Summary: Drainage problems on small properties often are tied to structural issues and not water-logged soil resulting from sub-surface conditions.
Question: Our last house had all kinds of drainage problems and water-logged soil. Our new home and property is smaller (downsizing) what are some things we can look out for and work on to prevent any drainage issues in the landscape and especially on the patio/terrace? Valerie, Buffalo Grove, Illinois
Answer: Valerie, drainage problems on a small property are more often tied to structural errors of one kind or another than to water-logged soil in the landscape resulting from sub-surface conditions. Typical difficulties are:
1 A badly-pitched terrace. The terrace should be constructed so that water runs off gently into garden areas away from the house and foundation; it should not flow towards the house, or towards one spot close to the house from where it can seep into a basement.
The standard pitch for patio drainage is one-eighth to one-quarter inch per foot. On a large patio/terrace, it may be necessary to pitch in more than one direction. If there is a wall or parapet (retaining wall) round the terrace, openings (weep holes) should be provided at the base to allow water to escape from the surface.
Make sure of the plants planted in the area where the water drains can become “over watered.” Planting patio trees like Hibiscus may need to grow in containers.
2 A terrace that cannot drain because it is below the level of adjoining turf.
3 A walkway that is too steep, so that water rushes down it and accumulates in a puddle.
4 Landscaping steps that have been constructed without a slight wash, or pitch, to enable water to run off; or with a pitch in the wrong direction, so that water runs back towards a riser and forms a puddle.
5 Failure to provide weep holes in a retaining wall. In freezing weather, the accumulated water expands and causes masonry to crack.
6 A raised or flush bed, with an inadequate edging of wood or masonry, so that soil is washed out onto the walk.
7 A roof overhang from which water beats onto plants close to the house, or makes a furrow in the soil. A french drain is one common solution.
8 A downspout not connected with an underground drainage system or sewer, causing water to wash out the soil and make a hole below the spout.
9 A poorly graded lawn leads to surface water drainage patterns into areas which water runs rapidly, forming “mini lakes” which drain slowly.
10 Pockets of poor drainage caused by the burial of tightly packed stones and concrete building debris.
11 Water in the basement, caused by bad grading round the house and foundation, or failure, when the water table is high, to provide subsurface drainage.
When a bad condition does exist, sometimes the only satisfactory solution is to tear out the old work, troublesome though this may be. Often, however, a little ingenuity will put things right.