Gravel Voids On Flat Roofs May Shorten the Life Expectancy or Cause Leaking

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Published: August 13, 2014 Last Updated: January 26, 2018

A common type of roofing for flat roofs is what’s often called a “Tar and gravel”, hot mopped, or a built up roof. It is basically composed of alternating layers of bitumen and reinforcing sheets (membranes) with hot tar applied between layers and gravel on top.

These types of roofs have been used for over a 100 years and can be a very good type of roof.

Gravel voids and cracks

Wind, weather and small animals may cause gravel voids. For example, cats may climb onto the roof and use the gravel as if it’s their litter box and they scratch the gravel back and into piles.

When the gravel gets pulled back or is not covering an area, the suns UV rays will hasten the roofs deterioration and/or cracks in the tar may appear.


Cracks and voids should be patched or sealed to prevent moisture from entering the cracks. Also, the gravel voids should be properly covered.

Much of the time, limited maintenance or repair will handle this issue. However, roofs that are very old and in bad condition may need to be re-roofed.

Who to consult? Roofing contractor.

Generally fixing gravel voids is a maintenance item for a roof and roofers do the maintenance on these roofs. In most circumstances a home owner may do limited maintenance items as well.

Additional Resources

  • Blisters on a flat roof may result in leaking if they get popped. Just stepping on them when doing work or maintenance on the roof may pop them.

  • Flat type roofs often have leaves and other debris that gathers on them overtime. If the leaves and debris are not occasionally removed, the drains may get clogged or restricted by the debris. If water builds-up, leaking may occur and if the water builds up high enough, it can cause structural damage.

  • Deterioration or leaking may occur if water stands on a roof too long. A little puddling is acceptable provided that it is not too deep.

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