A Guide to reinforcing/retrofitting an existing foundation
(This is a follow up to the article titled: Inspecting a foundation)
Sometimes there is a combination of the previously outlined issues (see Inspecting a foundation) and it isn’t clear what needs to be done, if anything. A main criteria of an existing foundation is to be able to hold the epoxy retrofit bolts and anchor the structure to its foundation. The best and cheapest first step for foundations that are difficult to visually assess is to install some anchor bolts in them and test them. They can be tested with a “torque test” or “pull test,” whereby a certain amount of torque/tension is applied to the bolt. If the bolt can hold in the foundation without breaking or cracking the foundation, then the connection is sufficient and the foundation will most likely serve its purpose during an earthquake. Most foundations however, can be visually assessed.
Making the decision on what to do with your foundation also depends on your performance criteria. If the cracks in the wall and sloping floors are the only issue, you may not choose to replace or reinforce your foundation. However, if you wanted to put new tile in the bathroom or other finishes more sensitive to movement, you may elect to have a more stiff foundation that requires some work.
I’ve outlined some options below on what can be done with an existing foundation.
Encase existing foundation: Depending on the access to the existing foundation, it may be possible to add some new concrete adjacent to the old foundation and avoid removing the existing foundation. This is a common option and one that adds significant strength to the foundation system of the house and will extend the life of the foundation considerably. It will also give you the ability to bolt the house to the newer foundation making for a more secure bolted connection.
Reinforce: There are numerous ways to do this and the best solution will be based on site conditions, access for equipment, and performance criteria. Some options are installing bench piers every 6′-8′, capping the existing foundation with fresh concrete, creating a concrete curtain wall on the inside of the existing foundation, and even pouring drilled piers in the case of more extreme movement.
Replacing: A new one is almost always the most expensive and best performing option. Though costly and labor intensive, a new foundation will last the longest and could save major damage to your house. Replacing a foundation also gives you the chance to add new drainage alongside the new foundation if water infiltration and expansive clay soils have been an issue. It some circumstances, it is also possible to replace only portions of a foundation.
Not doing anything: Always an option and sometimes just a fine one. Some foundation “issues” are often more aesthetic than they are structural problems, such is the case with settlement. It would be important to keep an eye on the foundation over the years.
If you have more questions about your property or project, feel free to give me a call. I am happy to consult with you.