Why a Balcony Over a Room Leaks Into a Stucco House

Most of the custom and semi-custom stucco houses north of Steeles have one somewhere: a walk-out balcony off the primary bedroom sitting over the garage, or a covered porch with a deck on top of it, or a sun deck over the family room on a Kleinburg or Woodbridge rear elevation. The calls about stucco balcony leaks almost always start the same way. Somebody sees a brown ring on the garage ceiling, or the porch soffit starts to sag, and the first question is whether the stucco is cracked. Sometimes it is. Usually the crack is the symptom, and the water came in at a junction a few feet away. This is the guide I wish people had before the first contractor showed up with a caulking gun.

Why do balconies over a room leak so often?

A balcony over living space or a garage is a flat roof that people walk on, shovel and furnish. Its waterproof layer is a membrane under the surface you see, and that membrane has to turn up behind the stucco, pass under a door, and survive railing bolts and a drain. Each of those is a joint between trades, and joints are where leaks start.

A deck beside the house is a different animal. Its boards let rain fall through to the ground, so the only thing that has to stay dry is the ledger against the wall, which I cover in bolting a deck ledger to a stucco house. A balcony over a room has nowhere for the water to fall. Every drop that lands on it must be carried off the edge or out a drain, and anything that gets past the membrane lands in a ceiling.

Where does the water actually get in?

Four places, in roughly this order of how often I find them: where the membrane meets the wall, the door sill, the railing posts, and the drain or scupper. The flat middle of the balcony is almost never the leak unless the surface has been cut, punctured or never sloped to drain.

1. The membrane turn-up at the wall

The membrane on the walking surface has to run up the wall several inches and lap behind the building paper and lath of the stucco, so water running down the wall lands on top of it. Then the stucco has to stop above the walking surface on a metal casing or weep screed, with about two inches of daylight, the same gap I hold above any hard surface in stucco clearance at grade.

What I find instead: membrane turned up an inch and caulked to the face of the stucco, or stucco run straight down into the tile and grouted in. In the first case water running down behind the finish lands behind the membrane. In the second the bottom of the stucco sits in standing water and wicks it up all winter. Either way you see cracking and a dark band along the bottom foot of the wall, and the damage is behind it.

2. The door sill

The walk-out door is a hole through the wall at floor level, on the one side of the balcony that collects the most water. It needs a sill pan underneath that the membrane laps into, and the door sill has to sit above the finished walking surface, not flush with it. A door set flush looks tidy and takes on water every time snow melts against it. The usual giveaway is a stain on the ceiling below that lines up with the door, not with the middle of the balcony.

3. The railing posts

A railing post bolted down through the walking surface puts four or more holes through the membrane, and the post rocks a little every time someone leans on it. The sealant around the base gives out long before the post does. Posts fastened to the side of the balcony framing, or to the top of a properly capped guard wall, keep their holes out of the water path. If yours go through the surface, the seal at each base is a maintenance item, and a rusty streak below a post means water is already moving down the fasteners.

4. The scupper and the guard walls

Plenty of balconies here have stucco-clad half walls instead of open railings. Then all the water leaves through a scupper, a short metal sleeve through the wall at deck level. The sleeve has to be flashed into the membrane on the inside and stick out past the stucco face with a drip on the outside. Caulked to the stucco instead, it leaks into the wall, and you get a white or rusty streak running down from the scupper outlet. One scupper with no overflow also means a leaf blockage can flood the whole deck up to the door sill. The tops of those guard walls fail the same way a parapet does, which I go through in stucco parapet walls.

How do I work out where my leak is coming from?

Use the stain underneath as a pointer. Water inside a ceiling travels along joists and down the slope of the membrane, but it rarely goes far. A stain at the outside edge points to the guard wall or scupper; one near the house wall points to the turn-up or the door. Check the ceiling below the morning after rain.

That table narrows it down. It does not prove anything. If the ceiling below is finished and you want an answer before anything is opened, probe readings along the bottom of the wall above the deck will usually show which side is wet; I explain what those tests can and cannot find in stucco moisture testing.

What should a homeowner check on the balcony itself?

Five minutes, from the balcony, no tools. You are looking for anything that holds water against the wall or puts a hole through the surface. If you find two or more of these, have it looked at before the freeze, because one winter of meltwater against a bad junction does more damage than a summer of rain.

• The bottom edge of the stucco. You should see a clean metal edge and a gap above the floor. Stucco disappearing into tile or grout is a red flag.
• The door sill. Lay a level or a straight board on the balcony against the door. If the sill is at or below the top of it, snow will melt against the door.
• Standing water after rain. Puddles against the house wall mean the slope runs the wrong way. The surface should fall away from the house, a quarter inch per foot is the usual minimum.
• The base of each railing post. Open caulk, rust or a post that moves when you push it.
• The scupper. Clear of leaves, sleeve sticking out past the stucco, no streak down the wall below it.

Who fixes what, and in what order?

The membrane belongs to a roofing or waterproofing trade, the wall belongs to the plasterer, and the order matters more than who is cheaper. The bottom band of stucco has to come off first so the membrane can be turned up the wall properly. Then the stucco goes back on, stopping above the deck.

Done in the wrong order, one trade seals against the other trade's mistake. I see it most when a roofer re-membranes a balcony and caulks the new membrane to the face of the old stucco, because cutting the stucco back is not their job. The surface is new and still leaks, because the water was getting in behind the stucco above the caulk line all along. A proper repair runs like this:

1. Cut the stucco back along the bottom of every wall that meets the balcony, usually a band about a foot high, and around the door.
2. Open up whatever is wet and replace it. Wet sheathing and soft framing get found here, not before.
3. The waterproofing trade installs the membrane, turned up the wall, lapped into a sill pan under the door, and flashed into any scupper.
4. New building paper and lath lap down over the turned-up membrane, then a casing or weep screed sets the bottom edge of the stucco two inches above the finished surface.
5. Base coat, mesh and finish, blended into the old wall. Railing posts go back on the side or on a capped wall where that is possible.

If the framing under the balcony has to be rebuilt, that is structural work, and it is worth reading the City of Toronto's list of when a building permit is needed before anyone starts. Other GTA municipalities publish their own lists.

What does the stucco side of a balcony repair cost?

For the wall work, the same bands we use across the site: a few hundred dollars to reseal a scupper or the posts, low thousands to cut back and rebuild the bottom band of stucco around a balcony, and $5,000 and up once wet sheathing and framing come out. The membrane is priced separately by its own trade.

I will not put a number on the membrane or the framing, because I do not do that work and a guess from me would only make your real quotes look wrong. Get those priced by the trade that does them, and ask both quotes the same question: who cuts the stucco back, and who puts it back?

The new-floor trap

One way a dry balcony starts leaking deserves its own warning. Somebody lays porcelain pavers on pedestals, or tile over the old tile, to freshen the balcony up. The finished surface rises an inch or two, the gap under the stucco disappears, and the door sill is suddenly flush. Nothing looks wrong. Two winters later the ceiling below has a stain. Before any new floor goes down, measure from the planned finished height to the bottom edge of the stucco and to the door sill; if either drops below two inches, the floor needs a different system or the wall needs adjusting first.

The $99 patch-and-pray version of all this is a fresh bead of caulk where the deck meets the wall, painted to match. It photographs well. It does nothing for water that is already behind the finish a foot higher, and it hides the junction from whoever comes next.

If you have a stain under a balcony, our stucco repair crew will open the junction, show you what is behind it, and work in sequence with your roofer or waterproofer. On new houses our residential stucco work sets the casing above the deck line before the finish goes on. We see a lot of these over garages and front porches on the newer streets in Vaughan, Woodbridge and Kleinburg. Send us three photos: the ceiling stain, the bottom of the wall where it meets the balcony, and the door sill. That is usually enough to tell you where to look first.