External Airtight Membranes - an Introduction

Why are airtight membranes needed?

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. Housebuilders 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.

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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 housebuilder, 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® 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.

Products In Practice - Tighétébhu, Perthshire

An impressive new contemporary award-winning Eco House in Perthshire is set to benefit from the superior airtightness performance qualities of Wraptite. The house “Tighétébhu” was constructed by SIPS Scotland and has been chosen as the winner of the Best SIPs Home in the Build It Awards 2018.

The new property is a self-build project designed by Allan Corfield Architects, Dunfermline who are specialists in Self Build.

Wraptite, the only self-adhering external vapour permeable air barrier certified by the BBA, was installed as part of the Structural Insulated Panel (SIPs) construction of the home.

The split-level eco-house was designed with two main elements, the first is the L-shaped 2-storey accommodation and the second is a large sweeping single storey curved entertaining area. Both elements are seamlessly linked by a large 2-storey atrium which gives access to all areas of the home.

The combination and introduction of an integrated approach within the construction have ensured that the final outcome is an award-winning, A-Rated energy efficient house, which has been designed with best practice principles of managing the balance of Heat, Air, Moisture movement (HAMM).

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