Is the driveway being lifted, or is it sinking?
Root damage is uplift. The Georgia Forestry Commission describes roots growing into the uncompacted, oxygenated soil under a driveway or sidewalk and buckling the concrete four inches or more, which it calls a significant hazard. A panel that has risen along one edge, with the high side nearest the tree, fits that pattern.
Settlement is the opposite problem with different causes, among them a washed-out or poorly compacted subgrade. The distinction decides the repair. Filling voids under a slab raises concrete that has sunk, and a slab lifted by a root has a root under it rather than a void.
Both can show up on the same driveway. The panel closest to the trunk is the one to read first, because that is where the diameter rule below applies most directly.
How far do tree roots reach from the trunk?
The Georgia Forestry Commission gives a rule of thumb: root systems generally extend about one to one-and-a-half feet out from the trunk for every inch of trunk diameter, measured about four feet above the ground.
Its own worked example puts a 12 inch tree's roots roughly 12 to 15 feet out in all directions, so treat the right-hand column below as an outer bound rather than a prediction.
| Trunk diameter (measured about 4 feet up) | Root reach at 1 foot per inch | Root reach at 1.5 feet per inch |
|---|---|---|
| 6 inches | 6 feet | 9 feet |
| 12 inches | 12 feet | 18 feet |
| 18 inches | 18 feet | 27 feet |
| 24 inches | 24 feet | 36 feet |
| 30 inches | 30 feet | 45 feet |
Which tree species crack driveways in DeKalb County?
No species list appears in the state's guidance. The Georgia Forestry Commission document on this exact subject frames the risk entirely by trunk diameter and distance from the slab, and names no tree at all as a culprit.
Contractor pages in this market publish confident species lists anyway. The federal reference work on the subject, the USDA Forest Service's Silvics of North America, records no rooting habit data whatsoever for water oak, which means at least part of the popular list is repetition rather than research.
Diameter and distance are the more useful measurements in any case, because a homeowner can take both with a tape measure. A species name only gestures at what a trunk measurement answers directly.
Can the roots be cut instead of the tree?
Two thresholds set the limit, and both come from the Georgia Forestry Commission. Cut roots more than three inches in diameter are particularly susceptible to insect and disease attack, often rot back into the trunk, and leave the tree structurally unsound over time.
Roots less than two inches in diameter regenerate. Cutting and pruning at the edge of the driveway can therefore become what the Commission calls an every two year ritual rather than a repair that holds.
Stability is the third constraint. Roots running under the driveway are adding to the structural integrity of the tree, so removing them may compromise its support system and leave it prone to being blown over in the wind.
What are the realistic options for a lifted driveway?
The Georgia Forestry Commission sets out four, and is direct about the trade-off inside each one:
- Prune the roots at the slab edge. Workable only below the three inch threshold, and anything under two inches regrows, so the job repeats on roughly a two year cycle.
- Bridge the damage. A new form is poured over the existing damage, which leaves a hump in the surface and will be compromised again over the years as the roots keep growing.
- Change the surface. Geotextile fabric under 3 to 4 inches of uncompacted crusher run is one option; 6 to 8 inches of coarse mulch is another, though the Commission notes mulch washes out in heavy rain.
- Remove the tree. In the Commission's own words, once a tree becomes large and the damage severe, removal of the tree is the best long term plan if the driveway is to be replaced.
- Have the tree assessed before the concrete is quoted. The Commission warns that building contractors who replace driveways may not be as knowledgeable as they should be about construction impacts to root systems, and recommends a certified arborist assessment.
Who repairs a cracked public sidewalk in DeKalb County?
In every DeKalb jurisdiction checked for this page, the structural repair of a public sidewalk is a government function rather than a homeowner purchase. What the abutting owner owes is upkeep and clearance.
| Jurisdiction | Who handles structural sidewalk repair | What the abutting owner is responsible for |
|---|---|---|
| City of Decatur | The City. It contracts each year with a local vendor to remove vertical separations between sidewalk panels, and programs panel replacements and curb ramp upgrades. The City also states that, given the volume of maintenance requests and the annual sidewalk budget, only a fraction of the locations can be addressed each year. | Upkeep and de-littering to the curb, pruning plants back behind the sidewalk edge, keeping 7 feet of overhead clearance, and clearing debris and vegetation. |
| City of Brookhaven | The City, which is responsible for the entire construction process for roads, sidewalks and stormwater infrastructure on City-controlled areas. GDOT controls construction and right-of-way activity on state-maintained highways such as Buford Highway and Peachtree Road. | Landscaping, grass cutting and tree maintenance in the right of way, not sidewalk structure. |
| City of Dunwoody | Public Works, which is responsible for the care of the city's streets and sidewalks. Broken sidewalks are reported through the city's SeeClickFix portal. | Reporting the defect. |
| Unincorporated DeKalb County | The county's Roads and Drainage Division, which lists sidewalk construction and ADA sidewalk compliance review among its own services. Residents report sidewalk maintenance issues on 404-297-3840, and requests are triaged red for public safety at 30 days, blue at 60 to 90 days, and green at 90 days or more. | Reporting the defect. |
| Chamblee, Doraville, Tucker, Stonecrest | Not verified for this page. Each incorporated after 2005 on a services-city model similar to Brookhaven and Dunwoody, which makes the same answer likely, but likely is not checked. | Confirm with the city before assuming either way. |
Is freeze-thaw cracking the concrete, or is it the roots?
Freeze-thaw is the standard explanation offered for cracked concrete around Atlanta, and the climate record makes it a weak one. NOAA's 1991 to 2020 normals for Atlanta Hartsfield-Jackson record 35.7 nights a year at or below 32F, and only 1.2 days a year with a high at or below freezing.
Read that carefully and it cuts both ways. The ground here freezes overnight and thaws by day on all but about one of those days, so the number of crossings is high, roughly 35 a winter. Each crossing is also shallow, a few hours deep, with no sustained frozen ground and effectively no road salt program behind it.
Freeze-thaw damage requires concrete that is critically saturated at the moment it freezes, which a well graded, well drained driveway rarely is in this climate. Drainage and standing water sit ahead of temperature on the list of things worth checking, and a large trunk within the reach in the table above sits ahead of both.
Related conditions in DeKalb County
Sources
- Georgia Forestry Commission, Tree Roots, Driveways and Sidewalks: https://gatrees.org/wp-content/uploads/2020/02/Tree-Roots-Driveways-and-Sidewalks.pdf
- City of Decatur Public Works, Sidewalks: https://www.decaturga.com/publicworks/page/sidewalks
- City of Brookhaven, Right-of-Way: https://www.brookhavenga.gov/486/Right-of-Way
- City of Dunwoody Public Works, Report a Problem: https://www.dunwoodyga.gov/government/departments/public-works/report-a-problem
- DeKalb County Public Works, Roads and Drainage Division services: https://dekalbcountyga.gov/departments/public-works/roads-and-drainage/services
- NOAA NCEI 1991-2020 Climate Normals, Atlanta Hartsfield-Jackson (station USW00013874): https://www.ncei.noaa.gov/access/services/data/v1?dataset=normals-annualseasonal-1991-2020&stations=USW00013874&dataTypes=ANN-TMIN-AVGNDS-LSTH032,ANN-TMAX-AVGNDS-LSTH032
- USDA Forest Service, Silvics of North America, Quercus nigra (water oak): https://www.srs.fs.usda.gov/pubs/misc/ag_654/volume_2/quercus/nigra.htm