It is easy and economical to install metal roofs over houses, sheds, barns, warehouses and even commercial buildings. With proper care, galvanized or powder-coated metal rooftop sheets should last a lifetime. However, as we know, moisture combined with oxygen is the worst enemy of iron.
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One solution to preventing such condensation-related problems is to replace the entire roof with plywood or fibreglass sheets. Many have also tried attaching plastic sheeting to the tin roof as a vapour barrier, but it is a cumbersome and ineffective process.
One common method of insulating the roof is to use glass wool in a bag attached to the underside of the metal roof. Humid air penetrating through gaps and cracks can still reach metal and condense causing water to collect and wet the insulation.
This water does not dry out quickly and combining with oxygen in the air corrodes iron sheets quickly. In such cases where roofs have under-decks, the problem is not apparent until a large portion has corroded and water starts to drip in when it rains.
This can be resolved by coating the underside of metal tin roofs. Painting can prevent corrosion but it cannot prevent condensation. Water will still drip. A better way to protect tin sheets, and at the same time prevent condensation is to cover the underside of the roof with foam. This acts as a vapour barrier and also as an insulating material, preventing warm air inside from touching the cold metal surface and thus preventing condensation.
You can get sheets of flexible foam with an open-cell or closed-cell structure and glue them to the underside of the tin roof. However, in a majority of cases, such roofs usually have some form of under-decking that makes this a difficult process. The answer, therefore, is spray foam insulation.
Moisture no longer condenses. You are no longer bothered by the problem of water drips. Your roof and the under deck remain dry, safe and retain their physical integrity for years.