Leak or Flood?

By Terry Bartholomew

Weather patterns are definitely changing. The reasons for this are widely debated but climate change can no longer be denied.

July 2019 was one of the hottest months ever recorded by modern instruments. According to accepted research this is partly attributed to the underlying warming of the planet, with burning fossil fuels increasing the level of carbon dioxide in the atmosphere but also the behaviour of the jet stream which has brought about some big heatwaves.

Heatwaves and long periods without rain lull us into a false sense of comfort concerning property maintenance but it is at this time that essential maintenance should be considered to ensure that when the rain does come, rainwater disposal systems etc. are able to cope.

We have seen a large number of instances over the past few weeks where water damage has occurred in buildings following rain deluge, with property owners and property managers reporting leaks in numerous areas which have resulted in damage to the internal fabric. Many of these leaks, it transpires, are actually floods, whereby something has happened which has caused a normally watertight structure to leak.

There can be various factors which contribute to this, firstly the fact that rainfall now seems to be more ferocious when it comes, often with extremely heavy storm conditions at very short notice, which can deposit many hours/days of average rainfall in a matter of minutes.

Secondly, the lack of periodic and essential maintenance on buildings means that rainwater disposal systems, which can ordinarily cope with general rainfall conditions cannot cope with storm deluge. Blocked outlets and drains/gullies are the most common factor yet the costs of maintaining these essential conduits can be very low.

The general state and capacity of sewage systems, particularly in urban areas, also means that in deluge conditions the sewers surcharge and cannot cope with the sudden influx/water capacity.


In London, where the majority of our work is based, we have seen incidences in recent weeks of the sewers surcharging causing storm water to back-up and flood out into the buildings at the lowest point of entry (often manholes, basement gullies or basement WC’s), and this can simply be due to the fact that the ferocity and velocity of storm water means that the sewer system cannot cope.

It is important to differentiate between leak and flood issues, as they require different analysis and solutions. Leaks can be prevented by simply maintaining the fabric of the building to ensure that there are no areas where water can penetrate, for example ensuring that lead flashings are properly detailed and correctly installed to roofs, that gutters are properly jointed and sealed and that masonry/window frame junctions are weathered with a suitable flexible sealant.

Flooding may not be totally preventable due to physical features beyond the boundary of the Clients property (e.g. public drainage), but things can be done to reduce the likelihood and effects:

  • Regular cleaning out of hoppers, downpipes, weirs, gutters etc. must be undertaken. This is essential and it is not cost effective to postpone maintenance as the damage from a single flood can far outweigh the costs incurred in keeping gutters etc. free flowing.
  • Non-return flaps can be considered to the private side of drains from a property before they enter into the sewer. This can reduce the likelihood of storm water backing-up the building.
  • Flood relieving outlets can be considered in gutters etc. where it is evident that the gutter could fill up to beyond the safe capacity level. This is something that can be considered in box gutters, parapet gutters etc. where overflow chutes can be provided and installed just below the flood line to ensure that there is a route for water to leak out over the building in the event of deluge conditions.