Why Porches Can Be a Problem
Home with wide porches across the front or back of a house can be a problem because they often require expensive foundation work. If your house has a front porch it is possible that the foundation is under the front of the porch as shown by the red arrow rather than under the floor below the front wall which is where the house floor is as shown by the blue arrows.
Go stand on your front porch and look at the floor in front of your front door. Notice how you need to step up 2 or 3 inches to get into your houses. This is because you have two floors independent of each other. The porch has a floor and the main house has a floor. In a retrofit we are trying to keep the floors from falling from their foundations.
If we protect the porch floor we will not have protected the house floor. You can live in a house where the porch floor has fallen from its foundation. You can’t live in a house where the house floor has fallen from its foundation. Connecting the front of the porch to the foundation will not protect your house.
Many contractors do not understand this and connect the porch floor to its foundation with a shear wall. In such cases there will still be nothing under the front of the house to resist earthquakes. You will only find a few posts that can tip over taking the house floor along with them. A floor only supported by posts is very vulnerable.
What Can I Do About It?
In the illustration below you can see how the home’s foundation is located under the porch rather than under the main house. The main floor is supported by posts that can tip over and collapse, taking the house with it. The best solution is to install a new segment of foundation under the house floor where the posts are, build a new shear wall, and attach it to the floor. It is not necessary to put a new foundation under the entire porch, just a segment long enough to resist anticipated earthquake forces. If your house does need foundation work make sure all the regulations on foundation construction are followed.