A gravel driveway that survives NH is a three-layer structure with somewhere for water to go. Here's the build spec, the numbers, and the maintenance schedule.
Subgrade: topsoil and organics stripped to mineral soil, shaped and compacted — with woven geotextile fabric on soft ground so your expensive stone doesn't slowly sink into the mud. Base: 8–12 inches of bank-run gravel, compacted in lifts; this is the structure. Surface: 3–4 inches of crushed gravel that locks together underfoot. Spread-and-go driveways skip the first two layers, and that's why they're re-bought every few years.
A driveway sheds water or it becomes a stream bed. Crown the surface 2–4% (about ¼–½ inch per foot of width) so water runs off the sides. Ditch the uphill side. Culvert every place water needs to cross — undersized or missing culverts are behind most washouts we rebuild. On steep grades, angled water bars or broad dips shed water in stages before it gathers speed.
Built to this spec, new construction runs $15–$30 per linear foot at standard 12-ft width in the Lakes Region — driven by length, terrain, soils, and culvert count. The calculator turns your dimensions into gravel yardage and an installed range. Annual regrade-and-crown maintenance costs a small fraction of that and is the difference between a 5-year and a 25-year driveway.
March–April is when driveways confess how they were built. Frost leaves the ground saturated; thin or uncrowned surfaces pothole and rut. If yours goes soft every spring: it's usually base (too thin), fabric (missing over wet subgrade), or shape (no crown). A targeted rebuild of the failing section plus a proper regrade is often all it takes — you rarely need to redo the whole run.
New builds, rebuilds, and rescues — quoted flat after a quick look.
