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Moisture Balance and appreciating what is important

Even before the period of Neanderthals, basic protection from the environmental climate, rain, heat and cold has been key to the survival of humans. Add in fire and security from outside predators and we can see how building methods have evolved and will hopefully continue as new materials come to market.

The basic construction methods have moved from using bones and hide to protect our families, to mud huts, stone to the well-ventilated Georgian houses of the 18th Century and then the subsequent introduction of cavity walls in the late Victorian period, to protect from rain penetration. This has progressed in the modern day when Passive House is used by many as a yard stick for the balance of moisture issues, coupled with sustainable temperature control and a healthy building envelope.

In all this evolution the key principles are addressed and basic instincts of protection being key.

We are living in unprecedented times and due to a pandemic most are spending more time at home not just for leisure and relaxation, but for work too. The recently rolled out vaccination programme gives us all hope, but there is no doubt that these challenging times have brought peoples appreciation of the important things in life, such as time with friends and family over materialistic possessions.

The energy crisis in the early to mid-1970s added to, and continues to validate our appreciation that we cannot rely on the earths existing resources for basic comfort goals.

At the A. Proctor Group (APG) we like to take account of the HAMM (Heat Air Moisture Movement) principles that looks at the effect of insulation type and placement along with the vapour permeability of the various layers. This leads to a balance of key factors producing a healthy building envelope that protects the occupants.

One of the features of balancing these principals can involve calculations to assess condensation and/or moisture risks. Glaser calculations can do this but can have limitations, which a WUFI calculation can help overcome e.g., rain and drying out of residual moisture in the construction. With a WUFI (BS EN 15026) calculation, it can be shown what effect differing performing VCLs can have on the structure and whether it is critical. It is difficult to argue that a VCL is not a good thing but similar to the first COVID-19 injection, a VCL should be used to reduce the moisture risks to acceptable levels but not be relied upon as the sole method of protection. Remember a VCL is a vapour CONTROL layer not as previously referred to in the antiquated terminology of a vapour barrier, that led to its over reliance.

Installation Guides
Material Properties
BIM Objects
UK Availability
Global Availability

Material Properties


Property Test Method Result
Roll Size 1.5 x 50 m
Thickness Calibrated Deadweight Micrometer 0.65 mm
Weight Electronic Weigh Scale 292 g/m2
Application Temperature - Air & Surface Minimum -10 C
Service Temperature -40 to 80 C
Water Penetration - Before Ageing EN 1928:2000 Method A W1 Class
Water Penetration - After Ageing EN 1928:2000 Method A W1 Class
Air Permeance EN 12114 0.01 m3/m2/hr @50Pa
Water Vapour Resistance Sd EN ISO 12572(C) 0.039 m
Water Vapour Transmission BS 3177:1959 893 g/m2/24hr
Peel Adhesion EN 1939 5.01 N/10mm
Tensile Strength - MD EN 12311-1 417 N
Tensile Strength - XD EN 12311-1 252 N
Tear Resistance - MD EN 12310-1 412 N
Tear Resistance - XD EN 12310-1 286 N
Dimensional Stability - MD EN 1107-2 0.3 %
Dimensional Stability - XD EN 1107-2 +0.1 %
Reaction to Fire EN 13501 - 1 B Class
Flexibility at Low Temperature EN 1109 No cracks at -40C

BIM Objects

File Format
Wraptite - BIM Object - Steel Frame IFC
Wraptite and Facadeshield UV - BIM Object - Steel Frame IFC
Wraptite - BIM Object - Steel Frame With Reflectite Tape Over Board Joints IFC
Wraptite - BIM Object - Steel Frame Wraptite Tape Over Board Joints IFC
Wraptite - BIM Object - Wraptite Tape Over Board Joints IFC
Wraptite - BIM Object - Ventilated Timber Frame With External Airtight Membrane Wraptite IFC
Wraptite - BIM Object - Ventilated Timber Frame With External Airtight Membrane And Wraptite Tape Over Board Joints IFC
Wraptite - BIM Object - Warm Roof Slate With Softwood Sarking RVT
Wraptite - BIM Object - Warm Roof Tile With Plywood Sarking RVT

UK Availability

North East Scotland & Islands
Linda Kay
Regional Sales Manager


South London & South East
Josephine Matchette
Regional Sales Manager


Wales & South West
Marc Blackie
Technical / Regional Sales Manager

07968215 755

North London & East England
Ben Cremer
Technical / Regional Sales Manager


Head Office
The Haugh

Kieran Basi
Regional Sales Manager


Anthony Ruth
Regional Sales Manager

Global Availability

North America
Jeff Dibdin
International Account Manager.


South America
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.


Generally, where the insulation is placed externally a VCL is less critical compared with insulation solely between framing behind the sheathing board. This has led to the introduction of externally applied self-adhered vapour permeable yet airtight membranes like Wraptite®.

It is the properties of Wraptite in being a self-adhered, airtight, yet vapour permeable membrane, that allows it to be placed on the external face of the sheathing board. This allows for temporary water protection, airtightness and long-term vapour permeability, which along with the correct balance of insulation means a VCL may be less critical - yet it is important to assess this fully on a project by project basis.

There is little doubt that a VCL (especially variable resistance membranes) can be advantageous in a number of applications to reduce the moisture flow through a building envelope, but less critical in some areas, depending on the insulation placement. For example, when placing insulation purely in between the frame of a timber frame building, the moisture risk may be too high to omit the VCL and therefore should be used to reduce vapour progressing through the structural frame. However, if this is balanced with insulation placed external to the structural frame the dew point potential is reduced due to the warm frame and the VCL becomes less critical yet still good practice.

Once the insulation is installed, depending on its type, it may be advisable to install a second layer, this time on the cold face of (outside) the insulation, to avoid moisture pick up through the insulation and potential loss of thermal performance. This can include the use of a reflective material to fur ther enhance the thermal performance of the structure, this time with APG vapour permeable Reflectashield® TF 0.81.

For any moisture concerns or questions, The A. Proctor Group have years of experience in across all areas of the building envelope, such as pitched roofs, walls and floors. Our team of technical exper ts at Head Office and external Regional Technical Sales Managers are all very well educated in the companies HAMM (Heat Air Moisture Movement) principles to ensure an effective balance is reached, ensuring a healthy building envelope.

A good appreciation of the key balancing of heat, air and moisture movement can work together for the benefit of the industry.

To summarise-

APG have many VCLs in our range, one being a variable VCL, and it is not our position to persuade the industry not to use them. Our stance is to show people that VCLs should not be relied upon solely to reduce moisture build up but can have benefits when balanced with other factors. APG now have Wraptite and Procheck® Adapt passed as Certified Passive House components, tested by the Passive House Institute.

APG provide a respected technical back up service which includes-

  • Ensure the external wall make up allows for vapour diffusion from the interior to exterior vented spaces (BS5250 standard to be referenced and followed in a design)
  • Tool Box talks, virtual if required
  • Specification guidance
  • Site visits (dependant on COVID restrictions) that can give a Compliance report showing areas that are well installed and areas of improvement in the installation

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Contact Us

  8:30am - 5pm, Mon - Fri

  01250 872 261

  01250 872 727


  A. Proctor Group Ltd., The Haugh, Blairgowrie, PH10 7ER





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