Classification of Work within the International Existing Building Code (IEBC) might sound like a boring task, though understanding the nuances of how a project is classified changes which chapter of the IEBC applies, which could drastically affect scope and cost of a project. Completing a structural code review in concert with managing the scope of a project can lead to a scenario where significant structural interventions can be avoided. At LeMessurier, we impact a project by how much can be achieved with the least structural cost, and not by how much structural work we can introduce to a project’s scope. Sometimes our biggest value is by providing a project team a path that minimizes our own involvement.
The IEBC specifies project requirements based on whether the work is an Addition, an Alteration or a Repair – the required structural evaluations (and interventions) are in descending order of intensity.
Addition – An extension or increase in floor area, number of stories, or height of a building or structure.
Alteration – Any construction or renovation to an existing building other than a repair or an addition.
Repair – The reconstruction, replacement or renewal of any part of an existing building for the purpose of its maintenance or to correct damage.
Broadly speaking, an addition is often the most invasive and requires that all new structural members – and all the members supporting new construction – be designed for present-day loading, even if the building is very old. A repair is often less rigorous, and allows for a damaged structural member to be restored to its pre-damage condition which considers the loading at the time of original construction. An alteration is usually in between these two extremes and depends on how extensive the scope of the renovation is (referred to in ascending order as Level 1, Level 2 and Level 3). Level 1 is updating old materials (carpet, mechanical units, roof membrane) and Level 3 could be a full gut renovation down to the studs. Determination of the level of alteration could be its own article, but this will suffice here.
Of course, the IEBC provides a wide array of exceptions, limits and escapes for each of these classifications – and knowing these limits and how even small changes in a project scope can radically change the amount of structural work required to meet the requirements of the IEBC can influence project schedule and budget. While the definitions provided above are straight from the Code and sound simple enough, real world projects are rarely quite as straightforward. This article serves as background to a longer – interactive – discussion around how we classify work in an existing building.
You may have already seen the introductory post on our LinkedIn, but if you haven’t – please check it out! Over the coming weeks, we will be publishing (on LinkedIn and here on our website) a series of poll questions with scenarios of varying complexity that will challenge how you think about the IEBC and how projects are classified – thus defining the scope of structural interventions. Check back next week for our thoughts on the first poll question, and continue to check in weekly for more detailed descriptions of this important topic! We’ll show you how LeMessurier’s deep understanding of the Code can help steer a project in the right direction to avoid unnecessary work and expense.
Scenario #1
Scenario: A project involves an existing three-story building, with a new 4th story introduced on top of the building. Is this project an Addition, an Alteration or a Repair?
Bonus Question: What if the new story isn’t above the building, but is inserted between the 2nd and 3rd floors?
Response: The Scenario described above is an ADDITION because there is increase in floor area, number of stories, and height of the building. The Bonus Scenario is also an ADDITION because it is an increase in floor area, and number of stories.
Project Reference: The repositioning of One Post Office Square and the Tufts Dental Vertical Expansion are recent examples of this type of addition. Additions are designed to meet the full present-day code provisions, though when added to an existing building, there are limits about the influence on the existing lateral force systems. In both of these projects careful study early in the project confirmed the maximum size of the addition without having to reimagine the entire wind- and seismic-force resisting systems within the structure.
One Post Office Square
Tufts University Dental School Expansion
Check out our LinkedIn next Monday for the Scenario #2!
Scenario #2
Scenario: Investigation of existing steel columns shows they are deteriorated and are now a smaller size (section loss). The columns will be restored by adding steel reinforcing plates.
Bonus Question: What if the damaged steel columns are not reinforced, but are replaced with concrete columns?
Response: The Scenario above describes a REPAIR because it renews the column of an existing building for the purpose of its maintenance or to correct damage. The Bonus Scenario is also a REPAIR because the columns are reconstructed to correct damage.
Project Reference: LeMessurier recently investigated an existing recreation facility, and the columns near the swimming pool were deteriorated to the point of nearly wholesale section loss, calling the load path into question. LeMessurier immediately had the pool drained, the floor above shored and closer access provided to observe the full deterioration. While the building was safely shored, a full repair of the columns with steel reinforcing plates was completed. Supplemental waterproofing measures were introduced to prevent to the future corrosion of the columns.
Check out our LinkedIn next Monday for the Scenario #3!
Scenario #3
Scenario: An existing warehouse building needs a mezzanine to hold equipment. The project introduces a mezzanine level supported on the existing columns.
Bonus Question: What if the new mezzanine is separated from the building columns?
Response: The Scenario above describes an ADDITION because it is an increase in floor area of the building while making use of the existing columns. The Bonus Scenario is also an ADDITION because it still represents an increase in floor area of the building even though it is on new columns and potentially new foundations. The differences between the Scenario and the Bonus come in how the existing structural elements are influenced by the addition.
In the Scenario, the existing columns support the load from the new mezzanine; the Code indicates that the columns must be able to support that load, plus the present-day requirements of all loads acting on those columns, even if the present-day loads are larger than those at the time of original construction. This can be a challenge with snow loads – even though the portions of the columns above the mezzanine are not experiencing load from the mezzanine itself, they are required to be updated to also include the effects of snow and other loads.
Further, the mezzanine arrangement in the Scenario adds mass to the building, and will thus change the manner in which seismic effects are distributed throughout the existing lateral force resisting system (LFRS); note that the mezzanine is interior, so there is no change in the effects from wind. The Code allows up to a 10% increase in demand-to-capacity ratio on existing LFRS, thus depending on the size and location of the mezzanine as well as the position of the components of the LFRS, the project may require full LFRS upgrades, or none at all. It is important to identify this critical Code trigger early in the process.
The Bonus Scenario takes away almost all of the discussion above by removing the effects of both gravity and lateral loads from the existing columns. The Bonus Scenario can structurally be treated as designing a small building inside another building with its own columns and its own LFRS. Careful attention should be paid if existing foundations are being used for the new columns or if new foundations are being installed to support the loads. The only significant drawback to this layout is that there are more columns in the space, which could challenge programming or egress.
Project Reference: LeMessurier is currently working on a confidential conversion of a warehouse to a medical production and distribution center. Multiple small mezzanines are required within a very large warehouse. We identified very early in the project that isolating the mezzanines from the warehouse structure would vastly reduce the structural interventions – and therefore costs – for a successful conversion project. We often find that the best way for LeMessurier to help a project is to find ways to reduce our own involvement.
Check out our LinkedIn next Monday for the Scenario #4!
Scenario #4
Scenario: An existing 3-story building needs to remove the entire second floor to create higher ceilings for an amenity space.
Bonus Question: What if the entire second story is removed? Does it matter if the partial removal is at the interior of the building, or at the perimeter that supports the façade?
Response: The Scenario above describes an ALTERATION; the project is neither an addition (does not increase floor area nor building size), nor a repair (does not correct damage). The Bonus Scenario of the removal of the entire story is also an ALTERATION. The difference between the Scenario and the Bonus is a matter of extent.
While any of the project descriptions in these scenarios are all alterations, the amount of structural intervention varies. In the last installment we discussed the demand-to-capacity ratio of existing structural elements – and the removal of a floor (either partial or in total) will have the effect of reducing the capacity of the columns, both ones that support only gravity loads as well as those that resist wind and seismic loads as part of the lateral force resisting system (LFRS).
If the entire story is removed, all of the columns and therefore the entire LFRS, is influenced and the new configuration must meet the requirements of the Code when considering the reduced capacity. In a situation where only a portion of the story is removed, some structural elements may have a reduced capacity, and others may not; attention should be paid not only to the columns but also to floor beams which may comprise the LFRS and the continuity of the diaphragm that helps to distribute loads to vertical frames.
Special attention should be paid when the partial removal of a story is along a perimeter wall. The floor plate not only carries the load of occupants within, but will also support the weight of the façade assembly and often resists wind and seismic loads perpendicular to the face of the building. Ensuring that any of the components that remain are able to resist loads both vertically and horizontally will be critical to determine the extent of floor removal near a perimeter wall.
Project Reference: Recently opened is a new amenity space at a high-rise building in downtown Boston. The project involved the removal of several bays of the fourth floor, including the interior beams, some of the beams were part of moment frames comprising the LFRS. The resulting columns became unbraced for two stories, thus reducing their capacity both for axial loads from gravity as well as flexural loads from the frame action within the LFRS. The columns were readily reinforced for their newly longer unbraced lengths, though the evaluation of the LFRS posed more challenges. The Code allows for a 10% increase in demand-to-capacity ratio of components of the LFRS; even though the project area was limited to just a portion of Level 4 of a very tall building, a finite element model of the full-building LFRS was undertaken to validate that the change in demand/capacity of the system was less than the Code threshold.
The floor removal project also happened at the corner of the building, influencing two intersecting perimeter walls. The framing at Level 4 (and a very thin strip of slab) was left in place along the perimeter, and the wide flange floor beams were converted into closed wall tube shapes to allow them to effectively support the weight of the façade as well as the wind blowing on its face.
Above and beyond the unique loading scenarios was the project sequencing, which was of critical importance near the bottom of a high-rise building. It was not safe to merely remove the portion of the fourth floor, but the column reinforcement needed to be in place and functional prior to the removal of the Level 4 slab and framing. Careful consideration was planned and documented to describe the necessary sequencing of reinforcement, demolition, and temporary loading conditions to accommodate this transformative alteration.
Check out our LinkedIn next Monday for the Scenario #5 – the final and most complicated study!
Scenario #5
Scenario: An existing 3-story building is totally damaged at Level 2 and that story needs to be rebuilt. The project is to rebuild the floor with the same types of materials, but it’s better for the building if the floor is rebuilt at a slightly higher elevation.
Bonus Questions: What if the building is occupied after the damaged floor is removed, but before the floor is rebuilt? What if it is rebuilt at the same elevation, not at a new elevation?
Response: This Scenario isn’t quite as black-and-white as some of the earlier ones. A careful reading of the Code will indicate this Scenario is an ALTERATION. While it is true that the floor is reconstructed to correct damage, that is not the sole extent of the project,
which involves relocating the floor a bit higher in the building. There is no increase in floor area nor number of stories, so it’s not an addition, thus it must be an ALTERATION.
The Bonus Scenarios get even more complicated when we introduce the concept of time. The removal of a story – as we’ve seen in prior weeks – is classified as an alteration, and that introduction of a new floor is an addition. Let’s break this discussion down: Simply removing a damaged floor is an alteration; removing and rebuilding a damaged floor is a repair. But what if the reconstruction happens over time – say the removal of the damaged floor happens and the building is occupied, and then the floor is added back at a later date? In this case, the scope of the permit will classify the work. In this situation – removal of damaged floor, occupy the building, then put in the new floor, re-occupy the building – would involve two separate permits, and thus two separate classifications: alteration and addition. Even if the final effect is the same as a repair.
This implies if the work – removal and reconstruction of a damaged floor – happens within the duration of work of a single permit, then it would be classified only once, as a repair.
Furthering this, when reconstruction of a damaged floor is at a new elevation, even if it is within the duration of work of a single permit, it remains classified as an alteration.
So, in summary:
Rebuilding a damaged floor in the same elevation: REPAIR
Removing a damaged floor: ALTERATION
Rebuilding a floor at a new elevation: ALTERATION
Rebuilding a damaged floor at a new elevation: ALTERATION
Rebuilding a floor that was previously removed (for any reason): ADDITION
The contents of the permit and when the building becomes occupiable will govern how the work will be classified, even if the final effect will be a restored floor due to damage.
Project Reference: The preservation and improvements to the former New England Confectionery Company (Necco) buildings at the corner of Necco Court and Necco Street (Formerly the General Electric Headquarters) embodies this scenario in full. The existing roof of the Necco building was damaged due to long-term neglect and water infiltration to the extent that the structural members comprising the roof were not able to reliably resist loads. To improve the building to make it occupiable, a new roof was reconstructed, but it was positioned about a foot higher to accommodate rooftop access, modern drainage and waterproofing requirements. If the original roof had been in good condition it may have been left in its original position, however its damage necessitated that it be rebuilt; reconstructing it at a new elevation meant that this scope of work was classified as an alteration.
The Necco project also had many other elements: new stories increasing the vertical height (addition), horizontal expansion (addition), voluntary seismic upgrades (alteration), historic preservation (repair and alteration), and selective strengthening of other deteriorated
members (repair) making the overall project impossible to classify only one way, but as an amalgam of several discrete classifications.
Thank you for joining us on this lengthy discussion about the IEBC and how classification of work can influence the outcomes for projects of all types within existing buildings.