Building components · Service Zones & Penetrations
Service Penetration
Explains the penetration as a position in the fabric, distinct from the sealing assembly that is applied to close 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 penetration is
A service penetration is the point at which something passes through a building element rather than around it. The element it crosses was built to be continuous: it may carry structure, and it may be relied on to resist the passage of air, moisture, sound, smoke or heat, or several of those at once. The penetration is the place where that continuity stops.
It matters because the crossing is a position rather than an event. Every layer interrupted there has to be brought back together around whatever passes through, and each layer is returned by a different means. Naming the position keeps all of those requirements attached to one place, instead of leaving them to be handled separately by whoever arrives next.
Boundaries
How it differs from nearby elements
The distinctions that keep this entry from being a restatement of its neighbours.
- It is not an envelope penetration sealing system. That system is the assembly of sleeve, seal, collar and plane-by-plane return applied at the crossing; the penetration is the position being closed, and it exists whether or not anything has yet been done about it.
- It is not a builders work opening. A builders work opening is formed in advance of the service and is commonly larger than whatever eventually occupies it; a penetration is the crossing itself, described by the service that makes it, and some builders work openings never become one.
- It is not a pipe sleeve. A sleeve is one thing that may be built into a crossing so a pipe is not bonded to the structure; many crossings carry no sleeve at all, and a sleeve on its own has closed nothing.
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.
- penetration
- pipe penetration
- cable penetration
Dependencies
What it depends on
What has to be right elsewhere for this element to do its job.
- What the element it crosses is actually relied on to do, since structural, air, moisture, acoustic and fire continuity are separate properties and a single crossing may interrupt several of them.
- Whether the crossing was planned before the element was built or cut into it afterwards, which is a distinction owned by the opening it was formed in, and which shows in the material around the service rather than in the service itself.
- What passes through it, since the movement, temperature and surface of the crossing element govern how the interrupted layers can be returned to it.
- Whether the position stays reachable once construction is complete, because what is done at a crossing is concealed almost immediately afterwards.
Considerations
Topics that genuinely apply here
Subjects worth discussing about this element. These are discussion topics, never measured values, ratings or performance claims.
A crossing through an external element is a path for liquid water and for vapour in both directions, and the control layers interrupted there have to be returned to the service rather than simply stopped at the edge of the hole.
Where the element crossed is one the building's fire strategy relies on, what is required at the crossing is a regulated determination made by qualified professionals against tested arrangements, and nothing here states what it is.
A separating element with an unsealed crossing has a direct air path through it, and an air path carries sound far more readily than the element's own mass resists it.
The gap around a service is the product of how the opening was formed and how the service was set out, so it is variable rather than nominal, and whatever closes it has to cope with what is actually there.
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 sealing the visible face closes the penetration. An element commonly has several layers through its thickness, and closing the one face you can see does not return the ones you cannot.
- That a small crossing is a small problem. The consequence follows from what the element was relied on to do, not from the size of the thing passing through it.
Conversations
Questions for qualified professionals
Questions worth asking someone with the project in front of them. This page cannot answer them.
- What is this element relied on to do — structurally, and for air, moisture, sound and fire — and which of those does the crossing interrupt?
- Was this opening formed in advance or cut later, and was the element's designer consulted before it was cut?
- How is each interrupted layer returned to the service, and who is responsible for each of them?
- What record will exist of what was done at this crossing once it is concealed?
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 opening size, clearance, seal type, fire rating or period, and none can be inferred from it.
- Forming or altering a crossing through a structural or fire-separating element is design work for qualified professionals; 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 →