Home additions create extra livable space, but they could create problems.
I have been receiving calls from homeowners wanting advice on home improvements. One particular question dealt with a tile problem (the tiles were cracking, and they were bound to crack again- the issue was the foundations). We are becoming stationary in our movement. If we leave our homes for another part of the country for a job, we loose out financially on the sale of our home, so we do not move. To cut back on expenses, we stay in to watch a movie and dinner, rather than going out. There seems to be a trend to let our homes take on further importance in our lives. Having the space for our interests by creating additions to our homes may be the desire of homeowners.
Our natural inclination is to expand our homes into existing space. The patio becomes an extra living room. The garage become an extra bedroom or family space. Patios are already sitting/dining space, and the garage may already have a family room atmosphere, so we are formalizing this function. The slabs of a patio or garage are not the same as our foundation though. We have an easier time converting the garage, but with the patio we have to create a new foundation. Or we should; this sometimes is not the case, and this is the first problem. If you are building the addition on your own, and you are not obtaining a building permit, you may be cutting corners. A simple slab of a patio does not carry the load (weight) of a room; moreover, the grading of the ground could lead to moisture problems.
Most of us will hire a contractor to build the addition. The standard way for this extra space to be created (by good and bad contractors) is to start with a new foundation. You may not realize that you probably walk into buildings with more than one foundation. As commercial buildings expand, new foundations are poured. More than one foundation is acceptable, but there is a difference between a commercial and residential structure: the tie-in between the addition and older structure. Having an expansion joint on the wall, ceiling, and floor is not really a problem in a commercial setting; however, we do not want to look at this joint in the home. The two foundations will be moving differently, and this can lead to cracks. We may not need an expansion joint for the wall or ceiling in residential construction, but the floor will be a problem. Tile over the joint between the two foundations will crack. Solid wood may buckle. A laminate wood may have more play. Carpet is the best for dealing with this joint, or you can have a joint strip like the covering which goes into the threshold of a doorway.
You may not need the expansion joint, but the contractor should connect the new structure into the older structure properly. I have seen entire additions pull away from the home, because they were not attached properly. How the old and new are connected depends upon the addition being built, but suffice it to say a few nails will not do. The new structure has to become integrated into the older framing. You cannot have two separate framings, and then a wall covering over these two sets of framing, and think that you have a connection. The wall covering will crack.
The next area of concern is how are the services from the existing structure routed to the new structure. Electrical wiring may be better on its own circuit. I see breakers double lugged, or the wiring tied into an existing circuit. This only leads to electrical problems down the line (think shorts). Air conditioning and plumbing lines should be properly attached. With air conditioning, you may find that you existing appliances cannot handle the new square footage. Air conditioning units are sized for the existing space, so adding space may mean a new air conditioning system. Plumbing lines do need connections to be done well, or you may have leaks.
Expanding our space is a wonderful option. Personally, I like the idea of finding ways to make use of existing space wisely. You can build up, keeping the existing foundation footprint. I have seen homes with attic space that could have been part of the living space. In this scenario, we do have to look at the framing and older structure. Can the home take the extra weight of living space in the attic? This is where you will need a structural engineer. Adding loads to the framing can cause problems in other parts of the home, so you need to know if this plan will be alright. In fact, going through the steps of obtaining a building permit, having a structural engineer approve plans, and having an architect draw up the plans can be the best assurance for a job done correctly.