Anybody connected with the real estate business who has seen this word on an inspection report or an appraisal knows they are in for an interesting day.
Specifically, foundation movement can be anything from a hairline crack in the garage floor to major structural problems requiring piering up the foundation and mud jacking.
I recently attended a seminar in Dallas sponsored on the topic of soil movement and foundation failures. It was an eye-opener!
It seem quite a few things can cause a foundation fail, from fast growing trees and shrubs near the house to leaking underground water lines and poor drainage.
On a percentage basis, very few foundations ever need repair but every one involved in a real estate transaction has become increasingly aware of being absolutely sure there are no problems.
Regarding drainage, the site should drain water away from the home. A three or five per cent slope is recommended. Anything less will prevent water from running off and anything more can cause soil to erode away from the foundation.
We often find with pear & beam foundations that water runs right under the house. This not only causes the piers to move but can also cause rotting of the structural members of the foundation as well cause termites to become interested in the area.
I have even seen crawlspace areas so damp as to cause the formation of fungi and molds, causing health problems for the occupants. These are exaggerated exponentially if the crawl space under the house isn’t vented properly.
Certain types of trees (most notably willows, Chinese elms, cottonwoods and tallowoods) have extensive surface root systems and should not be planted close to the foundation (“close to the foundation” can be defined as within one to one and half times the mature height of the tree to the slab).
So, an elm with a mature height of 60 feet should be not closer than 90 feet to the house. Also, built-up flower beds or landscaping border (that black plastic stuff that comes in long rolls) that trap water close to the foundation should be avoided.
Gutters can help poor drainage areas but downspouts should be extended away from the foundations as far as practically possible.
If not possible, put splash blocks at the end of the downspouts to prevent soil erosion from exposing the grade beams and compromising the structural integrity of the of the foundation.
Real estate agents, appraisers and inspectors should get to know which areas of town have a higher than average percentage of clay type soils which typically expand and contract more then other types of soil and can cause foundation movement.
Montmorillonite clay is found extensively in a wide swath of Texas extending roughly from northwest to southwest and unfortunately running right through the most densely populated parts of the state. This type of clay has been known to exert pressures up to 16,000 pounds per square foot and lift slabs up to 18 inches out of the ground! I have personally seen slabs which have heaved up 9”!
Should a foundation need repair (most slab repairs cost between $15-20,000) be sure and get at least three bids from established, bonded companies who will give the homeowner a five year (min.) warranty against future movement. A pier is usually needed every 8′ around the perimeter of the home and these piers cost $350 – $500 each. Sometimes only a portion of the home needs repair. Only a structural engineer can say for sure.
Calling the Better Business Bureau and getting references from each company (and structural engineers) will further indicate who is good and who is not.
If the slab isn’t showing big problems it may only need “hydro-pier” (a watering system put around the slab which drips water when the soil gets too dry). This is much less expensive. The same effect can be had by using a soaker hose around the house.