Sources of Flat Roof Failures - Inspection Guidance

Procedure code:
750001G
Source:
Hspg Prepared For Nps - Sero
Division:
Thermal and Moisture Protection
Section:
Membrane Roofing
Last Modified:
06/08/2017

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We’ve reviewed these procedures for general consistency with federal standards for rehabilitating historic buildings and provide them only as a reference. Specifications should only be applied under the guidance of a qualified preservation professional who can assess the applicability of a procedure to a particular building, project or location. References to products and suppliers serve as general guidelines and do not constitute a federal endorsement nor a determination that a product or method is the best alternative or compliant with current environmental regulations and safety standards.


This standard includes guidance on identifying sources of flat roof failures by looking at specific problem areas.

Inspect Exterior walls of building:

Look for:

  • Settlement cracks
  • Stained or displaced flashing or drainage facilities
  • Efflorescence on the wall - this may be a sign of leaks in the coping or parapet above.

Inspect interior walls of building:

Look for:

  • Damp or stained walls
  • Chipped or discolored paint

Inspect underside of roof deck:

Look for:

  • Wood deck: rotted or warped boards
  • Concrete or gypsum deck: cracks and stains; spots ofrust may also appear on a concrete deck from wet reinforcing rods in the concrete; a gypsum deck may spellas a result of leaking water.
  • Metal deck: rust spots

Inspect roof surface:

Look for:

  • A sprung board in a wood deck. Identified by sharp indentation of roof surface, often caused by a broken board.
  • A noticeable "give" in the roofing under weight.
  • Cracks in membrane.

Inspect drainage:

Make sure drains are flush with the roof and free of debris.

Look for:

  • Change in original slope of roof
  • Standing water
  • Blocked drains and/or gutter

Inspect copings:

Look for:

  • Cracks, gaps or damage to coping joints

Inspect flashings:

Look for:

  • Loose, torn or missing flashing
  • Improper bond between base flashing and edge of mat or between counterflashing and wall
  • Flashing that is not turned up enough potentially allowing water to back up, stand against the wall and leak down into the roof deck
  • Rust on flashing or lack of protective coating on corrosive metals
  • Inspect roof at least twice a year and inspect after any severe storms:

Look For:

  • Debris accumulation and vegetation growth
  • Deterioration of the surface and membrane
  • Deck deflections (sometimes from structural problems)
  • Ponding and tensile splitting of water weakened felts and/or membrane
  • Ice formation and resulting membrane damage
  • Positive drainage
  • Wear spots at curbs and penetrations
  • Ruptures, bare spots, splits, metal flange splits, deteriorated felts
  • Warping, cracks, splits, slivers, cupping and rot

Note priority of defect

  • (i.e. none, minor, major, complete failure.)

Note changes from last inspection.

  • i.e. none, minor, major,
  • Note what changes occurred
Last Reviewed: 2017-08-13