Last Updated on May 1, 2023 by Barry Gray
You only need to look up pictures of Westminster Abbey in London, England, built-in 1355, to see the effect a vaulted ceiling has on a construction. Although on a smaller scale, including a vaulted ceiling in your new home’s design adds space, character, and individualism to a home.
The trusses needed to create the space for a vaulted ceiling need to be installed on a structural component (wall). While the truss is designed to contain the lateral and vertical loads the roof imposes on it, you may need to reinforce the foundations and walls depending on the truss’s complexity.
Vaulted ceilings increase the physical size of a room, and while they will increase the cost of heating a home, a well-designed and built ceiling certainly adds to the character of a residential home.
Vaulted Ceilings Need Load Bearing Walls
A “truss” is formed when structural members are joined together in triangular configurations.
The purpose of a truss is to act as a self-contained structure that contains the vertical and lateral loads of a roof structure within its design, with the only load transferred to the walls being the vertical weight of the roof.
The trusses used to create a vaulted ceiling space are designed to carry the load imposed by the roof across the area below.
In a regular home, the one truss would extend over the whole width of the room, with no supporting elements (walls, girders) being required in the middle of the room.
The base angles (the two bottom edges) must be attached to a load-bearing wall as these are the only parts of the truss that attach the roof to the house structure.
As with all roofs, the trusses used to create the space for a vaulted ceiling must be attached to a load-carrying wall.
The purpose of trusses is to carry the lateral and vertical loads within the truss structure. They only need a strong enough wall to be installed on. The exception is a complex hammer-beam truss that cannot contain the lateral load, so it transfers some of these to the load-bearing wall.
Depending on the type of truss, from the simplest (Scissor Truss), through to the most complex (Hammer Beam Truss), the design of the walls will need to be carefully engineered by the architectural team.
How Do Vaulted Ceiling Trusses Work?
The function of the truss is twofold.
- To contain any lateral loads (sideways instead of vertical) within the structure.
- To ensure that the vertical loads are spread evenly by the truss structure.
A simple King post trust is shaped like a triangle where the apex is the top of the roof, and the two base angles lie on the structural walls, while a base joins the two base angles.
A vertical member is connected to the apex and the center of the bottom chord (base).
Two additional pieces (the top chords) connect the middle of the bottom chord to the center of both sides, leading to the apex.
This design has many variations; however, the intent is to balance the vertical loads evenly across the structure.
A vaulted ceiling requires a truss with the base and the vertical member removed or modified. It is a structurally inefficient design. Architects choose them because they allow space to be created under the roof, which develops an open feeling of a stretch.
If the bottom chord and vertical member are not replaced by another load-carrying design, the force of the roof’s weight, pressing down on the two remaining components, would spread laterally, collapse the roof, and possibly damage the load-bearing wall structure.
To compensate for this change in design, engineers use one of three truss shapes that allow for vaulted ceilings.
- Scissor Truss
- Cathedral truss
- Hammer Beam Truss
Scissor Trusses
A scissor truss has the single bottom chord removed and replaced by two new bottom chords which angle up from the base angles to the middle of the opposite top chord.
A further element is added called the king, a structural piece joining the apex to the point where the two new “bottom chord” pieces cross over.
The point where the king truss meets the two bottom chords is called the apex and is the point where all of the loads are transmitted to the other members of the truss.
Without the vertical load-bearing king piece, the scissor trusses will fail laterally when the roof load is applied, spread outwards, and collapse.
The engineers will also consider whether the scissor roof truss is a fixed connection to the walls or whether some lateral movement is allowed. If it is fixed, it will place lateral loads in the walls, which may weaken them unless they have been designed to manage this.
Cathedral Truss
A cathedral truss is a non-standard truss used mainly in residential homes to achieve a vaulted ceiling effect.
Like a scissor truss, a cathedral truss has the bottom chord removed and replaced with two horizontal members, each about 25% as long as the room’s width.
The remaining 50% length becomes the vaulted ceiling.
The ends of the two new bottom chords are joined to the apex of the roof by a load-bearing unit (girder trusses).
The bottom chords and the two girder trusses are connected to the top chord (outer lengths of the triangle) by a series of girders. These girders spread the lateral and vertical loads within the truss structure.
Hammer Beam Truss
Hammer beam trusses offer the most significant space for vaulted ceilings; however, they also impose the highest lateral loads on the load-bearing walls.
A hammer beam truss is the most complex of the trusses and one of the most structurally inefficient.
An example of a hammer-beam truss is seen here.
Hammer beam truss requires exceptionally strong bracing, and they should never be placed on exterior walls which experience high wind speeds.
Can You Install A Vaulted Ceiling In An Existing House?
Anything is possible; however, if a home uses conventional King post or queen-post trusses designed to carry a load of a traditional roof, without any space for a raised ceiling, the cost of redesigning the roof will be very high.
The structural engineers calculated the loads the trusses and walls could carry when designing the home.
Changing the truss design to allow for a vaulted ceiling will require removing and replacing every truss.
In addition, if a more complex truss design is chosen, the wall and the wall’s foundations themselves may need to be reinforced.
Conclusion
The trusses used to create the space for vaulted ceilings need to be installed on structural walls. The function of trusses is that they carry the loads over vast areas and do not require any inside walls, beams, or poles to support the structure.
Vaulted ceilings add a whole new sense of space and increase the apparent size of any room. If the structure is new, you should ask your architect to consider including a vaulted ceiling; however, it probably does not make economic sense to install one if you are in an existing home.
