You are laying out the top plates and need the roof truss spacing. Read the current placement information and individual truss drawings against the building plans. If they disagree, stop the affected layout and ask the manufacturer and building designer to resolve it. Do not choose spacing from a rule remembered from another house.
Spacing is part of the design basis. SBCA’s drawing-reading resources identify spacing and loads as linked subjects. Use the spacing specified for your roof package, supports, and installation details.
Confirm who sets and checks the spacing
Ask the building designer and truss manufacturer to identify the intended roof layout and design criteria. Confirm which document establishes the placement and which records the individual truss assumptions. Name who reviews any mismatch before fabrication or installation.
SBCA separates building-system responsibility from individual truss design. That division matters when a layout change affects the rest of the roof. Do not choose the easiest dimension to mark when the drawings disagree.
Use a short request for information: project, drawing references, conflicting dimensions, affected truss marks, and requested answer. Attach the relevant sheets together. Ask for a written answer that identifies the drawing revision to use.
The roof truss design guide explains the broader handoff. Use it to name the people involved before the roof package reaches the site.
Read on-center dimensions correctly
An on-center dimension measures between corresponding centerlines, as used in AWC’s framing tables. Keep it distinct from the clear gap between members and from the first-member offset at an edge. Ask the manufacturer to explain the starting reference if the placement information is unclear.
Mark the reference end and orientation on the working layout. Then follow the actual dimensions for common trusses, girders, end frames, and special areas. Do not extend a repeated-spacing note through a condition drawn differently.
SBCA distinguishes girder trusses, gable end frames, and ordinary component terminology. Each type has a different job. Ask which marks are repeated and which require separate positions before preparing the crew’s layout sheet.
Use this document check:
Scroll to read all columns.
| Document or record | What to compare |
|---|---|
| Building roof plan | Overall geometry, openings, supports, and current revision |
| Placement information | Truss marks, locations, orientation, and dimensions |
| Individual truss drawings | Design spacing, loads, bearings, and notes |
| Sheathing specification | Product and installation requirements for the roof assembly |
| Connection details | Supports, hangers, and special framing interfaces |
| Bracing information | Details applicable to the selected arrangement |
Use this table to compare documents. Ask the design team what a mismatch means for the roof.
Check spacing against design loads
A framing member’s design depends on the load it receives. AWC’s span tables for joists and rafters use spacing and specified loading as inputs. Those tables do not size a manufactured truss, but they demonstrate why spacing is a design variable.
For the truss package, ask the responsible designer to identify the spacing used in each component’s design. Confirm the intended roof use and any special loading conditions. Avoid substituting a generic table for the project-specific truss drawing.
If the owner changes roofing, equipment, ceiling material, or attic use, send that change to the design team. Ask whether it affects the component criteria or layout. Keep the response with the package. The original spacing does not prove the changed design works.
Review supports at the same time. SBCA explains that roof-truss bearings transfer reactions to the building. If spacing changes, have the design team check the affected supports and connections along with the trusses.
Coordinate sheathing with the support layout
Ask the building designer to reconcile the framing layout and roof sheathing specification. Identify the specified panels and applicable installation requirements before the order is placed. If a proposed panel substitution changes those requirements, request review.
APA’s roof-construction guidance covers panel sheathing, spans, fastening, and roof diaphragms. Obtain the relevant details for the actual roof. Check the full panel specification and installation requirements, not thickness alone.
Ask the design team:
- Does the selected panel specification match the designed support arrangement?
- Which installation direction and edge-support details apply?
- What fastening schedule belongs to the assembly?
- How are panel edges supported at openings and special roof conditions?
- Who checks the proposed substitution before the sheathing crew starts?
Ask the designer to issue the applicable details. Do not move a truss to catch a panel seam without design review. Resolve the mismatch in the documents first.
Get openings designed before changing the layout
A skylight, chimney, attic access, or equipment route may interrupt the repeated layout. Mark the intended opening before release. Ask the manufacturer and building designer to coordinate the required framing and support.
If an opening changes after delivery, show the affected truss marks and the proposed dimensions. Request a reviewed solution. Do not widen a bay, remove a truss, or move a girder because the adjacent space looks available.
SBCA warns about field modification without consultation. Use the damaged or cut truss process if an alteration has already occurred. Keep the affected work accessible while the responsible professionals evaluate it.
For a roof still in planning, the truss versus rafter comparison helps organize the selection. Whichever system you choose, resolve openings before the crew receives its final instructions.
Match restraint and bracing to the layout
Spacing is one part of installation coordination. Ask the installation contractor to identify the applicable restraint and bracing information for the selected package. Have the responsible parties resolve special conditions before setting trusses.
SBCA’s BCSI guide addresses installation stability and permanent bracing. Request the actual details and responsibilities for your roof. A repeated-spacing note is not a complete installation plan.
Discuss the sequence for the first set, special trusses, and remaining installation. Confirm document access and required material with the framing lead. Keep unresolved questions visible in the work plan.
Arrange delivery and storage so component identification remains available. Ask the receiver to report a missing or unreadable mark before the crew sorts the package. Check both spacing and truss marks at each location.
Check the installed layout before covering it
Give the framing lead one current working set. Identify the reference dimensions and any special placements at the preinstallation meeting. Ask the lead to report field conditions that prevent following the accepted layout.
Before sheathing conceals useful access, compare installed marks and locations against the current documents. Record differences and ask the design team for direction. Avoid closing the issue with a note that the change is “only a little.”
Retain the accepted layout, issued revisions, and required completion records together. Tell rough-in trades who receives questions about service routes or new loads. Carry that contact into the next construction stage.
Where Cercha fits
Cercha lets you search for framing contacts by trade and location. Messages helps you start the conversation with a crew or supplier. Confirm spacing, revisions, and installation details through the project’s responsible design and construction parties.