One of the critical areas in building a house is the floor framing. If the floor of your house is not sturdy and level, it will be noticeable to everyone who walks on the floor. Learning how to correctly do floor framing will go a long way in ensuring that you will be happy with the finished product—a level, sturdy, squeak-free floor.
Two keys to a level floor are a level foundation and a level sill plate. Taking the time to make sure that both of these surfaces are level will make the entire floor framing process easier. You will probably have to rely on your concrete contractor to do a good job in pouring a level foundation, but you can erase any minor irregularities in the foundation with your sill plate. Any time that lumber is in contact with cement, you must use treated lumber to prevent moisture damage to the wood. Your cement contractor should have placed bolts into the concrete, to which you will attach the sill plate. Use metal shims where necessary to ensure that the sill plate is level. Take the time to make the sill plate perfectly level.
Before you install your floor joists, make sure that the size of the joists and the spacing meet the UBC (Uniform Building Code) minimums for the span you are crossing. Your building department will have the information you need to determine the requirements for floor joists that are required for your span of floor.
I highly recommend using engineered floor joists for your project because they are more uniform, lighter in weight, and can span greater distances than traditional dimensional lumber. You can also more easily drill holes in the middle of the beams to run wires and pipes through.
The next step is to set the rim joist on the sill plate. The rim joist is a joist which sits atop the sill plate and forms the perimeter of the floor framing. If your sill plate is level, you can simply attach the rim joist to it by toe nailing into the sill. If there are any irregularities in your sill plate, despite your best efforts, you can eliminate them at this point in the framing by using metal shims to raise the rim joist, or a plane to shave the sill plate if it is high.
Use metal joist hangers to attach each floor joist to the rim joist. Joist hangers have metal flanges that control the alignment of the floor joists, helping to make your finished floor level. Mark out the spacing of the joist hangers along the rim joist, making sure you start measuring from the same side of the floor. Special nails, known as Tico nails are used to attach the joist hangers to the rim joist and to the floor joists. Buy or borrow a pneumatic palm nailer because you will be pounding A LOT of nails to secure the joists.
Once all of your floor joists are in place you need to cross brace the joists to add stability to the floor. Cross bracing is accomplished by nailing small wooden braces from the top of one floor joist to the bottom of the adjacent joist, and vice versa to form an X. Work your way across the floor, and by the time you are finished, you will have a sturdy, level floor.
And that’s all there is to it.