Sources of Flat Roof Failures - Inspection Guidance
- CSI Division:
- Division 7 - Thermal and Moisture Protection
- Membrane Roofing
- Last Modified:
Technical Procedures Disclaimer
Prior to inclusion in GSA’s library of procedures, documents are reviewed by one or more qualified preservation specialists for general consistency with the Secretary of Interior Standards for rehabilitating historic buildings as understood at the time the procedure is added to the library. All specifications require project-specific editing and professional judgement regarding the applicability of a procedure to a particular building, project or location. References to products and suppliers are to serve as a general guideline and do not constitute a federal endorsement or determination that a product or method is the best or most current alternative, remains available, or is compliant with current environmental regulations and safety standards. The library of procedures is intended to serve as a resource, not a substitute, for specification development by a qualified preservation professional.
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:
- 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:
- Damp or stained walls
- Chipped or discolored paint
Inspect underside of roof deck:
- 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:
- 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.
Make sure drains are flush with the roof and free of debris.
- Change in original slope of roof
- Standing water
- Blocked drains and/or gutter
- Cracks, gaps or damage to coping joints
- 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:
- 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