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

Common drainage defects

  • Inadequate slope of the roof surface (especially “low-slope” roofs) leads to ponding water and accelerated membrane deterioration, leaks, and possible structural overloading.
  • Clogged gutters, scuppers, and drains from leaves, granules, and debris cause water to back up under shingles, over fascia, and into soffits and walls.
  • Improper gutter slope or sizing results in standing water in gutters, frequent overflow, and ice buildup at the eaves.
  • Missing, damaged, or undersized roof drains, strainers, or scupper openings on low‑slope sections allow water to pond around penetrations and seams.
  • Downspout defects (clogged, 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.
  • Lack of secondary (overflow) drainage on low‑slope roofs above living space can allow deep ponding during heavy rain if primary drains clog, increasing collapse risk.

Resulting damage and risk

  • Foundation and site problems where overflowing gutters and short downspouts dump water at the perimeter, contributing to settlement and basement/crawlspace moisture.
  • Water intrusion and leaks into sheathing, insulation, ceilings, and wall cavities, often appearing as interior stains and wet drywall.
  • Structural damage from chronic wetting and the weight of standing water, including sagging roof decks and, in severe cases, partial roof collapse.
  • Deterioration of roofing materials at eaves, valleys, and penetrations, including shingle edge rot, membrane seam failure, and corrosion of flashings.
  • Moisture-driven biological growth (mold, algae, moss) that degrades shingles, creates slip hazards at discharge points, and can affect indoor air quality.

Typical inspection red flags

  • 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.
  • Sagging or pulling‑away gutters, or gutters with obvious back‑pitch away from downspouts.
  • Interior ceiling stains near exterior walls or below low‑slope sections, especially below areas with known ponding or overflowing gutters.
  • Downspouts terminating right at the foundation or onto lower roofs in a way that scours shingles or overwhelms lower gutters.

Prevention and correction themes

  • Provide and maintain adequate slope on “flat” roofs (about 1/4 inch per foot) and add crickets or tapered insulation where water tends to collect.
  • Size and pitch gutters correctly, add sufficient downspouts, and keep all conveyance components clear with regular cleaning and guards where appropriate.
  • Ensure roof drains, scuppers, and strainers are properly located at low points, secured, and protected from debris, with overflow routes where required.
  • Extend downspouts several feet away from the foundation and avoid discharging directly onto roof surfaces whenever possible.