Design feedback needed on removing part of a garden wall

[Bruce P.]

Hi,

So my friend is building a ~600 sq foot ADU (Accessory Dwelling Unit) in their backyard to be rented out as a "private residence" (think of it like a 1 bedroom studio/apartment with its own living space/bedroom/bathroom. It will be fenced off to shield prying eyes from the house and have its own gated entrance on the side of the house.

The whole house lot is surrounded by a 2 foot high (approx 4 foot wide) brick walled "garden" where shrubs and trees currently grow. There's a sprinkler system throughout the garden.

One possible headache is the fact that the homeowner (my friend is the owner but there will be other renters in the 4 bedroom house) may end up subsidizing the cost of watering the garden trees/shrubs by virtue of the fact the brick walled garden surrounds the entire backyard.

Other than leaving everything as is and just explaining to potential renters that the people in the home end up footing the water bill for the shrubs / trees, is there a low-cost design and easy to rehab design tweak that could be made to the garden wall to alleviate this concern? Or is my friend overthinking it? Since the sprinkler system runs throughout the soil in the garden wall and the soil is also basically a moderately inclined "hill", it might not be too easy to demolish the part of the wall that surrounds the ADU and fence it off, but my friend is fairly new to the rehab process.

Here is a link to a diagram that explains it visually: ADU diagram (for some reason picture attachment isn't working)