Vapour Control Layers Advice & Quick Guide

installing VCL Vapour control layer with advice and guide

Vapour Control Layers (VCL) are used to prevent condensation or vapour within a property’s structure.

Condensation or vapour can be a serious problem and one that’s expensive to remedy. Using a Vapour Control Layer is one way to protect the fabric of a building and reduce the chance of damage to the insulation and timbers.

In this advice & quick guide, we look at how vapour barriers work, the differences between them, why you need them and how to install them.

What is a (VCL) Vapour Control Layer & how do they work?

A Vapour Control Layer (VCL) or vapour barrier is a plastic layer that restricts the movement of warm, moist air from inside a property into the fabric of the building.

VCL or vapour barriers prevent excess moisture entering a floors, roofs and wall cavity, behind the insulation. Having these manages and reduces the risk of condensation and any moisture build up within the cavity.

Any small amount of vapour that does exist within the wall cavity will evaporate outside due to the porous nature of bricks. It is therefore important that any paints or potential barriers are removed from the exterior brickwork so that this evaporation process can occur.

Below is a typical example of where a vapour control layer would be used in a wall.

The difference between the types of Vapour control layers

Vapour Check Vapour Barrier & VCL Barrier
Condensation Risk Level Low Medium High High
BS5250 Conditions  Class 1  Class 2 & 3 Class 4 & 5 Class 4 & 5
Application Method Loose Laid Loose Laid Loose Laid Self-Adhesive
Water Vapour Min
Resistance (MNs/g)
260 530 1100 2000
Building Types Factories
Warehouses
Industrial Units
Storage Areas
Domestic Dwellings
Apartment Blocks
Offices
Schools
Textile Factories
Paper Mills
Swimming Pools
Laundries
Communal Shower Blocks
Canteens
Sports Halls
Wet Industrial Processes
Textile Factories
Paper Mills
Swimming Pools
Laundries
Communal Shower Blocks
Canteens
Sports Halls
Wet Industrial Processes

 

View all our Vapour Control Layer Membranes.

As per the above comparison table and in accordance with BS 5250:2002, in a typical house extension - such as a kitchen or bathroom extension - the minimum product required is Class 2-3 Vapour Barrier.

In order to ensure a vapour tight seal, all laps should be securely taped using Vapour Tape or Vapour Edge Tape.

The importance of a Vapour Control membrane

Whenever you add insulation to a building’s floors, walls or roof, you are creating a cold space between the insulation and outer structure. This means there is a potential area where condensation can occur between the warm surface and cold surface.

It is therefore important to control the movement of warm, moist air to stop it condensing on the cold outer surface as this can create mould and cause the rotting of structural timbers. Vapour control layers control the amount of moisture that is able to pass through, meaning that the structure can cope with the levels of moisture.

When is a Vapour Control Layer needed?

Building Regulations require vapour control layers in certain new builds and existing properties might require a VCL if you are:

  • Having an internal stud wall and insulation
  • Installing a new concrete floor with insulation
  • Modifying a roof space

Areas of high humidity would also need consideration.

Benefits of a VCL 

  • Prevents condensation which reduces the chance of mould and rot
  • Protects concrete floors
  • Reduces heat loss and improves energy efficiency

Installing a Vapour Control Layer 

For installing vapour control layers in walls 

When you install a VCL to the walls of existing properties normally you would be installing a stud wall with insulation.

  1. Install the VLC to the warm side of the insulation after the insulation.
  2. Stapled the VLC to the timber studwork.
  3. Any joints will need to be sealed with Single Sided Foil Tape.

Please note, it is very important to seal everything and not just seams of VCL membrane. These include the ceiling joint, floor joint and any vertical joints where the VCL meets adjoining walls. As well as foil tape, expanding foam is another possible option for this.

Once installed, plasterboard can be screwed to the studs and then skimmed.

Ensure that the joint between the bottom of the plasterboard and the floor is sealed. Ask your plasterer to leave a 20mm gap between the bottom of the board and the floor which can then be filled with expanding foam.

For installing a vapour control layer under a floor

A typical concrete floor that incorporates a VCL between the layers as follows:

  1. Hardcore
  2. Sand blinding
  3. Damp Proof Membrane
  4. Concrete Slab
  5. Insulation
  6. Vapour Control Layer
  7. Screed

Overlaps of the VCL membrane are sealed together with Double Sided Tape and the face of the joint sealed with Single Sided Foil Tape.

How to install a vapour control layer in a roof or loft

Condensation can occur in insulated lofts which have non-permeable roofing felt. This results in white fluffy mould on the underside of the roofing felt.

  1. Install the VLC to the warm side of the insulation after the insulation.
  2. Stapled the VLC to the timber studwork.
  3. Any joints will need to be sealed with Single Sided Foil Tape.

Installations vary but usually the VCL is used in conjunction with breather membranes and ventilation systems when used in a roof space to encourage air flow.

For further installation and jointing details please refer to our website.