Block retaining walls in Cumming and Forsyth County

Which kind of block wall fits the job?

The words a contractor might use: "segmental" or "SRW" means dry-stacked interlocking units; "modular block" means roughly the same thing; "gravity wall" means one that stands by weight alone. Large precast walls can reach about 18 feet without reinforcement, by Redi-Rock's own figure, under the right soil conditions. That's a manufacturer's limit, not a rule for your yard.

How is a segmental block wall built?

1. Mark the lines: Georgia law requires a Georgia 811 request at least 3 business days before digging with machinery. It's free.
2. Dig the trench and base: Allan Block calls for at least 6 inches of compacted wall rock, in a trench deep enough to bury part of the first course. Heavy clay or wet soil under the base comes out and is replaced with granular material.
3. Bury the first course: The common minimum is 6 inches below grade. Allan Block's rule adds 1 inch per foot of wall height.
4. Stack with the setback: Each course steps back slightly into the hill, built into the block's shape.
5. Gravel and pipe behind it: At least 12 inches of clean gravel directly behind the block, with a drain pipe at the bottom that runs to daylight.
6. Backfill and cap: Soil goes in compacted layers, topped with a cap and sloped so surface water runs away from the wall.

When does a block wall need geogrid?

HomeGuide says segmental walls generally handle up to 3 or 4 feet without reinforcement. Above that, or with a driveway or a steep slope above the wall, the design usually adds geogrid: sheets of plastic mesh laid into the soil behind the wall to tie a big block of earth to it.

Allan Block's guidance sets grid length at 60% of the total wall height and vertical spacing at no more than two courses. Those are starting points. The design for a tall wall comes from an engineer, who works from your soil and load. See the page on engineered walls and permits.

What about the red clay under a Cumming block wall?

Clay shapes two parts of the job. Used as backfill, clay holds water against the wall, so the gravel zone matters more than on sandy ground. Allan Block prefers free-draining fill with less than 10% fines. Under the base, soft or wet clay needs to be dug out. Removing it costs money up front, and a quote that doesn't mention it is worth asking about.

The slope below the wall matters too. Keystone's manual asks for at least a 4-foot flat bench in front of the wall where the ground drops away.

How much does a block retaining wall cost in Forsyth County?

HomeGuide puts a concrete block wall at $15 to $40 a square foot of wall face. LawnStarter's interlocking block row is $15 to $35. To figure the square feet, multiply length by height: a wall 50 feet long and 4 feet tall has 200 square feet.

Whole projects run higher than the block price alone, with footings, drainage and access added. HomeGuide's example for that 50-foot, 4-foot wall is $7,000 to $13,000. Angi notes that sloped lots can push labor up by 50% or more, and that's common around Cumming.

Common questions