Where does water under the steel sheet come from and how do you find the right cause?

Begin the inspection from the safely accessible interior. Mark the edge of the dampness and take photographs for comparison. Do not immediately open up the entire lining. If water is approaching the electrical installation, an urgent risk assessment is needed. Do not climb onto a wet or icy roof to look for the gap yourself.

The first group is the fastenings. A screw may be crooked, seated outside the support, or have a damaged seal. Overtightening also causes harm. This is not repaired by further compressing every washer. The second group covers the sheet overlaps. Their direction, geometry and the sealing intended for the given pitch must be checked.

The third group is the edge flashings, roof valleys and penetrations. A fault may direct water under the covering instead of onto its upper surface. The fourth is the area around the chimney. The side facing the ridge is inspected with particular care. Leaves accumulating there obstruct drainage. A new strip of sealant over old dirt does not restore correct drainage.

The fifth cause is sometimes damage to the sheet or coating. A deep scratch can lead to corrosion over time. The sixth concerns drainage: blocked gutters, outlets or roof valleys. Water backed up in a place not intended for it seeks a path through the joints. Blockages must be removed and their cause then assessed.

The seventh problem is incorrect pitch or local deflection of the roof slope. Even a nominally correct fall will not help if a depression has formed. The eighth cause is condensation. Warm moist air can reach the cold steel sheet through gaps in the inner layer. In that case, sealing the covering from above alone does not remove the source of the water.

A leak often depends on the rain and the wind direction. Condensation may appear over a larger area of the underside. These are indications, not a certain diagnosis. Damp insulation can release water for a long time after rainfall. A single thermal bridge can also produce a local patch.

In a heated back room, it is worth measuring temperature and humidity over several days. At the same time, ventilation and the tightness of the joints in the vapour control layer must be checked. In a difficult case, a thermal and moisture assessment of the building envelope is useful. Not every additional membrane is a correct repair. If incorrectly positioned, it can restrict drying.

The covering changes dimensions under the influence of temperature. A rigid bead of sealant in a random location can crack or block drainage. A proper repair restores the function of the joint. Sometimes this means replacing a fastener. At other times, new flashings or redoing the overlap are needed.

Repair materials must be compatible with the coating and adjacent materials. Arbitrary metals should not be combined, nor should compounds of unknown compatibility be used. If the defect concerns the structure or deflection, correcting the sheet metal alone is not enough. In such a case, the repair must be determined with the person assessing the load-bearing capacity of the entire system.

After the repair, observation under conditions similar to those in which the problem occurred is needed. The disappearance of dripping on one day does not mean the insulation has dried out. Check whether the damp materials can dry and whether they have lost the required properties. Damaged built-in components may need to be replaced.

It is worth keeping a description of the cause, photos of the repair and information about the components used. With several similar pavilions, this makes it easier to inspect the remaining roofs. However, they do not need to be repaired identically in advance. The same symptom can have different sources. The best result comes from removing the specific defect and planning subsequent inspections.