I would like to inquire concerning the proper method and material for refilling sunken ground around a residence. The situation is that our area was a wet area that was built up for houses and over the years the ground has settled, is depressed and needs to be built up. I have added clay and then topsoil to the area around the open areas of the foundation of the house to maintain a slope away from the house. This has worked well, having to be done every three to four years. However, the areas that are now most noticeable and problematic are under the cement stairs, which are anchored to the house through the basement walls, and also under the driveway, especially close to the garage entrance. I have added river stone to areas under the stairs thinking that adding sand would just wash down to the weeping tile and plug the drainage of water and adding clay is difficult to do under stairs. However, every year I have to add this stone since it settles or compacts more. I was wondering if it would be better to add crushed limestone under the stairs since this will compact and maybe form a more solid foundation and fill in the gaps left by the river stone. I am hoping that this would not settle anymore or is this like adding sand and will it cause a problem with weeping tile drainage after time? I would appreciate your thoughts on this problem.
This is an excellent question to a regular maintenance issue on almost every older home. It is also very timely as we see the snow melting and approach the warmer weather where the focus of our homes normally moves from the interior to the exterior.
Settlement of soil around foundations and under concrete steps, sidewalks, & driveways is a normal occurrence due to erosion and other normal forces of nature. Building up the soil in these areas is critical to maintaining a dry basement, especially in older homes. The majority of minor moisture intrusion situations that I see in basements is directly attributable to a combination of poor grading and damaged or improperly routed downspouts. This is partially due to the property of our notorious Red River Valley clay that allows it to compact and shed surface water when properly sloped. The downside of this is that the soil will also shrink when dry and may leave gaps along the foundation that can channel water toward the foundation walls. This is most prevalent under concrete steps, porches, and patios like yours, where it is hard to replace lost material.
When a house is built a drainage system is installed beside the footing, below the foundation walls, that is commonly called “weeping tile”. In older homes, these were small cylinders laid end to end with small gaps in between. The oldest ones were made of clay, hence the name. These were later replaced with concrete tubes, which served much the same function. These tubes created crude pipes along the outside of the foundation that collected excess ground water and channelled it to the house drains, underneath the basement floor. After many years of use, these tubes become plugged with clay, which makes grading and water management around the foundation much more important. On newer homes this drainage system is a continuous, perforated plastic pipe which does not easily get blocked with soil or debris
The reason for elaborating on the weeping tile issue is that the answer to your question largely depends on the age of your home. If the house is less than twenty years old, there is a good chance you have plastic drainage tile and the choice of backfilling material may make some difference on performance of this critical system. Typical installation of drainage tile in a new home includes wrapping the pipe in a filter cloth sock and covering it with several inches of stone to prevent clogging with newly backfilled soil. In slightly older homes, this may not have been done, so plugging of the small perforations is more likely. If this is your situation, clay is still the best material to use for preventing erosion and helping with compaction, despite the difficulty in getting it under your steps.
If your home is more than thirty years old, the choice of material is much less relevant. In homes with the older styles of weeping tile, they are often partially or completely blocked with clay, after decades of use. There should be little concern for any material washing down through the numerous layers of clay and topsoil to plug the tubes. At that stage, filling the void under steps, any way possible, should be the focus. Sand will be the easiest to shovel in, but may slump back toward the opening and will not be very effective. Crushed limestone or similar material should work better and will not immediately fall back when piled up in the void.
The biggest concern with any void under your steps or driveway is the creation of an ideal area for a “swimming pool” after the snow melt or heavy rains. Any depression can fill with water and standing water against a concrete foundation will often find a small crack or opening to leak through. Clay is the best material for compaction and shedding excess water, but any material that raises the grade under the steps higher than the surrounding area will prevent moisture intrusion and a damp basement.