Basement walls are subject to unique stresses because the wall temperature and moisture content varies for the portions of the wall that are above grade and below grade (or above ground level and below ground level). The base of the wall is below grade and maintains a fairly uniform temperature whereas the upper portion of the wall is above grade and subject to a wide range of seasonal temperature variations.

Water Penetration through Concrete Foundation Walls or Floors

Moisture is always present in the soil. The amount of moisture may temporarily increase during the spring when the snow melts and during heavy or prolonged rains. Builders take a number of construction precautions to ensure water at the surface and moisture in the soil does not accumulate against the foundation of your home or under your basement slab.

The most effective course of action to managing rainfall and water build up is to direct water collected on the roof and flowing on the ground away from your house. This is accomplished by:

  • Ensuring the foundation backfill is graded so that water will flow away from the foundation;
  • Using downspouts with extensions to direct rain collected by the roof away from the foundation;
  • Shaping the sub-grade of the lot so that water flows away from your home towards “swales” and is carried away from your home;
  • Installing window wells to keep the ground away from windows near grade;

Water present in or below ground surface can be managed by:

  • Protecting walls below grade from moisture penetration into natural pores in the concrete by coating walls with materials such as a spray applied bitumen and/or specialized drainage mats that can resist the movement of water the wall exterior;
  • Collecting and draining water that comes in contact with the exterior wall below grade by using weeping tile systems and diverting water to storm sewers or a sump pit.

Unless there is an unusual amount of water accumulating against the wall (such as in a severe rainstorm or grade slopped toward the house) water should not enter the basement. However, because concrete is a porous material and coatings are not continuous under the footing where the wall meets the foundation, small amounts of water may be transferred through the concrete and show up as dampness on the inside of the concrete wall.

A sump pump is a small pump installed in the lowest part of a basement or crawlspace. It works to keep the area under the building dry and to protect the basement from flooding. Check your sump pump and pit in the spring and fall to ensure that it is operating properly. Make sure the power cord is in good condition, the pipes are connected and the pump turns on when the float is lifted.

As a homeowner, you must ensure that the systems the builder puts in place are maintained and working properly.

  • Ensure the clay layer beneath the topsoil maintains a slope away from the house. Fill areas that have settled with clay, not topsoil;
  • Ensure downspout extensions are down and clear of debris year round to direct water away from your house;
  • Ensure window wells are free of leaves and debris and extended above grade;
  • Maintain a positive grade around window wells to direct water away from your homeʼs foundation;
  • Ensure your sump pump is in good condition and working properly;
  • Install a discharge hose during the spring and summer to move water collected by the sump pump further away from your home;

Did you Know?

In colder winter months, frost may accumulate on above-grade inside basement walls – this is considered normal.

Damp Basement Floors

Concrete basement floors sometimes feel damp to the touch. This usually happens for two reasons. First, during the first year after basement concrete is poured there is still water present in new concrete. This water evaporates to the inside of the basement and may result in floor that feels damp to the touch. Avoid placing materials such as carpet or boxes directly on the floor during the first year of owning your home. Second, small voids in the concrete act like tiny straws that draw small amounts of water from the soil into the basement slab. The rate of this movement depends on the amount of moisture under the slab, the relative humidity in the basement, and the porosity of the concrete. If the basement is very dry and the ground very wet, the movement of moisture can occur more quickly.

The movement of moisture through your basement slab can be stopped by breaking the connection between the source of moisture under the slab and the slab itself. Builders use measures such as granular fill, polyethylene membrane or foam insulation underneath the basement floor slab to create this break. If the dampness persists ensure water collected on the lot and on the roof is being directed away from the house by:

  • Make sure downspouts are in place, extensions are down and water is being directed away from your homeʼs foundation;
  • Check to see if the earth around the home has settled. If there is a depression near your home, remove the topsoil and fill this area with clay (not topsoil) so that there is at least a 10% slope away from your house;
  • Make sure your window wells are not accumulating water;
  • Use a de-humidifier or increase the amount of ventilation to the area where moisture appears to be collecting;
  • Check to see if your sump pump is working properly;

Before you apply a finish over a concrete floor (paint, carpet, solid flooring), be certain that the concrete is dry.