We all want more space. Garages are turned into rooms. Porches are also converted into rooms. However, this may not be a wise idea.
My wife wanted a roof over our porch last year.After the job was done, she claimed what a wise investment this would be, because we could eventually turn this space into a room. An outdoor room, I responded. You see, I did have plans that we should add a room in that space. No, she argued, we can convert this into a room by adding walls. She was quite adamant in defending her position. Why was she so convinced? Because the remodeler told her that this was all we had to do. I reminded her that I am a home inspector, and that I do know something about building. We would have to take down the structure that was erected for the roof if we wanted a room, and this seemed a waste to her if we were going to build the room. The evidence piled up against her belief, but she did hold onto it. I finally found some proof that will put the nail in this notion.
Why can we not build a room on a porch? You have to understand foundations. A foundation is designed to hold the weight of the structure resting on that surface. The foundation also has to deal with being lifted by frost in the ground, so we make it deeper than the depth the frost reaches in our area, the frost line. In Houston, we go deeper with our foundations than needed, because we base the frost line for the state on temperatures in the panhandle. All of this means that the foundations are deep. Areas that do not need to support the home do not require such depths. To save money by using less cement, builders will make these cement slabs shallow in depth. Garages do not have the deep foundations along the entrance edge, since the house is notsupported there. The driveways have a shallow depth too. Then we come to porches. Porches which are attached to the house may have a proper home foundation along the edges that touch the home, but most porches are separate slabs, which are about as deep as the driveway. These can be different depths, but I see these averaging about a foot deep at most. With frost and the weight, these cement slabs crack. In fact many porches crack without this weight. Frost and moisture in the ground will raise these slabs unevenly, causing cracks.
Iimagine that my wife’s plans fall into the course homeowners do take. You set a table on the porch to eat outdoors. I even built a sideboard, added side tables, and a carpet. We built the roof to make this space feel more like a room. The insects bother you, so you enclose the space with screening. Finally, you want more use of this burgeoning room, so you take the final steps of adding walls, air ducts, and wiring. When you first put everything up, the room looks good, and you notice no problems. Shortly, you will notice the cracks, starting in the floor. Then you may realize your mistake.
I cannot always determine exactly the cause of every problem in a home inspection, but experience and clues hint to the culprit. This was the evidence to present to my wife if she had thoughts of adding walls to our porch. In the photo, you can see that there are large cracks in the tile and slab. To enter this room you have to step down from a door that was originally the back door. On the exterior, we see that the cement slab has been tiled. This is common in Latin America. What struck me was how low this foundation was. Home additions are often not on foundations which are attached properly to the old foundation. In fact, they are often lower and on a separate foundation. That might have been the case here, yet they are a bit higher than what I was seeing. The next clue came from experience, which was confirmed when I was up on the roof. Builders add porches outside of the door in backyards in homes built after 1950 from my experience. This is not always the case, but the other homes that I could see from the roof had this porch. The last bit of evidence was the nature of the cracks. They fit with what I would expect when weight was applied to the slab of a porch. Maybe more cement was added to the porch slab. I think that is a possibility with this room.
Can you use the porch for a room? There is a chance that your porch may have sections that are part of the home’s foundation. In the case of the home in the photos, could we build on a porch slab that is not a proper foundation? You can dig down to create the correct foundation depth along the edges, and then a new slab could be poured over the old porch slab. This will save on some cement if you are looking to cut costs, but you need those deep edges to support the weight.