Having solved leak problems at over a hundred buildings, I can tell you that the #1 contributing factor to building leaks is not the windows and not the caulk as many might think.
It’s the parapets and copings!
What are parapets and copings?
The parapet is the part of the exterior wall that extends above the roof. It might be short, only a few inches or it might be tall at 6 feet or taller. Most of the parapets we see extend about 3 feet above the roof.
The coping is the cap that sits on top of the parapet. It might be made of metal or stone.
Why do parapets and copings often leak?
Lots of components
Copings and parapets are composed of many components that come together all in one assembly. Whenever different components come together, the chances that something will go wrong increases. As glaziers are fond of saying about windows: “Glass doesn’t leak, aluminum doesn’t leak. It’s the stuff between them that leaks.
These components include the outside face of the parapet, the coping and its splices and attachments, the roof-side of the parapet, the roofing, its termination method, the wall cavity and the flashings. It’s a lot!
Tough weather exposure
1. Parapets and copings are exposed to the most brutal weather conditions being at the top of the building.
2. The roof-side of the parapet sees the same brutal weather that the exterior face sees.
3. With alL that weather brutality, the materials wear out faster than in the “field” of the wall.
4. The copings, weather metal or stone, have joints, seams or splices between each piece. Because of the daily cycling of direct sunlight, the joints between pieces are stressed. Their failure occurs on an accelerated basis.
5. Stone copings can be porous. Water may seep through them, so another component is needed beneath them: a through-wall flashing.
6. Through-wall flashings also have splices or seams which are rarely sealed, so water that permeates the copings can penetrate the wall through seams in the flashing.
7. Through-wall flashings are often loose-laid onto the top of the parapet with no sealant connecting the two. Wind-driven rain can be blown under the flashing and into the wall.
8. Through-wall flashings should extend a short distance beyond the face of the wall in order to create a “drip”, to deflect rainwater that might otherwise run down the face of the wall. Often, we find these drip edges missing, so water more easily enters the wall beneath them.
9. The roofing material generally terminates at the roof-side of the parapet. This is often accomplished by pinning the upturned edge of the roofing material to the parapet with a continuous “termination bar”. Often, we find the termination bars unsealed along their edges, splices and fastener heads. They sometimes even have unused holes. All of these unsealed lines can allow water into the space below the roofing and also into the wall.
10. If the roof-side of the parapet is unpainted masonry, the masonry can leak water right behind the termination bars and into the roof or wall. Remember: masonry is porous. It is not a waterproof material.
11. Wind uplift has a strong effect at the tops of buildings. It can drive the rain uphill into the gap where the metal coping overlaps the parapet. We often find these gaps open with the amount of overlap insufficient to resist the water
Take-away about leaks at copings
Whenever you are confronted with a hard-to-solve building leak, even if it looks like the windows or walls, look up!
