Imposed (live) load on an accessible roof in building design: What value should be considered for service load calculations in traditional kg/m² terms?

Introduction / Context:
Live load selection for roofs affects member sizing, slab reinforcement, and serviceability. Many codes provide tabulated imposed loads for “accessible” roofs (used for maintenance and occasional occupancy) versus “inaccessible” roofs. The question uses traditional units (kg/m²) common in older texts and exams.

Given Data / Assumptions:

• Roof is accessible to people for maintenance or intermittent use.
• Load value is a nominal uniformly distributed load used for design.
• Units are kg/m², matching classic building practice problems.

Concept / Approach:

Accessible roofs carry higher live loads than roofs accessible only for inspection. A typical tabulated value in many curricula is 150 kg/m² for accessible roofs, used along with wind loads and, where relevant, ponding checks for drainage.

Step-by-Step Solution:

Verification / Alternative check:

Modern codes provide similar ranges in kN/m²; conversion shows 150 kg/m² ≈ 1.5 kN/m². This aligns with common practice for accessible roofs in non-assembly conditions.

Why Other Options Are Wrong:

(a) Nil is for inaccessible roofs only; (b) 75 kg/m² is too low for accessible; (d) 200 kg/cm² is a unit error (immense load); (e) 300 kg/m² is conservative for ordinary accessible roofs unless special use applies.

Common Pitfalls:

Confusing accessible with inaccessible roofs; mixing units (kg/m² vs kN/m²); ignoring superimposed dead loads (screed, waterproofing) in addition to live load.

Final Answer:

150 kg/m²