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Using Polythene Sheet in Construction: Understanding Vapour Barriers

Polythene sheet for construction has quite a few applications; as a protective dust cover, as a packaging material – and even as a means to cure concrete properly. One of the key uses of polythene in construction is as a vapour barrier. Understanding the purpose and proper use of polythene vapour barriers is an important factor in the longevity and safety of any building. Let’s take a look at what vapour barriers are for, and why polythene is a great choice of material.


Construction site skyline, seen from a distance. Cranes can be seen against a twilight sky, with a smattering of clouds. Greyish blue tones dominate the moody sky


What is a vapour barrier?

A vapour barrier is a material used to prevent moisture from getting into a building. Vapour barriers are applied to the inside face – the warm side – of stud frame walls. Imagine there’s cold air outside; if that warm air is allowed to make its way into the wall cavity, as it will if the vapour barrier is not there, then droplets of condensation are going to form somewhere within that wall cavity.

This will kickstart mould growth, which is dangerous for air quality and health. That’s why vapour barriers are applied to the warm side of a wall, so that warm air can’t make its way into the wall cavity. That way, the wall cavity stays dry.

So, by blocking the passage of moisture, vapour barriers prevent condensation within walls, ceilings and floors – reducing the risk of rot and mould, and corrosion. It also protects any property stored inside from the same fate; ever noticed that bikes stored in a garden shed get mouldy saddles and handlebar grips? Well, that’s all because there’s no moisture barrier in a typical garden shed.

Vapour barriers also help maintain the temperature of a building leading to better energy efficiency and comfort.

Polythene vapour barriers in construction

Polythene is the preferred material for vapour barriers for many reasons. It’s moisture proof, for a start – but it’s also highly cost-effective, light and workable. The versatility of polythene sheeting means it can be applied to complex projects with more than one use in mind, like as a dust cover or temporary flashing. 

Microperforated polythene film can be used in high humidity areas, to allow interior vapour to be drawn out.

Polythene vapour barriers are widely used in construction due to their effectiveness, affordability and ease of installation. It’s used all over a building – from the foundations, to walls, roofs, and even loft spaces – making it a versatile solution for moisture control in different parts of a building.

Learn more about polythene sheeting in construction

What gauge of polythene does a vapour barrier need to be?

The thickness of polythene sheeting used as a vapour barrier is important. Ideally, the lightest and most efficient gauge possible is preferred. Here’s a quick reference guide to what gauge of polythene vapour barrier to use – but please note that each project is different, and an experienced tradesperson should be consulted first.

250 to 500 gauge

Suitable for light-duty applications where minimal moisture control is needed. For a garden room or outbuilding, 500 gauge is a good baseline.

1000 gauge

Commonly used in residential construction for underlay beneath concrete floors and within walls, to prevent moisture ingress. 1000 gauge (heavy duty) polythene has excellent tensile strength and can last for centuries.

1200 gauge

Super heavy duty polythene is ideal for applications in commercial and industrial settings, where enhanced moisture resistance and tolerances are required

Is sizing an issue?

Selecting the appropriate size of polythene sheeting is important, but a roll of polythene sheet is always going to have an upper limit for width. Covering the entire area with a single sheet isn’t always going to be possible without seams or joints. But this can be overcome by overlapping edges by at least 150 mm, and sealing the joints with aluminium tape (or another suitable adhesive). Polythene can also be welded into larger sections, but this may not be as practical as using adhesive.

If in doubt about what gauge to use, just remember that a thicker polythene sheet (higher gauge) offers better resistance to tears and punctures. If you’re concerned about durability, go thicker.

Polythene sheet for construction

Polythene vapour barriers are just one use of this magic material in the construction industry. For more comprehensive information and further details, make sure to read our post on polythene sheeting in construction.

Are you ready to order polythene sheet for construction? Get a quote now, or call us on 01773 820415 to start your order.