Wet Basements

All basements and other areas below grade (ground level) are vulnerable to water entry.  Water can appear in a basement in one of three ways:

1)     Direct leakage through cracks, construction joints, windows, or over the top of the founda­tion wall; 

2)     Seepage through porous building materials such as concrete block or old lime mortar, or poorly mixed concrete; 

3)     Condensation of the water vapor in the basement air on the basement walls and floors and water pipes.

Beware of misleading claims!  There are no miracle cures for wet basements.  Claims may be made for unique waterproofing methods.  These often end in failure despite so-called guar­anties.  Costs for such methods may be high.  Often the solution is simple.  Usually the source of the leaking or seeping water can be traced to roof and ground run-off.  Roof and surface water runoff must be directed away from the building to avoid water intrusion into the building. In fact 96% of all wa­ter problems are due to poor control of roof and surface water run-off.

The concrete walls and floor of the basement act like a warm sponge on wet ground. Water will move through them by diffusion from wet soil on the exterior of the building to the drier basement air. This can add as much as 3 liters of water per day to the air in a home. Water intrusion into a building creates the conditions necessary for the growth of mold and bacteria, infestations by powder post beetles and carpenter ants, deformation and rot of wood framing members and rust and deformation of steel framing members. Water intrusion into the soil within six feet of the foundation of a building will cause compaction of the soil under the foundation footings and subsequent settling of the building’s foundation, sidewalks, driveways and parking lots. It also creates the conditions necessary for ice formation next to the foundation walls and as the water turns to ice it will expand and push against the foundation walls causing them to crack and bulge until they no can no longer provide adequate support for the weight of the building.


The place to start is on the outside:

The structure should have functional gutters and downspouts, which are maintained and cleaned regularly.  Large roof areas demand large gutters properly drained.  Lead water away from the foundation with downspout extensions.  Large (3X4 inch wide) downspouts can be installed on regular residential gutters (rather than the regular 2x3 inch downspouts). Their larger opening decreases the likelihood of clogs.  Abandon clogged or broken underground drainage pipes and install elbows with above ground piping and extensions. When you need your underground drainage the most (early spring and late fall) it may be frozen solid. In areas with high trees, install rigid plastic gutter covers with mesh screening, to keep leaves, pine needles and seeds out of the gutters (“Sheer Flow Gutter Filters with Screen” at Menards). To prevent wa­ter entry through the basement windows clean and maintain window wells so the dirt or gravel in them stops 3-5 inches below the windowsill.

It also can create conditions favorable to mold growth. Before grading against the structure seal/repair any visible cracks or voids in the foundation walls. Then, using pulverized (or shredded) topsoil, pile the dirt against the house so that slopes away from the house. The slope should be about a one inch drop per foot out to about six feet. Keep the soil at least four inches below any siding to avoid rot and carpenter ant infestations. 

 (See the picture #1 below)


If there is a driveway, sidewalk or patio next to the building, and it is made from masonry (e.g. brick and mortar or stone and mortar), or concrete or asphalt, it need only be graded to ¼ inch per foot. If it is not economically feasible to change the pitch of the surface, make sure that the joint with the house is well sealed. In urban areas where there is very little space between houses a driveway between two buildings should be constructed with a V shape so that water from either side of the drive collects in the middle and drains away, preferably to the street. If it is a shared drive enlist your neighbor’s participation. When changes you make to your grading are going to increase run -off onto your neighbor’s yard, enlist their aid in constructing a swale (a gentle V in the soil) between the two homes to collect the water and carry it past both houses.  


If it is not possible to obtain the proper slope away from the house and still maintain a 2 - 4 inch clearance below the siding, build a low retaining wall set 6 inches out from the house. Place some landscape fabric and/or an inch of pebbles between the retaining wall and the house to prevent weed growth. Begin grading the soil at the outside edge of the wall. (See the picture #2 below)


Poor grading is a common cause of seepage and leak­age. The soil can then be planted in grass or covered with geo-synthetic fabric or plastic and rocks, bark or some other landscaping material. Protect outside cellar stairwells and doors with covers and drains.  Slabs or exterior sidewalks should be poured or repaired to slope away from the structure.  If repairing incor­rectly sloped slabs or sidewalks is prohibitively expensive, keep the joints where they meet the structure caulked.  If the structure is on a hill, a swale may have to be created in the yard to divert downhill run off around the sides of the building.  If the hill is steep it may be necessary to construct a retaining wall to redirect the water. In low lying areas or areas that drain very slowly, bentonite can be roto-tilled into the soil to prevent the water from seeping into the soil near the foundation.


On the inside:

If the basement or crawl space has a dirt floor, cover it with a polyethy­lene vapor barrier.  The crawl space should be vented into the house or basement. These two measures will reduce humidity. Use a dehumidifier in the basement when the humidity is high (summer months). This will prolong the life of the furnace heat exchanger by reducing rust and prolong the survival of any foundation mortar joints.


If in spite of the above measures:

Porous foundation materials are damp - coat them with a waterproofing material,

Seepage is experienced through cracks in the basement floor or walls or at the floor wall joints - seal them with hydraulic cement or caulk sealant.

If the wall is constructed of sandstone, it should be repaired with a Type 0 mortar  so that it is not too hard for the surrounding stone. If the foundation wall is constructed of limestone or other relatively hard stone, a standard Type N tuck-pointing mortar may be used.

If after taking these measures the basement is still wet, the following expensive methods may be needed either singly or in combination: 1) the excavation of the soil around the house and the re­pair of all cracks, 2) the application of a waterproofing layer to the foundations exterior, 3) the in­stallation of exterior or interior footing drains and sump pumps, or 4) the installation of curtain or French drains.

It is, usually less costly to keep water away from a house than to seal the building and create a means of removing the water once it has reached the structure.


 Picure 1                                                                      Picture 2

grading your house