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What Causes a Damp Basement? How to Fix Water Problems at Foundations


The problem of water entering a basement can get particularly acute in spring and summer. First, when snows melt in the early spring, it turns into ground water and seeps through the soil. This causes hydrostatic pressure which forces it through the foundation walls of the basement. While in summer, the humidity in the air condenses on basement walls, often forming puddles on the floor and leading ultimately to a damp basement.

A house with a 1,500 square foot roof sheds about 1,000 gallons of water for every inch of rain. This can cause a veritable lake to form around your home if not checked. In many cases, rising ground water either due to snow melt or fed by an underground spring accumulates around the foundation and works its way through cracks, joints and porous material.

Before you set out to dry your basement, the first thing to do is identify where the water is coming from.

There are basically three major ways water can enter your basement: condensation, runoff and subsurface penetration.


Condensation usually shows up as water droplets, wet spots, or puddles on the floor. This is caused when moist, warm air hits the cool foundation walls or the un-insulated water pipes. It can dampen your carpets, rust appliances, damage the woodwork and turn your basement clammy. It can also be a standing invitation to mold and mildew to do additional damage. In severe cases, it can lead to a full-blown pest attack and/or can also de-laminate plywood.

One can easily confuse condensation with runoff or subsurface water. Tape aluminum foil over damp spots and check it a day later, if moisture forms on the outer foil surface the water is in the air. If moisture is forming underneath the foil, water is seeping in from the outside. If you have a regular occurrence of wet walls in your basement, you should perform this check before things get out of hand.


Air your basement out by opening the windows and running fans. Installing a dehumidifier is a good idea, ideally in a spot with accessible drainage. Make sure you have the heat turned up in the basement during winter months to avoid condensation. Cold water pipes often are also major culprits when it comes to condensation. Use foam insulation around them to keep the moist air from contacting the pipes.

If you have a clothes dryer in your basement, and if it vents to the outside, check for duct leaks regularly.

Drying clothes or storing wet materials (like firewood) in the basement is also an invitation to humidity, and thus condensation, in your basement. If you see the problem recurring, consider damp-proofing your walls with a waterproof coating. You can also increase the number of foundation vents to promote air circulation. 


The most common reason for a damp basement or a crawlspace is rainwater or melted snow not being diverted away from the house. If your gutters or downspouts designed to divert water away from the house are clogged, it may result in water overflowing and seeping into your basement or crawlspace. If there is no debris clogging the drains and water is still overflowing, your downspouts are choked or of a smaller size than what you need.

Make sure that the ground slopes away from your house at least 1 inch vertically for every 1 foot of horizontal travel. Divert the water in a way that it does not pool or percolate into the soil near the foundation. Look for any unsealed cracks in your driveway and check that the curbs are channelling the runoff into the street. Always check regularly to ensure water is being moved away from the house.


Patch the cracks in the foundation and seal the basement walls that present leakages. A polyurethane masonry caulk would come in handy here. For cracks larger than ¼ inch, use hydraulic cement which expands as it dries. Consider installing a sump pump to enable more effective basement waterproofing. (You can find a wide selection via our Amazon Product Program, here.)

Address outside entry points for water by patching cracks in the driveway. You can use cement for the same if you have a concrete sidewalk or driveway. Installing rain barrels or cisterns can reduce the risk of soggy yards and basements while saving water for a “rainy day,” pun intended. Make sure the grade of your yard is allowing water to flow away from the house instead of collecting around it.

You can also consider installing Dutch drains, gravel-filled barrels with holes at the bottom which can slow the flow of water and allow the ground to absorb it.

Benefits of Waterproofing: Protection, Preservation, and Prevention

Subsurface Penetration

If your basement presents wetness which appears like runoff but does not seem to abate, you may be dealing with high groundwater levels. If your house is surrounded by soil heavy in clay, it can become saturated with rainwater or a subsurface spring.

This water seeps through the porous layer of the soil and collects near the base of the foundation. It then begins to rise through gaps and cracks in the walls or foundation due to that hydrostatic pressure (aka capillary action) I mentioned above.


You can try patching the cracks that allow for seepage from the inside, but in serious cases you may need professional help. Using a basement waterproofing membrane is always a good choice for internal basement waterproofing.

In addition to a sump pump, installing perimeter drains of 4-inch perforated PVC drainpipe laid in gravel inside the foundation footings may also be suggested as a course of action. Address any and every crack in the foundation, as these may be the cause of subsurface water penetration leading to severe damage to the house later. Because these solutions are expensive, make sure your contractor does quality work, is insured and get detailed specifications of what is required to be done.



If your basement has been accumulating water over some time, remove it with the help of a pump and run a dehumidifier for a few days. This will dry out the space and give you the time to identify where the water is coming from. Make sure the outlets for your pump and dehumidifiers do not pool the water around the house or it will only complicate matters further.

Your home deserves to be warm and dry, do not allow simple oversights to eat into your building foundations and wreak havoc. Take measures to dry your basement today.


All images with permission from AquaMasters Drain, Plumbing & Waterproofing. For more from Building Moxie on getting the most of Basement space, please see our top level category, Basements.

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