Expansion joints in brick masonry — nominal thickness guideline In building construction practice, the nominal thickness of an expansion joint provided in brick walls is generally kept more than which of the following values? Select the closest standard threshold.

Introduction / Context:
Expansion joints in masonry walls are intentional gaps that accommodate movement due to thermal expansion, moisture changes, creep, and minor foundation movements. Without an adequate joint width, compressive stresses can build up and lead to unsightly cracking, bulging, or distress at openings and corners. This question checks your familiarity with typical nominal joint widths used in brickwork for serviceable performance.

Given Data / Assumptions:

• Masonry unit: fired clay brick walls in typical building envelopes.
• Objective: provide a practical nominal thickness for expansion joints.
• Normal temperate climates and standard detailing with sealant and backing rod.

Concept / Approach:
Thermal and hygric movements in long brick walls are handled by placing expansion joints at suitable spacings and with adequate joint width. A commonly adopted nominal thickness is just over 20 mm, which allows room for a compressible filler and an elastomeric sealant while maintaining constructability and durability. Thinner joints (5–15 mm) tend to be insufficient to accommodate movement, especially in long, sun-exposed elevations.

Step-by-Step Solution:

Verification / Alternative check:
Design guides align joint width with calculated movement (coefficient of expansion * length * temperature range) and sealant capability; values commonly round to approximately 20 mm or slightly more for brick facades.

Why Other Options Are Wrong:

• 5 mm, 10 mm, 15 mm: Generally too small for reliable performance with sealant movement capability and construction tolerances.
• 40 mm: Possible for special cases but unnecessarily large for standard brickwork.

Common Pitfalls:
Placing joints too far apart or too narrow; omitting backing rods; failing to continue joints through lintels or parapets, causing stress concentrations.

Final Answer:
20 mm