Two-Year-Old Paver Patio That Rocks, Dips, and Grows Weeds
You are replacing a 12 ft × 18 ft paver patio installed by another contractor two years ago. The pavers rock underfoot, there is a 1-inch dip at the bottom of the two steps, sand has washed out along the downhill edge, and the client says weeds come up through the joints every spring. Excavation reveals 2 inches of sand over native silty clay, no geotextile, no edge restraint on the downhill side, and a base that is only 2 inches thick and was never compacted in lifts. The patio drains toward the house at about 1%, and the steps above shed water onto the patio. The client wants a fix that will not fail again, and asks whether the 14-inch planting wall along the uphill edge needs a permit.
1. Explain the failure mechanism for each symptom, then state whether the 14-inch wall needs a permit and why.
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Symptom → mechanism:
- Weeds in joints: no geotextile over the clay subgrade let fines pump up and the joint sand migrate down. Weeds follow the open joints. Geotextile does not stop weeds by itself in most failures - the missing sand and open joints do.
- Sand washed out at the downhill edge: no edge restraint. The sand is free to migrate out laterally, so joints empty and the pavers lose interlock.
- Pavers rocking: zero to 2 inches of uncompacted base over silty clay. There is no load spread; the bedding sand is acting as the structure.
- 1-inch dip at the steps: water shed from the steps is concentrated at the worst possible point, and the base under it was never compacted in lifts. Fine particles migrated and the bedding consolidated.
- Drainage toward the house at 1%: incorrect direction and at the low end of acceptable slope. The patio is delivering water to the foundation.
Permit question: a retaining wall that retains no more than about 4 ft of unbalanced fill is typically exempt from building permit under the residential code adopted in Oregon, so a 14-inch planting wall normally does not require a permit - but confirm with the local jurisdiction, because walls near a slope, walls acting as a surcharge, or walls in a floodplain or on a property line can be treated differently. If the wall retains more than 4 ft, expect a permit and an engineered design. Say "typically exempt, confirmed with the city" rather than "no permit needed."
2. Compute the correct excavation depth and the material quantities for this patio, given a 6-inch compacted base, 1-inch bedding, and 2⅜-inch pavers.
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Depth of excavation: 2⅜ in paver + 1 in bedding + 6 in base = 9⅜ in ≈ 0.78 ft, plus the subgrade scarification allowance. Excavate to that depth and add fall.
Area: 12 ft × 18 ft = 216 sq ft.
Base aggregate (compacted): 216 sq ft × 0.5 ft = 108 cu ft = 4.0 cu yd compacted. Order loose at a 25–30% compaction factor: 5.0–5.2 cu yd of 3/4-inch-minus crushed base. Spread in 2-inch lifts, 95% modified Proctor, plate compactor with water.
Bedding sand: 216 × (1/12) = 18 cu ft = 0.67 cu yd - screeded, not compacted, and no more than 1 inch.
Joint sand: about 1 bag of polymeric sand per 80–100 sq ft → 3–4 bags for 216 sq ft, plus edge and cleanup allowance.
Excavated spoil: 216 × 0.78 = 169 cu ft ≈ 6.3 cu yd in place - order a dumpster accordingly; swell will push the haul volume higher.
Other takeoffs to include: woven geotextile covering the full subgrade plus 6-inch overlaps (about 300 sq ft with laps), aluminum or paver edge restraint on all open sides with 10-inch spikes at 8–12 inch centers, and check dams or a drain channel at the base of the steps. Price the base compaction as a line item - that is the missing work in the original install.
3. Give the drainage and construction spec that prevents a repeat, and explain how you would sequence the work around the existing steps.
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Specification:
- Minimum slope of 2% (never less than 1%) away from the house, with the high point at the house side and discharge to a splash apron, channel drain, or daylighted swale. Simply matching the existing 1% toward the house is a defect, not a match.
- Intercept the step water. A 4-inch trench drain or a channel at the base of the steps, piped to the discharge, plus a slight cross-fall in the patio. Without this, water re-concentrates exactly where the failure started.
- Woven geotextile over the full excavated subgrade with 6-inch laps; separation fabric, not filter fabric.
- 6 inches of 3/4-inch-minus crushed base in 2-inch lifts, each compacted to 95% modified Proctor, at near-optimum moisture. Test it if the job is large enough to justify it; photograph lift thickness as documentation.
- 1-inch bedding sand, screeded to grade over the base, never used to correct base error.
- Pavers at 2⅜ inch, laid to a pattern that locks, with edge restraint on every unrestrained edge.
- Polymeric sand swept into joints, vibrated, wetted per manufacturer instructions, refilled after curing.
Sequencing around the steps:
- Set the finished patio elevation from the bottom stair riser first - that fixes the finished height and the cross-slope.
- Excavate and place the drain and geotextile before base.
- Build base in lifts; check grade with a level and straightedge after each lift, not after all of it.
- Lay pavers from the steps outward so the cut row lands at the outer edge, not against the house.
- Finish slope away from the wall, and verify with water - a hose test at the step base before you hand over is worth more than any warranty language.