We'd like to bump out the front gable wall over our half-walled front porch to gain six foot room additions in two tiny upstairs bedrooms. The porch has three steps up, and is as wide as the house. Will we need a stronger foundation under the porch for the weight of the room additions?
Peter L. ~ Detroit, Michigan
Hi Peter. The only way to know for sure is to have an architect or engineer take a look at your porch foundation to determine what you have. It can also depend on how old your home is. Most of the time a builder will dig the footings for the entire outline of a home at the same time and they are poured with the same thickness of concrete unless there is a particular area that requires a deeper footing.
If the foundation is block or formed concrete, the contractor will have all of those done at the same time as well. A front porch is not handled any differently than the rest of the home and the foundation thickness is usually the same. If that's what happened with your home, then your foundation will probably be sufficient.
Unfortunately, during the days before building inspections were required there were sometimes things done that could be considered questionable to say the least. If your home is located right in Detroit, then your front porch may have escaped this type of construction. Most of those questionable methods of building happened out in the countryside away from prying eyes.
You are going to need drawings of your bedroom expansion to get a building permit from the city. Whoever you use to do the drawing is going to have to show the foundation on the drawings and prove to the inspectors that it's capable of supporting your bedroom expansion above. I'm not sure how the codes read in Michigan, but where I live drawings of this type can be done by an architect, draftsperson, or engineer. I would imagine that they will want to dig a few test holes at the perimeter of your front porch to make sure the foundation is uniform on all sides.
My guess is that your porch foundation is going to be sufficient, but the floor system may need to be beefed up and depending on whether you plan on enclosing the porch--the posts will need to be supplemented with additional support for the expansion above.
If for some reason no one mentions your front porch foundation or checks for its depth or size, you should insist that it be checked before the extension is started. The last thing you want is for the front of your home to start sagging and a contractor having to prop up your addition while a new foundation is poured underneath it. That could get very expensive.