You have a leak in your waterproofing.
Any house that is "greenroofed" or has a living roof on the upper surface usually has a waterproof membrane between the structure and the live roof.
- For that matter it usually has several layers of root barrier, and drainage board between the waterproofing and the soil.
- Visit this U.S. EPA website to learn more about the layers and components of a live roof.
Your landscaper usually can help with everything BUT the waterproofing. This usually needs to be taken care of by a roofer.
- Given when your house was constructed it is highly unlikely that the waterproofing is still under warranty so I would call on a local roofer with green roof experience for help with this.
- If you're a do it yourself kind of guy, I'd recommend contacting Soprema or Henry roofing manufacturers for materials that work with a greenroof.
For more information:
Read "What type of waterproofing system is used under these green roofs, and what is the expected lifespan of the actual roofing material?" a Q&A answered by Polly Osborne.