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This article explains the causes of water entry, leak, or actual flooding of buildings when water is entering at or near basement or crawl space windows. In the page top photo shows water leak stains below a basement window. Inspecting outdoors it is often easy to recognize where this water is coming from and thus how to stop it from entering the building.. Observing evidence of the frequency, extent, source, and causes of leaks, water entry, and actual building flooding is a critical step in evaluating a building as well as in planning the cure for building leaks, water entry, and mold.

Readers having problems with basement moisture should also see WATER ENTRY in buildings, see WET BASEMENT PREVENTION and also see BASEMENT WATERPROOFING. If your building suffers from a wet or damp crawl space or crawl space mold, see Crawl Space Dryout Procedures.

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Basement Leaks, Water Entry, Flooding, Moisture due to Leaks at Ground-Level Windows

Visual inspection of a the exterior and interior of a building can provide ample evidence of the history of leaks and water entry at a property. Even when a building is brand new, an experienced home inspector or waterproofing or de-watering contractor can spot conditions that are likely to lead to future leaks, water entry, flooding, and moisture or even mold problems at a structure. If you see a downspout spilling right by the building foundation, certainly you'll want to correct this condition before calling an expert to diagnose "basement leaks". But some very common sources of basement water entry are a bit more difficult to recognize unless you are familiar with common causes of leaks into buildings. A client troubled by basement water leaks that were developing on her home sent the outdoor and basement interior photos we show here and at page top and asked for advice.

Guide to Possible Sources of Leaks at a Basement Foundation Wall

The outdoor photograph (left) show quite a few possible sources of leaks at or near the building corner in the center of this picture: a below grade basement window with what looks like no window well to stop surface runoff in-slope grade near the window opening a patio around the corner that probably drains to near that location an inside corner on the patio that may be spilled onto from a roof valley overhead two downspouts that drop near that opening, both using a very long extension that, if blocked, adds to spillage there.

Priority of Steps to Take to Stop Leaks at or Near a Basement Window

Inside the homeowner noticed leaks beginning to enter the basement at or near the top of the foundation wall, confirming that water was most likely coming from the ground surface. Therefore we advised the following steps:

• Start at the roof with the gutter and downspout system to be sure it's working and kept working, and that where the downspouts finally empty that is running clear and does not drain back towards the building.
• After those steps have been taken, add a window well at the window to protect against surface runoff entering at the window.
• If you're still getting runoff from the patio you might need to install an area drain that intercepts that spillage at the patio and carries it to daylight behind the home - same direction in which runs that long downspout extension across the house wall. If that step is taken I'd also put a drain in the bottom of the window well that connects to that runoff drain.
• If water is entering a basement from high at ground surface level, the above steps are the most appropriate to try first. Deeper groundwater and wet soils can also be a problem but they generally cause water entry lower in the foundation wall.

The two half-round corrugated steel window wells shown in our photo (left) look like a proper step in reducing surface water runoff into this basement at the windows themselves. But notice that the ground appears to slope back towards the building to the right of those stairs? An inside foundation corner tends to trap surface runoff against the building. This detail may not be a problem in this home provided that roof drainage is not spilling at the foundation, and provided that there is no hillside sloping to drain into this area. At WET BASEMENT PREVENTION we describe more aggressive (and costly) steps to stop basement water entry and foundation leaks using exterior drainage systems and foundation waterproofing systems such as plastic coverings and drain systems.

Here we show two more problem windows at building basements.

At above left is a wood framed basement window buried in backfill. This construction detail invites both basement water entry from surface water outside, and also termite or carpenter ant damage to the structure. A window well is badly needed here.

At above right is a wood frame basement window below ground level, with its sill in dirt, and although the owners installed a window well, the well has become overgrown. Soil level in a window well needs to be about 4" below the top of the soil.

The window well at above left looks nice and neat; if the steel surround is not at least 2" above soil level, ground water may run into the window well. The owners installed a plastic cover over the window well to prevent spillage from the roof eaves falling into the well.

The window well at above right is almost a great job. A concrete window well floor was installed along with a drain (hopefully conducting water to daylight away from the building). When we see details like this we guess that a previous owner or contractor was sure that water was entering the building at this spot.

Unfortunately, burying the window sill in concrete creates a risk point for rot or insect attack on the building.

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WINDOW LEAKS INTO BASEMENT

• Thanks to client R.G. (anonymous) for discussion of basement leak points at or near windows, 11/3/2009

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