My 11-step process: what I do and how I do it
A common mistake is to assume that foundations are either perfectly rigid or flexible to the point of regularly bending so much as to cause structural damage to load-bearing elements in the frame structure of the house. This assumption is wrong-headed. Slab-on-ground foundations rarely fail catastrophically nor are they so rigid as to not cause any damage or distress to the house. Homeowners in Southeast Texas should accept there is an ownership risk that their house will suffer some degree of distress and damage due to expansive soil movement.
The real question is: what damage or distress is a specific homeowner or buyer willing to accept? That is a question each person must answer for his of herself; no one can answer that question for you, not even a structural engineer.
What a structural engineer can do to help you
In a structural design of a slab on ground foundation, one the first steps is to decide what the structural performance requirements are for the foundation. The foundation must be proportioned so that the weight of the house, the furnishings in the house and the weight of the foundation concrete does not exceed the bearing capacity of the soil supporting the foundation. In addition, the slab foundation must be designed so it will flex or bend within certain limits so as to not damage the house to a severe extent.
A Professional Structural Engineer can provide you with guidance on the following issues:
1. Is there damage to the house that is likely to have a significant effect on the ability of the structural frame to carry normal expects loads in a safe manner?
2. What is the apparent distortion mode of the foundation?
3. Is the foundation performing in a normal manner based on the engineer’s experience, the area where the house is located, the way the house was constructed, the materials used in building the house, and how foundations for other similar houses have performed.
4. Has the foundation damaged the house to a degree that makes foundation repair either necessary or prudent?
Step one – look at the client’s specific concerns
I ask you to show me the specific things you have seen that lead you to think you may have a foundation issue or problem. I then look at those specific items. I do this to make sure I can address these concerns.
Step two – walk the outside looking for irregularities due to foundation distortion
I surveil the outside of the house looking for any irregularities that might be due to foundation movement or distortion. Examples are stair-stepped cracks in the brick veneer and separations between the brick veneer and other materials. Brick veneer cracks and separations will be used later to estimate how much distortion the foundation has experienced.
Step 3: step off the foundation footprint
My report almost always includes a sketch of the foundation footprint. This will be used to record elevation measurements that will be used in my analysis.
Step 4: walk the interior of the house looking for distress that could be caused by foundation bending
Inside the house, I look for any irregularities, distress and damage to the finish materials that are consistent with the way the foundation distorts due expansive soil movement. The main thing I look for is drywall cracks, door issues and perceptible floor sloping. I note the extent of the distress and damage and whether it is cosmetic, functional or structural.
Step 5: make elevation measurements to assess how unlevel the foundation is due to movement caused by expansive soil movement
This is a widely misunderstood issue. Many people focus on this to the exclusion of all other criteria. In my view, this is a mistake. Levelness is a legitimate performance criteria but it is widely misunderstood. It has to be considered and assessed in context with published construction tolerances and how much of the unlevelness is due to foundation tilt and bending.
Step 6: make elevation measurements to assess how much the foundation has tilted and bent in at least two directions
All slab foundations tilt and bend. They do so in both principle directions: from the rear and from the left side to the right side. Tilt is rarely a structural problem although even a 1% tilt can result in large elevation differences. Bending, on the other hand, can cause severe structural damage to the house and the foundation itself.
Step 7: compare the bending estimates
I compare the degree bending in each direction based on an analysis of the cracks and separations in the brick veneer with the degree of bending as analyzed using elevation measurements.
Neither method is exact; they each provide an estimate, nothing more. I have found it very useful to compare the estimates.
Step 8: making repair recommendations
I am opposed to the idea that the question of whether a foundation should be repaired is essentially a math problem. Several items must be considered to arrive at a defensible common sense repair recommendation. How extensive is the damage caused by foundation movement.
1. How extensive is the damage caused by foundation movement? The more extensive the damage, the more likely you will get a significant benefit from foundation movement.
2. How severe is the damage due to foundation movement? The more severe the damage, the more benefit you are likely to get from repairing the foundation.
3. Is the damage cosmetic, functional or structural? Correcting structural damage might not nbe possible unless the foundation is repaired.
4. Can the damage be repaired without repairing the foundation? If that is the case, and if the damage is cosmetic, but not severe or extensive, making repairs to the house and not repairing the foundation is an acceptable option for many people.
5. What is the dominant distortion mode as indicated by the elevation measurements? This is important because slab foundations that are in an edge lift distortion mode do not usually make good candidates for foundation repair.
6. What is the age of the foundation? Older slab foundations were not designed for use with expansive soils. Some of these have performed adequately, but many have not. Repairing these foundations are less likely to be successful as newer slab foundations.
7. Is there an obvious cause of any excessive foundation distortion? If so, foundation repair may not be as effective as it should be if the cause of the problem is not addressed. In many cases, correcting the cause of the excessive distortion may be as effective, or more effective, in making the foundation more stable than foundation repair.
8.Is the foundation concrete in good condition and is it strong enough to be able to withstand the forces involved with repair? Just to take an extreme case: if a slab foundation was constructed with oyster shell for aggregate, it would be foolhardy to repair the foundation.
9. How much benefit are you likely to see after foundation repair? The idea that foundation repair will fix your foundation is a myth. At best, it will improve the performance of the foundation, but there is no guarantee that your house will not continue to have drywall cracks, brick veneer cracks, etc.
Step 9: write the report
Every report I create is specifically written for the specific client and addresses his of her concerns. I strive to make the technical aspects as simple as possible so that it can be read and understood by non-engineers.
Step 10: review the report, make any needed corrections and then sign and seal the report
Once the final editing is done, it is time to seal and sign the report. The seal means that I am taking legal responsibility for the engineering decisions and recommendations in the report.
Step 11: email the report
You receive the report via email. I use email because it is fast. You can make as many copies as you need or want. Should you lose the report, you can usually get it it back unless you deleted the email. In that case, you can contact me and I can almost alway find it on a hard drive.