Trained Eye

 
 
 

Heaving Basement Floor

Question:

Our house was moved onto a new concrete basement in 1990. The basement was dug in an area where there were maple trees that were cut down. The house is an older bungalow built in 1957. We are experiencing heaving in the middle of the basement floor, to the extent that the main floor is starting to slope. Someone has suggested that it could be water pressure underneath causing the heaving. Or could it be the maple tree roots that are causing the problem? Any ideas, advice or suggestions would be most appreciated.

Thank you very much for your help.

Answer:

Unfortunately, you live in the heart of the Red River Valley and our expansive clay soil is subject to major swelling and expansion problems. It is quite normal for non-reinforced basement floor slabs to heave and crack, even after just a few years in a home. The floor movement itself should not be of much concern, but the main floor movement will require attention and I will elaborate on this further.

The perimeter of your home is likely built on a concrete foundation, supported on a footing buried approximately four to six feet below grade. The center of the house is normally supported on teleposts that rest on other rectangular footings below your basement concrete floor slab. It is these footing that are likely moving or settling at a different rate than that of the perimeter foundation.

Whether this soil expansion is due to removed trees is unimportant, at this stage, and will be difficult to determine. What you should concentrate on is the remediation required to straighten your floor and minimize structural and cosmetic damage to the house. The good news is that it should be relatively easy to fix, as long as you have access to certain areas in your basement. The teleposts underneath the main beam or beams in your home have a threaded adjustment rod at the top. These can be rotated to lower the teleposts, which will straighten the bowed beam. Once the beam is relatively straight, you should notice a marked difference in the floor slope.

Care must be taken to adjust the teleposts at a very slow rate to prevent dramatic movement in the floor and wall structure. The teleposts should be lowered over a period of several weeks to months, depending on the extent of the heaving. Some contractors like to do the adjustment in one shot, which may cause excessive wall cracking and cosmetic damage. A rule of thumb for this adjustment is to turn the threaded rod no more than one quarter to one half of a rotation at a time. Also, there should be a settlement period between adjustments of approximately 1 to 2 weeks. This careful method will let the structural components in the home adapt more gradually to the movement and should minimize damage.

The majority of the movement and settlement in a home is typically in the first ten to fifteen years after construction. This is due to the extreme disturbance of the soil when the home is built. As in your situation, removal of trees or excess vegetation may dramatically change the moisture content of the soil and also its retention properties. You are now at or near the end of this timeframe with your new foundation, but that does not mean the movement has ended. Very dry years, such as that just experienced, or periods with higher than average precipitation can cause swelling or shrinking of the clay soil and settlement may continue. After the telepost adjustment is complete, it is important to monitor the home for further movement and make periodic minor telepost adjustments as required. The simplest way to do this is to monitor the interior doors and floors for movement. If interior doors begin to bind at the floor or jamb, you know the footings below the beam are moving. If the gap between the tops of the doors and the jamb increases or decreases significantly, it is a sign that adjustment is required. Doors and windows are normal installed square, level, and plumb when a home is built, so when they are out of whack it is a visible sign of structural movement.

The question you may now be asking is: “Who can I call to do this telepost adjustment”? The difficulty with this answer is that there is no formal trade person that is trained to be an expert in telepost adjustment. You will get various different opinions, methods, and prices for doing this common yet complex adjustment. Many foundation contractors are doing telepost adjustments, but often will suggest using the one time method, to keep costs down. As previously stated, this can be a big mistake. Also, many well educated general contractors are providing this service. That may be your best approach, as some minor renovations may be required to expose the teleposts for adjustment. Once the adjustments are complete, the general contractor should also be able to provide the services to repair wall cracks and other damage caused by the floor movement.