Insight / Curtain Wall Leaks
Fixing a facade leak is cheap. Finding it is not.
Facade leaks come from two things: sealing that was not done properly, and a system that does not suit the building's exposure. What sets the cost of putting one right is how much of the facade has to be opened up before anyone can say where the water is getting in, and that differs sharply between a stick system and a unitized one.
Where the water gets in
These five account for most leaks on an aluminium and glass facade. Four of them are settled before the first panel goes up.
Sealing done on site
On a stick system every joint is sealed at height, from a gondola or a cradle, in whatever weather the day gives. Work like that rests entirely on the care of the person doing it, and the next panel covers it before anyone can check it again.
A system that does not suit the exposure
Wind-driven rain on the thirtieth floor does not behave like rain on the third. A system that is perfectly adequate on a mid-rise will let water through higher up, and that call is made when the system is chosen, before anything is installed.
The unit-to-unit joint
On a unitized facade the leak is nearly always on the line where two units meet. That joint is built to catch water and drain it back out, so what usually fails is the drainage path rather than the gasket.
A drainage path sealed shut
A working facade lets a little water in and weeps it back out through small openings at the face. Seal those during a repair or a finishing trade, and the cavity behind them becomes a reservoir.
Sealant and gaskets ageing out
Sealant and gaskets have a shorter service life than the aluminium and glass around them. Both need inspecting and replacing on a maintenance cycle, and on a facade that has stood for years a leak is often nothing more than that.
Leaks that are not the facade
Water at a window sill is not proof that the facade let it in. Establishing whose work it is comes first.
Condensation presents almost identically: wet on the inside, around the glass, usually seasonal and worse in air-conditioned rooms. The source is the air in the room, and sealing the facade will not stop it.
Interfaces with other trades account for much of the rest: the parapet and roof above, the junction into concrete at the edges, and pipe or duct penetrations cut after the facade was finished. Water can enter several floors above where it appears and travel inside the structure.
The difference shows when it leaks
Stick and unitized can pass the same tests. What separates them is the work required once water does get in.
On a stick system the sealing happens on site, joint by joint. Across that many joints, at height, the odds of a miss are never small, and no one joint is more suspect than another.
Finding it means masking off an area, testing it, and narrowing down until the area is small enough to be certain. The wider the area, the higher the bill, and all of that runs before a single joint is repaired.
On unitized the sealing happens in the workshop, at ground level, where it can be inspected and inspected again before the unit ships. Water that still gets in almost always comes through a unit-to-unit joint, so the work stays around that unit.
For an owner, the number worth planning for is the cost of finding the leak. It appears on no quotation, and it is only felt years after handover.
Questions we get asked
The one that comes up most is about the system: which is right for a project, and how it goes up.
- Which facade system is right for my project?
- Height, how much the panels repeat, access to the site, and the programme you have to meet. One more thing rarely gets weighed: how a leak will be traced if one happens. Stick is usually cheaper and more forgiving on a mid-rise, while unitized pulls ahead once the building is tall and the panels repeat.
- Why can a curtain wall leak after passing its tests?
- Performance testing is done on a mockup built for the purpose, under supervision, with its joints made as well as they can be made. That proves the system is right. What it cannot prove is that every joint on your building was made to the same standard, and on a stick facade there are a great many of them.
- How do you find the source of a facade leak?
- By water testing in stages: mask off the suspected area, spray it in a controlled way at a controlled pressure, then watch from inside. If nothing appears, move or widen the area and repeat. On unitized this usually stops at one unit. On stick, the area that has to be masked can be far larger.
- Is a unitized facade guaranteed not to leak?
- No. What changes is where a leak sits and how far it reaches. On unitized it is usually small and at a unit joint, so the repair can be isolated. A facade that does not leak comes from joints that were detailed correctly and then built as detailed, on any system.
- What does it cost to repair a facade leak?
- There is no single figure. It is set by how much has to be opened up to find the source, plus the cost of access at that height. Repairing one joint can require work over an area many times its size.