Foundations & Drainage Diagrams
6 diagrams · 2 calculators
French-drain trench sections, filter-fabric wraps, drainage slope, and retaining-wall cross-sections and geogrid — how to move groundwater and hold back soil the right way.
Calculators in this category
Foundations & Drainage · 6 diagrams
- Foundations & Drainage
Retaining wall cross-section — base, buried course, batter, drainage gravel, and pipe
Most of a retaining wall is hidden: a compacted stone base with the first course buried, blocks that step back (batter), a drainage-gravel chimney with filter fabric, and a perforated pipe at the base that daylights the water out.
- Foundations & Drainage
Why retaining walls fail — hydrostatic pressure without drainage
Trapped water is the #1 reason retaining walls fail: it builds hydrostatic pressure that tips the wall. Back the wall with gravel, filter fabric, and a perforated pipe so the water drains out and never loads the wall.
- Foundations & Drainage
Retaining wall geogrid reinforcement and when an engineer is required
Above ~3–4 ft a wall needs geogrid: layers between courses reach back into the backfill (≥ 0.6 × H) to tie the soil into one reinforced mass. Get a permit + engineer when the wall is over 48″, carries a surcharge, has a slope above, or is tiered (IRC R404.4).
- Foundations & Drainage
French drain trench cross-section — bedding stone, perforated pipe holes-down, stone cover, and filter-fabric wrap
Inside a French-drain trench (IRC R405.1): ≥2″ of washed #57 stone bedding, a perforated pipe laid holes-DOWN, ≥6″ of stone cover, the stone column wrapped in filter fabric, and the trench run ~12″ beyond the footing. Holes face down so water enters as soon as the water table rises.
- Foundations & Drainage
French drain slope — 1% (1/8 inch per foot) minimum fall to daylight
A French drain runs on gravity: pitch the pipe at least 1% — that's ⅛″ of drop per foot, or 1 ft per 100 ft — continuously to a lower outlet (daylight, dry well, or pop-up). Too flat and it stagnates; over ~5% and fast flow scours the gravel.
- Foundations & Drainage
French drain filter fabric — burrito wrap vs sock vs none
Filter fabric keeps soil fines out of the open-graded #57 stone. A burrito wrap protects the whole stone column (the pro default); a sock wraps only the pipe and clogs faster; no fabric silts up. Order ~20% extra for laps and the top fold (overlap factor 1.20).