Waterproofing: The facts

Waterproofing is the term used to describe the process of protecting the exterior of a building or structure from water. Unlike damp proofing, which describes efforts to protect a building against rising, lateral or penetrating damp, waterproofing covers any method used to protect the substrate from the ingress of moisture and damp, usually from above.

Waterproofing covers such areas of the building as roofs (flat and pitched), balconies, patios, parapets, guttering, down pipes, flashing's etc. Any structure designed to channel rainwater away from the substrate is covered by this terminology.


Parapet Walls. The top section of walls bear the most amount of weathering from the sun and rain and, if not properly water proofed, can crack and lead to water ingress. Since moisture will descend under the force of gravity, it follows that plaster on the lower sections of walls will be contaminated and even ceilings and off-leading walls if the source of moisture ingress is not stopped. It is, therefore, a good idea to protect the tops and immediate sides of the walls with some form of waterproofing.

Flashing's/Gulley. All Joints between walls and roofs need to be adequately insulated. Flashing's are a common source of leaks and it is important to ensure that these are properly sealed. Flashing's are normally constructed of metal and should be recessed into the brickwork structure to provide full protection. Leaks need to be repaired promptly to avoid damage to structures and ceilings.

Flat Roof/Balcony/Patio. All three these areas require adequate waterproofing to prevent moisture from penetrating the ceiling beneath or spreading laterally and invading the structure walls. This type of waterproofing is usually covered by the addition of either a screed or tiling. A flat roof must have an adequate “fall” to water outlets (minimum of 2%). The outlets should ideally be 10cm flanged outlets to accommodate heavy rain and prevent the build-up of moisture at the walls.