Home ›
Case studies ›
Flat roof, Lennik
Flat roof leak: the water came in at the chimney flashing
Workshop
Flat roof
Thermal imaging
Fluorescent dye
RESULT
Leak confirmed at the collar of the chimney flashing, without replacing the roof.
Location
Lennik
Building type
Workshop under a flat roof
Problem
Water on the ceiling every time it rains
Methods
Thermal imaging, fluorescent dye
Conclusion
Source confirmed
The problem
Every time it rained, water ran down the ceiling of a workshop in an annex with a flat roof. The owner wanted to find the source of the water ingress without needlessly opening up the ceiling or the roof.
Our intervention
1. Visual inspection of the workshop, where drops appeared around the chimney flue, then of the flat roof outside: no obvious defect visible to the naked eye.
2. Thermal imaging of the ceiling: a colder area around the stainless steel flue, and a second one in the rear corner of the ceiling. Cold areas like these point to moisture.
3. Fluorescent dye test: from the roof, area by area, with green then blue fluorescein and gradual watering. At the collar of the chimney flashing, the water got inside and ran down along the flue.
The result: the flat roof leak located at the flashing
The source is confirmed: a sealing defect around the collar of the stainless steel chimney flashing. The rest of the roof is not involved.
Without precise location, water ingress under a flat roof often leads to replacing a large area of roofing. Here, the repair is limited to the flashing collar and its joints.
Our recommendations
• Repair or replace the collar of the stainless steel chimney flashing.
• Have the whole flashing and the flue joints checked.
• Entrust the work to a roofer or a flue specialist.
• Repeat a watering test after the repair to check it is watertight.
• Good practice for flat roofs is published by Buildwise (formerly BBRI).
