In a building-permit application, the architect’s construction drawings must include a codes review section (best on or near the cover sheet) that proves to the local authorities having jurisdiction (AHJs) that the building’s design meets the locally adopted codes. Two predominant codes govern the basic construction requirements of the building’s shell (comprising the roof, exterior walls, structure and floor plates) and/or the interior tenant improvements (circulation and egress paths, rooms and spaces, finishes, fixtures, and equipment). They are the locally adopted codes for building construction—for example, the 2015 International Building Code (IBC)—and fire and life safety—for example, the National Fire Protection Agency’s 2015 NFPA 101 Life Safety code. Both appear in this series as the guiding references.
An important building designation is its “construction type,” which is determined by the parameters and requirements in the IBC’s tables and tenets for all of the building’s proposed architectural components. These components include the building’s volume (of maximum height, stories and area), its minimum distance to property lines (or to adjacent buildings on the same site), whether it will be fully sprinklered (with an automatic system through the entire building), its maximum percentage of unrated exterior-wall openings, the types of combustible materials allowed and the fire-ratings of the major “building elements” (being primary structural frame, exterior and interior bearing walls, exterior and interior nonbearing walls, floor construction, and roof construction).
Buildings come in one of five construction-type categories: Types 1 and 2 are for noncombustible construction; Type 3 requires noncombustible exterior walls but allows interior building elements to be any material permitted in the code; Type 4 is heavy timber, which requires noncombustible exterior walls but allows interior building elements to be heavy timber; and Type 5 allows any material permitted in the code. But Construction Type is less a selection and more a product of several factors.
Determining Construction Type
The several factors that go into determining a building’s construction type are (1) use and occupancy classification, (2) heights and areas, (3) fire resistance and (4) fire suppression. Following the requirements listed in a project owner’s development program (which includes desired budget, building SF, number of stories and quantity of server racks) that’s been developed in accordance with the parameters from the owner’s selected site (area, configuration, easements, etc.) will answer the questions created by the several factors. Subsequently, these answers set the building’s construction type. So, usually without them realizing it, ownership ultimately establishes what Construction Type the project will require.
1. Use and Occupancy Classification
First in determining construction type, one must start with the use and occupancy classification proposed for the project (also known as the “use group”). Although the NFPA defines their use groups in 20 separate chapters, the IBC classifies all buildings into 1 or more of 10 different use groups: assembly, business, education, factory, high-hazard, institutional, mercantile, residential, storage or utility/miscellaneous. Data centers typically fall into dual group designations (called “mixed use”) of storage and business, with high-hazard occasionally being added. Below are descriptions of these three classifications.
- Storage Group S is for “storage that is not classified as (high) hazardous occupancy.” Data centers are in Group S owing to the equipment stored in their server rooms, electric rooms, air-handler rooms and battery rooms, all of which obviously constitutes most of the facility’s total square footage. Storage is divided into two subcategories: Group S-1 for moderate hazard and S-2 for low hazard. Data centers most often employ UPS batteries with sealed lead-acid, and in my experience, the AHJ is the entity that decides whether the batteries are moderate or low hazard (S-1 or S-2). The IBC, however, automatically bumps the UPS batteries to high-hazard (Use Group H) if they fail to meet certain guidelines, two of which are safety venting caps (which safely pressure releases the off-gassing from the batteries’ acid) and mechanically expelled off-gassing, thereby preventing explosions and asphyxiation.
- Business Group B in data centers is due to the presence of offices and conference rooms—provided that all areas used for assembly total under 50 persons and no individual assembly space (such as a conference room, lunch room or meeting hall) is over 750 sf.
- High-Hazard Group H is divided into five categories, H-1 through H-5, with H-1’s explosives designation being the most dangerous and H-5’s semiconductor fabrication being the least dangerous. Avoiding a high-hazard designation in a data center is important owing to many additional requirements (increased fire-resistance ratings, decreased length of egress travel, decreased allowable height and area, requirement to sprinkler, etc.) and because for new construction, it’s easy to avoid. The two things that can trigger a Use Group H designation in data centers are fuel-fired generators and standard UPS batteries. Thus, care is necessary to ensure that the potentially explosive fuel tanks of generators reside outside the building shell (at least five feet away) and that all of its UPS batteries meet High-Hazard Use Group’s Exception #9 (being stationary, equipped with safety venting caps, having aggregate hazardous materials not exceeding the quantities set in IBC’s Table 307.1, and set in battery rooms with proper mechanical ventilation).
2. Heights and Areas
Next, in determining construction type is defining the project’s proposed height, stories and area. These parameters are a product of both the owner’s program requirements (mostly based on the square footage needed to house, energize and cool the server racks, whose quantity depends on past or comparable projects) and the parameters accompanying the project site (where a small site or one with onerous easements could force additional stories).
The maximum height, stories and area allowed in each of the five construction-type categories (noncombustible down to combustible) are separately defined in 2015 IBC’s Tables 504.3, 504.4 and 506.2, which logically assign the most-restrictive limits to the most-combustible construction (Type 5B Unprotected) and the least restrictive for the least combustible (Type 1A Protected).
3. Fire Resistance
IBC’s Table 601 defines the fire-resistance ratings for each major building element (structure, bearing walls, etc.) allowed in each of the five construction-type categories. This table logically requires higher fire-resistive ratings for larger and taller buildings as well as lower ratings for smaller ones. For example, Type 1A construction requires most of the major building elements to be three- or two-hour rated, whereas Type 2B allows them all to be zero hour. Note that each of the five construction types is subdivided into “A” and “B” categories, with “A” being “protected” (protecting the structural members from exposure to fire by spray-on fireproofing or by other means, or through concrete construction) and “B” being “unprotected.”
IBC’s Table 602 defines the minimum fire-resistance ratings required by various fire-separation distances, which are the perpendicular distances from the building’s exterior walls to the nearest part of the property line or to the nearest building on the same lot. This table is meant to limit the spread of fire by sensibly assigning the most-restrictive fire-resistance ratings to the smallest fire-separation distances (from 0 inches to 5 feet away) and the least-restrictive ratings for fire-separation distances that are 30 feet or more.
4. Fire Suppression
The last consideration in determining construction type is to establish whether the building will be fully fire sprinklered or not. For Use Group S-1, buildings that have fire areas exceeding 12,000 square feet on a single floor or 24,000 square feet combined on all floors, along with those located more than three stories above the grade plane, fully sprinklered is a requirement. But if the building is Group S-2 and isn’t being claimed as an “unlimited area” building, or it’s a single story surrounded by open space (yards at least 60 feet wide) that is being designed as an “unlimited area” building, then the decision to sprinkler or not is usually up to the project owner. Although the fire marshals encourage the use of fire sprinklers and increased openness to and around the buildings for firetruck access, the IBC rewards these things and does so by typically allowing increases in the height, area and stories limitations (as defined in Tables 504.3, 504.4 and 506.2).
So, most data center owners elect to have their buildings fully sprinklered, since not only does it help protect their invaluable data and large financial investment, but it also allows for a larger floor plate, additional building height and additional stories. The result is room for more income-producing data servers.
As noted above, defining use-group classification, allowable heights and areas, fire resistance and fire suppression (per the code’s narrative and tables) will set the building’s required construction type. But keep in mind that the best two rules are to (1) fully sprinkler and (2) always set the construction type in the permit at its lowest allowed designation, then build with materials that will accommodate construction speed and desired aesthetics—even if it’s built with materials used in a higher construction type. Doing so will be safer for the occupants and will help protect the data and investments. It may also reduce insurance rates, get the project online sooner and increase return on investment.
Leading article image courtesy of DVA Architects
About the Author
Dean Ventola, RA, NCARB, LEED AP BD+C, is the Director of Construction Administration at DVA Architects in Gaithersburg, MD, a nationally prominent mission-critical data center architect.