The thickness of each leaf of a cavity wall shall not be less than:
🔬 Understanding Cavity Walls
A cavity wall is a type of wall construction consisting of two separate walls, called "leaves" or "wythes." These two leaves are separated by a continuous air gap or "cavity" and are joined together by metal wall ties at regular intervals. This construction method is primarily used for external walls to provide superior thermal insulation and prevent moisture penetration.
Function of Each Leaf:
• Outer Leaf: The exterior wall that faces the weather.
• Inner Leaf: The interior wall that forms the inside surface of the room. It is typically the main load-bearing element.
The question asks for the minimum required thickness for each of these individual leaves to ensure they are structurally stable.
⚖️ Detailed Analysis of the Requirement
Building codes and standards specify minimum dimensions for structural elements to ensure their stability and strength. For a cavity wall, each leaf must be thick enough to be stable on its own and to properly engage with the wall ties.
(b) 7.5 cm
Why it's correct: According to building regulations (such as the National Building Code of India), the minimum thickness for either the inner or outer leaf of a cavity wall is specified as 7.5 cm (or 75 mm). This thickness is considered the minimum necessary to provide adequate stability and strength for each individual wythe before they are tied together to act as a composite wall system.
(a) 5 cm
Why it's incorrect: A 5 cm (50 mm) thick brick leaf would be too slender and unstable. This is less than the standard width of a brick and would be prone to buckling and difficult to construct properly.
(c) 10 cm
Why it's incorrect: 10 cm is the nominal thickness of a standard half-brick wall and is a very common thickness for the leaves of a cavity wall. However, the question asks for the absolute *minimum* thickness permitted by code, which is 7.5 cm, not 10 cm.
(d) 15 cm
Why it's incorrect: This is a substantial thickness and, while structurally sound, it is much greater than the required minimum.
💡 Study Tips for Masonry Dimensions
- Memorize the Minimum: For cavity walls, 7.5 cm is the key minimum value to remember for the thickness of a single leaf.
- Distinguish Minimum vs. Common: While 10 cm (a half-brick wall) is a very common thickness for a cavity wall leaf, it is not the *minimum* required by the standards. Exam questions often test these specific minimum values.
- Think Stability: The minimum thickness is dictated by the need for each leaf to be stable enough during construction and to function correctly as part of the overall wall system.