternative structural measures such as steel frames, wind posts or engineered calculations can achieve the same level of safety while preserving the intended architectural design and lateral stability of the building.