By: Sarah Swan
WHY A NEW LUXURY ROOFTOP GARDEN MAY ACTUALLY LEAVE YOU CROSS
Solar panels. Lithium-ion battery energy storage. Exterior cladding. Rooftop gardens.
What do these seemingly diverse items all have in common?
They have all been identified as important pillars in the race to be more eco-friendly with the impact to the fire safety of users and first responders lagging behind their adoption.
You may be familiar with the hazards of the first three items. Solar panels cannot be disconnected, leading to issues during fire-fighting operations. Lithium-ion battery fires are a fairly regular presence in the news. And everyone watched the exterior cladding on Grenfel Tower in London burn.
Does my inclusion of rooftop gardens in that list seem out of place to you? I wouldn’t be surprised if it did. Many people were surprised by a proposed change for the 2024 International Building Code which would require the height of an occupiable roof (if provided) to be considered when determining whether the building is a high rise structure or not.
The argument I heard most often stating that this should not be the case was that the occupants on the roof are outdoors, and therefore are not exposed to the heat and products of combustion during a fire as occupants inside the building envelope are. Therefore, there wasn’t an increased risk for the people on the roof if the roof was more than 75 feet above the fire department access as there is for those inside the building envelope at that height.
I disagree. I’m happy to say that the Code Council disagreed as well.
And so, in the 2024 IBC, a high-rise will be a building where either an occupied floor or an occupied roof is located more than 75 feet above the level of fire department access.
This change doesn’t mean much for those who own or design low rise buildings. And building that were already intended to be high-rise buildings won’t be impacted either. But those who own mid-rise buildings? Including a rooftop area for tenants to use could force the entire building to comply with high-rise rules.
What Makes High-rises Special?
High-rise buildings historically have stricter rules when it comes to fire and life safety requirements than other buildings. This is because there is significant physical effort associated with both occupants exiting the building and the fire department accessing the fire floor.
The typical fire truck ladder is approximately 100 feet. Allowing for the building to be set back from the street and potential obstructions to use of the ladder such as parked cars or overhead wires, the generally agreed upon effective length of use for these ladder trucks is 75 feet. Once a building is taller than that, ground-based fire-fighting operations will not be sufficient for either fighting the fire or rescuing occupants. Why? Stairs, water pressure, and communications.
Stairs represent a major choke point in a high-rise building, especially during a fire. The stairs are needed for people to exit the building and for the fire department to both fight the fire and rescue occupants. And since the stairs represent a mostly unusable and unleasable area, they are typically as narrow as possible. This limits the ability of faster people to pass slower people, particularly if the fire department is also using the stairs for their operations. If traffic in the stair slows too much, doors into the stairwell will be held open during exiting activities. This allows smoke and heat to enter the stair, opening up a pathway for the fire and its effects to spread throughout the building.
Water is pretty heavy stuff. It takes 4.33 psi of pressure to lift water 10 feet. When a building is 75 ft tall, that’s a minimum of over 30 psi that is needed to get the water to the top of the building. Add in other sources of friction loss such as air resistance or the interior of the fire hose, and there can be significant pressures associated with getting water up near the seat of the fire. Since a conventional fire hose nozzle requires 100 psi of pressure to operate, and fire pump trucks can be rated for as little as 120 psi, these tall buildings can easily require more pressure than is available to effectively fight the fire.
Fire fighters use radio signals on the fire ground for a variety of purposes – to coordinate attack strategies, to notify others of changing conditions, to call for help, etc. But radios, like cell phones, work best when there is a clear line-of-sight between the antenna and the radio/phone. The more that comes between these two items, the more the signal gets distorted. Radio is particularly susceptible to metal interference. Unfortunately, high-rises are full of metal. There are steel structural elements, metal pipes, metal conduit, metal HVAC equipment, etc. So it can be quite easy for radios to be ineffective when used in a high-rise. When the radio can literally make the difference between life and death, this is not an acceptable situation.
Because of these and other challenges, it was decided that high-rises required special attention. So the International Building Code has an entire section dedicated to the protection of high-rise buildings. From mandatory automatic sprinkler systems and standpipe systems to smoke removal systems; from remote stairs to emergency fire fighter communication systems, the requirements in this section are focused on three things – provide a safe path for people to escape the fire affected floors, reduce the reliance on ground-based fire fighting equipment, and improve fire fighter safety.
Why is this a problem for mid-rise buildings
Let’s consider a mid-rise office building. While the building is 80 feet tall when measured from the ground to the roof line, the highest occupied floor is only located at 70 feet above the ground. Therefore, this building is not currently a high-rise building.
The building owner is looking to do some remodeling in order to entice new tenants and existing tenants to sign leases. With the increased push for remote work, the building owner has decided that additional benefits are required to sweeten the deal. When consulting with you, his architect, for suggestions for the remodel, your attention turns to the roof. This is a large, unused space, perfect for a vegetative roof to get some extra LEED points. But it can be so more than that.
Put in a patio with tables and umbrellas where people can eat lunch. String up some lights so the space can be used after dark. This could even be an event space that could be rented out at night for office functions! The owner is excited for this new benefit to offer to existing tenants during lease renewal and to offer to potential new tenants – for a premium rent of course.
The plans are drawn up. Everything seems to be moving along. The owner has even gotten some early signatures on lease renewals based on the plans for this perk.
But then, during permitting, disaster strikes.
For years the definition of a high-rise had been the same – A building with an occupied floor located more than 75 feet above the lowest level of fire department vehicle access. Since the definition of floor area is based on the area enclosed within the perimeter of exterior walls, your understanding was that this did not pertain to the roof. But the building code official has different ideas. The official is of the opinion that a floor is also defined as a walking surface. And since the roof is now planned to be occupied and can be walked on, it becomes the highest occupied floor. Since it is more than 75 feet above the ground, this means that the building would now be considered a high-rise.
You try to argue this point with the code official, but it is in vain. The official points to the new definition of high-rise in the 2024 International Building Code as proof that their interpretation is correct and the previously understood interpretation is no longer valid.
So you put together a breakdown of the rules for both the project-specific mid-rise and for high-rises, along with an evaluation of how the differences apply to the project. The results are eye opening.
The building owner and architect are now left with two choices – give up the rooftop garden or increase the cost and scope of the project to address the high-rise rules that are now applicable. Since leases were already signed with the promise of this new amenity, the owner is stuck between an expensive rock and a costly hard place.
The last thing we in the AEC community want is to have surprise costs appear late in the project. These surprises either lead to expensive redesigns (which often cannot be charged to the client) and pricey change orders from the installing contractors (which upset the “blindsided” owners). Surprise costs have never resulted in anything on a project other than annoyance and frustration for all involved.
I’ve experienced for myself how clients react when we have to inform them that their building which met code when the building was designed is now under protected due to changes in a standard resulting in the need for a costly retrofit. Retrofitting to accommodate the new definition is exceedingly costly and often exceptionally difficult. The earlier they are able to plan for this eventuality, the better for everyone involved.
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