Controlling the flow of water drainage around and away from buildings is important in any location but even more so when living in a rain forest such as the wet West Coast of British Columbia. When drainage systems aren’t doing their job properly moisture problems, musty smells and mold can all start to show up in the lower floors of the home.
Ideally all buildings should have a six foot area around the immediate outside wall that slopes away from the building and prevents water accumulation at the foundation wall.
The lay of the land will determine the complexity of the drainage system. Steeply sloped lots on hillsides such as Vancouver’s North Shore and TriCities areas require special attention on the high end of the property so that water flowing downhill at grade and underground is intercepted before it can reach the house.
Deep basements which can be found throughout the entire Greater Vancouver region need to be properly sealed around the outside since water pressure increases with depth and water ingress becomes more likely.
Low lying areas such as Richmond, Ladner and along the Fraser River basin typically do not have basements or crawlspaces below grade. Properties in these areas have a high water-table and good drainage systems are needed to remove surface water that collects on the property.
Weeping tiles or drain tiles have been used underground for many years to catch and divert water away from the home. In older houses these were connected to the sanitary sewer but over time they are being changed to drain into a municipal storm sewer. There are a number of drain pipes in use, from older clay and concrete types to a variety of plastic piping of which the white PVC piping is now the most common.
Traditionally one perforated pipe ran underground at the base of the foundation wall to deal with both ground water and roof water. Building practices have developed over time and currently two levels of piping are used, one perforated at the base of the foundation that deals with ground water only and a higher non-perforated pipe to deal with roof water only. Recently some structures, depending on their location and depth in the ground, also have their foundation walls wrapped with a drainage fabric to prevent water penetration and improve water flow to the drain tiles as well.
In order to assess the adequacy of the existing drainage system the home inspector will note the age of the house to help determine the type of piping used. The inspector will estimate how much debris is visible in the piping from ground level and will check the interior of the underground portion of the house for any signs of leakage. If the drain tiles are older and significant debris is noted they should be cleaned out by a drainage specialist. Complete failure of the drain tiles will result in an expensive repair costing in the range of $10,000 to $15,000 for complete replacement.