Field note
What is a Demising Wall?
A demising wall is a partition that separates one tenant space from another tenant space. Why is a demising wall important? Because it usually separates adjacent properties or real estate entities from each other and establishes limits between one property and another.
Many Names for a Demising Wall
There are many different names for a demising wall. Some call them a separation wall, fire wall, party walls, divider wall, common wall, or occupancy separation walls. They can be structural or non-structural walls and can be located in almost any building type.
Residential structures such as apartment buildings, townhomes, and condos could all have demising walls. Commercial buildings such as shopping center, schools, hospitals, industrial warehouses, and office buildings could also include demising walls.
The Purpose of a Demising Wall
Typically, a demising wall is used for creating a separation between tenant spaces, but the use of a demising wall doesn’t stop there. There are many purposes for a demising wall beyond simply dividing areas.
Another primary use of a demising wall is to create separation in the event of a fire. This is the reason a demising wall is also referred to as a firewall. In construction and real estate, safety is always the first priority.
One of the most important aspects of building safety is to contain or prevent the spread of a fire if one occurs. This is where the demising wall plays a major role.
The Fire Rated Demising Wall
In the event of a fire, demising walls prevent the spread of the fire from one private space to the next. If your neighbor starts a fire in their kitchen, a demising wall prevents the spread of that fire into your unit.
In these situations, proper construction of a demising wall needs to follow strict guidelines and be built to certain specifications to assure a “fire rating” is achieved.
Architects specify the exact assembly and material for use in constructing demising walls. As they are built, typically, inspections are held to assure the architect’s specifications have been carried out during construction.
One Hour Rated Demising Wall Assemblies
There are many different one-hour-rated assemblies for demising walls. It’s the architect’s job to specify the type of wall and the material to be used for construction of the demising wall.
The blueprints are usually submitted to a city or local building jurisdiction to approve or deny the design the architect has proposed. Once approved, the construction process will be inspected to assure the approved plans and specifications have been followed and the building meets applicable laws.
One of the most common 1 Hour fire-rated interior wall, which could also be a demising wall, is shown in the detail above. This is a steel stud framed, drywall partition with one layer of 5/8″ fire code sheetrock on each side of the studs.
You might notice the description on the right column noting “UL Des U419.” This is a wall assembly approved by United Laboratories (U.L.), which has undergone extensive certification and testing to ensure the wall actually prevents fire spread for a minimum of one hour.
There are dozens of special construction assemblies, such as the one-hour-rated assemblies, including many different material combinations. Each assembly includes slightly different materials to accommodate the different conditions and building types where they are used.
All these one hour rated assemblies do have one thing in common, and that is the UL-rated designation, which means they have been rigorously tested and approved by United Laboratories.
Two Hour Rated Demising Wall Assemblies
Two-hour rated demising wall assemblies are designed with many of the same concepts as the one-hour demising wall. The main difference is their construction will assure a fire-resistance rating to withstand a standard fire resistance test for two hours instead of one.
In the two-hour rated wall assembly above, steel studs are used to frame the fire wall, then two layers of 5/8″ fire-code drywall are applied to each side. You can see the U.L. designation appears in the right column noted as “UL Des U419.” Commonly referred to as a “UL 419.”
Many Types of Demising Walls
There are so many different types of demising walls; it’s almost tough to count them all. Many demising walls are constructed out of concrete, CMU block, wood framing and drywall, and so many different combinations.
Again, it’s the architect and building designer’s job to specify the specific demising walls to satisfy the local building codes. And it’s the construction contractor’s job to assure the walls (and the rest of the building) are built exactly to the standards laid out in the plans and specs. It’s also the local building inspectors’ job to verify and confirm all instructions were carried out to the fullest extent.
The Importance of Demising Walls
Maybe you are new to the term “demising walls,” but I can guarantee this partition wall has played a major role in the safety of thousands of people over the years. For any building that has multiple occupancies and uses, the potential for fires is endless.
One of the primary objectives of the demising wall is to not only delay the spread of the fire throughout the building but to protect the building’s structural members from preventing a total collapse. Giving occupants enough time to exit the building safely is the job of the demising wall. Apartment complexes could have hundreds or even thousands of separate units, all protected by demising walls.
It’s not only demising walls that protect occupants from a fire in a building. Sprinkler systems, fire alarms, and numerous other systems all play a part in fire safety to protect people in the event of building fires. But the demising wall, when designed and constructed properly, plays a vital role in public safety.