Slab Foundation Care and Inspection
The big problem in The Houston/Galveston area is GUMBO CLAY SOIL which most of us have under our houses. It is expansive – which means it will swell up when it gets wet and contracts when it dries out. Remember, too much water near the house is bad and too little water near the house is bad. The trick is finding that happy medium.
In the greater Houston area we normally have a lot of rain so diverting the water away from the slab is important. Gumbo clay soil that is too wet will swell and can lift a house up.
Here are some things to keep in mind.
- Surface drainage should be diverted to a storm sewer or other approved point of collection that does not create a hazard
- That soil around the foundation should slope away from the house 6” in the 1st 10 ft
- If the lot does not extend 10” from the building or physical barriers prevent the 6’ in 10’ slope the drains or swales should be constructed to ensure good drainage away from the structure.
- Gutter systems are not required but if they are present the downspouts should discharge 18 to 24” away from the exterior walls. If you can discharge 5’ away that is even better. This is all in an effort to keep the gumbo soil from getting too wet, but too dry is a problem also. If your soil starts to dry out and crack - you are in real danger of the foundation settling. Things that contribute to settling include:
- Trees and large shrubs too close to the house – the root system will pull water from the soil under your slab
- Seasonal dry spells make the root systems more active under your slab.
These things may cause a need to water your foundation. If you use a soaker hose, keep it 18” to 24” away from the slab and allow capillary action to wick water back to the slab. A soaker hose placed against the slab can wash away soil needed for support and/or cause small sink holes under the house. An underground lawn sprinkler system is a great way to add water when needed. Just be sure the sprinklers never spray directly onto the building.
Inspecting for signs of foundation movement and above picture.
Here are the most common things to look for.
- Stair step or diagonal cracks in brick or stucco type sidings -straight line cracks are usually NOT a sign of foundation movement- unless, the crack gets wider as it goes up.
- Diagonal cracks in interior walls - straight line cracks are usually NOT a sign of foundation movement- unless the crack gets wider as it goes up.
- Frieze board “kick out” - Look up at the corner trim over the brick wall. Where the wood or cement board trim meets at a corner the joint should be perpendicular and well sealed. If the wall is leaning, as it will with a settling foundation, it will push the joint apart so that the bottom of the trim is farther out than the top.
- Doors and windows that don’t open and close easily, that are out of square, or won’t latch.
- Stress cracks in glass doors and windows. A hole caused by a projectile may cause a crack but a stress crack will not have a hole associated with it. • Attic framing that is pulling apart and or damaged. This is most noticeable with traditionally framed houses with rafters and a ridge board. These joints should be tight.
- If your tennis or golf ball rolls across the floor with no help from you or your pet.
Here a couple of other things to keep in mind. Most slab foundations are never perfectly level even when brand new. And, all slabs on gumbo clay soil will settle eventually. There is normally some nominal settlement in the first year. Taking proper care of the soil around your slab will keep it in serviceable condition much longer.
Posted: Jun 9, 2012
Posted by: Ed Fryday, ACI, CMI® | TREC License: #6932
Space City Inspections, LLC