Assertion: In urban areas, roofing on built-up areas, concrete and asphalts surfaces are major factors that inhibit infiltration and surface retention.
Reason: The presence of pervious surface areas decreases infiltration and initial losses and leads to consequent increase in the effective rainfall.
Correct Answer: C. Assertion is true, but Reason is false.
Solution:
The Assertion is correct. Urban surfaces like roofs, concrete, and asphalt are largely impervious, meaning they prevent water from soaking into the ground. This significantly reduces infiltration and increases surface runoff.
The Reason is incorrect. Pervious surfaces (like soil and vegetation) actually increase infiltration and initial water losses, which reduces the amount of effective rainfall (runoff). The statement describes the opposite effect.
Correct Answer: B. Two coats of paint over primer
Solution:
For maximum protection against weather, moisture, and pests, a complete system is essential. A primer seals the timber and provides a strong base for the paint to adhere to. Two subsequent coats of paint create a durable, protective barrier. This multi-layer approach ensures the longevity of the timber truss.
Correct Answer: B. Mansard roof
Solution:
A Mansard roof is a distinctive four-sided roof with a double slope on each side that meet to form a low-pitched roof. The lower slope is much steeper than the upper one, creating the characteristic break.
Correct Answer: D. Bay
Solution:
In structural framing, a "bay" is the open space between two repeating structural elements. For a roof, this is the longitudinal space measured from one truss to the next.
Correct Answer: B. Roof covering
Solution:
The corrugated profile gives thin steel sheets significant strength and rigidity, making them lightweight, durable, and easy to install. This makes them an extremely common and cost-effective material for roof covering, especially for industrial buildings, warehouses, and sheds.
Correct Answer: D. 15 × 7.5 × 2.5 cm
Solution:
Madras terrace roofing is a traditional flat roofing technique that uses specially made flat bricks or tiles. A standard and commonly cited size for these bricks is 15 cm in length, 7.5 cm in width, and 2.5 cm in thickness. They are laid in courses over wooden joists and bonded with lime mortar.
Correct Answer: C. 1 in 60
Solution:
Although called "flat roofs," they must have a slight slope (gradient) to ensure proper drainage of rainwater and prevent water from pooling, which could lead to leaks and structural damage. A typical minimum slope for an RCC roof is 1 in 60.
Correct Answer: A. 3.5 m or less
Solution:
A couple roof is the simplest type of pitched roof, consisting of pairs of rafters that lean against each other at the ridge. It has no tie beams or internal bracing, so the weight of the roof can cause the walls to spread outwards. Therefore, it is only suitable for very small spans, generally considered to be 3.5 meters or less.
Correct Answer: C. Hip roof
Solution:
A hip roof is defined by its four sloping sides that come up from the walls of the building to meet at a ridge. This design is more complex to build than a simple gable roof but provides better stability in high-wind areas. [Image of a Hip roof design]
Correct Answer: A. 1:60 to 1:100
Solution:
Lime terracing is a traditional roofing technique known for its cooling properties. A very gentle slope is required to allow rainwater to drain effectively without causing erosion to the lime concrete surface. The standard recommended slope is between 1 in 60 and 1 in 100.
Correct Answer: A. Barrel vault shell roof
Solution:
A barrel vault is essentially a semi-cylindrical arch extended along an axis. This form is well-suited to cover rectangular spaces, but it can also be adapted to cover circular or curved structures by resting on the circular walls, transferring the load down through the masonry.
Correct Answer: B. Valley
Solution:
A valley is the internal angle or channel created where two sloping roof surfaces meet. It's the opposite of a hip, which is an external angle. Valleys are critical components that must be properly flashed to direct water off the roof.