Short answer
Yes—most basement window leaks can be reduced or stopped with a combination of exterior drainage fixes and targeted sealing. Practical DIY methods include improving grading and window well drainage, adding clean gravel and a proper well cover, resealing the frame with polyurethane sealant, and patching cracks with hydraulic cement. If water is driven by groundwater pressure or you see structural cracking, bring in a pro.
Why basement windows leak
Water typically intrudes through:
- Poor grading that slopes toward the foundation
- Clogged/missing window well drains and lack of gravel
- Gaps where the frame meets masonry (dried caulk, missing mortar)
- Cracked concrete/block around the opening
- Rusted metal frames or rotted wood sills
- No flashing/sill pan during installation
Understanding the source helps you fix the cause, not just the symptom.
Materials and tools you may need
- Polyurethane concrete/masonry sealant (non-sag for vertical joints)
- Backer rod (for joints 1/4–3/4" wide)
- Hydraulic cement or rapid-set patching mortar
- Masonry crack filler or injection kit for non-structural cracks
- Exterior acrylic masonry caulk (for above-grade hairline gaps)
- Window well (steel/composite) and clear cover (egress-compliant if required)
- 3/4" clean gravel; landscape fabric
- 4" perforated drain pipe and fittings (optional tie-in to sump/daylight)
- Trowel, margin trowel, pointing tool, caulk gun
- Cold chisel, hammer, wire brush; angle grinder with diamond cup (optional)
- Drill/hammer drill with masonry bits
- Shovel, tamper, utility knife, shop vac, buckets
- PPE: gloves, safety glasses, dust mask/respirator, hearing protection
Exterior fixes (best results)
1) Improve grading around the window
- Add soil to create positive slope away from the foundation.
- Keep mulch/landscape edging from trapping water near the window well.
Target slope: 1" per foot for the first 6–10 ft away from the house.
Top of window well: 4–6" above surrounding grade.
2) Rebuild the window well and drainage
- Remove the old well if it’s rusted/dented or sitting below grade.
- Excavate to the bottom of the window, and at least 12–16" out from the wall.
- Lay landscape fabric in the bottom to prevent silt.
- Add 4–6" of 3/4" clean gravel. If there’s a drain tile stub, locate and clear it.
- If no drain exists, add a 4" perforated vertical stub tied to a horizontal 4" line that either:
- Connects to the footing drain (if accessible and code-appropriate), or
- Drains to a dry well/daylight away from the house, or
- Ties into a sump basin (common in retrofits).
- Set a new window well so it sits above grade and is anchored to the foundation per manufacturer specs.
- Fill the well with 8–12" of clean gravel to just below the window sill.
- Install a clear, sloped cover that sheds rain while allowing egress if this is an egress window.
3) Seal exterior frame-to-masonry joints
- Clean the perimeter joint with a wire brush. Vacuum dust.
- Insert backer rod where the gap is deeper than 1/4" and about 2/3 the joint depth.
- Gun in polyurethane sealant, tool it to a slight concave shape for movement.
- Avoid silicone on raw masonry; it adheres poorly.
4) Address masonry cracks or gaps
- For cracks up to ~1/4", use polyurethane crack sealant.
- For larger voids or deteriorated mortar, chisel to sound material and pack with hydraulic cement. Work quickly; it sets in minutes and expands slightly to seal.
- Hairline surface cracks above grade can be bridged with flexible masonry caulk.
5) Flashing/sill pan (if replacing the window)
- Install a sloped sill pan (peel-and-stick or metal) that drains to the exterior.
- Flash the jambs/head with compatible flashing tape overlapping shingle-style.
Interior stopgaps (helpful but secondary)
- Chip out and pack hydraulic cement at the cold joint where wall meets window frame or sill.
- Seal interior frame gaps with polyurethane sealant and backer rod.
- Consider a dehumidifier to control residual moisture.
These measures can slow seepage but won’t cure exterior drainage failures or hydrostatic pressure.
Best-practice tips
- Work in dry weather; prep and adhesion suffer on wet surfaces.
- Polyurethane sealants cure slower but outperform acrylic in movement and adhesion.
- Cleanliness determines success: remove dust, loose mortar, and rust before sealing.
- Use clean, angular gravel (not pea gravel) for drainage.
- Choose covers that fasten to the well, shed water, and meet egress requirements where applicable.
Common mistakes to avoid
- Only sealing from the inside. Water will still collect and push through elsewhere.
- Using foam or silicone as the primary exterior seal—both are short-lived here.
- Setting the window well below grade or without gravel—turns into a bathtub.
- Forgetting a drain path. A well without drainage will overflow in heavy rain.
- Blocking or undersizing egress windows with non-compliant covers.
Safety considerations
- Call 811 before digging. Avoid hitting buried utilities.
- Water and electricity don’t mix—turn off circuits if working near outlets.
- Wear PPE when grinding/chiseling masonry; silica dust is hazardous.
- Mold may be present. Use respiratory protection and follow remediation practices if you see visible growth.
Rough cost and time
- Polyurethane sealant and backer rod: $20–40
- Hydraulic cement: $20–30
- Gravel (10–15 bags): $50–100
- New window well: $150–400; cover: $60–200
- Drain materials (pipe/fittings/fabric): $75–200
- Time: 2–8 hours for sealing and well service; more if adding a drain
When to call a professional
- Recurrent leaks despite proper grading, gravel, and sealing—likely hydrostatic pressure.
- Structural cracks, bowing walls, or settlement around the opening.
- Need to tie into footing drains or install a sump/french drain system.
- Converting to or modifying an egress window (code and structural implications).
By tackling exterior water management first and then sealing the window opening correctly, most homeowners can stop basement window leaks with a weekend’s work and common masonry tools. If water persists or you see structural signs, get a foundation or waterproofing contractor involved for a lasting solution.