Curb Design
Jump to one of the following sections:
HISTORY
The original design for shower pans and bath tubs had a flat curb, which shower curtains would tuck in behind. Curtains do a notoriously poor job of containing the water, so during the mid 50’s shower doors became a thing. Because these sat on the curb, the industry started to slope their curbs slightly towards the shower/tub. This stopped the water from pooling on the curb, but did nothing to stop leakage under the doors as the moving shower water easily overcame these mild slopes. Shower door manufacturers soon learned that they needed to provide thresholds under their doors (see example to the right) which essentially incorporated a water dam.
In the mid 90’s frameless enclosures started to become popular. As the idea was to eliminate as much metal as possible, those thresholds had to go and the huge issue of leakage returned with a vengeance. Water that hits the door wants to stick to the door, and the downward motion is converted to an outward motion which easily travels up the curb and onto the washroom floor.
The solution
Framed and semi-frameless enclosures still come with thresholds and therefore do not leak. But for frameless enclosures there are three options:
The industry standard is to provide an extruded poly-carbonate diverter/sweep on the bottom of the doors. Because they are clear, when new they look okay, but they quickly yellow and collect soap scum and organic material leading to blackish mold and mildew. They can cheapen an otherwise great looking door. Yeach.
In the vast majority of cases the only other option is to add a threshold, just as the industry did with the framed and semi-frameless enclosures. The benefit of these thresholds over sweeps is that they are easier to clean and thus do not look as unappealing with use.
The best and simplest solution, however, is to modify the curbs to incorporate a water dam. A very small minority of prefabricated bases have that feature, so that industry is painfully slow to adapt. But so too are tile setters. We might be the only firm that shows proper curb designs in our showroom or provides guidance on how to properly tile a shower where a frameless enclosure is contemplated. Note that the design ideas would also apply for framed and semi-frameless enclosures as those enclosures don’t need to be installed with their metal thresholds.
Note: A common industry error we see is to leave a very small gap under the door, reasoning that the less room you leave for water to leak the less leakage you will have. This will fail because the leakage is a sheeting action. All this accomplishes is making it impossible to provide a later solution short of replacing glass. This is but one of many pitfalls of buying from whoever is cheapest.
VARIATIONS on a theme
The general idea is simply to provide a two-tiered curb. There are variations on this idea, so the important thing is to understand the concept and design accordingly. The important component is to have the lower portion, which slopes toward the shower to prevent puddling, under the door for certain. For simplicity it generally extends under the fixed panels, but lowering the height under the door only, such as in the design to the right, which also incorporates buried U-Channel for the panels, can look very professional. The higher portion towards the outside of the shower acts as the dam.
The door must clear the dam so that it can still swing out (typically a code requirement for safety reasons), but while water still whips around the bottom of the door, by the time it reaches the dam it will have dropped enough to hit the wall and be sent back to the shower pan.
It is impossible to provide exact specifications required for this to happen. Water pressure, showering habits, tolerance of the homeowner to water escapement, and numerous other factors all play their part. It is thus best to err on the side of caution. The higher the dam, the further away the inside edge is from the glass, and the greater the slope under the glass, the more effective the system will be.
sample construction
Frame the curb. A couple of 2x4’s or 2x6’s (brown in the picture) is common.
Cover with a suitable wall board such as concrete board (gray in picture).
Apply a continuous waterproof membrane that accepts tile (not shown). This modern technology is most highly recommended over the older and much inferior system that uses a membrane that cannot accept tile directly. Those require a layer of concrete on top which becomes a perfect medium for mold and mildew.
Tile (blue in picture) the surface using thin set (not shown). Tile on top of curb should be sloped towards the shower. The raised portion on the outside of the curb should be at least 1 inch ahead of the center of the curb and at least 1/2 inch tall.
We typically install the glass door (green) and panels (not shown) over the center of curb, with door clearing the high point of the curb by 1/8-inch.