Window Well Drain: Why Basement Windows Leak and How to Fix the Well

Now compare that with how much the well can hold before water reaches the sill. Take a small well with about 3 square feet of floor, 6 inches of open space between the gravel and the sill, and a foot of gravel underneath. The open space holds about 1.5 cubic feet, or 11 gallons. The spaces between gravel stones, roughly a third of the volume as a rule of thumb, hold about 7 or 8 more. That is roughly 20 gallons before the window is under water. A 9-square-foot egress well holds roughly three times that, around 55 to 60 gallons.

So an inch of rain falling straight into the well adds 2 to 6 gallons, which even a slow drain can handle. A clogged gutter spilling over it can add 90 gallons in the same storm, and a downspout emptying beside it 300 or more. That is enough to fill any well and top it up several times over. When a basement window leaks “every time it rains hard,” look up at the gutter and along the ground before you dig at the drain. Grading and yard runoff are covered in depth by our sister site's guide to water pooling near the foundation.

For window wells serving emergency escape (egress) windows, the International Residential Code requires drainage. In the 2015 IRC, section R310.2.3.2 reads:

The same section sets the size of egress wells: at least 9 square feet of floor with at least 36 inches of projection and width, and a permanently fixed ladder or steps once the well is more than 44 inches deep (the egress window calculator checks a window and its well against each of these rules). Section numbers have moved between editions, and states and cities adopt the IRC with their own amendments. New Jersey's plumbing subcode, for example, lets window wells of 10 square feet or less drain into a foundation drain through a 2-inch minimum drain or indirectly through a porous filter bed.

Two practical points follow. First, a non-egress well isn't exempt from physics: it fills the same way, code or no code. Second, “connected to the foundation drain” only helps if that drain is itself working and discharges somewhere. In an older house with no footing drain, or a clay tile drain that has silted up, the well has nowhere to send water. Treat the code as the minimum and your local building department as the authority; this page is not code advice, and egress windows are a life-safety item.

Many older homes have wells with a few inches of gravel and no drain at all. In sandy soil they may work fine for decades. In clay they are effectively buckets. If you're not sure what's under yours, dig carefully at the gravel near the wall: a pipe opening, grate or cap means there is a drain, and a solid layer of soil or clay a few inches down means there probably isn't.

Cleaning a well once or twice a year, usually after leaf fall and again in spring, prevents most clogs. A cover cuts that to an occasional check.

A cover is the cheapest way to cut the water a well collects. It keeps rain, leaves and snow out of the gravel, which also keeps the drain from silting up. A sloped or domed cover sheds water away from the house; a flat grate keeps people and animals out but lets rain straight through.

A cover does not help when water arrives from the side: a downspout or patio sending water under the liner, soil that slopes toward the well, or groundwater rising from below. In those cases it just hides the flooding well.

Frame and caulk. Older basement windows often sit in a wooden frame (a buck) set into the concrete. The joint between the buck and the concrete dries out, and the wood can rot. If Stage 2 of the test leaks, reseal that joint with a sealant rated for masonry, after scraping out old caulk, or replace the window and buck together if the wood is soft. Do this after the well drains; caulk is not a dam.

Cracks at the window corners. A window opening is a weak point in a foundation wall, and shrinkage cracks often start at its lower corners and run down or diagonally. Those carry water from the wet backfill under the well into the basement. In a poured wall, see how to seal a leaking foundation crack and leaking basement wall cracks. A crack that is widening, offset or horizontal needs a structural look before sealing.

Water rising in the well from below. If the gravel is wet from underneath with no rain, the groundwater is higher than the well bottom, or the footing drain the well connects to is full. Connecting a drain won't help; the fix is groundwater drainage. See hydrostatic pressure in a basement.

Condensation. Water on the inside of the glass on humid summer days or cold winter mornings is condensation. See basement humidity targets.