KEYWORDS:

SHORT DESCRIPTION:

• The metal sheets are either galvanized iron or aluminium, whereby gi is susceptible to rapid corrosion if the zinc coating is not sufficiently thick (a common problem with cheaper varieties). Aluminium is lighter, more durable and reflects heat more efficiently, but is more expensive and produced with an extremely high energy input.

• The corrugations make the thin sheets stiff enough to span between two purlins without sagging. Thus large areas can be roofed with a minimum of supporting construction, making the roof light (good in earthquake zones) and cheaper (less timber or steel framework).

• Thin gauge sheets are often too weak to walk on, can be dented, punctured or torn off by strong winds.

• Major problems of metal sheet roofing are the immense heat transmission to the interior (less severe with aluminium) during sunshine, and water condensation on the underside when the roof cools down at night; unbearable noise caused by heavy rains; havoc caused by whirling sheets that are ripped off in tropical windstorms; poor fire resistance.

• Many of these problems can be alleviated with good design, material qualities and workmanship.

Further information: Bibl. 00.55, 23.17, 25.06.

Construction of Corrugated Metal Sheet Roofing

• Such roofing should tee avoided in areas of intense solar radiation and rapid temperature changes, to avoid hot indoor climate and condensation problems.

• In most cases it is advisable to construct a suspended ceiling (of a light reflective material), providing a ventilated air space which removes the accumulated heat before it can reach the interior.

• The air space also reduces the noise problem during rains. In addition, shorter distances between purling, as well as felt or rubber washers at the suspension points, rigid bolt connections and thicker gauged sheets help to reduce sound transmission.

• Similarly, thicker sheets, rigidly fixed hook bolts with large metal washers (underlaid with felt or rubber to avoid bimetallic corrosion) and avoidance of overhangs, are measures to prevent damage by strong winds.

• A fire-resistant suspended ceiling and other common-sense fire precautions can eliminate the fire risk completely.

Overlaps of roofing sheets must take into consideration the main direction of wind; Rafters should be firmly held by a fastening strap or reinforcing bar, which is embedded in the concrete or masonry. (Bibl. 25.06); A ridge ventilator can help to improve indoor climate and also reduce internal pressure and thus decrease the total roof uplift. (Bibl. 25.06)