Wraptite External Air Tightness Barrier

It's Airtight Outside

The Problem - In many constructions, about half of all heat loss is due to air leakage through the building. Given that approximately half of all energy used in the UK is from buildings, it is easy to see that air leakage, or draughts, account for a considerable amount of energy - and therefore cost.

As thermal insulation requirements have increased over the last few years, the proportion of energy lost through air leakage has become more evident. The ever-increasing thermal insulation required will however be rendered largely ineffective unless the airtightness of the structure itself is addressed. Tests indicate that air leakage can reduce the effectiveness of thermal insulation by up to 70%; therefore if energy efficiency is to be improved within buildings, this is the most critical area to focus on.

In addition to improved insulation, energy efficient heating systems will also be ineffective if warm air can escape the building and cold air can seep in. This is reflected in the fact that total space heating costs in an airtight construction may be as much as 40% less than in a leaky one.

Another issue associated with air leakage in buildings is that warm and often moist air can escape to colder parts of the outer construction where it can cool and condense, leading to a build-up of moisture. This in turn can lead to:-

Air leakage through cracks, holes or gaps causes a significant reduction in the thermal performance and efficiency of a structure. However this can be remedied by careful design and good quality construction practice.

The Solution - Wraptite and Wraptite Tape are effective methods of stopping unwanted air leakage. Wraptite is a self-adhering airtight membrane which consists of a triple layer polypropylene micro-porous film laminate with a proprietary moisture vapour-permeable adhesive, plus a silicon-coated PET release liner. It can be used in full wall applications, on pitched roofs (under metal, tile, slate, wood shingles and clay tile) and for window flashings or other details.

Wraptite combines the best properties of a vapour-permeable membrane and an airtight membrane in one innovative, affordable self-adhering product. It fully bonds (no primer or mechanical attachments required) to almost any substrate for air tightness and ease of installation, negating the requirement for sealants or tapes.

Penetrations in sheet material such as pipes, ducts and electrical work also need to be sealed to ensure compliance with air pressure testing. Wraptite Tape is an air tightness tape that has all the benefits of Wraptite, but with the convenience of a tape. Air tight Wraptite Tape is tear resistant and offers high vapour permeability for internal and external applications. It is also suitable for permanent airtight sealing of membrane overlaps. Detailing is quick and easy, providing an effective, convenient solution to what can be an expensive problem.

Wraptite: All-in-One - Wraptite products do not require a primer and can be installed in temperatures as low as 0°C.Its wide service temperature range means it can be easily installed in all climates. It is very easy to install, with a tough facer laminate that resists rips, punctures and tears. Wraptite is fully bonded, hence fasteners are not required at installation; this prevents lateral air movement, further enhancing the building’s thermal performance, and increasing performance in an air leak test. Being highly water vapour permeable, Wraptite thereby reduces potential for trapped interior moisture and condensation. Wraptite is resistant for up to six weeks of UV and climate exposure.

Wraptite and Wraptite Tape are unsurpassed in performance. Both offering an SD rating of 0.039, Wraptite and Wraptite tape provide a highly vapour-permeable, yet airtight performance for a wide variety of applications and conditions, and offer an optimal solution for achieving excellent results in an air pressure test. They allow damp sheathing to dry quickly and moisture vapour to escape, ensuring good indoor air quality while reducing incidence of mould, mildew, condensation, timber distortion and metal corrosion. The unique characteristics of Wraptite allow the moisture vapour to escape the structure easily, while fully maintaining the integrity of the air-tight building envelope.

Not Always Easier From The Inside

Building air tightness is increasing in importance as designers seek to improve their energy efficiency measures without the need for an extra thickness of insulation that loses valuable foot print dimensions - especially in city centre commercial buildings.

The A. Proctor Group always strive to provide construction professionals with alternative, cost effective and easier to install solutions and the introduction of their air barrier systems are exactly that. With over 10 years’ experience of providing the harshest climates(both hot and cold) in North America, the group is promoting the external application of the air tightness membrane to improve airtightness testing results.

The UK has up until now assumed that sealing the building from the inside was the best route to meeting increasing air tightness test requirements, in the main this has included sealing up the Vapour Control layer or Vapour Barrier as some refer to it. This can make sense from a building physics point of view and help reduce condensation but the actual application can be fraught with problems when striving for low levels of air tightness in buildings.

From the earliest examples of weather boarded barns to modern skyscrapers, rainscreen construction has been part of the built environment for hundreds of years. Today, with increasing energy performance requirements, and intense competition between designers to produce unique, aesthetically innovative and eye catching structures, the flexibility offered by rainscreen systems is more important than ever.

In a typical rainscreen curtain wall construction, the insulation is placed continuously over the structural frame and overlayed with a secondary weatherproof layer. The outer cladding is then fixed on rail systems, giving a drained and ventilated cavity between the insulated structure and the façade. This gives several advantages, not least fully insulating the frame and substantially reducing cold bridging compared to in-frame insulation. This setup also allows for increased design flexibility, as the outer leaf can be lighter than traditional brick facades, and can therefore adopt more unusual layouts and configurations that would be difficult or impossible to achieve with traditional façade materials. It is also comparatively easy to retrofit insulated rainscreen systems to existing structures, giving a simple path to improving both appearance and energy efficiency.

In most rainscreen systems, the outer cladding panels are not fully wind and watertight, making the performance of the secondary weather protection membrane more critical than with brick or blockwork outer leaves. While most such membranes have adequate air barrier performance, they are heavily dependent on quality of installation to ensure the overall air leakage rate targets are met. Failure to meet the specified targets can cause substantial increases in the energy performance of the completed building, and this “performance gap” has been identified in many studies of predicted vs actual building energy use. Positioning an air barrier on the outside of the insulation rather than internally simplifies this process considerably, as there are less building service and structural penetrations to be sealed, however careful consideration of the specification and installation of this barrier remains critical during design and construction. While such construction is not widely used in the UK, the A. Proctor Group’s Wraptite external air barrier system provides a simple and robust solution that can be easily incorporated into existing site practices.

Wraptite, fully vapour permeable self adhesive air barrier, is available either as a membrane or as a fully permeable tape, with a unique vapour permeable adhesive backing. This allows a simple and fast installation procedure, with the fully adhered membrane sealing to all common substrate materials. Its microporous film core ensures a low air permeance of 0.01m3m-2hr-1 while maintaining a high permeable to water vapour, with an sdvalue of 0.039m. This versatile, high performance material can be used in full wall applications, at floor cassette or corner junctions or as an adaptable site-formed airtight flashing around door and window penetrations, providing an airtight seal without compromising moisture movement. In tape form, Wraptite can be used to seal panel joints in airtight substrates such as OSB, or used to seal penetrations from services or structural elements. Its excellent adhesion characteristics also make it an effective method of jointing conventional air barrier membranes, thus maintaining a high vapour permeability envelope across the entire building.

For nearly 30 years, the A. Proctor Group have been at the forefront of construction membrane technology. From the revolutionary air/vapour permeable Roofshield underlay to the low emissivity Reflectashield timber frame breather membrane, the A. Proctor Group continually work with suppliers and research organisations to ensure our products meet the most advanced technical requirements while providing exceptional value for our customers.

Airtightness from a Contractors Perspective

“Adam Taylor, business development manager (building envelope) at A. Proctor Group, talks to RCI about the role of contractors in installing effective air barrier systems as a means to controlling and reducing air leaks”

Air leakage through cracks, gaps, holes and improperly sealed elements such as doors and windows can cause a significant reduction in the performance of even thermally insulated building envelopes. Contractors have a key role to play in the installation of effective air barrier systems which have become essential in achieving the most effective means of controlling and reducing air leaks.

As thermal insulation requirements have increased over the last few years, the proportion of energy lost through air leakage has become more evident. The ever-increasing thermal insulation required will, however, be rendered largely ineffective unless the airtightness of the structure itself is addressed. Air leakage greatly reduces the effect of thermal insulation; therefore if energy efficiency is to be improved within buildings, this is the most critical area to focus on.

The two main ways to achieve airtightness in the building envelope are internally or externally, or in other terms, “inside of the services zone’ or ‘outside of the services zone’. For the contractor, the use of traditional internal air barriers can be more complex and costly to install, due to the need to accommodate building services such as electrical, lighting, heating and drainage systems. An internal air barrier is only as good as it’s installation. If all the service penetrations are not adequately sealed, performance will be compromised.

For many years, external air barriers have been commonly used in North American building design and construction. By moving the air barrier to the external side of the structural frame, external air barrier systems such as Wraptite® from A. Proctor Group allow for an almost penetration-free airtight layer, which can be installed faster and more robustly. This offers an effective but simple system comprising a self-adhesive vapour permeable air barrier membrane, plus vapour permeable sealing tape, Wraptite Corners and Wraptite Liquid Flashing, and provides effective secondary weather protection while preventing trapped moisture and air leakage. Far simpler than internal options an external air barrier system like Wraptite will maintain the envelope’s integrity, with less building services and structural penetrations to be sealed, and less room for error.

The Wraptite air barrier system from the A. Proctor Group is the only self-adhering vapour permeable air barrier cer tified by the BBA and combines the important properties of vapour permeability and airtightness in one self-adhering membrane. This approach saves contractors costs on both the labour and materials required to achieve the demands of energy efficiency in buildings.

An example in use is the administrative headquarters building of the Royal College of Pathologists in London where the Wraptite system was installed as a solution for airtightness, weather protection and breathability.

Cladding contractor Windell installed the Wraptite System as an external air barrier and alternative to a traditional standard breather membrane. The use of a standard membrane would have required mechanical fixing and provided some challenges given the concrete structure of the building. As an alternative, the Wraptite self-adhesive membrane was applied, quickly and easily to the external envelope in continuous pieces.

George Marcantonio, the Site Manager of Windell, commented: “The application of the self-adhesive Wraptite System has proven really easy to use, and quick to apply, with no requirement to return for additional fixing or accessories. We will certainly be using the system for future projects and recommend it without hesitation.”
By reducing the likelihood of potential failures to meet designed airtightness levels, the Wraptite System helps contractors to ensure compliance with building regulations, achieving an effective airtight barrier, whilst saving time and cost on site.