Foundation repair is the first thing most homeowners think of when they suspect they might have a foundation issue. The large majority would better off taking a deep breath and getting professional help. Before spending a ton of money on foundation repair, consider the following:
The Army Corps of Engineers publishes a book (in PDF) format titled: Foundations in Expansive Soils.
Is there one or more obvious source of instability?
There are numerous conditions that could be a source of instability in the moisture content of the supporting soil. The most common include poor soil grading adjacent to the foundation, no roof gutters, roof gutters that discharge roof water closer than five feet from the foundation onto soil that is not properly sloped, trees that overhang the roof and thereby overhang the foundation.
The sources of instability need to be corrected for two reasons. First, it is possible that correcting the sources of instability may result in improving performance to a point that the performance is acceptable. Second, if you underpin the foundation without correcting sources of instability the foundation repair may not work very if it works at all.
Is there a soil report available?
In my opinion, it is mandatory that no final decision be made concerning repair until a soil report is produced that shows what the active soil depth is and how much load it can carry. Soil reports are not cheap. Plan on $800 to $1200. There are areas where the underlying soils are not suitable to carry the loads necessary for underpinning to work.
I have seen situations where people decided against a soil report and then spent over $30,000 on foundation repair that was likely to fail from day one. They counted on a warranty from a no-name contractor in a fly-by-night business.
Are structural drawings available?
Structural drawings are rarely available, but when they are they can be a godsend.
Some years ago I visited a house in the Royal Oaks subdivision on the west side of town. The owner’s concern was that the floor tile in the master bedroom was badly fractured and some of the tiles were loose. The master bedroom was large, about 20-feet by 20-feet, the size of a typical two-car garage. Obviously, something was very wrong.
My first impression was that the problem was the installation of the tile. My reasoning was that foundation distortion would fracture tile, but it will not cause the tiles to become loose.
Since the owner was the original owner I asked if he had any drawings. He did not but was sure he could get them from the builder. Once I looked at the drawings it was obvious what the problem was.
There may have been a tile installation issue, but there was a far more serious problem: the stiffening beams were not continuous and they were spaced far too far apart. In the master bedroom area, the beams were only underneath the walls which were twenty feet apart.
The drawings were not sealed by an engineer. The drawing showed piers but the layout made no sense. The pier depth was 6.5 feet. Normally a soil report for the site would specify at least twelve feet. The builder insisted that a Professional Engineer had sealed the drawings.
Is the slab foundation reinforced with post-tensioned cables or with conventional rebar?
This is important. Let me explain why. As a slab foundation ages, the supporting soil is likely to settle. This means that the concrete floor between the beams will sag since it is no longer supported. In a post-tensioned slab, there is little or no resistance to the sagging. The post-tensioning steel does not and cannot bond to the concrete. In a conventionally reinforced slab, there will be significant resistance to sagging because the reinforcement is bonded to the concrete.
The result is that post-tensioned slabs often exhibit sagging between the beams that is more severe than is the case with conventionally reinforced slabs.
What is the condition of the concrete?
This is mainly a concern with older houses. The concrete is older homes is more likely to have been made with oyster shell in lieu of hard rock aggregate. You have to walk the perimeter of the slab and look for any exposed oyster shell. If you see rock aggregate there probably is no oyster shell aggregate. If there is no aggregate of any kind exposed, then there is no way to come to a definitive conclusion.
As you walk the perimeter also note any horizontal cracks or separations in the grade beam concrete. Horizontal cracks and separations are usually due to the reinforcing steel rusting due to water penetration. If this is an issue, this means that the slab, the reinforcing steel and possibly both may be damaged when the foundation is lifted.
Is there a structural safety or integrity issue?
If there are no structural safety or integrity issues, foundation repair is an option, but not a necessity. Even if there is a safety or integrity issue there is almost always a way to correct that without underpinning the foundation.
The most common safety issue is a fire escape door that sticks and is hard enough to open that a two-year-old child would not open it. Every bedroom must have at least two ways for escape in case of a fire. Normally one escape point is a window. The other one is a door.
Is the problem a continuing problem?
There are situations where distress is a continuing problem. You repair all the drywall cracks and a year or 18 months later the repaired cracks reappear. If this happens repeatedly the siren song of foundation repair may look better and better.
Has the foundation been underpinned in the past?
I looked at a house once that had been underpinned five times. There were still problems. Obviously, there was a severe problem and underpinning wasn’t working.
After looking at the house it was apparent that there were two significant sources of instability: two oak trees in the front. Once those two trees were removed, the house reacted very favorably. Doors that were sticking began to work again, cracks in the brick veneer began to close, and the drywall cracking stabilized.
There are two important points: if you underpin a foundation without addressing obvious sources in moisture variation, the repair may not be very effective and if you take care of any moisture variation, there may not be any need to underpin the foundation.
How will the slab foundation react to underpinning?
It is important that any homeowner understand that it is impossible to know in detail how the foundation will react to being leveled. If your goal is to make the foundation level, you are likely to be disappointed. The fact is that foundation repair is like a roll of dice. You never know ahead of time how it will turn out.
Are other options available?
There are almost always options to foundation repair. They may not be obvious to the typical homeowner, but the alternatives to foundation repairs are almost always available.
Which options (including foundation repair) are cost-effective?
By “cost-effective” I mean those options that give the most bang for the buck. Underpinning is rarely cost-effective. Correcting poor drainage and repairing distress drywall, brick veneer, and door problems are all more cost-effective than underpinning.
Many people have been convinced by foundation repair contractor ads and slogans that if a house shows minor distress that foundation repair is the only option. Not only is it rarely the only option, it almost always cannot compete on a cost–risk-benefit comparison.