How to choose a repair for a leaking metal roof
Renovation and maintenance
First establish whether water is actually penetrating the covering or is the result of condensation of water vapour beneath the metal sheet. That distinction determines the repair method, since tape and sealant will not fix every cause. Check the condition of the washers, the geometry of the laps, the flashings at the chimney and wall, and any corrosion of the sheets. Also assess the roof pitch and whether drainage is unobstructed. With sandwich panels, the core and the joint may matter. Only after locating the water path and assessing the substrate can a durable or temporary solution be chosen.
How to distinguish a leak from moisture condensation?
Water under the sheet metal does not always come from rain. When it appears on cooling, including without precipitation, the cause may be condensation. Warm, moist air then meets a cold surface. Applying sealant to the outer side will not solve the problem of ventilation or the tightness of the layers from the inside.
Note when the marks occur and from which side the wind blows. Inspect the loft and the accessible sections of the underlay. The position of the stain on the ceiling may be far from the source of the water. Moisture travels along battens, the membrane and the structure before it becomes visible in the room.
What to check at the screws?
The sealing washer should sit against the sheet metal without being over-compressed. A skewed or incorrectly selected screw may leave a leak. Not all fasteners should automatically be tightened further. An elongated hole or a crushed washer can then make the situation even worse.
The repair method depends on the condition of the hole and the substrate. Sometimes replacing the fastener with the correct one is enough; at other times a section of the covering needs repair. Sealant spread around the head conceals the symptom but makes assessment more difficult. It is worth first checking whether the fixing still transfers loads as it should.
How is the overlap of sheets repaired?
The lap must have the correct geometry, length and direction. If the sheets are incorrectly positioned, the mass alone may not stop water being drawn up. It is necessary to establish whether the system provides for a sealing tape and where it should run. Accidental adhesion of the tape may even create a place where moisture accumulates.
In the joint, materials are used that are compatible with the coating and intended for roof conditions. The substrate should be clean, dry and stable. Tape on dusty paint may quickly lose adhesion. After the repair, adjacent fixings should also be checked, because movement of the sheet loads the entire detail.
What to do at the chimney and wall?
Here, leakage often results from faulty flashings or the connection to the wall. An elastic sealant may be part of the solution, but it should not replace a proper overlap. The top edge of the flashing must be secured so that water cannot get behind the sheet. Cracked render or joints also require assessment.
Check the rear of the chimney, where snow and water can accumulate. A wide chimney may require a specially shaped drainage detail. The repair should allow for movement of the roof relative to the rigid wall. A rigidly bonded connection may crack again when temperatures change or the roof structure moves.
When is sealant not enough?
Perforation, large voids and extensive corrosion indicate weakening of the material. Covering them with further layers of sealant does not restore load-bearing capacity or the durability of the coating. In such cases, replacement of the sheet or flashing may be necessary. The scope is determined after inspecting the underside and adjacent sections as well.
The same applies to standing water caused by inadequate slope. Sealing the hole does not remove the cause of the ponding. With sandwich panels, the core and the joint also require assessment. Moisture hidden beneath the steel facing may be more serious than a small leak visible inside.
How do you carry out a temporary repair?
For a sudden leak, first limit damage inside and protect installations at risk from water. Do not go onto a wet roof without proper equipment and conditions. Temporary cover should be secured by a specialist. A loose tarpaulin can be torn by the wind and does not provide predictable protection.
If repair tape or sealant has been used, record the location and date. Treat such a measure as a solution with a defined scope, not as proof that the cause has been permanently eliminated. An inspection is needed after the weather improves. It is worth taking photos before covering the damage so that the repair method can be determined more easily later.
How do you check the effectiveness of the repair?
Monitor the location after subsequent rainfall, especially with wind from the direction that previously caused the problem. Drying of the assembly may take longer than the repair itself. Old marks do not always indicate further water ingress. Documentation and moisture measurement at defined points are helpful.
Ask the contractor for a description of the cause, the materials used and the scope of replacement. Keep information on the compatibility of the sealant with the coating. Then check the roof valleys, gutters and roof penetrations during routine inspections. The most durable result comes from a correct water drainage path, supported by proper sealing.
7 branches. Materials closer to your project.
