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Flat roof versus pitched roof

Short answer

Flat roof (slope <10°) provides a usable terrace but may leak and is costly; pitched roof (slope >10°) sheds water quickly, is lighter and cheaper for large spans, but lacks terrace and has fire risk.

Differentiate flat and pitched roof (comparative advantages and disadvantages of slope and flat roof).

A flat roof is nearly horizontal (slope under 10 degrees, only enough for drainage); a pitched roof has a slope steeper than 10 degrees.

PointFlat roofPitched (slope) roof
Slope0 to 10 degreesMore than 10 degrees (25-45)
MaterialRCC slab, jack arch, stone slabTimber/steel truss with tiles, slates, sheets, thatch
Rainwater drainageSlow, chance of water ponding and leakageFast, little leakage
Usable spaceTerrace for living, water tank, solar panelsAttic space, but no terrace
CostCostly in large spansCheaper for large spans with light covering
WeightHeavyLighter
ConstructionNeeds skilled labour and formworkQuick, can be made with local materials
MaintenanceWaterproofing needs renewalFrequent repair of covering
Fire resistanceVery goodPoor (thatch, timber)
Thermal insulationPoor unless insulatedBetter, air in roof space
Wind effectLittleLarger wind uplift in light coverings
ExtensionEasy to add storeyDifficult

Advantages and disadvantages

  • Flat roof: advantages are usable terrace, easy future extension, fire safety and strength against earthquake when RCC; disadvantages are leakage, cracks due to temperature changes, and high cost.
  • Pitched roof: advantages are quick drainage, lower cost for larger spans, good insulation; disadvantages are fire risk, high maintenance, no terrace.

✓ Answer checked by Claude Opus 5.5 (high effort)

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