Building envelope · Junctions & Terminations
Envelope Penetration Sealing System
Describes a penetration as a repeatable assembly of sleeve, seal, plane-by-plane return and replacement strategy rather than as an act of filling a hole, and marks regulated fire-resisting sealing as sitting outside this reference.
Educational reference entry. How this system behaves depends on climate, jurisdiction, loading, substrate, the adjacent systems it meets, how the building is used, the manufacturer's instructions and qualified professional design.
Overview
What penetration sealing is
Every service entering or leaving a building makes a hole in something that was continuous. A flue passing through a roof interrupts the covering, the insulation, the vapour control layer and the deck in one movement, and each of those interruptions is a distinct problem with a distinct remedy. What this system does is put each plane back, separately.
The assembly exists rather than a repair because the penetrating element will not hold still. Pipes lengthen and shorten with what they carry, ducts pass on vibration from plant, cable bundles are pulled and rerouted, and structural members deflect under load. A seal formed against a moving object either moves with it or is progressively defeated by it, and a rigid smear of sealant is a temporary illusion.
The nearest neighbouring entry is the rooflight kerb and upstand system, and the pair are separated by asking what the opening was made for. A penetration weathers something that passes through and keeps working afterwards, still carrying water, air or current. A kerb trims the structure to form an aperture that a manufactured unit will later sit on. The observable test is whether the opening was cut for a service or built as a hole in the structure.
Fire-resisting penetration sealing is a regulated determination made against tested systems by qualified professionals. It is named here only so that a reader knows it exists and is a separate subject; no rating, class, product or arrangement for it is given anywhere in this reference. Roof, wall and floor penetrations are gathered on this page, with the roof-specific concerns of falls, ponding and proximity to outlets treated as part of it.
Terminology
Common names and aliases
These names describe the same assembly. The encyclopedia keeps one entry per system so that a trade term or a regional name never becomes a second, thinner page.
- service penetration seal
- pipe and cable seal
- penetration collar assembly
- roof service penetration
- pipe and vent weathering
- roof collar and upstand detail
Purpose
What this system is intended to do
The job the assembly exists to perform, conceptually. An intention is not a guarantee that any particular build achieves it.
- Return each interrupted control plane individually, rather than treating a perforation as a single hole to be filled once.
- Hold a seal against an element that moves, vibrates and changes temperature while the building is in use.
- Keep water arriving at the perforation moving away from it rather than collecting against it.
- Allow the penetrating element to be altered or replaced later without destroying the planes that were returned around it.
Composition
The roles this system is made of
What each part does in the assembly and what it depends on — never a product, a thickness, a fixing or a determination that anything is adequate for the role.
This system is itself the junction between two others, so there is no build-up to read. The roles below are the conditions that have to be resolved where those systems meet, and no order is implied between them.
- Service zonePenetrating element
The pipe, duct, conduit, cable bundle, fixing or structural member that passes through. Its girth matters least; what governs the detail is how much it moves, how hot or cold it runs in service and how likely it is to be replaced within the life of the envelope.
- ProtectionSleeve or former
A collar cast, framed or fitted into the opening so that the hole has a defined edge belonging to the building rather than a ragged one belonging to nobody. It gives every later bond a fixed, known surface on the structure side of the joint.
- Jointing and sealingSeal, gasket or collar
The element closing the annular gap between the sleeve and what passes through it, formed as a wet-applied seal, a compressed gasket or a preformed collar. It is the only part of the assembly that has to tolerate movement for as long as the service runs.
- Control layerReturn to each interrupted plane
The tape, membrane skirt or liquid band that ties the collar back to the air barrier, the vapour control layer, the drainage plane or the roof covering. There is one of these for each plane crossed, and they are not interchangeable with one another.
- SubstrateBacking and support
The backer rod, packing or board behind a wet-applied seal that gives it a defined back face and stops it bonding on three sides at once. Without it the seal is restrained in the direction it most needs to stretch.
- Edge and terminationUpstand or raised termination
Where the plane crossed is horizontal, the arrangement that lifts the seal clear of the surface it sits in, so the joint is not the low point that water, silt and leaf debris collect against between visits.
- Drainage planePosition relative to falls and outlets
Where a perforation sits on a sloping surface decides how much water reaches it. Placed on the upslope side of an obstruction, or close to an outlet, the same detail has to handle concentrated flow instead of the sheet flow it was conceived for.
Interaction
How the parts work together
The reason this is a system rather than a list of parts: what depends on what, and what stops working when one part is changed.
The sleeve and the seal solve different halves of one gap and neither is useful without the other. The sleeve gives the building a clean, stable edge that a bond can hold to; the seal closes the remaining annulus around an object that will not stay still. Sealant applied straight into a rough perforation is being asked to be both at once, and it lets go at whichever edge moves first.
Each interrupted plane needs its own return, and the returns are directional in different ways. A bond to the drainage plane has to be lapped so water passes over it; a bond to the air barrier only has to be unbroken; a bond to the vapour control layer has to be unbroken on a particular side of the insulation. Making one good return and calling the perforation closed leaves the other planes open, and the symptom then appears wherever the open plane mattered rather than at the pipe.
Movement, temperature and future replacement all bear on the same joint. A pipe that lengthens as it warms drags the seal with it, so a rigid seal bonded to both the pipe and the sleeve is loaded on every cycle until it splits, and the split is hidden beneath the collar. That same rigidity is what makes replacement destructive: cutting a bonded service free takes the returned planes with it, which is why how a penetration is expected to be maintained is an input at the start rather than a discovery later.
Materials
Material families commonly met in each role
Commonly encountered, not recommended. Whether a material suits a given project depends on the whole assembly, the exposure, the manufacturer's documentation and qualified professional review.
Control layer
Tape and sheet families of this kind are commonly encountered returning an interrupted plane onto a collar. Whether a given product bonds both to the collar material and to the plane it is closing is set out in the manufacturer's documentation and confirmed by the designer.
Jointing and sealing
These families are commonly encountered closing and backing the annular gap. Movement capability, adhesion and behaviour against a given pipe material differ markedly between them, which makes this a question for product literature rather than for general guidance.
Edge and termination
Dressed and preformed collar families of this kind are commonly encountered weathering a penetration on a roof plane. Whether any of them can be bonded or welded to the covering already in place depends on that covering and on its own documentation.
Protection
Sleeves and formers are commonly encountered in these metal families. What a sleeve is made from affects what can be bonded to it and how it behaves in contact with the penetrating element, and neither of those is settled on this page.
Components
Building components that fill these roles
The discrete elements commonly occupying each role in this assembly. This is a different statement from the material families above: those name what a role is commonly made of, these name the positioned elements that occupy it. Commonly encountered, never recommended.
Edge and termination
Boundary
Where this system ends and meets another
The edge of this system. Everything above is inside it; each junction below is a condition at its boundary, where an adjacent system or an adjacent building condition takes over. Junctions are where most assemblies actually fail, so they are set out explicitly rather than left inside the prose. What resolves one is a detail designed for the specific building — not a rule of thumb.
The air barrier the perforation crosses
A penetration is a hole in a plane whose whole value is that it has no holes. The parent system describes where the barrier runs; this entry describes the collar and return that put it back, and the fact that a perforation is easy to make and awkward to close.
Read about Air Barrier System →The service zone that decides how many perforations exist
A penetration never made needs no seal, no return and no collar. Where services are distributed in a zone inboard of the control layers, the barriers are crossed at planned points instead of wherever a fixing or a bracket happened to land.
Read about Service Void →Outlets and the water that concentrates around them
An outlet is itself a penetration, and it is the one place on a roof where flow is deliberately concentrated. Other perforations placed near it, or upslope of it, meet water that has already been gathered rather than water spread across the surface.
Read about Roof Rainwater Drainage →Perforations through a layered flat roof
On a layered flat roof a single service crosses covering, insulation, vapour control and deck, each of which is continuous for a different reason. The order of those layers governs the order in which the returns have to be made, and once buried none can be revisited.
Read about Warm Flat Roof →Services emerging through a drained facade
A drained and back-ventilated facade expects water behind the cladding, so a service crossing it has to be sealed at the control layer rather than at the visible outer skin. Sealing only the outer panel makes the detail look finished while the plane behind it stays open.
Read about Rainscreen Facade →Vapour plane returned at each service crossing
Returns the vapour plane individually wherever a service crosses an insulated element, since a perforation breaks that layer in the same movement as the air and water ones and it is the layer nobody can see once the build-up is closed.
Read about Vapour Control System →Ground Gas Protection
Each service entry is a site-made closure around something that will move, settle or be replaced. How each is formed, and whether it remains serviceable when a cable or pipe is later changed, is the recurring weakness of the whole arrangement.
Read about Ground Gas Protection →Volumetric Modular
Every service taken from one unit to another passes through two finished walls and the void between them. Sealing that route is site work in a concealed location, and where it cannot be reached the route has to change rather than the seal.
Read about Volumetric Modular →Ground-Bearing Slab
Drainage, incoming water and conduits pass through the slab and the barrier below it. Each is a hole in a layer whose whole value is continuity, so their positions are a design matter fixed before the slab rather than a fitting matter afterwards.
Read about Ground-Bearing Slab →Suspended Timber Ground Floor
Pipes and cables crossing from the void into the room each puncture the air control layer and usually the insulation. Grouped and planned, sealing them is a detail; arriving individually and late, the layer ends up compromised in many small places.
Read about Suspended Timber Ground Floor →Barrier Waterproofing
Incoming water, power, telecommunications and drainage all cross the barrier, and each crossing has to be re-sealed by a means suited to that service and that barrier family. Penetrations formed after the barrier is complete are the most common late intervention and the hardest to make good.
Read about Barrier Waterproofing →Integral Water-Resisting Structure
Incoming services, drainage connections and any duct crossing the element pass through the resistance. Each needs a sealing arrangement suited to a cast element rather than to an applied layer, and each has to be known about before the pour rather than cut afterwards.
Read about Integral Water-Resisting Structure →Drained Cavity Protection
Every incoming service passes through the structure and then through the membrane, and the seal made at the sheet decides whether water stays in the drained space or arrives at the back of the finish. A crossing formed after the membrane is up is the case that most often reopens the route into the room.
Read about Drained Cavity Protection →Rooflight Kerb
A penetration seal restores continuity around something already crossing the envelope, whereas a kerb creates the aperture and forms the layers around it. Roofs commonly carry both, and confusing them leads to a service being detailed as though it were a kerb.
Read about Rooflight Kerb →Rendered External Insulation
Flues, vents, pipes, meter boxes, brackets and lights all cross a thin coat over soft board. Each needs backing that can carry it, a sleeve or profile that keeps the insulation edge covered, and a seal that tolerates the movement of what passes through.
Read about Rendered External Insulation →Vegetated Facade
Every frame fixing and every water line that reaches the building is a penetration made in a damp location and then covered by planting. The seal has to tolerate that environment, and it will not be inspectable once the assembly is established.
Read about Vegetated Facade →External Shading
Each attachment is a designed opening through the water and air control layers, made from outside and expected to remain sealed while the element moves. The number of penetrations is set by the shading layout drawn much earlier.
Read about External Shading →Cold Flat Roof
A fitting recessed into this ceiling is set into a bay whose depth is already shared between insulation and air space, so it displaces the path as well as opening the plane. Where an item can be kept out of the roof zone altogether, that is a simpler answer than closing it well.
Read about Cold Flat Roof →Inverted Roof
A penetration here crosses more layers than in an exposed roof and ends at a membrane nobody will see again. Grouping penetrations, and forming them before the roof is covered rather than after, is materially easier than working back down through a completed build-up.
Read about Inverted Roof →Cold Pitched Roof
Each item passing through the ceiling is a hole in the plane the roof space relies on, made at the warmest and most humid side of the assembly. Extract ducts are the sharpest case, because they can deliver moist air into the void by design rather than by leakage.
Read about Cold Pitched Roof →Standing Seam Roof Assembly
Every pipe, duct and support post crossing the metal is a hole in an otherwise unpierced surface. How it is weathered, and whether it restrains the tray it passes through, both matter, and the layers below have to be closed around it as well.
Read about Standing Seam Roof Assembly →Twin-Skin Metal Roof
Large single-storey roofs carry a great deal of plant, and every support and duct passes through both sheets and the insulation. The liner has to be resealed around each one, not simply cut, or the assembly's air control is undone item by item.
Read about Twin-Skin Metal Roof →Composite Panel Roof
Anything crossing the panel breaches the outer face, the core and the liner in one move. Cutting a panel also interrupts the member that was spanning between purlins, so the structural consequence is as real as the weathering one.
Read about Composite Panel Roof →Single Ply Roof
Every penetration is another termination of the single waterproofing layer, and plant supports add point loads and vibration on top. Grouping penetrations, and lifting plant clear of the membrane, reduces the number of these terminations.
Read about Single Ply Roof →Liquid-Applied Roof Build-Up
This is the interface the type exists for. A liquid layer can be worked around a group of penetrations that no sheet could be dressed into, provided each one gets its own reinforcement and the substrate around it is sound enough to bond to.
Read about Liquid-Applied Roof Build-Up →Rainwater Harvesting
Where a pipe or cable from a buried vessel enters the building it crosses the envelope below ground and becomes a sealing detail rather than a plumbing one. It is a familiar route for water to enter a building through a system meant to serve it.
Read about Rainwater Harvesting →Bracket Supported Balcony
Every bracket fixing is a penetration of the layers controlling water and air on that wall, and the general treatment of such penetrations belongs with the envelope penetration sealing system. What is specific here is that they are repeated, structurally loaded and permanently wetted.
Read about Bracket Supported Balcony →Guarding System
External base fixings are penetrations as well as connections, so penetration closure practice applies at every post.
Read about Guarding System →Mass Timber Wall Build-Up
A penetration here goes through the structure and the air barrier in the same operation, and the hole cannot be moved afterwards. Grouping penetrations and planning them before manufacture is a different exercise from sealing them where they happen to land.
Read about Mass Timber Wall Build-Up →Post-Tensioned Slab
A penetration through a post-tensioned slab is agreed before the pour and formed with the plate, not cut into it. That reverses the usual order of work, in which a route is sealed after it has been made, and it is the point at which a services drawing becomes a structural drawing.
Read about Post-Tensioned Slab →
Internal junctions
Junction conditions inside this system
Junctions between the components within this assembly, rather than at its boundary. An entry exists only where the condition between two elements governs how the assembly behaves — two parts touching is not on its own a junction worth naming.
Cavity Barrier to Service Penetration
Where a service crosses the one element installed specifically to stop a concealed cavity running continuously.
Fire continuity · Air leakage · Drainage · Buildability
Floating Floor Layer to Service Penetration
Where something passes up through a floor that performs by being disconnected from the structure, at the point that disconnection is most easily lost.
Acoustic continuity · Movement · Fire continuity · Buildability
Plant Support Plinth to Upstand
Where the waterproofing is turned up an isolated object standing in the field of a roof and terminated above the water running past it on every side.
Moisture · Drainage · Structural transfer · Acoustic continuity · Movement
Considerations
Topics worth discussing
Which topics genuinely apply to this system and what to raise about them. Measured values, classes and ratings come from a qualified professional's design for the specific building, not from a reference page.
- Moisture
- A perforation on a horizontal surface is a joint in the plane most likely to hold water. Whether that joint is raised clear, and where it sits relative to the direction water travels, changes what the seal is asked to resist between one inspection and the next.
- Movement
- Thermal and operational movement in the penetrating element is continuous and cyclical, while the seal is fixed. Which of the two is expected to absorb the difference is a design decision, and a seal bonded rigidly at both faces has effectively been given that job by default.
- Fire
- Where a penetration passes through construction with a fire-resisting function, the sealing of it is a regulated determination made against tested systems by qualified professionals. This entry addresses weather and air continuity only, and states no rating, class or arrangement.
- Maintenance and access
- Services are altered far more often than envelopes are. Whether the collar and its returns can be opened and remade without cutting into the surrounding plane is what decides if a future alteration is a small job or a much larger one.
- Buildability
- Perforations are frequently made after the envelope is closed, by a trade working from one side with no view of what is behind. Marking, sleeving or forming the openings while both sides are still open changes what is physically possible later.
- Interfaces
- A penetration belongs to a services package and the plane it crosses belongs to an envelope package. That split is why the collar is frequently in nobody's scope, and why an unplanned perforation appears without anyone deciding it should.
Design
Questions the design has to answer
The decisions this assembly turns on. They are questions rather than answers, because the answer depends on the building.
- Which control planes does this service actually cross, and has a return been designed for each of them separately?
- Is there a sleeve or former giving the opening a defined edge, or is the seal expected to bond to a cut edge?
- How much movement will the penetrating element make in service, and which component is intended to absorb it?
- Where does this perforation sit in relation to falls, outlets and the direction that surface water travels?
- Can the seal and its returns be opened and remade later without cutting into the surrounding plane?
- Are the perforations being set out in advance, or created by whichever trade arrives with a service to run?
- Which package is responsible for the collar itself, as opposed to the pipe on one side and the membrane on the other?
Boundaries
Commonly misunderstood points
Distinctions that are easy to blur, and the places where a familiar term means something narrower than it sounds.
- A penetration is thought of as one hole, when a single service usually breaks several planes that each have a different reason for being continuous.
- Sealant is treated as the whole answer, although a wet seal without backing or a sleeve is bonded on faces that will pull it apart as the element moves.
- A collar that looks sound from outside is assumed to be sound, when the joint that matters is often on the concealed side and moves every time the service warms or cools.
Conversations
Questions for qualified professionals
Bring these to the relevant qualified professional, manufacturer or authority. Requirements vary by project and location.
- Which of our services penetrate the envelope, and has each crossing been detailed rather than left to site?
- What is proposed to accommodate movement of each penetrating element at the seal, and how was that decided?
- Where a penetration passes through fire-resisting construction, who is making that determination and against which tested system?
- How will these penetrations be inspected before they are covered by insulation, cladding or finishes?
- What is the expected route for altering or replacing a service later without disturbing the control layers around it?
What this page does not do
- Weather and air continuity at a perforation are properties of the completed and correctly installed assembly, and never of a sealant or collar taken on its own.
- Nothing on this page addresses fire-resisting penetration sealing, which is governed by tested systems and by the relevant authority and belongs with qualified professionals.
- Whether a particular collar, sleeve or seal arrangement suits a given service and a given plane depends on the manufacturer's documentation and on professional design.
Related systems
How this system relates to others
Every link states what the relationship actually is, rather than leaving a bare list of related pages to be read as a suggestion.
Commonly built alongside
Systems routinely present in the same building without a junction recorded between them and this one. Where two systems do meet, the junction is set out above instead.
Applications
Building contexts this system is used in
The functional parts of a building this assembly is commonly met in. This is membership, not a ranking and not a recommendation: several systems answer any one context, and which of them suits a project is a design decision. A context appearing here does not mean the system is suitable, permitted or adequate for it.
- Building Envelope · Envelope
Go deeper
Related Build Design Hub guides
Planning guidance behind the decisions this assembly involves.
Preparation
Related planning checklists
Owner-side preparation before the conversation where this system comes up.
Envelope Junctions, Interfaces and Terminations
The places where continuous layers stop, turn, change plane or are pierced, and several duties collide inside a very small amount of construction.
Browse all junctions & terminations entries →