Replacing wood subfloor, joists and beams is only performed as needed on a pier and beam foundation.
Joists, sub flooring and beams may fail due to rot or termite damage.
Another common cause of pier and beam foundation failure is inadequate support.
A properly trained pier and beam foundation evaluator can usually spot most of the problems during a 30-45 minute inspection under the house.
Soil consolidation is a leading cause of concrete slab foundation failure of houses in Dallas and Fort Worth, Texas. The soil lacks the strength to adequately support the foundation.
Improper preparation of clay soil can cause consolidation, which means that the clay soil becomes more dense with time. Soil consolidation can continue for decades.
During building site preparation, the developer should assure that clay soil is at the correct moisture content to enable adequate compaction in thin layers using specialized heavy construction equipment.
If you suspect a foundation problem is caused by soil consolidation, you may want to hire an engineering firm to perform soil consolidation testing. Site testing can run upwards of $2500.
If your house foundation has failed due to clay soil consolidation, you should consult a construction attorney as you may be able to take action against the site developer and or builder.
The weight of a house will facilitate soil consolidation. One way to mitigate future consolidation damage is by having steel underpinning/piers installed to take the load of the house off of the top soil in the areas where consolidation is taking place. Sometimes it is necessary to pier the whole of the house to fix foundation problems caused by soil consolidation.
A pier and beam foundation problem usually centers around soil moisture under the house.
Let’s look at the construction of a typical 1900 to 1960 pier and beam house. Posts, which we call piers, were set one to two feet into the ground and extended 2 to 4 feet into the air. Atop the posts were layed beams. Atop the beams are the floor joists, and atop all of that is the hardwood or plywood flooring.
In some instances the posts were set into a concrete pad one foot deep and two feet on a side. More recently, atop the concrete pad or footing sits a poured concrete tube. And sometimes in place of the tube are one or more concrete blocks. Or even a more modern variation is when the pier and pad are one poured concrete assembly.
To see what we mean, take a look at the picture below of a modern pier and beam foundation construction using concrete block and pad.
Regardless of the pier type, piers are spaced 6 to 8 feet apart in a series of rows extending under the house.
Soil under a pier and beam foundation on clay soil must be as dry as dust. The least bit of additional moisture will cause the soil to expand. Soil expansion will drive one or more piers upward, raising the floor. Often times the moisture under a house is uneven, perhaps due to a leaky pipe, or poor drainage at the perimeter. Then, the pad and block assemblies will raise unevenly.
To stop a pier and beam foundation from moving, keep all moisture out, provide adequate ventilation, and assure that the soil remains dry and crumbly. Once the soil is absolutely, completely dry, the foundation can be shimmed to achieve uniform elevation across the house.
Cut and fill is a major problem due to the expansive clay soils in the Dallas and Fort Worth areas of North Texas.
Why does improper fill cause a foundation problem?
Clay soil that has not been properly compacted will consolidate over time.. and we are talking about decades. As the soil consolidates, it drops, and the foundation above it is no longer properly supported. A foundation that is not properly supported will fail as it too will drop.
What is required to achieve a proper fill?
To properly “fill” a building site, the expansive clay soil must be compacted in no more than 4 inch layers, and be at the proper moisture level during compaction. Proper moisture means that the clay soil can neither be too wet or too dry.
Why can a site cut cause a foundation problem?
When a site is cut down to a uniform height, expansive clay soil that was covered with over burden is now exposed to the water. Newly cut soil can be characterized as dry and compact. The compacted soil is good, but as the expansive clay hydrates (gains moisture), it will expand. If a foundation is built over a newly cut area, it may heave as the soil hydrates.
Cut and Fill is the worst case scenario for a foundation.
For all the reasons explained above, a foundation straddling a cut and fill is a disaster waiting to happen. The foundation tends to heave in the cut area, while sagging in the fill area.
During housing site development, some high areas of land are cut off, while the low areas are filled with the cut material. This is called cut and fill.
Clay soil deep underground may be drier than the surface clay. When the clay is exposed to surface moisture after the cut, the soil hydrates. The clay soil gains water content, and it expands. The expansive soil swells, forcing the foundation upwards, and we say that the foundation has heaved.
Expansive clay soil that is correctly compacted and maintained at a proper and consistent moisture level is not a problem for a foundation.
There are four changes in clay soil which cause problems for our foundations:
If the moisture level in the clay soil under a part of a foundation increases, that area of the foundation will rise or heave. If the moisture level continues to rise, turning the clay to mud, the soil will lose its ability to support a foundation, and that area of the foundation will drop or slump.
When the moisture level in clay soil under a part of a foundation decreases, that area of the foundation will drop or slump.
Clay soil that has not been properly compacted during site preparation will consolidate over time due to the weight of the house. If the consolidation of the soil does not occur evenly under the foundation, some parts will be less supported than others.
Is the patio separating from the house, or is the house moving away from the foundation?
A Granite Foundation Repair evaluator will look at both sides of the problem. What is moving and what is stationery? Most likely the separation of the two structures is occurring because one of them is moving down a slope.
Two common effects of slope failure are:
Retainer wall movement can be slow, or sudden. The picture below is an example of sudden retainer wall failure that led to slope failure under the patio, exposing plumbing. Left unattended, the whole house would soon fall.
Interesting soils in The Colony, Texas. That foot of soil may well be clay, covering a rocky substrate that is only a few inches thick, which overlays more clay. All of that clay is moisture sensitive and will cause a house to heave and settle, flexing it sufficiently until a foundation problem appears.
At Granite Foundation Repair, we have found that when doing foundation repair in The Colony, it is not unusual to drive steel pilings as much as 30 feet deep. But first, we have to jack hammer through a crust of rock.
Similar rocky conditions perhaps 1-3 feet deep are found in some parts of North Rowlett as well as in Hurst, Euless and Bedford.
While moisture under house tends to cause soil to expand, tree roots on one side can reduce moisture and cause foundation failure.
The impact of tree roots on concrete slab foundations is a controversial subject. In our experience tree roots cause substantial foundation damage in North Texas.
Tree roots can extend as much as 5 times the canopy height of a tree. In periods of drought, tree roots seek out water.
According to Dr. Tom Witherspoon, if the soil under your foundation is more moist than the soil outside, the tree roots will seek out the water from under your house. As the moisture content drops, clay soil shrinks, and the foundation support in that area is reduced. The net result is foundation failure and the need for foundation repair.
The goal is to maintain uniformly moist soil to maintain a properly supported foundation.
Each side of your house may require a different amount of water. The southwest side of a Dallas Fort Worth house in the summer may require 50% more water than the northeast side.
Trees and bushes absorb water, but also shade the soil from drying hot summer sun.
In areas where there is less than 20 feet between houses, you also have to take into account how much your neighbor waters. If you neighbor won’t turn down the sprinkler system and is creating a marsh around your house, a french drain or surface drainage system may be needed.
To avoid foundation problems from over or under watering, always keep the soil moist, and never alow it to dry or become muddy. This requires year around maintenance to avoid foundation problems.