Traditional Cantilever or Steel Stringer Staircases

As you may have seen on our projects page we have an entire section dedicated to our Traditional Cantilever and Steel Stringer Staircases, and we often get asked what the difference is between the two. The purpose of this blog is to try and explain the similarities and differences between these installation methods. 

At The Stonemasonry Company Limited we often find that the main reason our clients have for including a cantilever Stone Staircase in their design scheme is that this style of staircase creates the amazing illusion of weightlessness, whilst adding a sense of luxury and grandeur to a property. 

On occasion the design considerations required to accommodate a stone staircase are left until much later on in the project process, however, when considered early enough, and effectively designed, a traditional cantilever stone staircase can make a huge impact on the internal design of a home, making these beautiful feature staircases the basis upon which the remaining interior design scheme can be based.

Although these staircases appear to defy gravity they are, of course, supported. However they are designed and engineered in such a way that conceals the true fixing method. The fixing method itself will be dependent upon a number of factors and as each and every one of our projects is completely individual the implementation and design can vary considerably.  

Our traditional cantilever staircases rely on the stair treads being fixed into a solid wall. Often all that is required to do this is a block or brick wall for the steps to bear into, by as little as 100mm in some cases. The process is relatively straightforward, with pockets being created within the existing brickwork, into which the steps are then inserted. These are finally packed tightly into place using engineering bricks. A great example of a finished traditional cantilever staircase would be Chester Terrace (https://www.thestonemasonrycompany.co.uk/chester-terrace), a beautiful, four-flight staircase, manufactured in Portland stone.

However if a structure does not have the capability to support a traditional cantilever stone staircase then we would look at the possibility of introducing a steel stringer. Some examples of structures that might require this solution would be modern buildings, which often have stud walls, or certain listed buildings have strict control measures governing what changes can be made to a building's interior and exterior, in this instance a steel stringer can be used to ensure minimal impact to the main structure of the building. 

The extent of the limitations of the existing structure will dictate the amount of steel work needed to support the staircase design. The method of fixing the steps remains largely the same however instead of being inserted into masonry walls the steps are supported by the stringer, and clamped into place with steel plates that are bolted to the main frame. The end result can be seen in our work at Old Alresford (https://www.thestonemasonrycompany.co.uk/old-alresford) this staircase is supported by a full steel cage, which was bolted to the existing structure. 

With both fixing methods thestaircases would operate in the same way, with each step relying on one another. A typical stone tread will feature a rebate, with the back edge of the step carrying the weight of the step above it and the front edge being supported by the step below. With the vertical face of the rebate (or the crosset) being perpendicular to the soffit, there is a reduction in any counter-clockwise movement between steps. The crosset allows for the weight of the adjoining steps, and the torsion from the wall or stringer, to be distributed more evenly along the length of the tread, resulting in a balance between the opposing forces.

The bottom tread, however, would differ in both appearance and connection type. It is anchored into the floor (or a pad stone), to prevent any forward movement occurring, this is the starting point of the flight. The bottom tread (also known as the curtail step) is slightly larger in its footprint; this plays a huge role not only in carrying the weight of the staircase, but as a starting point for the handrail.

To avoid the steps sliding, the staircase must be secured; this is done when the final tread is put in place, with the structural design of the building determining how the flight is connected. In some cases a custom connection is required to create the solid backing needed to lock the steps into position. The top tread is almost the same as all other treads, apart from the back of the step which is made flat, this allows for a solid connection between the structural slab, and a smooth transition between other floor finishes. 

There are, however, certain additional design considerations that have to be made when incorporating a steel stringer. For instance the stringer naturally reduces the amount of workable void space as the steel is projected from the existing wall line. In addition when installing into exposed steel the process of hiding the extra support work becomes more complicated and wall finishes need to be adapted to accommodate the extra space taken up by the steelwork. Finally, the design time required also increases due to the fact that our team not only design the staircase but the support work as well, which needs to be carefully analyzed by our engineering partners to ensure that the structural elements are manufactured to the correct specification.

We hope you have found this brief article informative, but if you have any questions about the methods behind our work, or if you have a project in mind that you would like to discuss please do not hesitate to get in touch, our expert design team are always happy to help.