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Roof trusses are engineered, triangulated frames that transfer roof and ceiling loads to the building’s supports. In the common residential system—metal-plate-connected wood trusses—top and bottom chords form the perimeter, webs subdivide the frame into triangles, and toothed connector plates join the lumber at each joint. A reliable result depends on the complete system: project-specific design loads, approved drawings, correctly manufactured joints, designed bracing, and inspections timed before the work is concealed.
This guide follows that process from design through installation and inspection. It focuses on metal-plate-connected wood trusses; cold-formed-steel and other systems use different materials, connection rules, bracing details, and inspection requirements. The adopted code, approved truss drawings, and local amendments control every project.
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What a roof truss is
Chords define the outside edges
The upper members are the top chords. They follow the roof slope and support roof sheathing and other loads assigned by the design. The lower members are the bottom chords, which commonly support a ceiling or attic-floor load and tie the supports together. Chords are not interchangeable pieces of ordinary framing; their sizes, grades, lengths, and force demands come from the engineered truss design.
Webs create the triangulated frame
Internal diagonal and vertical members are webs. By connecting the chords, they divide the truss into triangles, allowing the assembly to carry tension and compression forces efficiently. The web layout is specific to the span, roof shape, support locations, applied loads, and bearing conditions. Moving, removing, or cutting a web changes the engineered load path.
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Connector plates join the members
Modern residential wood trusses most commonly use metal-toothed connector plates pressed into both sides of a lumber joint. The plate type, location, orientation, tooth embedment, and lumber condition are part of the joint design. The American Wood Council describes metal-plate-connected wood trusses as the predominant truss type used in residential construction (American Wood Council).
How the design is developed
1. Establish the project criteria
The designer starts with the building geometry and the conditions the truss must resist. Inputs typically include span and bearing locations, roof pitch, overhangs, ceiling configuration, spacing, lumber species and grades, sheathing and roofing weights, ceiling finishes, attic storage or other live loads, snow or rain loads where applicable, wind uplift and lateral loads, and any concentrated loads from equipment or framing. The governing building code and local amendments determine which load combinations and detailing provisions apply.
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2. Analyze the truss with design software
Roof trusses are normally designed with software that calculates member forces, support reactions, deflection, stability, and connection demands for the code-specified load cases. The output identifies the truss profile, each chord and web, lumber requirements, connector-plate requirements, bearing information, and any special loads or details. The software is a design tool; it does not make an unreviewed field alteration acceptable.
3. Design the members and joints together
A truss can fail to meet its design even when the lumber appears large enough if a joint, bearing, plate, or bracing detail is inadequate. Member checks and connector-plate checks therefore proceed as one system. The design documents should identify truss marks, reactions, required bearings, plate locations, bracing notes, and any special conditions such as girder-truss reactions or concentrated loads.
4. Apply the applicable standard and code
The Truss Plate Institute (TPI) identifies ANSI/TPI 1 as the standard for minimum requirements governing metal-plate-connected wood-truss design and construction. Its scope covers lumber and steel materials, member and joint design procedures, connector-plate evaluation, manufacturing quality assurance, and responsibilities in the design process. TPI’s update page identifies ANSI/TPI 1-2022 as the latest edition in its current update project and states that ANSI approved it on December 23, 2022 (TPI 1 Update). TPI describes a five-year maintenance cycle and says the next update project will begin in January 2027.
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Those facts do not mean every jurisdiction has adopted the 2022 edition. A permit office may enforce an earlier edition or local amendments. The designer and building official determine which code and standard provisions apply to the project.
What the design documents should show
A truss package normally includes individual truss profiles and marks, span and bearing information, member and plate details, reactions, design loads, and installation or bracing notes. It may also include a layout showing where each truss belongs and details for girder trusses, openings, outlookers, or other special conditions. The documents should be coordinated with the architectural and structural plans so that bearing walls, beams, mechanical openings, and ceiling loads occur where the trusses were designed to receive them.
Keep the approved drawings available at the job site. A supplier’s standard illustration or a similar-looking truss is not a substitute for the project-specific design.
How trusses are manufactured
1. Cut and sort the lumber
Manufacturing begins with lumber that meets the specified species, grade, moisture and quality requirements. Automated or guided saws cut chord and web members to the designed lengths and angles. Pieces are identified and staged so that the correct members reach the correct truss assembly.
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2. Set the members in a jig
Workers place the cut chords and webs on a production table or jig in the exact profile shown on the truss design. The jig controls the geometry while the members are positioned. A misplaced web, reversed member, incorrect heel, or wrong overhang can change forces and bearing locations, so setup verification is a quality-control step rather than a cosmetic check.
3. Press the connector plates
Metal-toothed plates are positioned over each designed joint and pressed into the lumber, generally on both faces. Pressing equipment must achieve the specified embedment without damaging the plate or splitting the wood. Plate size, orientation, and location are selected for the forces at that joint; substituting a plate or rotating one without approval can reduce capacity.
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4. Inspect before shipment
The American Wood Council notes that factory inspection includes checking connector-plate orientation and tooth penetration depth before shipment (AWC truss information). Manufacturers may also use inspection forms, quality criteria, and recurring inspection logs. TPI publishes manufacturing and inspection materials through its standards and guides page (TPI Standards and Guides). These factory checks verify production against the design; they do not replace the site inspection required by the local authority.
Bracing during erection and service
Why bracing is part of the design
A truss is stable as a completed, sheathed roof system, but individual trusses can be vulnerable while they are being lifted, spaced, aligned, and connected. Temporary bracing holds the assembly in position during erection. Permanent restraint and bracing limit lateral movement and help the completed system resist design forces. The required arrangement depends on the truss geometry, spacing, building shape, sheathing, loads, and erection sequence.
Use the project’s bracing instructions
Do not apply a universal “one board every few trusses” pattern. Follow the truss drawings, erection plan, and any sealed bracing design supplied for the project. TPI’s DSB-2022 is a voluntary standard addressing temporary and permanent bracing for metal-plate-connected wood trusses. It presents illustrated restraint and bracing concepts, a method for determining lateral-restraint forces, and ways to resolve those forces with a bracing system (TPI standards and guides).
Code examples are jurisdiction-specific
Code provisions illustrate why the adopted edition must be identified. The 2012 International Building Code wood chapter states that truss alterations require written concurrence and approval by a registered design professional (2012 IBC Chapter 23). A 2017 Florida Residential Code provision requires drawings to be supplied to the building official and approved before installation in that jurisdiction and edition (Florida Residential Code R802.10.1). A 2024 IBC chapter includes a special-inspection provision for bracing of cold-formed-steel trusses with clear spans of 60 feet or more (2024 IBC Chapter 17). These examples apply only within their stated systems, editions, and jurisdictions.
How installation should proceed
- Confirm the documents. Verify that the crew has the current truss layout, individual truss drawings, erection notes, and bracing requirements. Resolve discrepancies with the truss designer or the responsible design professional before lifting anything.
- Check bearings and supports. Confirm that bearing walls, beams, plates, and pockets are in the locations and dimensions shown. A truss should not be forced onto an offset or shortened bearing without an approved solution.
- Set and temporarily brace the first trusses. Establish a stable starting line and install the specified temporary restraint as the erection plan requires. Do not leave unbraced trusses standing while the crew moves to another area.
- Install the remaining trusses at the designed spacing and orientation. Match each truss mark to the layout. Keep heels, overhangs, girder reactions, and special trusses in their designated positions.
- Complete permanent restraint and bracing. Install required continuous lateral restraints, diagonal bracing, and end or gable details before loading the roof or removing temporary supports.
- Coordinate sheathing and follow-on work. Roof sheathing can stabilize the system, but it does not excuse missing bracing or unapproved changes. Complete the specified connections before trades add loads or cut openings.
How roof trusses are inspected
Factory quality assurance
Factory personnel inspect the assembled truss before it leaves the plant. Typical checks include the identity and grade of members, geometry, plate type and orientation, plate placement, and tooth penetration. Records may include a manufacturing quality form and periodic inspection logs. Ask the supplier what documentation accompanies the shipment and retain it with the project records.
Receiving and pre-erection checks
At delivery, check trusses for shipping damage, broken or displaced plates, split lumber, missing members, and identification marks that match the layout. Store them supported and protected from conditions that could cause distortion. A damaged truss should be isolated and referred to the truss designer or engineer; field nailing or welding a plate is not an automatic repair.
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Framing inspection before concealment
The American Wood Council points out that roof sheathing may be installed soon after trusses are set, which limits outside visibility of the framing. The truss system remains visible from inside during the building framing inspection (AWC truss information). Schedule that inspection while members, plates, bearings, connections, and bracing can still be seen. The local building department determines the required inspection stages and documentation.
Special inspections where required
Some projects require a special inspector in addition to the routine building inspection. The trigger may depend on the structural system, span, occupancy, seismic or wind provisions, or a locally adopted code. The 2024 IBC example for bracing of long-span cold-formed-steel trusses demonstrates that special-inspection rules are not interchangeable with wood-truss requirements. Confirm the requirement with the building official and the project’s structural specifications before construction.
Alterations, openings, and added loads
Never cut, notch, drill, splice, or otherwise alter a truss member without written approval from the responsible design professional. The 2012 IBC example expressly prohibits such alterations without written concurrence and approval and requires verification when additional loads are added (2012 IBC Chapter 23). Current local codes may use different wording, but the engineering principle remains: an alteration or new load must be checked against the actual truss design.
Common triggers for review include attic platforms, suspended ceilings, solar equipment, mechanical units, storage, new duct openings, skylights, and changes to bearing walls. Provide the designer with the truss mark, drawings, proposed change, dimensions, and intended load. Do not rely on a nearby truss, a sistered member, or a generic repair detail unless it has been designed and approved for that condition.
A practical inspection and handoff checklist
- Current approved truss drawings and layout are on site.
- Truss marks, spacing, bearing locations, overhangs, and special trusses match the layout.
- No member is cut, notched, drilled, spliced, or displaced without written engineering approval.
- Connector plates are the specified type, correctly oriented, fully embedded, and free of visible damage.
- Temporary erection bracing and permanent restraint are installed as designed.
- Roof and ceiling loads match the design assumptions; added equipment or storage has been reviewed.
- Framing inspection occurs before sheathing or finishes conceal the critical joints and bracing.
- Factory quality records, delivery notes, inspection reports, and approved change documents are retained.
- Any discrepancy is isolated and reported rather than corrected by improvised field work.
What to ask before approving the work
Ask which code edition and local amendments govern, who sealed the truss design, what loads were included, and where the approved drawings identify bearings and bracing. Confirm whether the authority requires a framing inspection, a special inspection, or both. Ask the manufacturer how factory plate and tooth-penetration checks are documented. Finally, establish who can authorize a repair or added load; that authority should be the responsible design professional identified in the project documents, not an informal field decision.
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