If you live in a semi-detached or terraced house, you may wonder what happens when only your property is having cavity wall insulation installed.
A common question we are asked is:
“What stops the insulation travelling through the cavity into my neighbour’s house?”
It is a sensible question.
Depending on the age and construction of the property, the external wall cavity may continue across the boundary between two adjoining homes. It should therefore not simply be assumed that the party-wall line automatically provides a complete barrier within the cavity.
Where containment is required, Arrow Energy Solutions installs a cavity barrier at the boundary of the property before the insulation is injected.
This creates a physical stop within the cavity and allows us to insulate the intended property while keeping the insulation within the area being treated.
From the outside, a pair of semi-detached houses or a row of terraced homes may look like completely separate properties.
Inside the external wall, however, construction can be different.
A typical cavity wall consists of:
an external leaf of brick or block;
a cavity;
an internal masonry leaf.
Where adjoining houses were constructed at the same time, portions of the external cavity can sometimes continue across the line separating one property from another.
The internal party wall between the homes does not necessarily mean that the external wall cavity is also completely closed at exactly the same point.
Construction varies considerably between buildings, particularly according to their age, design and any alterations that have taken place since they were built.
This is why the boundary conditions need to be considered as part of the cavity wall insulation installation.
Our EPS bonded bead insulation is installed through a series of carefully positioned injection holes in the external wall.
The beads travel through the available cavity before being bonded together.
If an open cavity continued into an adjoining property without a suitable stop, insulation could potentially migrate beyond the area intended to be insulated.
We therefore need to establish appropriate boundaries to the installation.
A cavity barrier provides that boundary.
Its job is straightforward: to contain the insulation within the property being treated.
For this purpose, a cavity barrier is a physical barrier introduced vertically into the wall cavity at the appropriate boundary between properties.
It extends through the cavity so that insulation cannot freely pass beyond it.
Once installed, the barrier effectively creates an end point to the section of cavity that we are insulating.
The bonded bead can then be injected up to the barrier while the neighbouring section of cavity remains separate.
Unlike many components used during new-build construction, retrofit cavity barriers need to be installed into a wall that has already been built.
This is specialist work.
The precise method can vary according to the wall construction and access available, but the principle is to create access to the cavity at the boundary and introduce the barrier vertically through the required section of wall.
The barrier is positioned so that it forms an effective stop across the width of the cavity.
Once the installer is satisfied that the cavity has been appropriately contained, the cavity wall insulation can be installed.
In a semi-detached property, there is normally one adjoining home.
If only one half of the pair is being insulated, we assess the cavity at the dividing line between the two properties.
Where the existing construction does not provide a suitable cavity stop, a barrier can be installed at this location.
This means that:
Your property can be filled with bonded bead insulation,
while:
Your neighbour’s property remains outside the area being insulated.
The aim is to create a clear and controlled termination point for the insulation.
A mid-terraced house presents a slightly different situation because it has a neighbouring property on both sides.
Where the cavity construction requires it, containment may therefore be needed at both party-wall boundaries.
This effectively creates a defined section of cavity corresponding to the property being insulated.
The principle can be visualised as:
Neighbour | Cavity Barrier | Your Insulated Cavity | Cavity Barrier | Neighbour
The insulation is then contained between those boundaries.
This allows an individual terraced property to be treated without intentionally filling the adjoining homes.
An end-of-terrace home normally has one adjoining property and one exposed end elevation.
The party-wall side is treated in much the same way as a semi-detached house.
Where necessary, a cavity barrier is installed at the adjoining property boundary so that the insulation remains within the home being treated.
Not necessarily.
Every property is different.
Existing construction may already provide an effective termination to the cavity, or the arrangement of the building may mean that a particular boundary does not require an additional barrier.
This is why cavity wall insulation should follow a proper survey rather than a one-size-fits-all approach.
We consider the construction of the property and determine where insulation needs to be contained before installation proceeds.
The dividing line between adjoining properties can often be established from visible features of the building and the internal layout.
However, the condition inside the cavity is equally important.
Where required, our installers and surveyors assess the wall construction to determine how the cavity behaves around the party-wall line.
This can include consideration of:
the position of the party wall;
brickwork and construction details;
wall thickness;
cavity width;
extensions and alterations;
changes in wall construction;
existing insulation;
existing cavity closers or barriers;
borescope findings where appropriate.
The objective is to understand the wall before deciding how the insulation should be contained.
Where cavity barriers are required, they form part of the preparation before the relevant section of cavity is filled.
A typical installation process is:
The installation team confirms the areas of wall that are to receive cavity wall insulation.
The party-wall boundaries and other cavity termination points are identified.
A physical barrier is introduced into the cavity to prevent insulation moving beyond the intended installation area.
Air bricks, vents and other features requiring protection are dealt with before filling begins.
EPS bonded bead insulation is injected through the installation pattern into the cavity.
The bead distributes through the available cavity and is contained by the barriers and existing building boundaries.
The installation is checked and the injection holes are made good.
Relevant installation evidence is recorded as part of the job documentation.
EPS bonded bead is designed to distribute through the cavity so that it creates a consistent layer of insulation.
This ability to move around wall ties and other normal cavity features is one of the reasons it works well in retrofit cavity walls.
But that also means installers need to understand where the cavity starts and stops.
Good cavity wall insulation is therefore not simply about drilling holes and injecting insulation.
Before filling begins, the installer needs to consider:
neighbouring properties;
party-wall boundaries;
roof lines;
extensions;
conservatories;
air bricks;
ventilation openings;
cavity trays;
flues;
changes in construction;
areas that should not receive insulation.
The wall should be treated as part of a building rather than simply as an empty space to be filled.
This is another common situation.
Your neighbour may have had their cavity insulated many years ago, recently, or under a completely different insulation scheme.
Where appropriate, the boundary between the two installations can still be controlled so that the new work relates specifically to your property.
They may have already had a barrier put in the cavity in the first place.
That does not necessarily prevent your home from being insulated.
Where your property is suitable for cavity wall insulation and an effective boundary can be established, your section of the cavity can potentially be isolated and insulated independently.
The purpose of installing the cavity barrier is precisely to create that separation where the existing construction requires it.
A cavity barrier inevitably occupies a small, localised part of the cavity.
However, its purpose is to provide an essential construction detail: containing the insulation at the boundary of the property.
The area involved is very small compared with the overall insulated wall and is in line with the party wall.
Trying to avoid a properly required barrier simply to fill every last millimetre of cavity would not be good retrofit practice.
The priority is to create a controlled, appropriate and durable insulation installation.
Our intention is to insulate the property we have been contracted to treat.
We do not intentionally inject insulation into an adjoining property that is outside the scope of the installation.
Where the cavity arrangement means insulation could otherwise migrate across the party-wall line, appropriate containment is established before filling.
This helps ensure the work remains within the intended section of the building.
When we insulate a semi-detached or terraced home, we don’t simply assume the insulation will stop at the boundary by itself.
Where the construction requires it, we physically contain the cavity insulation within the property being treated.
For a semi-detached home, that may mean installing a cavity barrier at the boundary with the neighbouring property.
For a mid-terraced home, it may mean creating a containment boundary on both sides.
This allows the cavity to be properly insulated while controlling where the insulation is installed.
If you own a semi-detached, end-of-terrace or mid-terraced home, our survey team can assess the wall construction and determine how the cavity should be treated.
We can inspect existing insulation, assess cavity suitability and identify where cavity barriers or other protective measures may be required before installation begins.