The house’s floor frame is a platform built on top of the foundation. It consists of sill plates, rim joists or band joists and parallel floor joists. These in turn support beams and blocking. Floor joists are commonly spaced at 16 inches (41 cm) in the center apart. Once the platform is built, the subfloor is laid. The subfloor can be made of plywood or OSB. This provides a level surface to attach the flooring to. It is actually the skeleton of your floor and in this article, we are digging deep and it’s gonna be an amazing experience. Read and build well everyone 😊
1. Part One: Planning your Floor Framing Project
A. Understand Local Building Codes First:
Be sure to know about the local (state, city, and in some places, municipal) building codes before cutting the first board. All codes specify lumber specifications, size and spacing of joists, fastening methods and load requirements.
Most cities and states provide access to their residential building codes online. They can usually be found through a search for “residential building codes + your city or state”. These codes usually require a permit for laying a floor in an existing building.
Not building to code can have consequences including fines and delays. Someone might tell you to tear out the whole floor and start again. If you plan and build according to code within reason, you have peace of mind that your investment, your time and your own safety are in good hands.
Pro Tip: Some areas might require moisture barriers, termite-proof materials in humid and coastal areas. Check with local codes to learn what is required.
B. Create a Floor Framing Plan:
After learning how the rules apply, draw a rough sketch of the floor framing plan. This will not be an architect’s drawing. It needs to show only the floor plan’s basic shape, with alcoves, stair openings, load-bearing walls and cut-outs.
If you find long spans, staircases or walls in the center inside your home, it may require beams or doubled joists. If these exist in the home, a meeting with a licensed contractor or structural engineer is necessary.
A good plan helps stop material waste, installation errors and expensive rework later.
C. Mark Accurate Dimensions and Joist Layout:
Now with a drawing, fill in the actual dimensions. If your floor measures 12 feet by 18 feet, specify the length of each perimeter board plus all the joists within that area.
Stick-framed floors are generally made up from three components:
- Sill plate (mounted on the foundation)
- Perimeter frame members are rim joists.
- Floor joists (provide internal support within)
Floor joists exist commonly at 16 inches (41 cm) on center in standard construction and load applications, closer spacing is sometimes specified in building codes or to accommodate heavier flooring such as stone.
Drawing to scale and taking accurate measurements are essential. Small errors within the drawing can be magnified in construction.
D. Calculate Materials with a Safety Margin:
The lengths of all the framing members can be added to check the plan and estimate the total amount of wood needed.
- The entire perimeter length counting the sill plate and rim joists occurs two times.
- All interior joists
- Additional blocking or bridging
Account for cuts, knots, warping, etc. by allowing around 10-15% more lumber than the measurements indicate.
Top Thought: Always check lumber at the store when able. A slightly bowed or twisted board can be detrimental to overall floor flatness.
E. Cut and Label All Lumber in Advance:
Next, use a circular saw to cut each of the boards to the dimensions that you drew up in your design. Many home improvement stores will cut lumber to length for you.
For cutting, apply labels such as sill plate, rim joist, main joist, etc. These basic labels will make installation that much easier and less confusing.
2. Part Two: Assembling the Floor Frame
A. Install the Sill Plate:
The sill plate (or mud sill) sits on top of the concrete foundation wall, as the first part of the floor system. Place the sill plate boards flat on the foundation near their ends flush with the exterior of the foundation.
Pressure-treated lumber resists water, rot and insects and wider boards, such as 2 by 6 inches (51 by 152 mm) or larger, have more stability.
B. Secure the Sill Plate with Anchor Bolts:
Drill with a hammer drill through the concrete foundation. Insert anchor bolts. Position the sill plate upon the bolts, add washers and nuts and tighten.
Anchor bolts are usually installed every 4 feet in the wall and also at corner and load-bearing locations, for preventing the wall from shifting or becoming misaligned in place.
C. Attach the Rim Joists:
Set the rim joists on top of the sill plate to flush with its outside edge. Drive nails through the ends of the rim joists toward the sill plate.
Rim joists effectively offer perimeter and a vertical surface for floor joist attachment and a 2×10 joist is adequate for most and many homes.
Metal connectors or brackets can increase the rigidity between the rim joists and the foundation.
D. Mark and Position Floor Joists:
The rim joist must then be marked out usually every 16 inches on center so every joist line has marks. This ensures a level floor and even load distribution.
Local codes should be checked because they vary with the joist size, the wood species and the floor load.
E. Install Floor Joists Securely:
Install the joists where you marked, as needed. When installed properly the joists should fit tightly between the rim joists from within.
Nail the joists together with framing nails or use metal joist hangers to quickly and easily install many joists.
F. Add Bridging or Blocking for Long Spans:
Add bridging or blocking between the joists to reduce flex and vibration if joists are more than 9 feet (2.7 m) apart.
Bridging is often at thirds but solid wood blocking works too and gives stiffness.
G. Install the Subfloor:
To finish mainly, lay ¾-inch tongue-and-groove plywood atop the joists, by securing it usually with construction adhesive and nails to eliminate squeaking and eventually creating a stronger bond.
Specifically use galvanized nails in order to fasten the panels to edges and joints. Work in sections while the panel adhesive remains wet for the time period.
The result is as a floor framing system that is structurally sound, level and ready for the next stage.