2.4 The model building codes used by all local jurisdictions stipulate that the Owner is responsible for obtaining a
permit to build the structure and is responsible for that structure’s compliance with the building code requirements.
The Owner may choose to retain others, such as the Contractor and Building Designer, and through Contract
delegates the responsibility of design, construction and code compliance to these individuals. At times, the
Contractor may also function as the Building Designer. The allocation of design responsibilities to the Contractor
in such instances is consistent with the model building codes, which state that building permit applicants (e.g.,
the Contractor) are responsible for ensuring the structure remains in full compliance with the building code. At times
the Owner may also function as the Contractor and quite possibly the Building Designer.
2.5.1
term effect on the performance of trusses and Structural Elements, such as moisture creates conditions conducive
to softwood decay; high temperatures can cause decreased capacity of wood members; corrosive chemicals and
gasses may affect zinc coated steel connector plates. For instance, an ocean exposure can cause connector
plate corrosion. The Structural Design Documents must provide such conditions so that corrective measures may
be incorporated into the Truss Submittals and Structural Element Submittals for the building.
2.5.2.1&2.5.2.2 The Structural Design Documents must the structure, although it is not necessary for the Structural
Design Documents to provide the size of the truss chords and webs, web patterns, or the truss design. It is important
that the full intent of the Structural Design Documents is understood and can be adequately transferred into the
appropriate Truss Designs and Truss Design Drawings. Sometimes roof plans are developed, showing slopes,
hips, overhangs, ridge and valley lines, etc. For anyone to produce a proper Truss Placement Diagram it is necessary
for the Structural Design Documents to show span and spacing of trusses, locations of supporting columns, beams,
girders, and/or load bearing walls. It is also necessary to show any raised or dropped ceiling areas and/or internal
accessible attic spaces.
2.5.2.3
Within the Structural Design Documents is critical to enable each truss to be designed and built to the correct
dimensions and for the intended support conditions.It is not the Truss Manufacturer’s responsibility to ensure that the structural
elements upon which the trusses will rest (e.g., wall, beam)
2.5.2.4 To ensure that the structural capacity of the the structure for which they are designed, all applicable
design loads must be expressly stated in the Structural Design Documents. Simply referencing a section of a
building code within the Structural Design Documents does not provide the Truss Manufacturer or others with the
necessary or required information. Furthermore, special loading conditions for drifting snow or localized wind loading
effects should be clearly indicated in the Structural Design Documents by text and/or diagram. Once the loadings
are known, the Truss Manufacturer’s Truss Designer will undertake the structural design of every truss component
needed to carry all the imposed loads and combinations of system by the Building Designer.
2.5.2.5 Contemporaneous preparation of the Structural Design Documents with that of the Truss Design Drawings
would allow for easier design of support and bearing conditions, temporary and permanent lateral and diagonal
bracing, and all the anchorage needed to resist uplift, gravity and lateral forces on the structure. However, as it is often
impractical, or even impossible, for the Truss Designer to provide input at the time the Structural Design Documents
are prepared, many engineering assumptions will need to be made in the design of the structure. Accordingly, the
Truss Design Drawings, when produced, may not exactly match with the assumptions used. For example, it is very
unlikely that the calculated uplift loads will match the uplift loads developed by the Truss Designer. They should not
be expected to be identical. For this reason, it is essential that the Truss Design Drawings be reviewed and approved
by the Building Designer as delegated to by the Owner, or the Owner. It is the responsibility of the Owner or the
Building Designer, as delegated, to specify appropriate uplift loads and connection requirements for use by the
Contractor for all anchorage and connection requirements of the trusses.
2.5.2.6
used in various types of construction applications are provided by all three major model building codes. These
criteria are intended to minimize damage of supported construction materials (e.g., plaster, gypsum wallboard,
etc.) and establish a minimum level of performance suitable to the Owner and those occupying the structure,
however, is a highly subjective matter. The finished to prevent cracking of grout, tile, taped joints and wall
board. Given the subjective nature of deflection and vibration performance and that the occupants can be very
all vibration issues. Since trusses can be designed to meet Design Documents.
scissors trusses), as gravity loads applied to these trusses produce both vertical and horizontal deflection. The
supporting structure and the truss-to-wall connection must be designed appropriately to account for any horizontal
displacement. Without these limits, trusses cannot be designed effectively to minimize cracking and bowing
that can take place at bearing wall locations. It is also important to have the proper shear walls to resist horizontal
deformations.
2.5.2.7 The engineering term that best describes the intent All truss loads must be accounted for on the Structural
Design Documents and properly transferred through the Structural Elements to the building’s foundation. The truss
Designer has the capability to add these forces to the truss design and adjust individual truss members and their
connectors accordingly, but the connections between the transferred load and the truss system must be shown on
the Structural Design Documents.
2.5.2.8 Truss-to-Truss connections, truss-to-truss girder connections, ply-to-ply connectors for multi-ply
Designer. All truss to non-truss connectors (e.g., truss to bearing walls, truss to steel beams, truss to masonry) are
not the responsibility of the Truss Designer and must be shown on the Structural Design Documents.
2.5.3 As trusses are simply Structural Elements, the Truss Manufacturer and Truss Designer assume responsibility
only for the internal design integrity of the individual are part of a Building’s Structural System) in which the
trusses are to be placed. As the design and performance Manufacturer and Designer, it is essential that the individual
Truss Design Drawings be reviewed and approved by the Building Designer as delegated to by the Owner or the
Owner. The goal is to ensure each individual component works appropriately within the systems and the structure,
and also serves as a double check to ensure that the Truss Designer and Building Designer have not missed any
details. In particular, (a) determining that the Truss Design Drawings and Truss Placement Diagram(s), if required,
have been prepared in accordance with the requirements of the Construction Documents, (b) verifying the design
criteria utilized in the Truss Design Drawings, (c) evaluating in the Truss Design Drawings are consistent with the
Construction Documents.
2.6.1 The Contractor or individual or organization responsible for the installation of the trusses and Structural
Elements is entitled to rely on the accuracy of the design calculations contained in the Truss Design Drawings
and the Truss Placement Diagram(s), if required, which set forth the Truss Manufacturer’s interpretation of the
requirements of the trusses as set forth in the Structural Design Documents. It is recommended that the Contractor
carefully review and approve the Truss Design Drawings and the Truss Placement Diagram to (a) determine if they
comply with the intent of the Structural Design Documents, (b) check for any errors that may potentially lead to costly
remedial work, and (c) plan for a systematic communication and coordination between the building trades with respect
to truss placement and installation requirements, thereby greatly reducing the potential of having to cut and modify
the trusses due to interference with plumbing, electrical, and/or HVAC runs and equipment. It is custom and practice
in the construction industry for the prime or general Contractor to coordinate the approval and return of all
Truss Submittals (i.e., Truss Design Drawings and Truss Placement Diagram(s) and Structural Element Submittals
(e.g., I-joists, glulam beams, laminated veneer lumber, etc.) for the project.
2.6.2 & 2.6.5 Once the Truss Manufacturer delivers the trusses to the job site, he/she has turned over title
of the trusses to whoever has purchased them. All work undertaken thereafter is the responsibility of the Owner
of the trusses or the person or organization to whom the Owner delegates this responsibility.
Trusses are planar structural components whose structural performance depends upon being installed vertically, inor
handling during erection. Failure to adequately install and brace the trusses can also result in damage to the trusses,
The majority of wood truss related accidents occur during truss installation. The principal causes of such
accidents include: (a) inadequate and/or improperly located temporary bracing, (b) improperly installed and/or
PDF created with pdfFactory trial version www.pdffactory.com inadequate connection of the bracing to the truss, (c)
improper and/or inadequate connection of the truss and/or bracing to the supporting structure, (d) overloading roof or
braced (e.g., stack of plywood), (e) overloading roof or materials such as plywood, drywall, etc.), (f) improper or
damaged, or improperly repaired trusses, (h) improper truss alignment before bracing, (i) improperly designed
or installed support structures (e.g., walls, beams, etc.), and (j) failure to provide during the installation process the
required permanent compression member bracing at the locations shown on the Truss Design Drawings.
The wood truss industry provides recommendations on the handling, installation, and temporary bracing of trusses
in the booklet BCSI 1-03 Building Component Safety Information: The Guide to Good Practice for Handling,
Installing & Bracing of Metal Plate Connected Wood Trusses. This eleven part information series contains
sections on handling, installing and temporary bracing; web member permanent bracing and reinforcement;
and installation errors; gable end frame bracing; bracing of parallel chord trusses; toe-nailing for uplift reactions;
multi-ply girders; post frame truss installation and bracing; and fall protection.
WTCA also has a Temporary Bracing Model showing the stiffening effect of proper temporary bracing on a
structure. These materials are available through local Truss Manufacturers or WTCA. The recommendations provided
in these documents are offered as guidelines and are not to be interpreted as superior to the Building Designer’s
handling, installing, and bracing of trusses.
2.6.3 & 2.6.4 As trusses are engineered structural components, their structural integrity can be substantially
altered by damaging, cutting, or modifying any of their members. Truss members may break if improperly handled
during the unloading, storage, installation and erection by the construction trades to avoid interference with other
building components, the Contractor is responsible for securing the documentation required for repairing the truss.
The Truss Manufacturer should be informed immediately able to assist in providing the required documentation.
BCSI-B5 Truss Damage, Jobsite Modifications and Installation Errors, describes how truss damage, alterations
and installation errors must be repaired according to an approved truss repair detail and the information that the
repair detail from the Truss Manufacturer.
2.6.6 Properly designed permanent bracing is necessary to maintain the integrity of the structure, especially when
the structure is subjected to lateral loads imposed by wind or seismic forces. The design of all permanent bracing for
the structure, including the trusses, is the responsibility of the Building Designer and not the responsibility of the Truss
Manufacturer and Truss Designer, as the loads resisted by permanent bracing must be transferred to, and supported
by the structure. Included as part of the permanent bracing for trusses is the
continuous lateral bracing required to enhance the buckling capacity of certain truss compression members. The
need for permanent lateral bracing or support for certain individual truss members (chords or webs) is determined
individual Truss Design Drawings. This bracing is intended to prevent bowing or buckling of individual truss members
under design loads and enables the truss component to perform as designed.
However, the Truss Designer must rely upon others to specify how the lateral bracing is to be anchored or
restrained to prevent multiple identical members from buckling out of the plane of the trusses, at the same time.
Permanent diagonal bracing at intervals in the plane of the braced member is one way to accomplish this restraint.
The Truss Designer will set forth in the Truss Design Drawings, the maximum axial compression forces in the
truss members, as well as the location(s) where this bracing is required. The Building Designer will then design the size,
connection and anchorage of the permanent bracing to the truss member, as well as to the supporting structure.
Additional information on the design and installation of permanent bracing, written with the Building Designer
in mind, is reviewed in detail in the following WTCA publications: Commentary for Permanent Bracing of Metal
Plate Connected Wood Trusses and BCSI-B3 Web Member Permanent Bracing/Web Reinforcement.
2.7 The Truss Manufacturer typically receives the Structural Design Documents directly from the Contractor.
From the information contained in the Structural Design the truss design criteria and, if required, creates a
Truss Placement Diagram. The truss design criteria as documented by the Truss Manufacturer are provided to the
Truss Designer, who then uses this information to prepare the Truss Design Drawings. Some Truss Manufacturers
directly employ Truss Designers; for others, the Truss Designers are retained on a contractual basis.
The Structural Design Documents contain appropriate information to enable the Owner, and/or Building Designer
or Contractor to adequately review and verify that the Truss Design Drawings conform to the requirements and intent of
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Reproduction of this document, in any form, is prohibited without written permission from WTCA. This document should appear in more than one color.
2.7.7 The Truss Placement Diagram prepared by the Truss Manufacturer is not an engineering document
and should never be considered as a replacement for a structural framing plan prepared by the Building Designer.
The preparation of the Truss Placement Diagram does not require the special education, training and experience
engineering laws).
Since the Truss Placement Diagram prepared by the Truss Manufacturer is not an engineering document, it
should not be sealed. When a sealed structural framing plan is required, it should be prepared by the Building
Designer responsible for the overall building design to ensure the adequacy and safety of the entire structure.
The Truss Placement Diagram prepared by the Truss Manufacturer should ordinarily be reviewed and accepted
for conformance with the overall building design by the Building Designer of record.
Additional information on Truss Placement Diagrams
can be found in the TTB brochure How To Read A Truss
Placement Diagram.
2.8.1 & 2.8.2 Truss Designers do not review, or check for errors or omissions potentially contained within, the
Structural Design Documents. The Truss Designer’s scope of work is to simply design trusses that have adequate
capacity for the design conditions shown on the Truss Design Drawings, so long as the truss is spaced as
referenced on the drawing (usually 24" on center) and the truss is properly manufactured, installed and braced.
The physical size and shapes of the trusses and the design loadings should be shown on the Structural Design
Documents. The Truss Design Drawings then become a but it is essential that the individual Truss Design Drawings
be reviewed and approved by the Building Designer as delegated to by the Owner or by the Owner themselves,
before the trusses are manufactured. In the absence of a professional Building Designer, or an
understanding by the Owner of how loads are applied or Truss Designer does not assume these responsibilities.
Truss Designers also have no responsibility to evaluate the effect of the trusses on the structural system of the
building. The Truss Design Drawings furthermore do not constitute a temporary or permanent bracing plan for the
structure.
2.8.3
Installation Errors, describes how truss damage, alterations and installation errors must be repaired according to an
approved truss repair detail. This detail shall conform to sound wood design practices and can be undertaken by
any design professional familiar with wood design. See www.woodtruss.com to review this brochure.