Retrofitting Non-Ductile Concrete Buildings: Step-By-Step Process

First, it is important to understand that there are many parties involved in a construction project, including:

• Owner or owner’s agent.
• Civil or structural engineer: Responsible for completing the inventory form, retrofit design, and construction administration.
• Possibly an architect, mechanical, electrical, or geotechnical engineer: Responsible for work triggered by the seismic retrofit.
• Possibly a geotechnical engineer: If there is no existing geotechnical report, a geotechnical engineer will likely need to be engaged to develop design parameters and include them in a geotechnical report for submission to the city.
• City building department: Responsible for checking drawings and calculations, issuing permits, and approving special inspectors.
• General contractor: Responsible for providing a cost estimate for permit and managing construction, including coordinating with the structural engineer, special inspector, and city inspector for site visits. May also participate in preconstruction investigation of the structure.
• Possibly subcontractors: May be selected by the general contractor to perform portions of the construction work.
• Special inspector and testing lab: Likely involved in pre-construction work. They are the owner’s representative involved in testing and inspection during construction.
• City inspector: City representative involved in inspection during construction.

Assumption

You own one or more buildings and have received notice from the local Authority Having Jurisdiction (typically the city), indicating that your building(s) is in the NDC seismic retrofit ordinance program. Note that even if the city has not notified you, if the building is an NDC building as defined by the ordinance, you should proceed as if you were notified. Further, the building is not exempt from the program based on its number of units, number of stories, or date of construction.

1. Hire an experienced and qualified design professional

A licensed civil or structural engineer can perform the evaluation and retrofit design. (A civil engineering license is a broader license. Those who go on to get a structural engineering license after qualifying for a civil license are typically more focused on buildings, and there are some projects, such as hospitals and public schools, on which only licensed structural engineers are permitted to serve as engineer of record.) Theoretically, the design professional could also be an experienced architect, but we will assume hiring a structural engineering firm for this example and will use the term “engineer” to refer to the design professional.

When hiring an engineer, look for experience in seismically retrofitting existing buildings, specifically NDC buildings. An engineer should also be familiar with the city’s ordinance and associated documents, such as technical bulletins.

If you receive proposals from multiple engineers, you should carefully compare what is and is not included in the proposed scope of work. Big-picture-wise, you want the proposal to cover developing drawings and calculations for submission to the city and for use by the contractor, and construction administration services (construction administration fees may be included in a separate later proposal once construction scope and schedule is determined). However, a simple comparison of fees can be misleading if, for example, one engineer’s proposal assumes original drawings are available and another does not. Similarly, if one engineer provides three structural observation visits during construction and another only performs one, simply comparing total fees is not appropriate.

Things that the engineer will consider when estimating their fee:

• Size of the building.
• Availability of drawings (if the drawings exist, the engineer will perform a preliminary review).
• Availability of material strengths (sometimes listed on existing drawings).
• Irregular building geometry (located on hillside, has lightwells, etc.).
• Type of foundation.
• Evaluation approach appropriate for use (Step 8). Some engineers may assume a standard linear approach, assuming, if necessary, a more sophisticated non-linear approach will be performed later (for additional fee), whereas some engineers may intend to do a more sophisticated analyses without doing a standard approach first.

The engineer you select to design the retrofit can be the same engineer who performed the screening or someone else. Typically, it is desirable for the engineer who developed the retrofit drawings to also perform the construction administration because they are familiar with the design and are in the best position to make changes if unexpected existing conditions are discovered.

You should meet with the engineer and discuss your project before they begin work. Points to discuss include:

• Are drawings available? Have you been to the city to look for them?
• Is the building considered historic and subject to restrictions about changing exterior elevations or interior finishes?
• Discuss your performance goal. Do you want to just meet minimum ordinance requirements, or do you want to consider better performance where it is cost-effective to do so? As the seismic criteria of the ordinance may be less stringent than what is required by the building code for renovations, the use of higher criteria could prevent the need for retrofit for future renovations.
• Share information you have about previous remodels, repairs, or known deterioration (e.g., large cracks, spalls, roof leaks). A deteriorated or weakened structure will not perform well in a seismic event.
• Share any recent work done to comply with other city ordinances, such as facade inspection. If the city has such ordinances, it may make sense to perform work related to these ordinances simultaneously with the retrofit work for cost efficiency and to minimize occupant disruption.
• Agree on the logistics of site access for the engineer to do the evaluation. Generally, the engineer will need to walk through most of the building (repetitive layout on multiple floors may mean this is not required). Some jurisdictions may also require evaluating non-structural items such as gas lines, chimneys, or masonry partitions to determine if those elements pose a hazard in an earthquake; therefore, a more thorough walkthrough to find these items may be required.
• Decide where it is acceptable to take samples for materials testing and localized destructive exploration to identify conditions during the evaluation and retrofit evaluation phase. In some cases, conservative assumptions about material strengths can be made and confirmed during construction, but this typically increases construction costs. This is less likely to be needed if high-quality original construction drawings exist (Step 4).
• Discuss retrofit limitations you wish to impose. Can window openings be closed, or is it required that the retrofit design maintain all openings? Can the openings be made smaller, or do they need to remain the same size? Generally, working on the exterior elevations is less disruptive to building occupants. Are there certain areas of the building where you do not want any work done? More limitations typically result in higher construction costs.
• Decide if construction work can be done in one phase. Will the contractor have full access to the whole building during construction, or does work have to be phased to maintain some occupancy at all times? Phased construction will generally be more expensive.

Identify any concerns that might require another design professional. An architect can address waterproofing issues or code compliance to satisfy disability requirements that may be triggered by the work. Mechanical or electrical engineers may be needed to relocate utilities. They may not be required for utilities temporarily removed and replaced in kind. A geotechnical engineer may be required to provide allowable bearing values for existing or new foundations unless there is an existing geotechnical report. Inform the engineer about any renovation or other similar work that you are planning to see if it has any impact on the seismic criteria that should be used for the retrofit.

2. Screening or inventory phase

A licensed civil or structural engineer must fill out the screening or inventory form available from the city (unless the city allows the owner to fill out for exemptions such as one- and two-unit dwellings or one-story buildings). It is relatively easy for an experienced engineer to confirm through visual observation that most concrete buildings are either NDC or not NDC and complete the form. However, for some buildings, it is more difficult because the building may have been altered over the years; this includes undergoing multiple kinds of construction, having finishes that hide key structural components, or having steel framing embedded in the concrete (exempt from the ordinance). For these buildings, reviewing available drawings will make the process faster and result in an answer with higher confidence. It is important to perform sufficient work to complete this task accurately to avoid future additional costs associated with the building being miscategorized.

3. Obtain existing drawings

If an owner does not have existing original structural drawings, someone should visit the city’s building department to determine if they exist in their archives. The engineer can perform this task, but the owner should expect a small fee if it is not included in the engineer’s proposal. An advantage of having the engineer visit the building department is that they can better judge what information will be useful in some cases. There is a fee for reproduction of records, so if the owner self-performs this task, he or she needs to make decisions about copying too much or missing valuable information. There is sometimes also a requirement that the original engineer and/or architect for the building be contacted to allow permission for reproduction. This can be challenging for older buildings and is sometimes not possible. If you inform the city that you tried but cannot contact the original designer, this is usually sufficient.

If the original structural drawings are available, the engineer must verify they appear accurate through a site visit.

If original drawings are not available, someone will need more extensive site visits to develop drawings by taking measurements and performing localized demolition and material testing. This will also require an additional fee if not included in the proposal. There are firms that specialize in just producing as-is background drawings using lasers, and they are typically much more cost-effective than having them developed by an engineer. These drawings will only provide the building’s geometry and structural elements and will not provide information on the details of construction that are not visible. This work typically involves accessing every room. The owner should rely on the engineer to help decide the extent of drawings required by the specialty firm. For instance, in addition to plans, exterior elevations and specific sections through the building will likely be required.

The resulting background drawings that have all the structural elements and dimensions can be used by the engineer after verifying them. Prior to including retrofit details on the drawing, the engineer can supplement them with additional information from localized demolition and materials testing.

4. Perform site visits

We recommend that the owner accompany the engineer on at least one site visit so that they can make decisions while at the building.

If there are no structural drawings, the engineer may want to remove some wall finishes. The owner can help decide the most appropriate locations and hire a contractor to open wall finishes (the engineer may be willing to do this if it is not necessary to close the openings until construction) to verify critical information, or the engineer can make assumptions and verify them during construction if permitted by the City.

During site visits, the engineer will verify that available drawings accurately represent the structure, look for locations where retrofit work can be done, verify that no significant deterioration has occurred, and look for unreinforced masonry partitions that need to be mitigated and/or included in the analyses. They may also perform some nondestructive testing to verify the presence and spacing of reinforcing steel.

It is important that the site visits are thorough and include basements, roofs, and penthouses. As the retrofit design work will typically include improving areas of structural irregularity (e.g., shear walls that do not continue to the foundation), these areas should be visited.

Once retrofit designs are developed, the engineer may need to revisit the areas where work will be performed to verify constructability.

5. Evaluate existing material strengths

If original drawings listing material properties exist, they can typically be used in the retrofit design with limited verification.

If no drawings are available, the engineer can assume default material strengths based on the age of the building. Such values are typically conservative and require applying a safety factor that will increase the scope of the retrofit. If material strengths in some areas of the building are critical, or if a material appears to be suspiciously weak (e.g., crumbling concrete foundation) or deteriorated (e.g., water damage), it is appropriate to do material testing. If testing is too disruptive, assumptions can be made, and this testing can be done during construction by the special inspector and testing lab (this approach must be approved by the city building department). However, if these assumptions are incorrect, the construction project may be delayed if needed changes to the drawings are made.

A comprehensive materials testing program can involve taking several cores and reinforcing samples for each floor for each type of structural element important to the envisioned retrofit design. Depending on the findings, it can substantially save on construction costs. It is important to realize that the construction costs are typically by far the largest costs associated with the project. We recommend that the owner remains open to suggestions for further testing or changes in engineering approach that require additional fee but have the potential to reduce construction costs.

6. Evaluate existing details

This is perhaps the most problematic issue for NDC buildings with no available drawings. To evaluate the building, the engineer needs to know the details of the construction of critical elements. In this case, details of construction generally mean size and spacing of reinforcing (rebars) as well as their configuration and detailing (e.g., do the bars have proper hooks on their ends, or are they spliced well?). This may include beams, columns, walls, and foundations. And this information can only be collected using either destructive or nondestructive investigation.

There are many means of nondestructive investigation, including scanning the concrete for rebar using a device such as ground penetrating radar. As the name implies, no exploratory demolition is required for this work. This work is typically performed by a testing lab, but some engineers can perform some of these tasks. However, nondestructive investigation is typically only effective as a supplement to destructive investigation (and materials testing). For example, nondestructive testing can help verify that conditions found through exploratory demolition at one location appear to exist in other locations.

Destructive demolition is typically performed by either a testing lab or a contractor hired by the owner. (A contractor is often needed when repairs are required. Areas that are demolished can sometimes be left as is if the area will be included in the retrofit and demolition is not too intrusive). The engineer will choose selected locations for initial work, and depending on the findings, may require additional work. Consequently, the fee for the engineer and the testing lab or contractor may require modification.

It is evident that it is not practical to perform enough exploratory demolition to find information on every condition in the building. On a given floor, conditions could vary in different walls. Conditions will vary from floor to floor, with more reinforcing steel likely at lower floor levels. For a column, reinforcing can vary over the height of a given floor. It is important that the engineer has sufficient experience and judgement to determine the practical extent of demolition. Once the engineer has a retrofit in mind, they know which elements are critical and should be investigated. If the retrofit concept is changed (possibly for cost reasons), additional testing may be necessary. Especially problematic are foundations. Determining the extent of foundation, especially deep foundations, may not be practical.

If only limited exploratory demolition is performed, it increases the likelihood that surprises will be encountered during construction and that changes in design (and associated costs for the engineer and contractor) will be incurred.

7. Potentially conduct a geotechnical review

Ideally, an existing geotechnical report is available for a building site, but for older structures, this is unlikely unless substantial modifications have been made. In some cases, geotechnical reports may be available for adjacent sites, which may include data useful for reference. Published geologic maps can also be referenced to gain an understanding of general subsurface conditions, including the presence of any geologic or geotechnical hazards (e.g., liquefiable or earthquake-induced landslide zones).

If no site-specific geotechnical report is available, in typical soil/bedrock areas, the engineer can usually use conservative code-allowed soil/bedrock bearing values in their retrofit design. This may not have much effect on the cost of the retrofit for smaller buildings, but for larger buildings, site-specific recommendations provided by a geotechnical engineer are recommended. The engineer can inform the owner if a geotechnical engineer is needed. Typically, the owner hires a geotechnical engineer directly, and engineers can usually suggest qualified geotechnical engineers to do the investigation. If you hire a geotechnical engineer, they can provide capacities for existing and new foundations, which may require borings or other subsurface investigations. Subsurface investigations can be a challenge for buildings without basements and no adjacent exterior space. Geotechnical investigations generally take more than a month, so it is important to start this work at the beginning of the project.

A geotechnical engineer may be required for sites with poor subsurface conditions or slopes. In these cases, the geotechnical engineer can evaluate the characteristics of the subsurface conditions and provide appropriate recommendations addressing any geotechnical hazards that could affect foundation performance. While publicly available geologic hazard maps can help identify the potential for adverse subsurface conditions, they tend to be conservative (i.e., they may indicate a site is in a zone of liquefaction when, in fact, a geotechnical engineer may be able to do a site-specific study and prove otherwise).

8. Perform structural evaluation

The engineer performs the evaluation, typically by computer analysis. Different levels of sophistication can be used, with higher levels costing more but providing lower construction costs for some types of buildings. In some cases, the engineer may propose a standard linear analysis but determine later that a more sophisticated nonlinear analysis is appropriate. Depending on the jurisdiction, several analysis approaches are available, but the most common approach is to use ASCE-41 – Seismic Evaluation and Retrofit of Existing Buildings.

• ASCE-41 is a national standard applicable to all existing buildings. It relies on performance-based design rather than prescriptive design. It assigns credit to structural elements with non-code-compliant details.
• The ordinance will likely specify one or more performance goals for the building, such as collapse prevention in a major earthquake or life safety in a moderate earthquake. The owner is free to consider using more conservative criteria.
• If the subject building is qualified as historic, alternate building regulations in the California Historical Building Code may be used after discussions with the building department

If a building is found to meet ordinance requirements as-is, the city may require the engineer to fill out specific forms along with other documentation (e.g., calculations, field investigation report) and submit this to the city. Compliance with the ordinance without some retrofit is unlikely unless the building was previously retrofitted or is small and relies on shear walls.

If the building was previously retrofitted to criteria that are different from (and less conservative than) those spelled out in the ordinance, it may be exempt from the ordinance’s retrofit requirements for several years.

9. Develop retrofit schemes

Generally, the owner should ask the engineer to develop the conceptual scheme or schemes for review before completing the design. There are often different ways to strengthen the building; the owner can ask for multiple schemes at the proposal phase and get a contractor to provide cost estimates and schedules to find which is most appropriate. Multiple concepts will require an additional engineering fee, but they might save construction costs or avoid undesirable building modifications.

After the owner selects a preferred conceptual scheme, the engineer can develop the final scheme and provide drawings and calculations suitable for a permit. In some cases (generally larger projects), separate specifications will also be provided, and in other cases, the engineer will rely solely on general notes on the drawings. If specifications are issued, they are not submitted to the city but are provided to the contractor.

10. Identify acceptable contractors and send drawings for bid

Often, the contractor is selected prior to the plan check, as the expected construction cost is used to determine the permit fee. It is generally better to identify a reasonable number (two to four) of qualified contractors rather than request bids from many contractors. Qualified contractors may not bid if there are many competitors, especially if some are not qualified and will provide lower costs. Engineers can usually provide suggestions for qualified contractors. It is good to ask for references and check them.

For buildings for which the original drawings are not available, some destructive investigation may be required. A contractor may be needed to do the demolition and possibly repair areas where concrete is removed to observe reinforcing steel detailing.

11. Hire a qualified contractor

You should hire a contractor who has experience in seismic retrofit work, preferably in more than just smaller projects like houses or apartment buildings. There are processes that should be followed on projects with engineers that smaller contractors may not be familiar with, such as the use of shop drawings to verify that the engineer’s drawings are interpreted properly.

If you have difficulty comparing different bids, you can ask the engineer for assistance, but this may require a small additional fee if the task is not listed in the engineer’s proposal. Sometimes contractors will include exclusions or assumptions that may not be clear to those who do not understand the drawings. Some contractors have been known to bid low and list a lot of exclusions and then increase their fees for change orders for items that were needed but not included in the bid. Even with a good contractor, it is not realistic to assume that the construction fee will not increase due to unexpected circumstances, especially when original drawings are not available. The owner should have a contingency for construction, engineering, and special inspection costs.

When you hire a contractor, you are typically hiring a general contractor. Often, a general contractor will have subcontractors work for them. For example, the general contractor may perform all the concrete work but hire a subcontractor to relocate electrical and mechanical items.

12. Submit drawings and calculations for city review

The next step is to submit drawings and calculations to the city’s building department for compliance review. These drawings are referred to as issued for permit (IFP) drawings. The owner, engineer, or contractor can submit them to the city. The advantage of having the engineer submit the drawings and calculations is that they can respond to questions from the plan checker, but the owner should expect to pay a small fee for the engineer performing this task if it is not listed in the engineer’s proposal.

To get a permit, the engineer must fill out the city’s Special Inspection and Structural Observation Form, indicating what work requires inspection by a special inspector and structural observation by the engineer. The city requires this to try to ensure that the construction quality is as intended. Typically, the owner, contractor, and special inspection and testing agency must sign the form. The owner needs to select the special inspection and testing agency before a permit can be issued.

Generally, the city will have questions that the engineer has to answer (e.g., plan check comments), which may require minor changes to drawings or calculations for city re-review. Unless some extraordinary issues arise that could not be anticipated (typically of a nonstructural nature), this service should be included in the engineer’s proposed fee.

Once the comments are resolved, the city will issue a permit. Typically, the owner pays the permit fee (possibly through the contractor). The revised drawings are typically referred to as the issued for construction (IFC) drawings and should be used by the contractor to do the construction.

13. Hire a special inspector and testing agency

As described above, the testing agency may perform nondestructive and destructive investigations during the evaluation and retrofit phase. This section discusses their role during construction.

The special inspector and testing agency are usually one company. The engineer can usually provide names of special inspection agencies, and the city has a list of qualified and approved agencies.

Each project requires a special inspection and testing agency to perform the work identified on the Special Inspection and Structural Observation Form (Step 13) required by the city.

The special inspector’s job is to inspect specific items during construction (e.g., anchor bolts installed in concrete, welding). They are there to ensure the quality of the critical items in the project and to represent the city and the engineer.

The special inspector will write reports to document the results of their inspection. The special inspection reports should be provided in a timely fashion to the owner, the contractor, the engineer, and the city at a minimum. The owner should provide the distribution list to the special inspector. If the engineer is not receiving the reports, significant problems can result.

If the special inspector finds a nonconformance, they should immediately contact the contractor. If the nonconformance is corrected, the special inspector can note this in their report. If the nonconformance is not corrected, the inspector should notify all parties on the distribution list in a timely fashion.

The testing lab will perform materials testing, such as required strength tests for concrete cylinders for new concrete and verify reinforcing is properly placed.

If the special inspector and testing agency review the drawings, they can provide the owner with an estimate for the work. For a more accurate estimate, the owner should provide the agency with the contractor’s schedule and provide a contact with the contractor that the agency can discuss questions with. Because these inspection and testing fees are somewhat dependent on the contractor’s schedule (which could change), the fees are sometimes adjusted during the project.

Some engineers offer to serve as the special inspector, and this can be appropriate, depending on the nature of the retrofit. In such cases, it will still likely be necessary to hire a testing lab to test material strengths. The special inspector is typically hired by the owner but may be hired by the engineer. They should not be hired by the contractor (this is not permitted by the building code), as that creates a conflict of interest.

The contractor must call the special inspector at appropriate phases of construction to inspect the work. Any work identified as requiring special inspection but not inspected is possibly subject to removal and replacement.

14. Begin construction

We recommend a pre-job meeting involving the owner, contractor, engineer, and special inspector. This could require an additional fee for these parties, but it is typically worth it to avoid misunderstandings and to open lines of communication. If verification of existing materials (Step 6) were delayed until construction began, this is a good time for openings in walls to be made. Required inspections and structural observations should also be discussed.

It is best if the engineer providing construction administration services is the original design engineer, as they are most familiar with the project. On some past projects, contractors have introduced their own engineers to do the construction administration tasks without informing the original engineer. If the engineer is hired by the contractor, they may prioritize the contractor’s interests over the owner’s interests. They also may encounter difficulties if unknown conditions are encountered, and the design must be changed because they are not the engineer of record on the project.

The engineer reviews submittals and shop drawings (if required) prepared by the contractor and subcontractors prior to construction. Once they are returned, the contractor can begin fabricating rebar, etc. Poorly done shop drawings may require resubmittal to the engineer for a second review, which could result in an additional cost to the owner.

The engineer will respond to the contractor’s requests for information (RFIs), typically through a formal written process that allows questions and answers to be properly documented and is more formal than a phone call or an email. RFIs typically involve unexpected conditions or deterioration or some part of the drawings that the contractor finds difficult to interpret. The engineer typically assumes a reasonable number of RFIs in their proposal. Additional RFIs could result in additional engineering fees.

Some RFIs are suggestions by the contractor to do something different than what the engineer specified. This may or may not be appropriate. If the contractor assumed that a less expensive way of performing the work than indicated on the drawings would be acceptable and it takes the engineer some effort to prove it and modify the design, it may be appropriate for the contractor to pay for this engineering effort unless the contractor can convince the owner it is worth their while, and passes on the savings to the owner.

The city inspector often requests to see RFI responses when conducting inspections, so the contractor should keep copies of RFI responses on the jobsite. It is generally a good idea for the owner to be copied on all RFIs and RFI responses.

Despite every effort by the engineer, it is common for unexpected conditions to be revealed when finishes are removed or foundations are revealed. This is especially the case when original drawings are unavailable. These unexpected conditions can be the result of modifications over the years or poor-quality construction. In such cases, the project may be delayed, and additional engineering fees may be required. Owners should anticipate this possibility.

The city inspector will visit the site during various stages of work. Usually, the contractor coordinates this. The special inspector will inspect at appropriate times during the construction as indicated by the engineer on drawings and on the Special Inspection and Structural Observation Form completed by the engineer and submitted to the city. The special inspector should also be notified by the contractor regarding the appropriate times to come to the site. Neglecting to notify the special inspector to visit can be a serious problem; the contractor may have to take samples or perform tests on new concrete to verify it is of sufficient quality or pull-test anchor bolts installed in existing concrete to verify they are installed properly. Extreme cases may require partial demolition of work that was just completed, so the work quality can be established.

The engineer will perform structural observations at appropriate times and should be notified by the contractor when to come to the site. As an example, structural observations may be required prior to pouring a concrete foundation because the engineer may want to review the placement of the reinforcing steel. Items requiring structural observation are typically listed on the drawings.

It is possible to reduce costs by limiting the number of structural observations, but this could have a negative impact on quality. The structural observations are not city inspections or special inspections. The structural engineer is looking for general conformance with the drawings and would not typically perform tasks, such as measuring spacing between the rebar. The structural engineer understands the design best and thus can make useful observations about items that the city inspector and special inspector might not detect. Detecting problems early can avoid costly delays. Omitting required structural observations can cause major problems at the end of the project (see below).

The contractor may also request a site visit by the engineer due to questions they have based on conditions they discovered or a problem they have in completing the work shown on the drawings. Usually, the engineer’s contract will allow for a certain number of observation visits beyond those scheduled, and if additional visits are required, it will result in an additional fee.

The city inspector, special inspector, and structural engineer are a team that helps ensure quality construction. However, it is still important that the contractor accepts responsibility for the quality of their own work and the work of their subcontractors. This means having a project manager or superintendent visit the site frequently and be present at key times.

15. Complete construction

At the end of the project, the owner and engineer should walk through the site with the contractor to ensure that all structural work appears to be completed and that the finished conditions are acceptable.

The special inspector is required to provide a letter indicating that all the work they inspected meets the design requirements. If the contractor did not require inspection for portions of the work, this could cause issues that may result in the need for more testing and, in extreme cases, demolition to verify construction. Therefore, the contractor must be aware of all special inspection requirements.

The engineer must provide a letter indicating that the work seems to comply with the drawings for submission to the city. To do this, the engineer must receive and review the special inspector’s letter. This letter from the engineer is required for the city to sign off on the project. If structural observation visits were not completed, this can cause issues that, in extreme cases, can result in local demolition to verify construction details. Therefore, the contractor must be aware of all required structural observations.

For an additional fee, the owner can ask the engineer for record drawings that include all the changes that occurred during construction. The city does not require this; this will be of more value to the owner if they do work on the building in the future if substantial changes were made after the drawings were approved by the city. At the very least, the owner should archive copies of the permit drawings and RFI responses for possible future use.