Short answer
Start at the surface. Improve gutters, downspouts, and grading first—these fixes stop a big share of basement seepage. For persistent water at the floor-wall joint (the cove) or during heavy rains, an interior perimeter drain with a sump pump is the most reliable, cost-effective retrofit. Full exterior excavation and waterproofing is the longest-lasting solution but is invasive and expensive, best for severe cases, new construction, or when you are already excavating.
Understanding the source
Not all leaks are equal:
- Water through wall cracks or pipe penetrations: often solvable with crack injection and sealing.
- Water at the cove joint (where wall meets slab): usually hydrostatic pressure; needs drainage (interior or exterior footing drains).
- Damp, musty walls without visible water: moisture vapor; manage exterior water and consider vapor barriers, dehumidification.
- Window well leaks: fix grading, covers, and add or clear well drains.
Run this quick diagnostic: after a heavy rain, trace where water first appears. If it starts at the cove joint and spreads, you likely need drainage. If one vertical crack drips, target that crack.
Priority order and costs
1) Surface water control (gutters, downspouts, grading): typically $50–$1,500 DIY; often solves or greatly reduces seepage.
2) Localized repairs (crack injection, window well drains): $60–$800 DIY per location.
3) Interior drainage + sump pump: $2,500–$12,000 DIY or pro; high success rate and least disruptive to landscaping.
4) Exterior excavation + waterproofing: $8,000–$30,000+; best long-term but major work.
Useful specs
Grade away from foundation: ~1 inch per foot for first 6–10 ft
Downspout discharge: 10+ ft from foundation (surface or underground)
Interior French drain slope: ~1/8 inch per foot to sump
Pipe: 4 in perforated (with sock) surrounded by 3/4 in washed stone (4–6 in envelope)
Sump pump: 1/3–1/2 HP, 1-1/2 in discharge, check valve, weep hole (~1/8 in) below valve
Step-by-step: start outside
1) Gutters and downspouts
- Clean and repair leaks. Upsize to 5–6 inch gutters if roof area is large.
- Add downspout extensions (solid pipe) 10–15 ft to daylight. Avoid tying directly into footing drains.
- Tools: ladder with stabilizer, gutter scoop, drill, pop-rivet tool, tin snips.
- Materials: extensions, elbows, splash blocks, hangers, sealant.
2) Regrade the soil
- Create positive slope for at least 6 ft from the foundation using clay-based fill (not mulch or stone alone).
- Compact in lifts; keep soil 6–8 inches below siding.
- Tools: shovel, wheelbarrow, hand tamper or plate compactor, 4 ft level or laser level.
- Time: a weekend for typical sides of a house.
3) Window wells
- Add well covers; ensure drain at the bottom connects to a dry well or footing drain.
- Add 6–8 inches of washed stone inside the well above the drain.
Targeted DIY fixes
1) Crack repair
- For actively leaking, moving cracks: use polyurethane injection; it expands and remains flexible.
- For structural cracks (narrow, dry): epoxy injection bonds the concrete. If the crack is wider than 1/4 inch or shows displacement, call a pro.
- Tools: caulk gun, injection ports, grinder with diamond cup, shop vac, PPE.
- Materials: polyurethane or epoxy kit, surface paste, ports.
- Time: 2–4 hours per crack; cost $60–$150 DIY or $300–$800 pro.
2) Pipe penetrations and honeycombing
- Clean, dry, and seal with hydraulic cement followed by polyurethane caulk.
3) Waterproof coatings
- Masonry coatings can reduce dampness after drainage and exterior control are fixed. They will not hold back liquid water under pressure by themselves.
Interior drainage and sump (most reliable retrofit)
If water rises at the cove joint or your water table is high, install an interior French drain tied to a sump pit.
Basic steps:
1) Plan the path and locate the sump near an exterior wall for discharge.
2) Sawcut a 12–18 inch strip of slab around the perimeter and jackhammer out to expose the footing.
3) Lay 4 inch perforated pipe (with sock) on washed stone, sloped to the sump. Drill weep holes in the bottom course of hollow block walls to relieve pressure.
4) Add dimpled drainage mat on the wall, lap into the trench.
5) Backfill with washed stone, set pit, plumb discharge with 1-1/2 inch PVC, add check valve and weep hole.
6) Pour new concrete to patch the trench, leaving a small gap at the wall if using a baseboard channel system.
Tools and equipment:
- SDS-plus rotary hammer or demolition hammer with chisel, concrete saw, shop vac.
- Buckets or debris cart, PPE (eye, hearing, gloves, respirator for silica), GFCI protection.
- PVC saw, primer and cement, hole saw for rim joist discharge.
Tips:
- Add a battery backup or water-powered backup pump.
- Discharge to daylight or a dedicated storm line; keep 5–10 ft from the foundation and prevent freezing with a sloped line.
Exterior excavation and waterproofing
Best for severe infiltration, failed exterior drains, or if you are already excavating.
- Excavate to footing, clean wall, patch, apply a rubberized membrane, then a drainage board, and install new perforated footing drain to daylight or a sump.
- Backfill with free-draining material.
- Safety: trench cave-ins are deadly. Use shoring or hire a pro; call 811 before digging.
Safety
- Wear eye, ear, and dust protection; silica dust from cutting concrete is hazardous—use wet cutting and a respirator.
- Use GFCI outlets for corded tools and a sump pump dedicated circuit if possible.
- Never enter an unsupported trench; keep spoils 2 ft back from the edge.
Common mistakes
- Sealing interior walls without fixing gutters and grading.
- Connecting downspouts to footing drains and overwhelming them.
- No check valve or air relief on sump discharge.
- Using flexible corrugated pipe that crushes; use rigid where possible.
- Discharging sump onto the foundation or into the sanitary sewer (often illegal).
When to call a pro
- Bowed or cracked foundation walls, cracks wider than 1/4 inch, or doors/windows binding.
- Continuous seepage regardless of weather.
- Need for deep excavation, structural epoxy injection, or code-required egress/window well rebuilds.
- High radon areas: you may need a sealed sump lid compatible with mitigation.
Tackle water management first. Many basements dry up with simple exterior fixes. If seepage persists at the cove joint, an interior drain and sump is the dependable next step. Reserve full exterior waterproofing for severe or comprehensive renovations.