Box gutters

The gutter that is part of the building

On a lot of Cincinnati houses the gutter is not hung on the building, it is built into it: a wooden trough formed as part of the cornice, lined with sheet metal or membrane, draining through an outlet cut down through the soffit. When the lining goes, the water has nowhere to go but into the structure.

Why this city has so many of them

Box gutters are what you build when you are building a masonry house with a deep decorative cornice and no interest in hanging metal across the front of it. The Italianate, Queen Anne and early four-square stock that fills the pre-1940 neighborhoods here was built that way as a matter of course, and much of it is still carrying the original trough with a fourth or fifth generation of lining in it.

The nationals will not touch them, because a lined trough that is unique to the building is the opposite of a scalable product. Most volume roofers will either decline the work or quote to tear the cornice off and hang a conventional gutter, which is the wrong repair on a house that is worth what these houses are worth.

How a box gutter fails

The lining splits at a seam

Metal linings move with temperature. Rigid solder joints and rigid seams eventually crack, usually at a corner or where the trough changes direction, and the leak is hidden inside the cornice long before it appears on a ceiling.

The outlet blocks

The outlet is a hole through the bottom of the trough into a downspout. Under a mature canopy it clogs, the trough fills, and a box gutter that fills becomes a pond sitting on top of the wall.

The pitch is gone

The trough floor is wooden and it sags where it has been wet. A sagging floor holds water even when the outlet is clear, and standing water finds every pinhole.

Ice

A full trough freezes solid. Ice expands into every seam and lifts the lining away from the wood, which is why a gutter that was dry in November leaks in March.

Somebody patched it with roof cement

The classic. Black mastic over a split, which holds for a season, cracks, and traps water underneath it where it rots the trough floor faster than the original leak did.

What a proper repair involves

1. Open it up and find out what is left

   The old lining comes out and the trough floor and the framing behind it get looked at and probed. Everything else depends on what that shows, and any scope written before it is a guess.

2. Rebuild the wood

   Rotten trough floor and cornice framing are replaced in kind, and the floor is re-pitched so it actually drains to the outlet. This is carpentry, and it is usually the larger half of the job.

3. Line it in one piece where possible

   A continuous membrane or a properly detailed metal lining, carried up the back onto the roof deck so roof water lands on top of the lining, and over the front lip so overflow goes outward. The laps run with the water, never against it.

4. Detail the outlet properly

   The outlet is the part that fails first. It wants a formed drop rather than a hole, with the lining dressed into it, and it wants to be reachable for cleaning.

5. Deal with the roof-to-trough joint

   The joint where the roof slope meets the back of the trough is the other failure point. The roofing must lap over the lining, with enough overlap that wind-driven rain cannot get under it.

Lining choices, and the trade-offs

Keeping one alive

• Clear the outlets twice a year, and more often under oaks and maples. A blocked outlet is how almost every one of these failures starts.
• Look at the ceiling below the cornice after a long rain, not during it. Box gutter leaks show up as a line of staining parallel to the outside wall.
• Do not let anyone put roof cement in it. It is the repair that guarantees the next repair is bigger.
• Check it after a hard freeze. Ice movement opens seams, and the damage is done in winter even though the leak appears in spring.