Roof Truss and Rafter Code in Georgia

IRC R802: Georgia's Roof Framing Requirements

IRC Section R802 covers wood roof framing for residential structures. Georgia adopts this section through the Department of Community Affairs (DCA), establishing the requirements for rafters, ceiling joists, collar ties, ridge boards, and engineered trusses in every home built or renovated in the state. The roof framing system is the structural skeleton that supports the roof deck, the roofing materials, and all the environmental loads that act on the roof surface.

R802 addresses two distinct framing approaches: conventional stick framing (individual rafters cut and installed on-site) and manufactured trusses (factory-built framing assemblies designed by an engineer and delivered to the job site). Metro Atlanta residential construction uses both methods. Custom homes in Buckhead and Johns Creek often use stick framing for complex roof geometries. Production homes and standard residential construction favor manufactured trusses for speed and cost efficiency.

The code's prescriptive tables (IRC Table R802.4 and related tables) provide maximum rafter spans for standard lumber sizes, grades, and spacings under assumed load conditions. These tables apply when the project falls within their parameters: standard residential loads, common lumber species, and conventional framing configurations. When the project exceeds these parameters (long spans, heavy materials, unusual geometries), a licensed engineer must design the framing.

Building inspectors in Alpharetta, Roswell, Marietta, Sandy Springs, and other metro Atlanta jurisdictions inspect roof framing during the framing inspection stage of new construction. They verify lumber grades, rafter sizes, spacing, bearing conditions, collar tie installation, and truss placement against the approved plans. Framing deficiencies fail the inspection and must be corrected before work continues.

Our team at 1 Source Roofing encounters roof framing during repair projects, storm damage restoration, and reroofing where deck removal exposes the framing for inspection. We assess framing condition, identify structural concerns, and coordinate with engineers when modifications are needed.

Minimum Lumber Grades and Species for Georgia Roof Framing

The IRC requires a minimum lumber grade of No. 2 for roof rafters and ceiling joists. Lumber grading classifies each board based on the number, size, and type of defects (knots, splits, wane, warp) that affect its structural capacity. No. 2 grade permits moderate defects that reduce strength below the clear wood value but still provide reliable structural performance for the spans and loads covered by the IRC tables.

In Georgia, Southern Yellow Pine (SYP) is the dominant framing species. SYP grows throughout the southeastern United States, and Georgia's lumber mills produce it in volume, making it the most available and cost-effective framing lumber in the state. SYP provides higher bending strength than many alternative species at the same grade, which translates to longer allowable spans or the ability to carry heavier loads.

Lumber Grade	Fb (Bending Strength, psi)	E (Stiffness, psi)	Availability in Georgia	Cost Premium
Select Structural SYP	2,050	1,800,000	Special order	40-60% above No. 2
No. 1 SYP	1,650	1,700,000	Limited stock	20-30% above No. 2
No. 2 SYP	1,300	1,600,000	Standard stock everywhere	Baseline
No. 2 SPF (Spruce-Pine-Fir)	875	1,400,000	Available at box stores	10-20% below SYP
No. 2 Hem-Fir	850	1,300,000	Available at box stores	Similar to SPF

The span tables in the IRC list allowable spans for multiple species. SYP spans exceed SPF and Hem-Fir spans at the same size and grade because of SYP's higher bending strength. A 2x8 No. 2 SYP rafter can span farther than a 2x8 No. 2 SPF rafter under the same loads. Homeowners and contractors who substitute species without checking the span table may exceed the allowable span for the substituted species.

Every piece of dimension lumber carries a grade stamp from an accredited grading agency. The stamp shows the grade (No. 1, No. 2, etc.), the species or species group (SYP, SPF, HF), the moisture content at grading (S-DRY for surface dry, KD for kiln dried), and the grading agency's mark. Building inspectors check grade stamps during framing inspections to verify that the installed lumber meets the specification shown on the approved plans.

Rafter Span Tables for Georgia Residential Construction

The IRC provides span tables in Section R802.4 that list the maximum horizontal span for common rafters based on lumber size, grade, species, spacing, and applied loads. These tables represent the core prescriptive path for sizing roof rafters without an engineer. If your rafter configuration falls within the table parameters, the table span is the code-compliant maximum.

The following spans apply to No. 2 Southern Yellow Pine under standard residential loading (20 psf live load, 10 psf dead load) with a maximum deflection limit of L/180:

Rafter Size	16" OC Span	24" OC Span	12" OC Span
2x6	10' 0"	8' 3"	11' 6"
2x8	13' 1"	10' 10"	15' 1"
2x10	16' 8"	13' 9"	19' 3"
2x12	20' 3"	16' 9"	23' 5"

These spans assume standard dead loads (10 psf) that correspond to asphalt shingle roofing over structural panel sheathing. Heavier roofing materials increase the dead load assumption and reduce the allowable span. If you plan to install concrete tile (adding 8-10 psf of dead load over asphalt), the span table for the higher dead load category applies, and the allowable spans shrink. See our roof load requirements guide for dead load values by material type.

Rafter spacing affects span capacity because wider spacing increases the tributary load area each rafter supports. A rafter at 24-inch OC carries 50 percent more load per lineal foot than a rafter at 16-inch OC. The wider spacing requires either a larger rafter or a shorter span to keep stresses within allowable limits.

A 2x8 No. 2 SYP rafter at 16-inch spacing spans 13 feet 1 inch. Move to 24-inch spacing and the maximum drops to 10 feet 10 inches. Wider spacing increases the tributary load each rafter carries, requiring either larger lumber or shorter spans.

For spans that exceed the table maximums, engineers specify engineered lumber products: laminated veneer lumber (LVL), laminated strand lumber (LSL), or glue-laminated beams. These products provide higher strength and stiffness per inch of depth than dimensional lumber, allowing longer spans in the same depth profile. Custom homes with open floor plans and wide roof spans often use engineered lumber in the roof framing.

Collar Ties and Rafter Ties: IRC R802.3.1 Requirements

IRC Section R802.3.1 requires collar ties or ridge straps on roof rafter systems where opposing rafters bear on opposite walls. The code distinguishes between collar ties and rafter ties because they serve different structural functions at different locations in the framing system.

Collar Ties

Collar ties connect opposing rafters in the upper third of the rafter span, near the ridge. Their primary function is to resist wind uplift forces that try to separate the rafters at the ridge. During a high-wind event, uplift suction on the roof surface pulls the rafters upward and apart at the ridge line. Collar ties hold the rafter pair together against this separation force.

The IRC requires collar ties to be at least 1x4 lumber (nominal), installed at maximum 4-foot spacing along the ridge. In practice, builders install collar ties at every rafter pair or every other pair, depending on rafter spacing. The connection at each rafter requires three 10d nails on each end. For metro Atlanta's 115 mph wind zone, collar ties at every rafter pair (16 or 24 inches OC) provide the most reliable uplift resistance.

Rafter Ties

Rafter ties connect opposing rafters at the wall plate line (the base of the rafter). Their function is to prevent the rafters from pushing the walls outward under gravity loads. A conventional rafter system acts as a triangle: the two rafters form the sloped sides, and the rafter tie forms the horizontal base. Without the tie, the gravity load on the rafters converts to a horizontal thrust at the wall plate, pushing the walls apart.

Rafter ties must resist the calculated horizontal thrust from the roof loads. The IRC provides tables for rafter tie sizing based on roof span, rafter spacing, and roof slope. For most metro Atlanta homes, 2x4 rafter ties at the rafter spacing (16 or 24 inches OC) satisfy the requirement. Long-span roofs or steep pitches may require larger ties.

Ceiling joists that run parallel to the rafters and connect opposing walls serve as rafter ties if they are attached to the rafter at the plate line with the proper connection. This is the most common configuration in residential construction: the ceiling joist doubles as the rafter tie.

Ridge Board vs. Ridge Beam

The IRC distinguishes between a ridge board (a non-structural member that provides a surface for rafter ends to bear against) and a ridge beam (a structural member that supports the rafter loads at the ridge). A ridge board works only when rafter ties or ceiling joists provide the horizontal tie at the base. A ridge beam works without rafter ties because it carries the vertical loads directly to posts and the foundation.

Cathedral ceiling designs that eliminate ceiling joists require a structural ridge beam because there are no rafter ties to prevent wall spread. The ridge beam must be designed by an engineer for the specific span and loads. Ridge beams in custom homes often use LVL or glue-laminated lumber to handle the required spans.

Manufactured Truss Requirements Under Georgia Code

Manufactured trusses dominate residential roof construction in metro Atlanta. Truss manufacturers design each truss as an engineered product, with the design sealed by a licensed engineer. The truss design specifies lumber grades, connector plate sizes, member sizes, and the loads the truss can carry. Georgia code requires that every manufactured truss delivered to a job site carry a stamped engineering drawing that matches the approved building plans.

The IRC requires the following for manufactured trusses:

• Engineered design: Each truss must be designed by a registered design professional per ANSI/TPI 1 (Truss Plate Institute standards)
• Stamped drawings: Truss placement plans and individual truss designs must bear the engineer's seal
• Installation per design: Trusses must be installed at the spacing, orientation, and bearing locations shown on the stamped drawings
• Bracing per BCSI: Temporary and permanent bracing must follow the Building Component Safety Information (BCSI) guidelines published by the Structural Building Components Association (SBCA)
• No field modifications: Cutting, notching, or removing any truss member without engineer approval is prohibited

The prohibition on field modifications is the most common code violation our team encounters in attics. Homeowners, HVAC contractors, and electricians sometimes cut truss webs to run ductwork, wiring, or to create storage access. Every cut reduces the truss's load-carrying capacity and may cause progressive failure. A diagonal web member in a common truss carries compression loads that keep the bottom chord from sagging. Cutting that web transfers its load to adjacent members, overloading them.

If truss modifications are necessary, a licensed engineer must design the modification. The engineer evaluates the truss design, calculates the effect of the proposed change, and designs reinforcement (typically plywood gussets or additional lumber members) to restore the truss's original capacity. The engineer's sealed modification drawing becomes part of the building record.

Cutting a single truss web member can trigger progressive overload across the truss system. Georgia code prohibits truss modifications without a licensed engineer's sealed design. HVAC contractors, electricians, and homeowners sometimes cut webs for duct runs or storage access without realizing the structural consequences.

Rafter and Truss Bearing Requirements in Georgia

Every rafter and truss must bear on a structural support that transfers the roof loads to the wall framing and foundation below. The IRC specifies minimum bearing lengths, bearing surface conditions, and connection requirements to ensure that loads transfer without crushing the bearing surface or displacing the framing member.

The minimum bearing length for rafters on wood top plates is 1.5 inches (the width of a standard 2x plate). For trusses, the manufacturer's stamped drawing specifies the required bearing length, which typically runs 1.5 to 3.5 inches depending on the truss design and applied loads. The bearing must provide full contact across the bearing surface, without gaps, rotation, or eccentric loading.

Rafter cuts at the bearing point (birdsmouth cuts) reduce the effective depth of the rafter at the most critical location. The IRC limits the birdsmouth depth to one-third of the rafter depth. For a 2x8 rafter (7.25 inches actual depth), the maximum birdsmouth depth is 2.42 inches. Deeper cuts remove too much material from the rafter at the highest-stress location and can cause splitting or crushing failure at the bearing.

Trusses bear on the wall plate without birdsmouth cuts. The bottom chord of the truss sits flat on the top plate, and the hurricane strap or clip connects the truss to the plate. The bearing length shown on the truss drawing must be maintained on-site. If the truss overhangs the plate or does not reach the plate fully, the bearing condition does not match the engineering design and the installation fails inspection.

Interior bearing walls carry roof loads from trusses or rafters that span from exterior wall to interior wall. These bearing walls must sit directly over a foundation element (beam, wall, or post) that transfers the accumulated load to the ground. Removing an interior bearing wall without providing an alternative load path (a header beam supported by posts) eliminates the support for the roof framing above and can cause the roof to sag or collapse. Our team identifies bearing walls during attic inspections and flags them when homeowners discuss renovation plans.

For the connection between bearing requirements and the broader structural load path, see our hurricane strap guide, which covers the continuous load path from roof to foundation.

Attic Conversions and Roof Framing Code Implications

Converting attic space from uninhabitable storage to habitable living area triggers multiple code requirements that affect the roof framing system. Georgia's adoption of the IRC means that habitable attic space must meet the same structural, fire, egress, and ventilation standards as any other habitable room in the house.

The structural implications center on floor loads. The IRC requires a live load of 40 psf for habitable floor space, double the 20 psf required for uninhabitable attic areas. The existing ceiling joists or bottom chords of trusses were designed for 20 psf (or less, if designated for no storage). Doubling the live load requirement may exceed the capacity of the existing framing members, requiring sistering, replacement, or supplemental framing designed by an engineer.

Manufactured trusses present the greatest challenge for attic conversions. Standard residential trusses use thin web members that crisscross the attic space, leaving no usable open area. Converting the attic requires removing or modifying these webs, which the IRC prohibits without engineering approval. The engineer designs a modified truss or replacement framing system (typically a room-in-attic truss or a conventional rafter system with collar ties) that provides the open space while maintaining structural integrity.

Knee walls, which create the vertical wall surface in the usable portion of the attic, must be braced to resist racking and must bear on a structural element below. The ceiling framing above the knee wall must support the required ceiling loads. The entire assembly requires engineering design because it falls outside the IRC's prescriptive provisions for standard attic construction.

For homeowners in Buckhead, Sandy Springs, and Alpharetta considering attic conversions, start with a structural engineer who can assess the existing framing and design the modifications. Building departments in these jurisdictions require stamped engineering drawings for attic conversion permits. The roofing implications include verifying that the existing roof covering, ventilation, and insulation systems accommodate the changed use of the space below.

Explore More Georgia Roofing Code Guides

• Georgia Residential Roofing Code Guide
• Roof Load Requirements in Georgia
• Roof Deck and Sheathing Code in Georgia
• Hurricane Strap Requirements in Georgia
• Wind Speed Requirements for Georgia
• Roof Fire Rating Code in Georgia
• Roofing Contractor Licensing in Georgia
• Roof Ventilation Code Requirements
• Minimum Roof Slope Requirements
• Roof Replacement Services
• Storm Damage Restoration
• Roof Repair Services