Hidden Gutter System / by keith messick

Left to act on its own, water can literally dissolve a house. It is critical to control the flow of water from the top of the roof down to the ground.  There are several options to control roof drainage.

Our Skyline Drive Project incorporates a flat roof and a hidden gutter detail to control and direct the flow of water. Our design is clean and simple. It minimizes the thickness of the roof profile and also minimizes the clutter of a downspout.

When it rains, water strikes the roof and begins its journey towards the ground.  It will move in the direction of least resistance.  You want to control the direction of that water and dictate where it goes.  We do this with roof slope, gutters, drains and/or scuppers, downspouts, and, ultimately, a drainage system at ground level.

Gutters collect the water coming off of the roof.  Traditional designs have the gutter simply hanging off the fascia board that is mounted to the overhang of the house.  A downspout is connected directly to the gutter.

This traditional design leaves a lot to be desired. The gutter is functional but has a very clutter and messy appearance. The gutter covers the fascia board and the downspout protrudes from the gutter and loops back to the face of the house.

Typical Gutter on a Traditional Sloping Roof

When considering a modern design, flat roofs are more typical.  In the past, flat roofs were flat (no slope). Today, flat roofs are not actually flat.  They have minimal slope.  At the least, a roof must have a 1/4" per foot slope.  This means for every 1 foot of horizontal distance, the roof will drop 1/4 inch.  

The drainage system on a flat roof is a little different than on a traditional sloping design.

Flat Roof Drainage-Note no overhang

A flat roof will utilize a drain(s) and/or a scupper(s), an overflow device, and some type of downspout (often called a leader, in this situation).  Flat roofs tend to use slope to direct the water to a drain or scupper.  The drain or scupper captures the water from the roof and directs it to a leader.  The leader brings the water down off the roof in a controlled fashion.

Scupper in Roof (Note: no leader-water would simply pour off of the roof uncontrollably-not good)

Scupper-Before installation

Some flat roofs have overhangs; others do not.  A leader connects to the drain or scupper and can be located either externally (down the face of the building) or internally (inside walls).  If a scupper is used, the leader will be mounter to the exterior of the building.  Utilizing drains gives you the option to route the leader internally or externally .  

At this point, its time to discuss the overflow (required by code).  On a flat roof, there is usually a small wall (called a parapet) at the edge of the roof.  If this parapet is much higher than the drain and the drain gets clogged, water will build up on the roof like a swimming pool.  This is a potentially very dangerous situation.  To avoid this from happening, the building code requires some type of overflow device if the parapet is taller than 2".  This device can be a scupper or an overflow drain.  An overflow drain is simply another drain located next to the primary drain positioned 2" higher.

Roof Drain with Overflow Drain-Note the collar around the overflow drain.

Scuppers can be used for overflow

In the design used on Skyline Drive, the parapet is kept lower than 2".  Thus, no overflow is required.  This simplifies the construction and the facade at the roof line.

The gutter system resides inside (hidden) the overhang of the roof.  A drain is incorporated into this gutter. The leader is attached to the drain, runs through the overhang, and directly down the exterior wall of the house.

This design is clean and simple.

Architectural Detail-The gutter is 1.5 inches deep.

Hidden Gutter-Less than 2 inches in depth. Note: Roof is a PVC membrane.

Hidden Gutter

Downspout drops straight down through overhang from gutter above.

Downspout sits tight against house. Clean and clutter free.

This hidden gutter system exemplifies a good modern detail. A gutter is required to properly control the flow of water. While utilitarian in nature, the aesthetic should still fit the design philosophy. It should be, most importantly, functional. But the functional resolution should be elegant.