Metal roofing
Water under trapezoidal roof sheets: a leak or condensation?
At a glance
Water can appear on the underside of trapezoidal sheets after a dry night. Before arranging to replace the sheets, note the weather, the time and the pattern of wet patches. Does the water appear around one roof penetration or over a broad area of cold metal? The first pattern can suggest a leak and the second condensation. Neither observation alone settles the cause. A roof section drawing and details of heating and ventilation will help a roofer trace the water and establish whether the repair concerns the covering or the layers beneath it.
Under what conditions does the water appear?
Record whether it had rained or whether droplets appeared as the temperature fell on a dry morning. Photograph the same area next time. A recurring pattern under similar conditions is more informative than a single photograph of a wet floor.
What does the pattern of wet patches tell you?
Mark the wet area on a plan and add the eaves, ridge, rooflights and fixings. Water can run along a rib or a structural member. The drip mark on the floor may therefore be some distance from the entry point.
Fine droplets on several adjacent sheets are a reason to check underside temperature and indoor humidity. Vapour can condense where the metal is cold enough. Water in one corner after wind-driven rain calls for a look at the nearby laps and flashings.
Which details need checking after rain?
For a suspected rain leak, the roofer can compare the installed lap with the instructions for that profile. Orientation, pitch and joint detailing all matter. A designation such as T18 or T35 does not give a universal sealing rule across manufacturers.
Fixing washers and the junction between penetration flashings and sheets also need inspection. Covering an entire area with sealant can hide the evidence or block a drainage path. Identify which detail has failed before deciding on the repair.
What changes when a garage or workshop is heated?
Converting a cold garage into a heated workshop changes the conditions under the roof. Describe the heating, hours of use and moisture sources. Note any replacement windows or air inlets that have been closed.
A cladding sheet alone does not insulate the roof. Before adding insulation from inside, review the build-up, airtightness and ventilation routes with the designer. A new ceiling lining may hide moisture beneath the sheets.
How do you prepare for an inspection?
Photograph the underside from a safe position. Give the roofer the photographs and the sheet layout if available. Do not step onto a wet roof to look for a leak.
Record findings separately from possible causes. A damaged washer beside the rooflight identifies a repair location. Suspected condensation calls for further checks on indoor conditions and the roof build-up.
How do you check whether the cause has been addressed?
After repairing a joint, observe the same point in similar rain. After changing ventilation, compare mornings with similar occupancy. A dry surface on a single sunny day tells little about the effectiveness of the work.
File the photographs and repair description with the profile and coating details. If moisture returns, the next inspection can start at a known joint or zone before considering further sheet replacement.
7 branches. Materials closer to your project.
- SEROCK — Dzierżenin 34 E
- BŁONIE — ul. Sochaczewska 138A
- RADOM — ul. Grobickiego 8
- ŁÓDŹ — Natolin 8
- OLSZTYN — Barczewo, ul. Prosta 9
- WROCŁAW — ul. Jerzmanowska 10C
- GORZÓW WLKP. — ul. Zielona 33/34
