© 2024 Timberlab Incorporated
Revised November 2024
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Information herein is shown for explanation purposes only. Examples shown are not suggestions for any particular project; they are presented as general considerations and do not apply to specific circumstances.
This guide is intended to help design teams understand the process and requirements for delegating the design of a complete mass timber structure to Timberlab. Delegation of this scope allows us to optimize the design for the project’s selected manufacturer and for our fabrication capabilities and preferences, resulting in a more efficient, cost-effective, and constructible building. Frequent two-way communication between the design team and Timberlab is crucial for the success of this process. We view our role as that of a close partner to the entire team, and in particular to the structural engineer of record (SEOR).
This guide covers most situations that arise on delegated mass timber projects and outlines our typical scope and preferred workflow. Because each project is unique, this guide is not exhaustive, and exceptions can always be made to suit the needs of the project.
A checklist is provided at the end of the guide to help ensure the necessary information is included in the documents submitted to Timberlab for our delegated design work.
For projects with delegated design for timber connections only, please refer to the “Timberlab Guide for Delegated Connection Design,” published as a separate document.
Full delegated design of the timber structure is ideally done with Timberlab brought on board as early in the design process as possible. Typically we recommend engaging with us no later than the initial stages of the Design Development phase, though for large or complex projects, we bring the most value by joining the team in the initial concept stages. The form of this early engagement can vary depending on the project’s overall delivery method.
Finalizing construction documents before onboarding a mass timber construction partner can be a barrier to optimal design, as projects are conceived and often permitted without input from builders, trade partners, and manufacturers. In implementing the design-bid-build project delivery method, lead times may be longer than typical to allow for thorough translation of design intent into fabricationlevel information, and penetrations for building services may not be incorporated into the production process.
However, we recognize that projects may be constrained to design-bid-build for a variety of reasons; in these cases, we aim to create a realistic schedule for delegated design to minimize any potential delays to the project delivery date. For projects that are locked into the design-bid-build delivery method, adding a design assist component during the design phase can be one way to maintain the competitive bidding process while still allowing for early engagement by the trades.
Design assist delivery methods allow key trades such as mass timber and building services (mechanical, electrical, plumbing, and fire sprinkler) to provide input early in design, promoting cost-effective and constructible designs without requiring a commitment to a trade partner for the construction scope of work. For design assist work, Timberlab typically contracts directly with the project owner, or with the project’s general contractor or construction manager if they are already engaged. However, our role as a design assist partner is to act as a fully integrated member of the design team, attending regular meetings, identifying primary cost drivers for the timber structure to support design decision-making, and providing guidance on procurement strategy, species selection, member sizing, and connection detailing. Our preconstruction team also provides input on cost, schedule, and logistics during this phase. Once the design assist scope of work is complete, a separate procurement process for the construction scope of work takes place. Owners may choose to negotiate directly with the design assist partners or to use an open, competitive bid process.
Alternative delivery methods such as design-build (DB), construction manager (CM) at risk, or integrated project delivery (IPD) allow an owner to hire the construction team from the beginning of the project, offering the greatest opportunity to maximize the prefabrication potential of mass timber and yielding cost certainty. Factory-drilling of penetrations for building services is enabled through early release of design-assist or design-build contracts with structural, mechanical, electrical, plumbing, fire sprinkler (MEPF), and façade trade partners, maximizing the schedule, quality, and safety outcomes we associate with mass timber. Where possible, we strongly encourage owners to consider one of these methods for a mass timber building.
Regardless of the project’s procurement method and whether Timberlab has been engaged during the design phases, finalized and thoroughly documented design criteria and intent are required for the work to be formally “handed off” for Timberlab’s delegated design Structural, fire, and architectural requirements for a mass timber structure are the main drivers of the design. Understanding the overarching goals and design criteria in each of these categories gives us a framework for our design efforts.
Structural design criteria are typically documented in the SEOR’s drawings and should include all applicable codes and standards, including editions. We also assume the structural drawings will include, at minimum, the design criteria listed in the 2021 International Building Code (IBC), Section 1603 – Construction Documents. In addition to listing these criteria in the general notes, provide load maps for each floor to clearly indicate the areas where each loading condition applies.
For calculating net uplift at roofs, loads which are allowed for but may not be present for the full life of the structure (for example, PV panels) can lead to unconservative designs. The drawings should clearly indicate any gravity loads which are provisional in nature; these loads will be neglected in load combinations with wind uplift. For projects with green roofs, both the minimum dry weight and maximum saturated weight of the system must be provided. The minimum dry weight will be used for uplift calculations unless the owner anticipates that the green roof may be permanently removed at any point in the future.
Deflection limits are typically assumed in accordance with 2021 IBC Table 1604.3 unless stricter limits are provided by the SEOR. Limits on deflections at the building perimeter, particularly for buildings with façade systems sensitive to relative deflections at slab edges in multi-story construction, should be explicitly given, as well as maximum expected wind and seismic story drifts. For projects in Seismic Design Category D and higher, the code requires seismic design drifts imposed on gravity framing to be accommodated. While some proprietary connectors and specific connection configurations have test data on seismic drift compatibility, other connection types may require engineering judgment to demonstrate their ability to meet this code requirement. Early in the project, Timberlab and the SEOR should review various connection types and available data to agree on the design approach to drift compatibility. Deflection limits for specialty items such as mechanical screens and folding partitions should also be provided where applicable.
For projects where floor vibrations are a concern, either for occupant comfort or for vibrationsensitive equipment, we recommend an early discussion of the vibration limits and approach to design with the SEOR. On most projects, Timberlab will not perform a detailed vibration analysis, but such an approach can always be included in our scope if the project warrants. On lab buildings, we assume vibration analysis will be required, but establishing specific design criteria early in the process is important to keep the project on schedule. Our analysis is typically based on the U.S. Mass Timber Floor Vibration Design Guide published by WoodWorks.
Selection of timber species and structural grades will dictate glulam member sizes and CLT panel layups as well as connection capacities. Even small variations in the final dimensions of a member can affect connection designs and potential for clashes. The architect and owner often have influence on species selection along with the SEOR, so having a clear decision on species by all stakeholders is necessary prior to the start of delegated design efforts. When Timberlab is engaged as a partner during the design phase, providing guidance on species selection is one of our key responsibilities, helping the team to make this choice early in the process.
Fire-resistance ratings are a critical component of the design. The building’s construction type and required fire-resistance rating for all mass timber elements and their connections must be clearly indicated. Where CLT panels or proprietary connections with fire test reports are available, we will use these tests as the basis of design. For all other mass timber elements as well as custom connections, we will typically design in accordance with the 2024 Fire Design Specification for Wood Construction (FDS), Chapter 16 of the 2024 National Design Specification for Wood Construction (NDS), and the 2021 edition of the American Wood Council’s technical report TR-10, Calculating the Fire Resistance of Wood Members and Assemblies. Connections are designed to match the rating of the connected elements.
Different construction types have varying fire-resistance rating requirements and limits on the amount of exposed mass timber permitted in the building. In addition, more stringent fire-resistance ratings may apply to certain components of the building such as egress paths, fire separations between occupancies, or structural elements supporting rated partition walls. Unless specifically directed otherwise, we will design the mass timber structure and connections based on the assumptions listed in Table 1.
Construction
III-A
III-B
IV-A
IV-B
IV-C
IV-HT
V-A
V-B
All mass timber except top of slab exposed. 1-hour rated structure.
All mass timber except top of slab exposed. Unrated structure.
All mass timber covered with noncombustible protection for the full required duration.
3-hour rated primary structural frame and bearing walls.
2-hour rated floor construction (reduced to 1-1/2 hour at roof).
All mass timber slab soffits exposed. Exposure of beams, columns, and walls provided by the design team. Covered elements are protected for the full required duration by noncombustible protection. 2-hour rated structure (reduced to 1 hour at roof).
All mass timber except top of slab exposed. 2-hour rated structure (reduced to 1 hour at roof).
All mass timber except top of slab exposed. Unrated structure.
All mass timber except top of slab exposed. 1-hour rated structure.
Potential to use heavy timber provisions for roof structure per 2021 IBC Table 601 footnote c.
All mass timber except top slab exposed. Unrated structure.
For construction types which require a fire-resistance rating, assuming all mass timber is exposed is conservative and provides maximum flexibility for the owner; however, it may be overly conservative in cases where the design has specifically accounted for noncombustible protection. In such cases, and for all Type IV-B buildings, provide key plans indicating which elements will achieve their fire-resistance rating through noncombustible protection and which are exposed.
If the SEOR intends elements to be designed to achieve a fire-resistance rating through a combination of protection and charring, those elements and the contribution from noncombustible protection must be clearly identified.
Design of noncombustible protection remains the responsibility of the architect of record. The design, detailing, and documentation of noncombustible protection must be closely coordinated with the SEOR and Timberlab to ensure compliance with the building code.
The structural drawings should include the layout of all framing members (columns and beams) and indicate the primary span direction of CLT panels. When Timberlab is engaged as a partner during the design phase, evaluation of different framing approaches will be part of a collaborative process, with the final selection of the framing system and member layout to be documented in the design team’s drawings before we begin our formal delegated design efforts.
The required information may be given on a combination of architectural and structural drawings and includes dimensioned gridlines, locations of members located off-grid, floor-tofloor heights, and top of structural slab relative to top of finished floor. The precise final location of all slab edges and openings may not be known until further in the coordination process, but any critical slab edge locations at the building perimeter and large openings such as atriums should be dimensioned to a reasonable level of accuracy. (See our “Designing for Fabrication” guide for a typical project timeline and explanation of Levels of Detail, including the final coordination of slab edges for LOD300.)
Since Timberlab is responsible for verifying all member sizes and panel layups, any restrictions (such as maximum beam depths) or minimum sizes for architectural purposes should be documented on the structural drawings.
Overall design intent for connections, whether for aesthetic or structural purposes, should be communicated through indicative details. Annotations to help document the thought process and key goals are immensely helpful. Though pictures are worth a thousand words, it can sometimes be difficult to know which parts of a detail are the most critical without additional commentary. Engaging Timberlab during the design phase helps create common understanding through the coordination process, but if we are brought on at the completion of construction documents, a page-turn meeting with the design team is recommended to review overall design intent.
Indicative details for structural purposes should be developed based on realistic design forces. This exercise can also help confirm member proportions, as connections can frequently drive member sizing in mass timber structures.
More careful attention to aesthetics will be paid to connections that are exposed to view in the completed structure, while hidden connections will be designed for economy and ease of fabrication and installation. Provide notes, key plan markups, or other documentation to indicate which connections are exposed and which are hidden. When uncertain, we will assume the connection is exposed to view, which is conservative but can add cost to the project unnecessarily.
Figure 1A. Indicative beam-to-column detail
An example of an indicative beam-to-column detail is provided in Figure 1A, with the completed Timberlab detail in Figure 1B. The indicative detail communicates the desire for most connection elements to be concealed but allowing the bearing plate to be exposed, and it shows the structural intention for a direct bearing connection in one direction and off-the-shelf beam hangers in the perpendicular direction. The final detail shown in Figure 1B has taken this basic concept and developed it fully, including the following modifications:
• The beam hangers are recessed into the column rather than into the ends of the beams. This approach avoids the need to install a plug in the bottom of the beam to conceal the hanger when looking up from below.
• The bearing area of the beam on the notched edges of the column is structurally sufficient for the design loads, allowing the steel bearing plate to be eliminated.
• The glued-in rod / knife plate column splice arrangement has been inverted, locating the pins within the architectural floor build-up and eliminating the need for plugs to conceal the pins.
• The location of the column splice is shifted slightly to ensure sufficient access to the pins above the CLT.
• The shallower beam is necked down to account for potential variation in the beam width after manufacturing (which is permitted by manufacturing standard tolerances) and ensure a consistent dimension.
• All critical tolerances and bearing lengths are noted.
2A. Indictive beam-to-beam detail
A second example, showing a beam-to-beam detail, is provided in Figure 2A, with the completed Timberlab detail in Figure 2B. The indicative detail provides two different options, which increases our flexibility when choosing a final strategy. The final detail shown in Figure 2B includes the following modifications:
• The option with two separate brackets is provided. The “saddle” version of the detail would involve added cost for steel fabrication (complete joint penetration welds are typically required at the corners) and can present fit-up issues in the field due to the bracket warping out of square due to the heat of welding.
• Once the brackets are separated into two pieces, each piece must resolve the eccentricity between the centerline of the bearing area and the vertical plate and screws. This eccentricity is taken out through bearing against the side of the beam at the bottom of the bracket coupled with tension in the fully threaded screws at the top of the bracket.
• The tension screws are offset to avoid clashing in the center of the supporting beam.
• All critical tolerances and bearing lengths are noted.
Many projects will include other delegated design items that have the potential to impact the mass timber scope, for example exterior cladding, elevators, stairs, and roof anchors. While we understand the design of these items will likely be finalized after the mass timber connections, a set of reasonable assumptions will need to be articulated as a basis of the mass timber design. Discussing and explicitly documenting the basis of design helps with future coordination when the other trades are brought on board. See Figure 3 for an example of design assumptions for exterior cladding.
DIAGRAM INDICATIVE DETAIL:
FINISH FLOOR PER ARCH CLT PER PLAN
ANCHOR (GRAVITY & WIND) ANCHOR (WIND) GLULAM BEAM PER PLAN COLUMN BEYOND EXTERIOR ENVELOPE
NOTES:
1. ALL CLADDING LOADS WILL BE DELIVERED TO CLT. CLADDING WILL NOT CONNECT DIRECTLY TO PERIMETER BEAMS. CONNECTIONS MAY OCCUR AT TOP AND BOTTOM OF CLT OR ONLY AT TOP, AT CLADDING DESIGNER'S OPTION.
2. WEIGHT OF CLADDING = 15 PSF
3. FOR GRAVITY LOADS, CLADDING IS BOTTOM LOADED AND SUPPORTED AT EVERY FLOOR LEVEL.
4. FOR WIND LOADS, CLADDING SPANS VERTICALLY FROM FLOOR TO FLOOR WITH LATERAL SUPPORTS AT TOP AND BOTTOM.
5. MAXIMUM SPACING OF ANCHOR POINTS TO CLT = 5'-0".
Accounting for fabrication and erection tolerances at connections is just as important to our designs as meeting the structural requirements. Understanding what tolerances are necessary or expected on a project, especially where industrystandard guidance may not exist, is a significant part of our process.
Manufacturing tolerances for mass timber elements are codified in the relevant product standards (e.g. ANSI A190.1 for glulam, APA PRG 320 for CLT); however, tolerances for CNC machining and erection are not standardized. The project’s structural specifications are the most appropriate documents to set these tolerances. Timberlab can provide input on the scope of these tolerances and reasonable limits that balance constructibility with the structural and architectural requirements.
For large glulam members, we also aim to account for expected dimensional changes to the timber and eliminate (or minimize) restraining forces associated with shrinkage and swelling perpendicular to grain. We typically assume glulam will arrive to our fabrication facility at a moisture content of 12%-15% and equilibrate in the completed building at 8%-10% for elements inside the building envelope. For exterior elements or other special circumstances, these assumptions may need to be adjusted.
Where mass timber interfaces with other materials, provide any project-specific tolerances that are more stringent than industry standard (i.e. AISC Code of Standard Practice for steel, ACI 117 for concrete, and TMS 602 for CMU). Unless noted otherwise, we will assume these standards apply and detail the timber connections to be able to accommodate the maximum tolerances permitted by the relevant standard.
The design approach for the building’s lateral system depends on whether the entire building is mass timber or whether the building is a hybrid, with lateral resistance provided by steel, concrete, CMU, or light-frame wood shear walls.
Fully mass timber buildings can provide lateral resistance using traditional CLT shear walls, CLT rocking walls, or glulam braced frames in combination with CLT diaphragms. Only traditional CLT shear walls currently have explicit design provisions in the codes: ASCE 7-22 provides R factors for seismic design, and the 2021 edition of NDS Special Design Provisions for Wind and Seismic (SDPWS) includes design requirements. For projects in Seismic Design Category B and higher with CLT rocking walls, glulam braced frames, or traditional CLT shear walls that deviate from the detailing requirements in SDPWS, approval from the authority having jurisdiction (AHJ) is typically required. This process falls under the IBC provisions for alternative materials and methods requests (AMMR). If Timberlab is engaged in a design assist role early in the project, we can attend meetings with the AHJ and support the SEOR in preparing documentation to support an AMMR as an additional service. However, responsibility for submitting the request and obtaining AHJ approval remains in the SEOR’s scope.
Once the path for code approval is clear, the design of a mass timber lateral system can be included in Timberlab’s scope if agreed upon with the SEOR early in the process. This scope includes design of the vertical lateral-resisting elements (walls or frames) as well as the CLT diaphragms, including the design of chords and collectors.
For projects that do not use a fully mass timber lateral system, the analysis and design of the overall lateral system remains the responsibility of the SEOR, including the vertical elements (walls, frames, etc.); categorization of the diaphragms as rigid, semi-rigid, or flexible; distribution of lateral forces to the vertical elements through the diaphragm; and the design of diaphragm chords and collectors.
If CLT is being used as the diaphragm, our panel-topanel connections can be designed for lateral forces if they are provided to us. Typically, these forces would be included as a maximum shear force per unit length at each level. For projects in high seismic zones where these forces may be significant, an overall shear diagram for each level can help economize on connections by allowing us to design for the actual force at each splice location rather than using the maximum force everywhere.
Where supplemental steel straps, plates, or other structural steel elements are fastened to the top side of the CLT to function as diaphragm boundary elements (chords and collectors), the design of fasteners to connect the boundary elements to the CLT can be included in our scope if the design forces are provided. If mass timber beams are being used as boundary elements, provide axial forces for both member checks and connection designs. Design forces associated with the lateral system must include any applicable overstrength factors from ASCE 7 or force multipliers from NDS SDPWS.
Even when Timberlab is engaged early in the process, our project schedules and fees are built on a certain duration for our delegated design work that begins once the information listed in the sections above (and reiterated in the checklist at the end of this guide) is finalized and provided in its entirety. We refer to this milestone as “Design Criteria Lock” in our project schedules. Having Timberlab involved in the project early effectively gives us a “jump start” on the work and will reduce the durations we build into the schedule following Design Criteria Lock, when compared to a traditional design-bid-build project.
We cannot guarantee that changes to the delegated design information after Design Criteria Lock can be incorporated without increasing our cost and/or jeopardizing the project schedule. We understand that no process is perfect, which will sometimes mean changes. We aim to accommodate them without changing schedule or cost if we can, but what can seem like a minor change (for example shifting a single grid line by 6 inches) can create re-design and re-documentation work on dozens of members and connections, depending on where are in the delegated design process.
We are also committed to a process that allows for multiple quality control checks along the way, and we do not want to compromise quality by rushing to incorporate last-minute changes. For significant changes, we may be able to maintain the schedule by reallocating resources internally (which represents an additional cost), but the reality may be that we need additional time. In such cases, Timberlab will work with the general contractor on the overall project schedule to minimize the overall impact to the project.
Coordination of mechanical, electrical, plumbing, and fire protection (MEPF) services is required to confirm the location and size of all penetrations through the mass timber structure. Early engagement with the MEPF trades is highly encouraged to allow this coordination to stay off the critical path of the project schedule and to ensure that openings can be cut in the fabrication shop rather than in the field. Coordinating and field-cutting small penetrations through CLT floor and roof slabs after fabrication can be accommodated (roughly 3 inches in diameter and less); however, all large slab penetrations and all beam penetrations, regardless of size, are considered structurally significant and must be individually checked by the Timberlab engineering team. While this coordination process typically extends beyond Design Criteria Lock, agreeing on a deadline for finalizing structurally significant penetrations is crucial to maintain the project schedule. Full coordination should be complete no later than the LOD350 milestone. (See the “Delegated Design Submittals and Review Process” section following.)
If reinforcement around penetrations is required, that reinforcement is included in Timberlab’s design scope. It is possible that some desired penetrations cannot be accommodated without overstressing the member, and an alternate solution must be reached.
Penetrations through fire-rated structural elements require particular attention to ensure the integrity of the fire rating. Timberlab’s scope related to fire-resistance is limited to char calculations for exposed elements and detailing of fire tape at joints; other firestopping details remain the responsibility of the architect of record.
Understanding typical timelines for the delegated design process, including review periods and the process for incorporating feedback, helps create a realistic schedule for the project. Intermediate milestones help keep the project on track while ensuring enough time is reserved for quality control along the way.
The SEOR’s drawings and specifications should clearly indicate that the mass timber structure is a delegated design item. This establishes the relationship between the SEOR as the registered design professional in charge of the project and Timberlab as a specialty structural engineer designing to the performance specifications given in the contract documents.
We typically assume our delegated design scope is treated by the Authority Having Jurisdiction (AHJ) as a deferred submittal, meaning it does not need to be complete at the time the design team files for a building permit. However, in some jurisdictions, the AHJ may expect the mass timber design to be complete at the time of building permit submission. The design team should confirm the timing of Timberlab’s submittals with the AHJ as early in the process as possible, preferably during the Schematic Design phase. For projects where Timberlab’s submittal needs to be included for building permit application, the overall project timeline shifts forward, and we need to be brought on to the team earlier to avoid schedule delays.
During these early discussions with the AHJ, in states which have a Structural Engineer (SE) designation, the design team should also confirm whether an SE stamp is required on Timberlab’s submittals. We typically assume a PE stamp is sufficient, unless the project is in a state with a full structural engineering practice act (e.g. Illinois and Hawaii).
Our typical project schedules include an initial submission of delegated design information two weeks prior to Design Criteria Lock. The checklist at the end of this document can be used as a guide for the design team to prepare this initial submission. Timberlab uses the first week of this review period to confirm the completeness of the information provided and ask any clarifying questions. The second week is a coordination period with the design team to finalize information for Design Criteria Lock. If this coordination process results in any additions or changes to the delegated design information, the final design and performance criteria should be incorporated into an updated set of contract documents.
Following Design Criteria Lock, Timberlab’s initial delegated design efforts are focused on member sizing and confirming CLT panel layups in conjunction with our modeling team’s work on the LOD200 submittal. (See our “Designing for Fabrication” guide for a full explanation of Levels of Detail and what is typically included in an LOD200 submittal.) The amount of time needed for this initial phase varies by project, but the minimum time allotted for smaller project is two weeks. Proposed member sizes and CLT panel layups are submitted to the design team for review and comment, with revisions made as necessary prior to developing typical details.
Once member sizing is complete, typical connection details are developed in conjunction with our modeling team’s work on the LOD300 submittal. (See our “Designing for Fabrication” guide for a full explanation of Levels of Detail and what is typically included in an LOD300 submittal.) These details are typically drafted in 2D format, though 3D views may be needed for connections with complex geometry that are difficult to visualize in 2D. The amount of time needed for this phase varies by project, but the minimum time allotted for smaller project is three weeks. The details then go through an internal Timberlab review by our fabrication and installation teams to provide constructibility feedback, with a subsequent period to incorporate any changes prior to submitting the LOD300 set and typical details to the design team. Once the design team’s feedback is received, we typically request a page-turn meeting to review the comments and come to agreement on any changes to the typical details.
A preliminary glulam and CLT billet list is generated after we receive comments back on the LOD300 submittal. Minor adjustments to glulam member sizes in order to accommodate final connection geometries may still be required during the LOD350 phase as detailed designs and clash detection progresses.
After completing the LOD300 set and typical connections, we begin detailed analysis and calculations for each connection type. Ultimately this work feeds into our signed and sealed submittal, which includes the LOD350 drawings and our calculation package. (See our “Designing for Fabrication” guide for what is typically included in an LOD350 submittal.) Depending on the size and complexity of the project, the length of this phase can vary significantly. Similar to the previous phase, we reserve time for internal review by our fabrication and installation teams as well as an engineering quality control review, plus time to incorporate any revisions as a result of those reviews. Once complete, the LOD350 drawings and calculation package are submitted to the design team and final billet lists created.
For projects where mass timber elements connect to structural steel framing, the LOD350 set also serves to communicate the information necessary for the steel fabricator to create their shop drawings. For example, Timberlab’s design for the connection of a glulam beam to a steel girder may require the steel supplier to provide additional stiffener plates or screw holes in their member. While the design of these connections is included in Timberlab’s scope, the supply of supplemental plates typically remains in the steel supplier’s scope to maximize the amount of work that can be completed in the steel fabrication shop and avoid costly and timeconsuming field work.
The Timberlab engineering team uses a variety of software programs as well as hand calculations as part of our design. Although software output can appear as a “black box,” we aim to include a detailed sample calculation for each main connection type to show the overall approach, the design equations being used, and the relevant inputs and outputs. The remaining design checks for similar connections may be presented in a summary format to reduce the length of the calculation package.
As with any delegated design scope, the SEOR’s review is necessary to confirm the delegated design complies with the performance and design criteria set forth in the contract documents and agreed upon during coordination prior to Design Criteria Lock. Consistent with AIA guidelines for design team review of delegated design submittals as outlined in AIA A201-2017, submittal review is “only for the limited purpose of checking for conformance with information given and the design concept expressed in the Contract Documents.” We recommend the SEOR review the following information:
• All general notes and/or narratives provided at the front of the calculation package
• Design loads
• Finite element model inputs and summary results
• Load path for each main connection type
• Spot checks of member sizes and sample connection calculations
• Effects of connections on the balance of the primary structural system where mass
The SEOR is responsible to issue a statement of special inspections in accordance with the building code. Because the code guidance on special inspections for mass timber is still developing, Timberlab is happy to discuss this scope with the design team to develop a list of third-party special inspections that is appropriate to the project.
It is helpful for us to understand what field visits are planned by the SEOR for structural observations and approximately when those reviews may take place. When practical, we may schedule our own field review visits to coincide with the SEOR.
Typical exclusions to Timberlab’s scope are noted below.
Alternative materials and methods requests (AMMR) requiring approval by the authority having jurisdiction (AHJ) are outside of Timberlab’s scope and remain with the SEOR. Meetings with the AHJ or preparation of documents to support an AMMR request can be provided as an additional service.
Because beam camber can complicate fit-up issues on site, we do not recommend cambering beams unless special circumstances warrant.
Where mass timber connects to steel embed plates in concrete or CMU construction, Timberlab’s scope includes the connection of the mass timber element to the embed plate, including field welds to the embed. The design of the embed itself remains the responsibility of the SEOR and must account for the loads imposed on the embed, including any eccentricities.
Information
Timing of delegated design submission
PE vs SE stamp required
All applicable codes, including edition
Structural design criteria per 2021 IBC §602.3
Load maps for each floor
Superimposed roof dead loads noted where they may not be present
Minimum dry weight of green roof assembles
Deflection limits
Deflection limits at building perimeter
Deflection limits for roof members and effect on slopes and drainage
Seismic design drifts (SDC D and higher)
Deflection limits for specialty items
Floor vibration design criteria
Requirements for special inspections and structural observations
Timber species and grades
Construction type
Fire-resistance ratings for all mass timber elements
Scope of exposed and protected mass timber
Noncombustible protection contribution to fire-resistance rating
Structural framing:
Dimensioned gridlines
Beam and column locations
CLT primary span direction
Floor-to-floor heights
Top of structural slab elevationspoints
Critical slab edge locations
Minimum or maximum member sizes
Indicative architectural details
Indicative structural details
Scope of architecturally exposed and concealed connections
Assumptions for exterior cladding loads and attachment points
Assumptions for elevator loads and attachment points
Assumptions for roof anchor loads and attachment points
Mass timber tolerances
Steel, concrete + CMU tolerances where different from industry standard
Mass timber lateral systems: code approval process
Mass timber lateral systems: scope by Timberlab
Hybrid buildings (non-mass timber lateral systems):
Diaphragm shear forces for panel-to-panel connections
Diaphragm forces for connecting CLT to steel chords or collectors
Diaphragm forces for beams acting as chords or collectors
Deadline set for finalizing size and location of structurally significant MEPF penetrations
