Building components · Service Zones & Penetrations
Riser Shaft
Explains the riser as a vertical position taken through a building's fabric, distinct from the wall construction that encloses it.
Educational reference entry. What this element has to do, and whether any particular arrangement of it is adequate, depends on the whole assembly, the loading, the exposure, local requirements, the manufacturer's instructions and qualified professional design.
Overview
What a riser is
A riser shaft is a space deliberately kept clear through successive floors so that services can travel vertically. It is made by openings in each floor aligned above one another, together with an enclosure around them, and it is one of the few parts of a building where a route rather than a room determines the plan.
Its significance is that it is a continuous vertical space, and continuity between storeys is exactly what a floor is built to break. Every floor the shaft passes is interrupted, so the shaft is bounded and closed at each level by deliberate provision rather than by the floor construction it displaced.
Boundaries
How it differs from nearby elements
The distinctions that keep this entry from being a restatement of its neighbours.
- It is not a shaft wall system. That system is the wall construction enclosing a shaft, arranged so it can be built and later penetrated from the accessible side alone; the riser is the space that wall encloses, and the same space can be enclosed in other ways.
- It is not a service void system. That system is the coordinated distribution zone taken as a whole, the same entity above a ceiling, below a floor or within a riser; the riser shaft is one position in the fabric — the vertical opening carried through the floors — and it is a hole through the structure whether or not it has been coordinated as a zone.
- It is not a service chase. A chase is a recess within the thickness of a single wall for a service to be buried in and covered; a riser passes entirely through the structure from level to level and is entered rather than covered.
Terminology
Common names and aliases
These names describe the same element. The library keeps one entry per component so that a trade term or a regional name never becomes a second, thinner page.
- riser
- service riser
- vertical service shaft
Dependencies
What it depends on
What has to be right elsewhere for this element to do its job.
- Alignment of the openings through each floor, since a route that steps sideways at a level is not one shaft but a series of separate crossings.
- How the shaft is closed where it passes each floor, which is what stops the space acting as an uninterrupted vertical path.
- Whether the enclosure around it is continuous over its full height, including where it passes a ceiling void or reaches the roof.
- Access at every level, because everything placed in a riser has to be reached again after the enclosure is finished.
Considerations
Topics that genuinely apply here
Subjects worth discussing about this element. These are discussion topics, never measured values, ratings or performance claims.
A vertical space linking every level of a building is one of the conditions a fire strategy addresses most directly, and how a shaft is enclosed and interrupted at each floor is determined by qualified designers and by local requirements.
A shaft passing rooms on several levels is a path between them, and it can also carry the noise of what runs within it into the rooms it passes.
A riser is entered rather than looked into, and whether it can be entered at every level governs how much of a building's distribution can be maintained without destructive work.
A riser is formed early and filled progressively by several trades, so what it contains when it is closed is rarely what any single drawing showed.
Assemblies
Building systems this element is met in
The role this component fills inside each assembly. A role describes what the element does there — it is not a statement that this component suits that system in any particular building.
Clarifications
Commonly misunderstood
- That the riser is the wall around it. The enclosure and the space are separate things, and a building can change one without changing the other.
- That a shaft closed at the top and the bottom is closed. What matters is what happens at every floor it passes, not only at its two ends.
Conversations
Questions for qualified professionals
Questions worth asking someone with the project in front of them. This page cannot answer them.
- How is this shaft closed where it passes each floor, and what was that provision intended to achieve?
- Is the enclosure continuous over the full height, including above ceilings and where it reaches the roof?
- Where is access to the shaft provided, and does it reach every level the shaft serves?
- What record exists of what has been installed in the shaft and of the work done at each floor crossing?
Go deeper
Related Build Design Hub guides
Planning guidance behind the decisions this element involves.
Preparation
Related planning checklists
Owner-side preparation before the conversation where this element comes up.
What this entry does not do
- This entry describes a position. It states no shaft size, enclosure construction, closure arrangement, fire rating or period.
- How a vertical shaft is enclosed and interrupted is a regulated matter settled by the building's fire strategy and by qualified designers; verify against local requirements.
Service Zones & Penetrations
The voids, shafts, chases and openings left in the fabric so services can pass through it and be reached again afterwards.
Browse all service zones & penetrations entries →