Zinc work · Town centre
The concealed box gutter of a terraced house
Invisible from the street, and for that very reason the leak that takes longest to be seen.
The situation
In Vilvoorde, Halle, Leuven and the Brussels core, the gutter is not at the roof edge but concealed behind the cornice, between two facades. The water runs there in a zinc or lead trough laid on a timber deck. As long as that trough is watertight, nothing happens. As soon as a soldered joint opens, the water does not go outside but inside — into the head of the wall, between the leaves of the cavity, and onto the ceiling upstairs only months later.
What we find
- A brown ring on the ceiling upstairs, often near the facade
- Efflorescence or plaster coming away on the inside of the facade wall
- A zinc trough with a soldered joint that has given way, or a tired expansion joint
- A rotten deck under the trough, letting the base sag and the water stand
What we do
- Strip the first course of tiles or slates to expose the whole trough
- Replace the rotten deck and restore the fall so the water finds the outlet again
- Form a new zinc trough with expansion joints at the right spacings, not one continuous soldered run from wall to wall
- Deal with the junction to the masonry with an upstand and a cover flashing, not with mastic
Zinc moves: a ten-metre trough with no expansion joint cracks again within a few years, however well soldered it is. It is that joint, and not the thickness of the zinc, that decides how long the repair lasts.
The matching serviceThe other situations
- Roof renovationThe 1970s concrete tile at the end of its runThe roof is not broken. It is finished. That is not the same conversation — nor the same quotation.Read more
- Flat roofThe flat roof over the rear extensionAlmost every Belgian house has one. Almost nobody ever goes up onto it.Read more
- CleaningThe north slope going greenMoss is not a cosmetic problem. It is a sponge that holds water against the tile.Read more
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