As more and more states move to adopt the 2018 IBC, it's important to know about a few code updates that impact the design of occupied roof spaces. And if you're jurisdiction is on the ball and already adopted the 2021 IBC, there are a few additional items that apply to you.

In the 2015 IBC and prior editions, the code remained silent in regards to occupied roof decks and requirements for allowable height and area.  Under the 2018 IBC, there are now specific provisions addressing this issue.

First, IBC 302.1 has been updated with specific requirements for classifying an occupied roof space:

This section limits the occupancy on an occupied roof to those allowed on the story immediately below the roof. So if your building construction type allows an assembly occupancy on the top story, you are also permitted an assembly occupancy on the roof. The code does offer two major exceptions:

1. If your building if fully sprinkler-protected (NFPA or 13R) and you have fire alarm notification on the occupied roof, you are permitted to have any occupancy on the occupied roof.
2. If your building is Type I or II construction, you are permitted to have assembly occupancies on the roof of parking garages.

Take the image below for an example, a 4 story building consisting of Type IIIA construction. If the building is fully sprinkler protected in accordance with NFPA 13, a Group A-3 occupancy would per permitted on Level 4. As long as occupant notification is provided on the roof, the 2018 IBC now explicitly allows a Group A-3 occupancy on the roof.

The 2021 IBC updates Section 503.1.4 to explicitly clarify that an occupied roof should not be included when determining building height or number of stories per IBC 504. Language was also added to clarify that this only applies when penthouse and other rooftop structures, when present, comply with IBC 1511. This further supports the notion described above that an occupied roof should not by itself trigger a classification as a high-rise building.

Additionally, the 2021 IBC clarifies that the Exception 1 to 503.1.4 for occupant notification would only require a voice fire alarm system on the roof if the system is required elsewhere in the building. In other words, if you aren't required to have a voice fire alarm in the building, you don't have to provide it on the roof in order to use Exception 1.

Finally, the 2021 IBC updates Section 1511.2.2, Use Limitations for Penthouses, to specifically allow "ancillary spaces used to access elevators and stairways" to be considered part of a penthouse. This means that a stair or elevator tower to the roof will not force an occupied roof to be classified as a story, even though those elements are taller than 48" from the roof surface.

In the last year or so, there have been several fire incidents during the construction of wood-framed residential buildings. Recently, in January 2021, a fire at the Ely at Fort Apache apartment complex in Las Vegas completely destroyed the building, racking up an estimated $25-30 million in damages. Or last year, a Jacksonville, Florida grew so large that it shut down a portion of nearby Interstate 295 and forced the local fire department to deploy 45 apparatus, including 14 engines and seven ladder trucks. In both of these cases, as well as other similar fires, there were two clear similarities:

• The building construction included wood structural members (Type III, IV or V construction)
• The building sprinkler systems were not yet active

In large, wood-framed apartment buildings, the window of time between enclosure of the structure and the building sprinkler system being functional is a clear vulnerability. The presence of a huge fuel load without an active fire sprinkler systems is a dangerous situation, where a single ignition source can lead to horrific fire losses. 

According to a recent NFPA report, between 2013 and 2017, "fires in structures under construction caused an average of four civilian deaths, 49 civilian injuries, and $304 million in direct property damage annually." In the same report, it is noted that three out of every four construction fires occur in residential buildings. During the 5 year timeframe in the report, 42% of the direct property damage was caused by fires starting from electrical distribution and lighting equipment.

Fires in wood buildings are certainly not a new development, but over the last several building code cycles, various code changes have been enacted that allow for larger and more complex wood buildings. For example, in the 2015 IBC, the "podium" concept, where a wood-framed buildings can be constructed on top of a Type IA podium, allowing for an overall larger building, was expanded to allow multiple levels of Type IA construction beneath the podium. More recently, in the 2021 IBC, Type IV construction has been significantly expanded to now include three different sub-categories (Types IV-A, IV-B and IV-C), allowing for substantially taller and larger heavy timber buildings.

Without a doubt, there are numerous benefits to wood-framed construction. Reduced carbon emissions, faster construction and reduced building costs - all are positive reasons for designers to choose wood buildings. But the very nature of wood being a combustible material brings inherent risks, particularly during construction where fire protection systems are not yet in place.

While recent code changes have allowed for larger and more complex wood buildings, requirements for safeguards during construction have evolved as well. For example, in the 2021 IBC, Chapter 33 has been updated with a few notable changes:

• Updated requirements for water flow to construction sites of buildings of Type III, IV and V construction. Depending on the size of the building and the fire separation distance, the flow requirements start at 500 gpm and continue up to the full required fire flow for the building when constructed (IBC 3313).
• Updated requirements for fire watch during construction, specifically authorizing the fire code official to require a fire watch for buildings exceed 40 feet in height when the area per story exceeds 50,000 square feet (IBC 3315.1).

NFPA 241, Standard for Safeguarding Construction, Alteration, and Demolition Operations, does provide requirements that are often more stringent than IBC Chapter 33. But many jurisdictions do not adopt or enforce compliance with this standard.

Apart from the model codes, many local jurisdictions have enacted their own requirements. In addition to requirements for protection during construction, I am also seeing local requirements for pursuing phased occupancy, where building owners want to occupy a portion of a building while other areas are still under construction. For example, Fairfax County, VA publishes a standard operating procedure document for phased occupancy that institutes a variety of building and site requirements that have to be met before phased occupancy can be considered.

But even with national and local codes addressing the issue, the magnitude of these fire losses does force you to ask: Is enough being done?

What trends are you seeing in your area? Does your local building or fire department have any specific requirements for fire protection during construction or phased occupancy, particularly for wood buildings?  While I don't think there is a one size fits all solution to such a problem, I'm very interested in hearing a variety of perspectives from across the country. Please share in the comment section below!

While working in the early phases of a project, a mechanical engineer recently asked for an estimate of the required stair pressurization system fan capacity. On this particular project, I am planning to do a CONTAM analysis, but won't start that portion until later in the Design Development phase.

Since I wanted to give the mechanical engineer an estimate for sizing purposes, I put together a quick calculator to estimate the fan size. Check it out at the link below!