Residential roof drainage problems usually come down to design, installation, or maintenance issues with the roof plane, gutters, and downspouts.

Common drainage defects

Steep-slope

  • Clogged gutters, scuppers, and drains from leaves, granules, and debris cause water to back up under shingles and into soffits and walls.
  • Improper gutter slope or sizing results in standing water in gutters, frequent overflow, and ice buildup at the eaves.
  • Downspout defects (clogged, damaged, disconnected, too few, or discharging too close to the house) cause water to overflow at the roof edge and collect at the foundation.
  • Poor roof geometry or drain placement (drains in high spots, no crickets, long dead valleys) traps water in localized low areas.

Resulting damage and risk

  • Foundation and site problems where uncontrolled drainage dumps water at the perimeter, contributes to settlement and basement/crawlspace moisture.
  • Improper or deteriorated  flashing can allow drainage to damage sheathing and/or drywall.
  • Moisture-driven biological growth (mold, algae, moss) that degrades roofing and can create slip hazards.

Typical inspection red flags

  • Lack of a drainage control system.
  • Damaged drainage system components.
  • Downspouts terminating at the foundation or onto lower roofs in a way that scours shingles or overwhelms lower gutters.
  • Damaged or separated downspouts.
  • Visible ponding on low‑slope areas that remains 48 hours after rainfall.
  • Gutters full of debris, standing water, heavy staining or streaking on fascia and siding below the eaves, and eroded soil at drip lines.
  • Damaged or improperly-sloped gutters.
  • Interior ceiling stains beneath or near roof penetrations or changes in slope or pitch.

Prevention and correction themes

  • Provide and maintain adequate slope on "flat" roofs.
  • Configure roof slope to shed water (install crickets where necessary).
  • Size and pitch gutters correctly, add sufficient downspouts, and keep all conveyance components clear with regular cleaning and guards where appropriate.
  • Add downspout extensions where necessary.
  • Ensure roof drains, scuppers, and strainers are properly located at low points, secured, and protected from debris, with overflow routes where required.
  • Avoid downspout drain-ties where ice formation is possible.