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Problems with flat roofs Coatings Frisco TX

Most architects and engineers agree that a roof should be inclined or sloped to drain water to internal or external roof drains or overflows.  In some countries a small incline is mandatory. An incline of not less than 2% is accepted as a practical minimum. This is ¼ inch in 1 foot. However it is not uncommon to inspect roofs that lack this minimum requirement.  The following list explains some problems associated with a level roof.

  1. Water ponding forms a reservoir that continually aggravates insignificant faults and gradually makes them worse.
  2. Water ponds penetrate accidental punctures or faulty flashings and fill all voids in insulated roof systems.  Vapor barriers may retain the water until the entire roof is floating. This can occur almost immediately after the roof is laid.  Venting will not dry out the system.
  3. Ponded water destroys all ferrous metals in flashings in a few years unless they are extremely well galvanized, painted both sides, factory enameled, or kept above the highest water level.
  4. Ponded water can stain the building exterior by running over the edges where there are no gutters.
  5. Ponded water can run over base flashings at walls when the design or workmanship is defective or where there is deck settlement or shrinkage.
  6. Ponded water can cause additional deflection of the roof deck, which results in more water and more deflection.  Water weighs approximately 5 lb per square foot for each inch of depth.
  7. Mechanical equipment such as air conditioning or exhaust fans may be installed on the roof in locations that contribute to deflection not anticipated in the original design.
  8. Unless drain flanges are recessed below roof level, the extra felt stripping covering the flange and the gravel stop on the drain will raise the outlet as much as ½ inch.  This can be added to the normal deflection of the deck, unless the drain is located in midspan.
  9. On some buildings, the normal shrinkage of the frame (wood or concrete) will raise the drain sump enough to fracture the roof membrane, or at least increase the depth of ponded water.
  10. Fly ash and other airborne debris can block drain strainers, causing a backup of water, which can run over flashings if overflow outlets are not properly placed.
  11. Ponded water holds airborne debris, which slowly floats to drain outlets, eventually blocking them.  Sloped roofs flush themselves more readily. Drains are often located at columns or beams, which means the water that accumulates in deflected areas between the columns does not reach the drains.  If a pretressed double-tee concrete slab without camber has a span of 60 feet and an allowable deflection of 1/240 of the span, 3.0 in. of water can accumulate. If it is designed for 1/360 of the span, water can reach a depth of 2.04 in.
  12. Ponded water on some roofs attracts water birds at certain times of the year.  They leave feathers and deposit undesirable materials that clog drains and create orders.
  13. Leaks in level ponded roofs are difficult to trace and expensive to repair, especially in winter when there is ice and snow on the roof.  The ice and snow can be floating on water.
  14. Some damage may be done by photo oxidation, removal of water soluble constituents in bitumens, and freeze-thaw cycles, but these are not serious hazards.
  15. Smooth-surfaced asphalt roofs should not be laid on roof decks with inclines of less than ½ in., and for selvage-edge cap sheet roofs, not less than 1 in. per foot.  

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