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Best Practice Approach - Intelligent Vapour Control Layers

An increasing number of experienced contractors are switching to a new best practice approach incorporating intelligent vapour control layers as a standard to protect buildings from structural damage.

What makes these vapour control layers (VCLs) intelligent is that they adapt to changes in humidity conditions. These highly advanced building materials have been created to provide variable permeability. Essentially, that means that the VCLs change their permeability, becoming more vapour resistant during winter and more vapour permeable in the summer.

Variable permeable membranes help regulate the natural moisture-loading and drying out cycle of the building envelope by protecting the building fabric in the colder, wetter months and allowing it to dry out effectively in warmer, drier months.

The industries growing understanding of the complexities of Heat, Air and Moisture Movement (HAMM) through the building envelope has led to a shift in the industry in two ways. First, modelling software like WUFI® provides hygrothermal assessment and better models the condensation risks. Second, a new generation of advanced construction materials is now available to support the long-term health and durability of a building.

Construction professionals in the UK will be familiar with BS5250:2021 ’ Management of Moisture in Buildings - Code of Practice’ as the authoritative resource on this topic. The Standard specifies the need to be aware of both the internal and external factors contributing to condensation control and building health, where it states: "In order to avoid the occurrence of excess condensation, which can result in mould growth and damage to the building fabric, designers should assess the amount of water vapour likely to be generated within the building ... and consider the effects of the external climate."

Hygrothermal assessment

Construction professionals have traditionally utilised the Glaser method to assess condensation risk. However, WUFI® software has been an enormous step forward for the industry in terms of condensation risk assessment. In contrast to the Glaser method, WUFI® calculations are ‘non-steady state’ simulations that constantly plots the movement of heat, air and moisture in a state of constant change relative to building usage, project aspect, and seasonality

WUFI® goes much further than Glaser by including other sources moisture such as ingress from the ground, worst-case scenario precipitation events, and the natural variation moisture content within individual building materials over time. As a result, the designer or contractor can simulate hour-by-hour condensation risk analysis over an infinite amount of time and projects optimised f longevity and the health and wellbeing of occupants

Introducing variable permeability in VCLs

The general use of a VCL (vapour control layer) along with a vapour-permeable membrane would, in theory, show a well protected building envelope. However, studies carried out by the Institute for Building Physics, Stuttgart, h demonstrated that if the VCL is not sealed correctly, or is punctured, this can have a damaging effect resulting in high levels of vapour getting into the building envelope.

Traditional, high resistant vcls can prevent drying out in any direction, other than to the outside, whereas a low resistance vcl could allow too much vapour to pass into the structure. In the UK, the vapour drive generally means that vapour will pass from inside to outside, however during warmer periods there will be times that this vapour drive could be reversed. Based on extensive research and development, the A. Proctor group developed Procheck Adapt, specifically designed to protect the building fabric from the potential risks of condensation whilst providing the added benefit of serving as an effective airtight barrier.

Thanks to its unique design, the membrane offers variable permeability that adapts to changes in humidity levels and allows the structure to dry out in the summer and sunny days in spring and autumn while protecting it from moisture overload in the winter and cold, wet days.

This high-performance intelligent vapour control layer adapts its vapour resistance to the environment, i.e. vapour tight in the winter and vapour open in the summer. The incorporation Procheck Adapt ensures that the building fabric is protected from damaging moisture levels during cold, wet periods a allows the fabric to dry out effectively in warmer, dri times.

Further, the translucent structure of Procheck Adapts eases fixing to structural frames and, in conjunction with i integral tape, allows for a fast installation time.

WUFI® assessment of Procheck Adapt

The graphs here show the results of a hygrothermal simulation, run for ten years, using 500mm of Sandstone (represented as 30% stone, 40% mortar, 30% stone (150, 200, 150mm)) provide an accurate mortar composition. First, Sandstone was insulated using 120mm of mineral wool after a 5 airspace. Next, the Vapour Control Layer (VCL) installed internally, followed by a 12.5mm plasterboard. The assessment measured the performance of two vapour control layers, Procheck Adapt and the higher vapour resistant Procheck A2.

The first graph displays the relative humidity of the internal surface of the stone. Humidity begins at 48%, assuming a relatively high moisture content for the masonry onto which it is applied. In both cases, this reduces over time. The green shows a standard VCL (with a vapour resistance of 1500MNs/g), which reduces towards a roughly stable equilibrium year- round. The blue line shows the relative humidity of the surface using Procheck Adapt. In the case of the humidity of the surface with Procheck Adapt, this is consistently lower than the case using a standard vapour control layer, as the masonry is more able to dry in summer and is protected against winter condensation.

Graphs 2 and 3 show the stone’s water content, especially for the innermost layer of masonry – so the 150mm where condensation is most likely. This means that any driving precipitation should be mostly mitigated by this point, so any moisture added to this section of the wall would come from interstitial condensation. Both walls show their maximum reduction in this value during summer as the wall dries, gaining roughly the same amount as each other in winter. The assessment indicates that the wall using Procheck Adapt can lose more moisture, leading to a widening gap where the Procheck Adapt offers even higher performance as time goes on.

The water content in the insulation is also lower using the Procheck Adapt, as shown in graph 4. The results confirm that there would be less risk using Procheck Adapt on this wall compared to a regular vapour control layer. With the drive towards efficiency and reduction of emissions, buildings are becoming increasingly better insulated, more airtight, and more energy-efficient. So the management of moisture in building design and construction becomes critical. In doing so, experienced contractors are increasingly turning to Procheck Adapt as the intelligent solution to best practice approach to vapour control layers.

Graph 1

Graph 2

Graph 3

Graph 4

Procheck Adapt is a Certified Passive House component, tested by the Passive House Institute, and is suitable for a variety of commercial and residential applications and provides airtightness to the structure and vapour control.

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Material Properties
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Material Properties

Procheck Adapt

Property Test Method Result
Roll Size - 1.5 x 50 m
Weight ISO 536 110 gsm
Nail Tear Resistance - MD EN 12310-1 350 N
Nail Tear Resistance - CD EN 12310-1 375 N
Tensile Strength - MD EN 12311-1 350 N/50mm
Tensile Strength - CD EN 12311-1 315 N/50mm
Elongation - MD EN 12311-1 20 %
Elongation - CD EN 12311-1 20 %
Water Vapour Resistance Sd EN 12572 0.4 - 90 m
Reaction to Fire EN 13501-1 E Class

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Linda Kay
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Marc Blackie
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07968215 755

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The Haugh

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Anthony Ruth
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Jeff Dibdin
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Jeff Dibdin
International Account Manager.


Jeff Dibdin
International Account Manager.


Jeff Dibdin
International Account Manager.


Jeff Dibdin
International Account Manager.


Jeff Dibdin
International Account Manager.


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