First Floor Additions: More Room More Happiness
(Part Two– Foundations: The Basis of Your Addition)

by: Liz Roberts

Now that you’ve decided about building your addition, it ‘s time to think of the foundation. Many homeowners don’t realize how important it is. Without a well constructed base, any home or addition is about as sturdy as a house of cards. To build a solid one, understand the options that are out there and which you want to take. Realize that the foundation has to be the most perfect part of your addition. It has to be done correctly to ensure that you will have a long lasting, durable structure.

Building a foundation can be time consuming and wearing. This is a project best done with a group (preferably not neophytes.). Some contractors will let the homeowner work with them depending about the relationship. Before attempting, think about the time involved and if you’re up to it. Laying a foundation is serious business. It will not be over and done with within an hour.

Another important factor is getting the right materials. There been horror stories where sandless cement was sent to homeowners and it had to be sent back. If you want to work with an environmentally friendly base consider using salad oil instead of the toxic petroleum products used for helping concrete to slide from the shaping forms.

If you’re installing a slab foundation then consider these facts. The concrete should always be level. If it isn’t then later on down the line the framing will have to be trimmed.. This is costly and time consuming. The water/cement ratio should be below .50 otherwise vinyl flooring will always be wet and moldy or tile grout will be mildewed and damp. This can also lead to excessive cracking that will eventually result in extensive damage. Air entrainment must be used in colder weather climates otherwise the water in the cement will and can expand. This causes the concrete to fracture during the first major cold spell. Control joints have to be used within the proper spacing, because again damage to the slab can occur. Wire mesh is not recommended because this will sink into the ground without the support of cinderblocks. The sub grade has to be compacted 89otherwise plumbing trenches underneath the house may collapse. The most vital thing to remember is to give the concrete time to cure. Moist cure it for about seven days to prevent shrinkage. It will provide a sturdy, less damageable base.

Before building any kind of foundation, offset stakes are placed in the ground. These will tell where the addition’s perimeters will be. There should be surveyor’s stakes marking the original building’s corners. The area will be excavated with a hole slightly larger than the foundation will actually be. This makes for extra space for you to work on when dealing with the exterior walls. When excavating, it is important to consider the soil, frost line and local water table. A structural engineer is needed for this and one can be found on line (or through a local contractor). Surface soil has to be removed to expose soil that is compacted enough to bear the addition’s weight. Keep in mind that the excavation must be deep enough to place the top of the intended footing above the frostline. However , don’t dig too deep and hit below the water table. Excavation limits vary from town to town as well. (The one under my addition is three feet). Find out exactly what your town allows.

After the excavating, dig trenches for the footing. These are pathways of poured concrete which spread the weight of the addition onto the surrounding soil area. Some local building codes require drainage pipes put in alongside the inside parameter. These are perforated drainage pipes embedded in gravel along the footings’ outside areas. What this system does is collect subsurface water and moves it away from the foundation. If your land is completely flat then you will have to use a sump pump to speed up the water drainage. This collects any more of the subsurface water that is left as well as acting as a complete drain system.

Foundation walls are another vital part in your building. These are constructed by pouring concrete between sets of form work (basically molds, hardware and whatever bracing is needed). This is removed when the concrete achieves its’ strength. A structural engineer can help in determining the thickness. However this is done simply by considering the height of the wall and the load it will eventually bear. Gravity plays an important part in this determining as does the wind factor and the earth itself. If you’re unsure about this, then consult with the pros. One wrong calculation can lead to disaster down the road..

Other important ingredients for a good foundation are the anchor bolts. These are bolts used to secure a wooden sill plate to concrete , masonry wall or flooring. You’ll embed them in the tops of the foundations walls. They’ll also play an important part during the next process when they will be used to secure the framing to the foundation.

Another important addition will be the beam pockets. These are pail like holders used to create large indentations in the foundations. The cavities formed will hold the addition’s beams in place. You can buy them in either disposable or reusable forms.

Your foundation will also have to be damp proofed and water proofed as well. A seal must be applied to the exterior of the foundation walls. This will slow or prevent rain or snow from soaking through the foundation. If your addition has a basement, then a three to four inch thick concrete slab will also have to be poured. This helps to stabilize the foundation’s walls. Last but not least is the backfill which is soil that is pushed around the foundation’s trenches for more stability. This should be soil that drains easily and will not have a build up after storms.

Follow these basics for a foundation that will be long lasting and durable. If you find you can’t go it alone, then call a contractor or friends to help. Remember a shoddily done foundation will lead to a flimsy framing which will lead to a badly built addition. Be cautious. Be careful but most of all be conscientious.

Next part of the series, framing the building