Bringing corrugated steel inside

By - , Build 77

We all know that corrugated steel is most commonly used as a roof or wall cladding, but it can be used in a variety of other ways. This article looks at using corrugated steel as an internal ceiling lining and some potential pitfalls with skillion roofs.

Figure 1: Skillion roof/wall intersection showing installation of air barrier.

Corrugated steel was used as a fire-resistant wall cladding in the late 1800s, as a former for concrete piles in the 1920s, it has been used for sculptures and more currently as a fashionable wall cladding and internal lining material. It is its use as an internal ceiling lining material that we will focus on here, particularly as part of a skillion roof construction.

Corrugated steel used as an internal lining has a number of advantages. It can be:

• curved

• prefinished (avoiding the need for stopping or painting)

• supplied in long lengths that avoid end joints.

Dealing with moisture

We know from research that moisture accumulates in building cavities because of indoor conditions. The main cause of this is air movement transporting moisture from the inside of the building. The high-risk areas are those where moisture is generated, such as bathrooms, laundries and kitchens.

However, preventing air movement, which we know carries the moisture, around a corrugated steel ceiling and into the ceiling space, is more difficult than with flush-stopped sheet ceiling linings. Where a corrugated steel ceiling is used as part of a skillion roof structure, it is important that air flow into the skillion roof cavities is prevented. The reason for this is that skillion roof cavities are usually small and are not able to effectively dissipate any moisture that enters.

Use an air barrier

An air barrier must be installed behind the corrugated steel ceiling to prevent air movement into the skillion roof. An air barrier is also recommended where a corrugated steel ceiling is installed in a wet space, even though there may be an attic space above.

Where a corrugated steel ceiling is used over a dry internal space and there is an undeveloped ceiling or attic space, an air barrier is probably not essential, but installing one would be considered prudent.

What material should be used?

Suitable materials to use as an air barrier include:

• black building paper

• synthetic building wrap (the type used as a wind barrier behind external claddings).

Although polythene sheet can be used as an air barrier it is also a vapour barrier and in most cases the use of vapour barriers is not necessary in skillion roofs in New Zealand. (See pages 20–21 for more on vapour barriers.)

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How should it be installed?

The air barrier must be installed immediately behind the cladding material and:

• have all laps sealed, usually with pressure-sensitive tape

• be turned down behind the wall lining at the perimeter of the ceiling (see Figure 1)

• have all penetrations through the barrier, such as those for wiring or downlights, sealed.

What else is needed?

There are other requirements when using corrugated steel as a lining:

• Install a profiled sealing strip to minimise air movement through the corrugation crests.

• Design an edge trim to accommodate the steel profile.

• Select fittings, such as downlights, that are suitable for use with the profiled steel. For downlights a flange may have to be fitted to allow effective mounting.

• Provide edge protection, such as a plastic sleeve, where any electrical wiring penetrates the corrugated steel. Neatly fitting lighting to corrugated steel can be difficult because of the corrugations and their spacing.

Figure 1: Skillion roof/wall intersection showing installation of air barrier.

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Articles are correct at the time of publication but may have since become outdated.

Figure 1: Skillion roof/wall intersection showing installation of air barrier.

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