A demising wall is a partition that separates spaces belonging to different tenants, or private tenant areas and common areas. Demising walls often have special considerations for energy efficiency, noise pollution, and tenant safety.
Demising walls are found in apartment complexes, where the shared wall between two apartments represents a separation between areas that belong to different tenants.
Demising Wall Uses
Energy efficiency: Insulation can improve energy efficiency. Each tenant can control the temperature in his or her own space, without worrying about paying for heating or cooling of the neighboring space.
Temperature control: Insulation can also be important when a demising wall separates an unusually hot or cold area from another part of the building, such as a shared wall between a commercial kitchen and a private residence.
Fire resistance: Demising walls may need a fire rating in order to prevent fires from spreading between tenant areas. Walls and doors with fire resistance are an important part of construction to control fires in the event they break out.
Liability protection: A demising wall with a high rating between two spaces can limit liability issues. For example, if one tenant's carelessness causes a fire, the neighboring tenant's space will be safe behind a fire wall.
Rules About Demising Walls
Within a building, there may be rules about what tenants can do with the walls they share with other tenants and common areas.
- Typically, tenants cannot move the walls, as they represent the outer boundaries of their space.
- Tenants may be barred from installing certain kinds of items on or near the wall, as a courtesy to fellow tenants.
- The lease agreement will provide information about any restrictions on property use so tenants know what is allowable.
Evaluating a Demising Wall
In a building inspection, the inspector can evaluate the demising walls in a building to make sure they meet code requirements. Sometimes internal rearrangement may create a new separating wall where one was not present before.
In this situation, it is important to check the code requirements before finishing the wall, in case it is necessary to take any special measures to meet the code. If the wall does not conform, the inspector may cite the structure's owner, and he or she will have to fix it before the building will be approved for use.
Is a Demising Wall Load Bearing?
Demising walls should not be load-bearing. As a firewall, a demising wall should be free-standing to prevent it from succumbing when the surrounding structure is damaged or destroyed. As the last line of defense in the case of fire, a demising wall needs to remain intact to contain the flames even after other structures have been destroyed.
To make sure that a demising wall in a building is not load-bearing, owners or construction personnel can get the blueprints of the original building from the local public records office. Alternatively, a simpler method of telling if a wall is load-bearing is to go to either the attic or the basement and determine if the wall in question runs parallel or perpendicular to the support joists. Walls that run parallel to the joists are not able to offer any support to the structure and can be determined to be non-bearing walls. Walls that run perpendicular to the joists have likely been put in place to support the structure and cannot be removed without degrading the stability of the building.
How To Build a Demising Wall
When building a demising wall, it is essential that the contractors know and comprehend the local building and fire codes. Beyond the common construction knowledge needed to build structural walls, those building a demising wall must meet many other requirements:
- The walls should run between two exterior walls, between an exterior wall and another firewall, or between two other firewalls. This preserves the wall's purpose of containing a fire.
- The walls cannot be load bearing so they can remain in place and sound even should the surrounding structure collapse.
- The walls must be constructed of fire retardant materials that meet the minimal fire rating for the type of structure being built. The most common material used today is X gypsum wallboard, a type of fire-resistant drywall.
- Walls should be joined with expansion joints that are resistant to distorting in the presence of high heat, protecting the stability of the wall in case of fire.
Are Demising Walls Fire Rated?
Although building codes can vary from state to state, in general, demising walls within a structure do have to meet the same fire codes as the rest of the structure. Many property owners treat demising walls with additional fire retardants to increase the fire resistance of a demising wall beyond the minimum requirements.
In many older tenant buildings, it is common to find structures called 1-hour firewalls. This rating indicates that the demising wall is rated to be able to resist full combustion for a full hour before the fire spreads from one residence to the next. The thought behind these walls was that an hour was a reasonable time to expect the fire to be detected and for other residents to be moved to safety by emergency personnel. Other structures, including some commercial and industrial buildings, may be subject to stricter code requirements and may have firewalls rated as high as 4 hours.
What If a Demising Wall Is Damaged?
Owners and residents living in a structure with a demising wall must understand that any damage to a demising wall can degrade the effectiveness of its fire-retardant purpose. Damage that results in even a small area of the wall losing its fire rating negates the fire rating of the entire wall and puts residents on either side of the wall at risk. Owners must do more than simply complete a patch repair that may be effective on another wall. Building and fire codes require that a demising wall be repaired in specific ways that reinstate the wall's fire rating and with materials that match the fire rating of the original wall.
Repairing a Demising Wall
Depending on the extent of the damage, it may be necessary to replace an entire panel of drywall to repair it. This panel should be an exact match for the original materials and should have the same fire rating. A panel that offers less or more fire resistance than the remaining wall creates a fractured barrier that will not be as effective against flames.
If the damage is minimal, it may be possible to repair it with a patch. The patch must be made of the same material as the rest of the wall and share its fire rating. Additionally, there are stringent requirements as to how the patch is held in place. It is not sufficient to use joint compound and tape alone. Patches generally need to be attached to a steel backing and secured to the studs.
Demising Wall vs Partition Wall
The terms 'demising wall' and 'partition wall' are often used interchangeably, but they are not the same thing. They do have many similarities, however. Both of these types of walls are used to separate one area of a structure from another, but the types of spaces they are used in and the building codes for each are very different.
A partition wall is used to separate one room or space from another within an individual unit; for example, the wall between a living room and a bedroom is a partition wall. Conversely, a demising wall separates one entire unit from the next; for instance, the wall between one apartment and its neighbor in a multi-unit building is a demising wall.
A demising wall should never be load-bearing, as it must remain standing even when the surrounding structure fails. Partition walls, however, can be either bearing or non-bearing walls. Partitions can also be hanging walls or temporary structures with little to no attachment to the rest of the building.
The codes that dictate the construction of demising walls are strict because these walls also serve as firewalls. Partition walls are held to the same codes as the rest of the internal structure and will have considerably fewer requirements for fire ratings and insulation.
A demising wall is a firewall. It is critical to the safety of a structure. Along with separating one unit from the next, its purpose is to protect the occupants on one side of the wall from a fire that occurs on the other side. A demising wall may also be heavily insulated to provide a sound barrier between units or to contain significant temperature differences between one unit and the next.
A partition wall has little structural significance unless it is a bearing wall. Its sole purpose is to separate two spaces. When homeowners want to open up a space, the walls they remove are usually non-bearing partition walls. A load-bearing partition can be removed as well but it will require the placement of support beams and posts to avoid de-stabilizing the structure. These walls can also be added to a space easily with basic framing.
Partition Walls Can Be Purely Aesthetic
Partition walls are a convenient and cost-effective way to add to the design of a space. Because they are not governed by strict building codes and are not essential to the safety of a structure, builders and homeowners have many options when adding partition walls to a space:
- They can be constructed out of a variety of materials like brick, glass blocks, wood or metal.
- They can be opaque or transparent depending on privacy requirements.
- They can be fixed walls that help segment and organize space by use.
- They can be free-standing, such as the wall dividers that are often used in an office space.
- They can be transitional, as in the instance of sliding accordion walls.
Can You Have an Opening in a Demising Wall?
Any opening in a demising wall will degrade its fire rating. Not only should there be no opening in a demising wall, even small openings where it buts up against other walls or joists should be sealed. This includes the placement of a fire door since the opening would compromise the rating of the wall. Even the best fire doors only have ratings of 60 minutes which is a significantly lower fire rating than many demising walls.
There are situations in which a demising wall can be opened up, but only when the purpose of the wall is no longer related to safety. In the instance that two spaces separated by a demising wall are integrated, meaning that a firewall is no longer required between units, it may be permissible to put an opening in the wall. For example, if a 4-unit apartment complex is purchased with the intention to make it into a single-unit living space, the owner may be able to get a permit to alter or even remove demising walls.
Likewise, the owner of a warehouse space who is expanding into an adjoining space may find that a demising wall is no longer necessary. In this case, the owner may be allowed to add openings to an existing wall. In industrial situations when a demising wall is no longer necessary, replacement with structures such as an industrial tall wall may be sufficient.
In either situation, owners should be aware that changes in demising walls such as those listed above may also require other complex changes such as zoning assignments and electrical service designations.