Most of the retaining wall work we do in Peachtree Corners comes down to a decision somebody else made decades ago. The subdivisions off Peachtree Parkway and Spalding Drive were cut into a landscape that falls away toward the Chattahoochee, and the quickest way to get a flat building pad out of a sloping lot is to push soil downhill and hold it there. Sometimes that was done with a proper wall. Often it was done with a timber crib, a boulder stack, or nothing at all, and thirty years of Georgia rain has been working on it ever since.
So the call usually starts the same way: a wall is leaning, a bed is sliding into the lawn, or a homeowner wants a flat area on a lot that has never had one. Here is how we approach that work in Peachtree Corners, including the permit numbers that decide the scope before a single block goes down.
What we build
Segmental block for most of it. The units are engineered to lock together and step back into the slope, they tolerate the small movements clay soil makes through a wet winter, and they can be tiered when one tall wall would be the wrong answer.
Natural stone and boulder walls where the setting asks for it, particularly on the wooded lots near Simpsonwood and along the older stretches of Jones Bridge Road, where a machined block face would look imported.
And repairs, which are half the enquiries. A wall that is leaning is usually not failing because the blocks are wrong. It is failing because water has nowhere to go, and that is a fixable problem if the structure itself is sound.
Three numbers decide your project, and they come from Gwinnett County
Peachtree Corners is in Gwinnett County, and the county’s retaining wall guidelines set out thresholds worth knowing before you plan anything.
Four feet. A building permit is required for a wall more than four feet high measured from the top of the footing, not from the ground you are standing on. That distinction catches people out, because a wall that looks three feet tall from the patio may be well over four once the buried course is counted.
Under four feet, with conditions. A shorter wall still needs a permit if the backfill behind it slopes more than one foot of rise in three feet of length, or if the wall carries a surcharge. A surcharge is anything pressing down on the soil behind the wall: a driveway, a parking pad, a pool deck, a second wall above it.
Six feet. Above six feet, the drawings and calculations have to be prepared and sealed by a Georgia registered professional engineer, and the calculations have to show a minimum factor of safety of 1.5 against both overturning and sliding. That is an engineering cost on top of the build, and it is not optional.
Ten feet. Beyond ten feet, a Gwinnett County approved third party geotechnical firm has to verify conditions in the field before work continues past the footing.
We raise all of this at the site visit rather than after the design is drawn, because the honest answer is sometimes that two four-foot walls with a planted terrace between them will cost less, last longer and look better than one nine-foot wall that needs an engineer and a geotechnical firm.
If your lot is near the river, a second set of rules applies
Peachtree Corners runs along the Chattahoochee, and the Metropolitan River Protection Act covers a corridor of 2,000 feet from both banks. Inside that corridor there is a 150-foot impervious surface setback from the river, a 50-foot undisturbed vegetative buffer along the river itself, and a 35-foot undisturbed buffer along flowing streams within the corridor.
A certificate is required when a proposal increases land disturbance or impervious surface beyond what already exists or has been approved. A retaining wall on its own is not usually the problem. A retaining wall plus a new patio plus a wider driveway can be, and the time to find that out is before the design is finished, not when the plan comes back for review.
What goes in behind the wall, which is the part nobody sees
A retaining wall is a drainage structure that happens to hold soil. Red Piedmont clay holds water, and saturated clay pushing against a wall weighs far more than dry soil does. Almost every failed wall we are called out to has the same story behind it: no way for water to leave.
So behind ours there is clean angular aggregate rather than the clay that came out of the hole, a filter fabric between that aggregate and the soil so fines do not migrate in and clog it, and a perforated pipe at the base that actually daylights somewhere sensible. A pipe that runs into the ground and stops is decoration.
The fill goes back in lifts and each lift gets compacted. Where the wall is tall or carries a load above it, geogrid runs back into the slope at set intervals, tying the block face to the mass of soil behind it so the whole thing acts as one structure. Skipping grid is the cheap shortcut that shows up in year four.
A build your street can live with
Technology Park means a good number of people on these streets are working from home on a Tuesday morning. Our machines run on batteries, so the noise on site is the sound of material being moved rather than an engine idling all day under someone’s office window.
We agree where the material stack goes before it arrives, keep the road clear, and sweep at the end of each day rather than at the end of the job. Block, aggregate and soil arrive in stages rather than all at once, so a driveway is not lost for three weeks.
Questions Peachtree Corners homeowners ask about retaining walls
My wall is leaning. Does it all have to come out?
Not always. If the block or stone is sound and the lean is coming from water pressure, the fix can be to open the back, put proper drainage in and reset the top courses. If the base course has moved, it comes out.
Do I need a permit for a low garden wall?
Under four feet from the top of the footing, usually not, unless the ground behind it slopes steeply or something sits on top of that soil. Those two exceptions catch more projects here than the height rule does.
How long does a wall take?
A straightforward twenty to thirty foot run at three or four feet is usually a week, including excavation and backfill. Engineered walls run longer because inspections sit between stages, and those dates are not ours to move.
What time of year is best?
Autumn and winter, for the same reason planting goes in then. The ground is workable, there is less standing water than in spring, and the disturbed soil has settled before the summer storms arrive.
Can you build on the property line?
The wall and its footing have to sit on your land, and the footing is wider than the wall. If the line matters, we set out the footing first and show you where it actually falls before anything is built.
Timber walls: repair or replace?
Replace, almost always. The crossties used through the 1980s and 1990s in these subdivisions are at the end of their service life, and a failing timber wall is usually rotten where you cannot see it.
Will the wall change where water goes?
Yes, and that is the point of designing it properly. A wall moves water as well as soil, and where the outlet goes is part of the plan rather than an afterthought. If your neighbour’s lot is downhill, that matters.
Can we plant on the terrace above?
Yes, and we would rather you did. Roots hold the surface, planting slows the water that reaches the wall, and a terrace of shrubs looks like a garden rather than an engineering solution.
Nearby
We work across the north metro. If you are looking at a wall in a neighbouring city, the ground is much the same and the rules are not: retaining walls in Brookhaven, retaining walls in Sandy Springs and retaining walls in Dunwoody each sit under a different permitting authority. Our Peachtree Corners page covers the rest of what we do here, and drainage and grading is the work that most often goes alongside a wall.
Book a site visit
We will walk the slope with you, measure from the top of the footing rather than from the lawn, tell you which side of the four foot line you are on, and say plainly if the better answer is two smaller walls instead of one large one. Book a site visit and we will come out.
Sources: Gwinnett County Department of Planning and Development retaining wall guidelines; the Atlanta Regional Commission on the Metropolitan River Protection Act.