QuestionI have a flower bed next to my house with heavy clay soil. I would like to build a raised flower bed on top of it and use brick or stone to build a retaining wall around the bed.
How far away from the house walls does this need to be?
The existing bed is between the house and the driveway. I want to make sure I don't to damage to my house with the drainage from a raised bed.
How would I go about installing a French drain in the raised bed if I build one?
AnswerIf you plan to raise the bed to an elevation that will be higher than the finished floor in your house I would not recommend doing it. You should never raise the soil against the house where it was not designed for waterproofing.
You never want water against a wall where it will be equal to or above the finished floor unless the wall was specifically designed for it. If the house was design and built right there may be substantial waterproofing behind the veneer material (brick, stone ,etc.) of your house but if not there may be nothing and putting water against the brick will lead to water infiltration.
If you must do this, then you need to apply a fluid applied water proof membrane and other drainage materials (liners, drain fabric, drain products, etc.) against your house with some form of french drain to catch the water at the bottom and divert it away from your foundation.
You could as an alternative leave the soil as is within 6 to 12" of the face of the house and then slope up and create a small berm around the house that is raised for flowers, etc. You need breaks in this berm to allow water from behind the berm to escape. You could also put a french drain just below the surface along the wall in this case and catch water behind the berm if you don't want to break the berm.
Your last option is to excavate and remove the old bad/clay soil and install gravel and a drain system under your beds. Then replace the old soil with good loamy/organic planting soil that is finished equal to the existing elevation thus getting the soil you need (well drained and high organic content) without "raising the bed".
Best Of Luck
Sean J Murphy, LA,ISA, LEED AP
Please check out my blogs and articles on landscape topics like this on my websites.
http://www.seanjmurphy.com
http://amenityarchitects.com
