Frame Walls and Install Beams
Framing transforms your foundation into a three-dimensional structure. This step includes installing the sill plate, floor joists, wall studs, and structural beams—creating the skeleton that will support everything from drywall to your roof.
Quick Summary
Time needed
1-2 weeks
Cost
$8,000-$20,000
Professional help
Framing crew
Why This Step Matters
The framing is your addition's structural skeleton. Every wall, floor, and ceiling hangs on these bones. Proper framing ensures your addition is structurally sound, square, plumb, and level—critical for everything that follows, from drywall to flooring to cabinets.
Critical Tie-In Point
Where your addition connects to the existing house is structurally critical. Improper framing at this junction can cause floor bounce, wall cracks, and even structural failure. Follow engineering plans exactly.
How to Frame Your Addition
Install the Sill Plate
The sill plate is a pressure-treated 2×6 or 2×8 that sits directly on top of the foundation wall, anchored by the embedded anchor bolts.
- Material: Pressure-treated lumber (ground contact rated)
- Sill seal: Foam gasket between concrete and sill plate
- Anchor bolts: 1/2" diameter, 6-8 feet on center maximum
- Level: Shim as needed—this sets the level for the entire floor
Pro tip: Check the foundation for level before installing the sill plate. Use a laser level to identify high and low spots. It's easier to shim now than fix a sloping floor later.
Install Floor Joists
Floor joists span from the sill plate to a center beam (if needed) and support the subfloor. Common options include dimensional lumber, engineered I-joists, or floor trusses.
- Spacing: 16" on center (OC) is standard; 12" OC for tile floors
- Rim joist: Install around perimeter, flush with sill plate
- Blocking: Install mid-span blocking for rigidity
- Joist hangers: Use Simpson or equivalent connectors at all ends
Engineered I-joists are increasingly popular—they're straighter, lighter, span farther, and don't shrink or twist like dimensional lumber. Cost is similar or less.
Install Subfloor
The subfloor is typically 3/4" tongue-and-groove OSB or plywood, glued and screwed to the joists.
- • Stagger joints by at least one joist bay
- • Leave 1/8" gap at walls for expansion
- • Use construction adhesive plus screws (not nails)
- • Walk the floor checking for squeaks before walls go up
Frame Exterior Walls
Walls are built flat on the subfloor, then tipped up into position. Standard construction uses 2×4 or 2×6 studs at 16" on center.
- 2×4 walls: Standard for mild climates, allows R-13 insulation
- 2×6 walls: Better insulation (R-19), required in cold climates
- Headers: Required over windows and doors (size per engineering)
- Double top plate: Required for structural integrity
Square is critical: Before nailing the wall together, measure diagonals. If they're equal, the wall is square. An out-of-square wall causes headaches with drywall, trim, and doors.
Install Engineered Beams
Engineered beams (LVL, Glulam, or PSL) carry heavy loads and span long distances without intermediate support. They're commonly used for:
- • Floor beam supporting joists at mid-span
- • Ridge beam supporting rafters
- • Headers over wide openings (garage doors, picture windows)
- • Opening between existing house and addition
Sizing matters: Beam sizes are specified by your structural engineer. Never substitute smaller beams—an undersized beam can sag, bounce, or fail. Larger beams won't hurt (except your budget).
Tie Into Existing Structure
The connection between new framing and existing structure requires careful attention. Methods include:
- Remove siding: Expose existing sheathing for direct connection
- Match floor heights: Align new floor with existing floor level
- Steel connectors: Use hurricane ties and hold-downs where specified
Warning: Before removing any wall in the existing house, verify it's not load-bearing. Load-bearing walls require temporary shoring and a beam replacement before removal.
Standard Wall Framing Specifications
| Component | Standard Size | Spacing |
|---|---|---|
| Studs | 2×4 or 2×6 | 16" OC |
| Bottom Plate | Single 2× (same as studs) | Continuous |
| Top Plate | Double 2× (same as studs) | Overlapped at corners/joints |
| Headers (4' opening) | 2-2×8 or 4×8 | Per opening |
| Headers (6' opening) | 2-2×10 or 4×10 | Per opening |
Header sizes vary by load and span—always follow engineering specifications.
Common Framing Mistakes to Avoid
Crown Down on Joists
Joists have a natural bow (crown). Install crown up so the joist straightens under load. Crown down creates a dip in the floor.
Misaligned Studs
Studs must align with joists and rafters for proper load transfer. Random stud placement can overload bottom plates and cause cracking.
Undersized Headers
Headers carry all loads above an opening. An undersized header will sag, cracking drywall and jamming doors. Size per engineering.
Skipping Metal Connectors
Modern code requires metal connectors (joist hangers, hurricane ties, hold-downs) at critical connections. Toenailing alone isn't sufficient.
Frequently Asked Questions
Should I use 2×4 or 2×6 exterior walls?
In cold climates (zones 5+), 2×6 walls are typically required by code for better insulation. In milder climates, 2×4 walls are acceptable but 2×6 gives you room for more insulation and reduces thermal bridging. The cost difference is about $1-2 per square foot of wall.
What's the difference between 16" and 24" on center?
16" OC is standard for walls and floors supporting heavy loads. 24" OC is acceptable for some interior walls and roofs but uses less lumber. Most inspectors and drywallers prefer 16" OC—the cost difference is minimal and the structure is more rigid.
Do I need an engineer for the framing?
For standard additions, your architect's plans typically include framing details based on prescriptive code requirements. For unusual situations—long spans, heavy loads, or connections to existing structure—a structural engineer should design specific beams and connections.
When is the framing inspection?
The "rough framing" inspection happens after all framing is complete but before insulation or drywall. The inspector verifies stud spacing, nailing patterns, header sizes, connectors, and overall structural integrity.
Ready for the Next Step?
Once your walls and beams are in place, the next step is framing the roof and creating the tie-in to your existing roof structure.