Water in the basement: where it gets in and what to do first

1. The joint between the floor and the wall
2. Window well
3. A crack, and the gap around a pipe through the wall
4. Over the top of the foundation wall
5. Up through the floor slab

SoilConcrete / masonryWoodInsulationWater

Where water gets into a basement

In my experience, the joint between the floor and the wall is where water most often gets into a basement, especially after long periods of rain. In a block wall, water can also come through the mortar joints, or fill the hollow cores of the blocks and come out at a lower point. Keep in mind that the puddle you see may not be where the water is getting in.

The entry points I see most, roughly in this order:

1. The joint between the floor and the wall (the cove joint), especially after long rains
2. Window wells, exterior doors and spots where the ground is too high against the house
3. Cracks in poured concrete walls, and gaps around pipes that pass through the wall
4. Over the top of the foundation wall, where siding, flashing or grading isn’t right
5. Through or around the floor slab, usually when groundwater is high

How to find where the water comes in

I always look outside before recommending a system. Inside, I look for where the water first appears, staining, efflorescence, mineral deposits, cracks, moisture at the joint between the floor and the wall, and whether the sump pump has been running. Efflorescence tells me moisture has traveled through the masonry. It won’t tell me exactly where water is getting in today.

Questions I ask first

• Does it only happen when it rains?
• Does it start during the rain or several hours later?
• How much rain does it take?
• Is it always in the same spot?
• Has it happened without rain?
• Was the sump pump working?
• Has anything changed outside the house?

What to check outside: gutters, downspouts, grading, window wells, patios, driveways and anywhere pipes or wires go through the wall.

Hydrostatic pressure, explained

Think of water building up in the soil around and under your foundation. The higher it rises, the more pressure it puts on the walls and the floor, and it will find any way in: a crack, a joint, a pipe opening or any porous spot. But hydrostatic pressure often gets blamed too quickly. If a downspout is dumping 200 gallons of water next to a corner of the house during a storm, I see that as a surface water problem first.

When I think it really is groundwater

• Water at several low spots
• Seepage along the joint between the floor and the wall
• A sump pump that gets water constantly
• Moisture under the slab
• Problems that continue after the gutters and grading are fixed
• Water during long periods when the ground stays saturated

Fix the outside first

The outside fixes that solve the most problems, in my order:

1. Downspouts that actually carry the water away from the house
2. Gutters that are clean, sized correctly and not overflowing right next to the foundation
3. Grading that sends surface water away from the house instead of toward it
4. Window wells that drain, with covers where they make sense and the rim above the ground
5. Hardscape: patios, steps and driveways can send a lot of water toward the house

On simple seepage problems, I often correct these items first and waits for the next rain before deciding whether a drainage system is needed. Sometimes that’s all the house needed. The Department of Energy’s Building America Solution Center says downspouts should discharge at least 5 feet from the foundation. Virginia’s residential code requires lots to be graded so the ground falls at least 6 inches within the first 10 feet from the house (R401.3).

Condensation or a leak?

If walls, pipes or the floor are wet on warm, humid days and the water doesn’t follow the rain, it may be condensation. See dew point and condensation.

When you need more

• Water keeps coming in after the outside is fixed: interior vs. exterior basement waterproofing
• The basement already flooded: flooded basement: what to do
• Water comes through a crack: foundation cracks
• The basement depends on a pump: sump pumps
• Gutters, grading and drains around the house: drainage around the foundation

Water alarms

I recommend water alarms. They’re cheap compared with a wet finished basement. For the sump pit, I especially like a high-water alarm, plus a battery backup pump if the basement relies on the sump pump to stay dry.

Where to put them

• Next to the sump pump
• Near the water heater
• At the lowest point of the basement
• Near equipment with water supply lines
• Anywhere that has had water before

Common mistakes

• Painting the wall before finding the source
• Filling everything that looks like a crack with hydraulic cement
• Buying a bigger sump pump without knowing where the water comes from
• Opening the windows to dry the basement
• Putting the drywall back right away
• Not looking at the downspouts
• Calling three waterproofing companies to ask which system to buy, instead of asking first why water is getting in

Who to call

Start outside the house. You or a handyman can usually extend downspouts and clean gutters. If the water doesn’t follow the rain, or it smells like sewage, call a plumber. If water still gets in after the outside is corrected, call a waterproofing company. If you also see horizontal cracks, bowing or cracks that are getting bigger, have a structural engineer look first. Daniel Mercer doesn’t want anyone treating a moving wall as a waterproofing problem; see horizontal cracks and bowing walls.