DESIGN SCHOOL Henri de Marne

Look to the Soil Around Foundation to Fix Basement Leakage

Q: I'd like your thoughts on how best to manage water in our circa-1860 home's basement with original stone wall. This is the last project in an otherwise completely renovated house.

Half the floor is finished with a thin, but solid, layer of old cement. The other half is dirt mixed with many inches of coal and coal dust -- it is visible in the picture covered in plastic. The walls are covered in foam insulation from top to about a foot from the bottom. Water seeps in the uncovered portion of the wall near the floor, especially after rodents have tunneled the dirt outside the wall creating channels for the water and sediment to enter the basement.

The house has no gutters, but sloping allows for water to flow away from the foundation for the most part. Any water coming in now drains fairly rapidly in the soil under the plastic and in small holes in the concrete floor section.

One approach recommended by a contractor is to create concrete channels along the base of the walls after laying a concrete floor throughout. The channels would collect water and send it toward a collection point to be removed by sump pump. The project would be done in stages to allow replacement of the furnace and appliances located on the current concrete portion of the floor. Replacement of an old bulkhead door also would need to be incorporated into the project -- another source of water entering the basement.

Question: Would a short concrete wall alone -- up to the point where the foam insulation stops -- be enough to seal the wall? More foam could be added to create a tight seal. The channels make sense, but I am wondering if there are other ways to manage this. Other thoughts you have are appreciated. Thanks very much. -- via email

A: Can you actually see the channels made by the rodents? They should be taken addressed and filled in.

The grading around the foundation should be carefully checked, and the areas not sloping away, since there are some, should be raised.

Because you have no gutters, is roof water allowed to fall onto the ground, creating a small trench? This may be responsible for some of the leakage.

Concrete or flagstones should be set flush with the soil at the roof's drip line in a gently sloping grade to prevent the formation of the trench and the percolation of the roof water.

A healthy stand of grass should be encouraged to absorb some of the water and direct the excess away.

Instead of building a concrete wall in the basement or adding more foam to completely cover the still remaining exposed stone walls, consider improving both the cellar's insulation and the water control as follows: Excavate the soil down 16 to 18 inches near the foundation, increasing the depth of the excavation to around 24 inches, four feet away from the foundation all around the house. Make sure the soil is smooth and free of stones and other irregularities.

Lay 2-inch-thick rigid XPS (blue, gray or pink) insulation and then backfill. Slope the grade gently, set a band of concrete pavers as detailed above at the roof's drip line, and grow grass.

When the bulkhead is replaced, make sure that the backfill around it is properly tamped in layers as the backfill progresses so that the backfill does not settle over time and channel water into the cellar.

The planned improvements to the cellar floor over time are a very worthwhile idea, but the new concrete floor should be poured over 4 inches of crushed stones covered with 6-mil plastic. Failure to do this may cause you some undesirable moisture problems later.

This means that some digging will be required, and it will be the time to incorporate a drainage system to a sump pump in case more leakage occurs. The end result will be healthier and provide you with better storage.

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