You always need a drainage system behind a retaining wall. by: Nancy Dransfield
Mary, I'm glad you were careful and noticed this omission. It will save you a costly repair later. Any height retaining wall needs a foundation drain and possibly a surface drain directly behind the top of the wall depending on if your site directs water towards the wall. On one of my jobs, a contractor did not price the drainage system and his reply to me was that it did not need it because it was installed without mortar and the water can weep out through the openings between the blocks. These openings are not enough! Also be sure that the modular wall being built is rated to a 3 foot height, not all of them are.
