Slab foundations and soil surface grading
This is the most common thing most homeowners do wrong. I cannot stress enough that the soil near the foundation must be sloped so surface water drains directly away from the foundation. I recommend that the soil fall 6-inches in 10-feet or to the property line, if the property line is less than 10 feet from the foundation.
Slab-on-ground foundations & subsurface drains
Underground drains should normally be the primary way to drain water away from your foundation. Underground drains are better used in a supplemental role for preventing the ground adjacent to the foundation from absorbing too much water.
I use the term supplemental because underground drains are less effective when they are used in place of properly grading the soil adjacent to the foundation. The best way to use an underground drain is to first grade the soil to drain the water directly away from the foundation and then direct the water into an underground drain.
If you leave the ground surface flat or grade it so that water flows to the foundation instead or away from it, you are asking for trouble. Underground drains clog easily and are prone to leakage.
Slab foundations & managing trees and large shrubs
Trees and large shrubs extract large amounts of water from the soil every day.
When the trees overhang the foundation footprint, or large shrubs grow adjacent to the foundation, they can remove enough moisture from the soil to cause damage to our house. This is especially true during drought conditions. Virtually every summer is dry in Houston. The dry weather usually starts no later than June. By August the phones at the offices of the foundation repair contractors are ringing off the wall. Trees and large shrubs are almost always part of the problem. They simply make the effects of dry weather much worse.
The harmful effects of trees on foundations can be mitigated using root barriers. Large deep-rooted shrubs should be remioved.. Shallow rooted shrubs such as azaleas can usually be left alone.
Slab-on-ground foundation performance and controlling roof water
When it rains a lot of water hits your roof. It has to somewhere. Ideally, you would like to be evenly spread around the perimeter of the foundation and then flow directly away. But this is not likely to happen unless you make it happen.
Roof gutters are the best way to manage water flow off a roof. I recommend that you should gutter all the eaves. Many builder will install gutters in the front but nowhere else. Do not follow their example. Guttering some of the eaves while leaving other eaves without gutters may make the problem worse, not better.
Ideally, you should not let the roof gutters discharge water onto the ground within five feet of the foundation. If the water is discharged onto the ground too close to the foundation, it can create more, not fewer, foundation problems. If it is not practical to discharge the water five feet from the foundation, make sure it is discharged onto a well-compacted sandy clay soil that is clearly sloped away from the foundation. If that is not an option, then discharge the water into an underground drainage system.
Any water that is discharged too close to the foundation may percolate through the backfill to the supporting soil underneath the perimeter of the foundation. If the backfill is a sandy soil, and this is quite common because sand is cheap, it cannot be compacted and water easily flows through it.
Maintaining ground covers around slab-on-ground foundations
It is not uncommon for older homes in Houston to have areas in the yard close to the foundation where it is difficult to get grass to grow. Usually, the problem is that the grass cannot compete with nearby tress for sunlight, water and nutrients. The result is that these areas are either bare of ground cover of the ground cover is very light.
The result is that these areas wet up and dry out very quickly, and this can result in unnecessary foundation movement and unnecessary damage to your house.
There are two things that may work for you:
- Plant monkey grass instead of St Augustine. In many cases, monkey grass will do fine.
- If planting monkey grass does not work, you can turn these areas into gardens and mulch them heavily. The mulch can be very effective in preventing the soil from wetting up and drying out quickly.
Maintaining lawn sprinkler systems for better slab foundation performance
Lawn sprinkler installers can be installed in a way that can create a problem to the performance of the foundation. The two most important things to watch out for are:
- Supply lines placed too close to the foundation. Lawn sprinkler supply lines are prone to leakage. It is better to keep them at least a few feet away from the foundation.
- Control values too close to the foundation. These valves should be checked frequently for leakage. Ideally, they should also be located at least 5-feet from the foundation.