Roof Iron

Roof Iron has a number of forms most common though is the corrugated and ribbed decking profiles, in both cases it has a performance quality that makes it very resilient to wind and hail storm damage.

For roofing iron to perform to a good standard it needs to be installed to a good standard and needs to be installed in suitable applications. For example using corrugated roof iron over large areas with very little slope makes the roof susceptible to leakage at the overlapping joins. A large flat roof area is where the appropriate use of ribbed roof decking iron should be made.

The main areas of failure in the two iron roofs are similar:

Rust is the biggest problem in older roofs however newer roof iron materials are commonly treated with newer technology providing improved corrosion protection.

The points of connection to the roof frame is the other main area of failure, in corrugated roofs, the roofing nails or screws can become loose and apart from the nail hole openings that are left behind it is the resulting weakening of the overlapping joins and subsequent wind blown penetration of rain water that causes leakage and rain damage. Ribbed roof decking suffers the same fate when the concealed clips have not been adequately secured during construction. In worst cases where sections of multiple nails, screws or clips have come loose a heavy wind storm will lift roof iron completely off the frame when it catches a leading edge.

Iron roofs can also suffer increased rates of corrosion when different metals are used in attachments above the roof line. Many building inspectors will observe significant rust around vent pipes and flues where neglect of the material choice results in two different metals combing for destructive chemical reactions.

Another area that can cause significant damage, results when there has been no "sarking" foil provided beneath the roof iron. The appropriate use of sarking foil in iron roof constructions protects the metal from corrosion by reducing condensation on the underside of the roof and any condensation forming is directed towards the gutter line as opposed to damaging the ceiling lining or insulation.

A Pre Purchase Building Inspector will assess an iron roof for all parts safely accessible - there are new safety laws that prevent inspectors accessing roofs in certain circumstances but to a trained eye the quality of workmanship and material use can lead to professional assumptions concerning the roofs performance so that the appropriate maintenance or expense of replacement can be made.

Article written by Jason Wier B. Eng (Building) principal Inspection Angel 2007.

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