25 questions
Retaining wall and drainage FAQ for Marietta and Cobb County
Straight answers on cost, permits, neighbors, how walls are built and how French drains work in Georgia red clay. Prices are typical published ranges, not quotes. Last updated October 27, 2026.
Cost and planning
How much does a retaining wall cost in Marietta?
Most walls are priced per square foot of wall face, which is length times exposed height. Typical installed ranges from LawnStarter's 2026 guide run about $20 to $50 per square foot for treated timber, $30 to $90 for concrete block, and $45 to $110 for natural stone. A 40 foot long, 3 foot tall wall commonly lands between $3,000 and $9,600.
How much does a French drain cost in Marietta?
Angi's 2026 data puts French drains at about $20 to $50 per linear foot installed, with most projects between $2,000 and $7,000. Deep drains along a foundation, long runs to an outlet, and replacing sod or hardscape add to the price.
Is a block or a stone retaining wall cheaper?
Block is usually cheaper. Typical installed ranges are about $30 to $90 per square foot for concrete block versus $45 to $110 for natural stone, mainly because fitting stone is slow, skilled labor.
What is the cheapest retaining wall that still lasts?
Treated timber has the lowest upfront cost but often lasts only 15 to 25 years in wet clay. For most Cobb County yards, a plain segmental block wall on a good gravel base costs more at first but usually costs less over 20 to 40 years.
How long does it take to build a retaining wall?
Many low residential walls take a few working days on site once materials arrive. Walls that need an engineer and a permit take longer, mostly because of design and approval time, not construction.
When is the best time of year to build a retaining wall in Georgia?
Walls can be built year round here. The main thing to avoid is working saturated red clay right after heavy rain, since wet clay does not compact well. Dry stretches in spring and fall are often the easiest to schedule.
Permits, neighbors and insurance
Do I need a permit for a retaining wall in Cobb County?
In unincorporated Cobb County, a wall over 4 feet tall, or any wall holding up a driveway, building or slope, generally needs a building permit. Walls 4 feet or less holding plain soil are generally exempt. Marietta, Kennesaw, Smyrna and other cities set their own rules, so check with the city for your address.
Does a retaining wall over 4 feet need an engineer?
In unincorporated Cobb County, walls over 4 feet generally need plans stamped by a Georgia licensed professional engineer. Angi's 2026 data puts engineering for a residential wall at about $350 to $750.
Who is responsible for a retaining wall between two yards?
Generally the owner of the land the wall sits on is responsible for it. If it sits on the property line, responsibility may be shared. Check your survey, plat, deed and any HOA documents, and talk to a real estate attorney if there is a dispute. This is general information, not legal advice.
Can I send drainage water onto my neighbor's yard?
Georgia law generally expects a lower lot to accept water that flows naturally, but an uphill owner should not concentrate or increase runoff onto a neighbor. A good drainage plan sends water to an outlet on your own property, a dry well, or an approved point. This is general information, not legal advice.
Do I need HOA approval for a retaining wall?
Often, yes. Many Cobb County subdivisions have an architectural review committee that must approve walls, especially ones visible from the street. Check your covenants before work is scheduled.
Does homeowners insurance cover a retaining wall collapse?
Often not for the wall itself. Many policies exclude retaining walls from collapse coverage, though damage to the house caused by a collapse may be treated differently. Read your policy or ask your agent.
How walls are built
How deep should a retaining wall be buried?
A common rule of thumb for segmental block is to bury the first course about one eighth of the wall height, with at least about 6 inches of compacted gravel base underneath. Taller or loaded walls follow the block maker's specs or an engineer's design.
Does every retaining wall need drainage?
Nearly every wall in clay soil does. Gravel backfill behind the wall, filter fabric, and a perforated pipe at the base that drains downhill relieve the water pressure that pushes walls over.
What is geogrid and when is it needed?
Geogrid is a strong plastic mesh laid in layers between courses of block and stretched back into the soil, tying the wall to the hill. It is common on segmental block walls taller than about 3 to 4 feet or walls with a load above them.
Why is my retaining wall leaning?
The usual causes are water pressure from missing or clogged drainage, a base that was not compacted, no geogrid on a taller wall, or rotted timbers and tiebacks. Bulges in the middle and gaps at the top are early warning signs.
Can a leaning retaining wall be fixed, or does it need replacing?
Small problems such as a few loose blocks or seepage can often be repaired; Angi's 2026 data puts typical repairs at $450 to $950. A wall that has moved at its base usually needs a section or the whole wall rebuilt, often $6,000 to $14,500.
Can an old timber wall be replaced with block?
Yes, and it is one of the most common wall jobs in older Cobb neighborhoods. The timber wall is removed, the base is dug and rebuilt with gravel, and a block wall goes in with proper drainage behind it.
Drainage and French drains
What is the difference between a French drain and a surface drain?
A French drain is a gravel filled trench with a perforated pipe that collects water soaking through the soil. A surface drain or catch basin collects water running across the ground. Many yards need a little of both.
How deep is a French drain?
Yard French drains are usually about 18 to 24 inches deep and about a foot wide. Footing drains along a foundation go much deeper and cost more.
Where should a French drain empty?
Downhill to a daylight outlet, a pop up emitter, a dry well, or a storm drain connection where the local rules allow it. The outlet is planned before any trench is dug.
Will a French drain work in Georgia red clay?
Yes. Clay drains slowly, which is why water sits on the surface or against the house. A gravel trench gives it an easy way out, and filter fabric keeps clay from clogging the stone.
Should downspouts be piped underground?
It is one of the cheapest ways to keep water away from a foundation. Angi's 2026 data puts one underground downspout extension at about $800 to $2,000.
How do I know if my yard needs regrading?
If the ground slopes toward the house, water stands next to the foundation after rain, or mulch and soil wash toward the walls, regrading may help. Angi's 2026 data puts land grading at about $900 to $3,000.
Quotes
Is the quote free?
Yes. Send a request, a local contractor follows up to see the site, and you get a written price with no cost and no obligation.
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