TriForm Linear Drain Shower System


Quick Specs

  • Type: Shower Bases
The TriForm is fast becoming the most popular level-entry shower former available. Its a structural shower foundation with pre-sloped drain planes contained within a mere 7/8"- thick edge profile. TriForms feature an integrated linear drain for a completely watertight assembly, and the drain trough offers 3 drain connector locations to ease installation. Showers may be constructed using the tile or stone of choice, and the versatile drain assembly allows for a stainless steel cover or a custom tile or stone look.

TriForms are easily installed in a day and offer a modern, reliable, completely predictable alternative to the old-fashioned method of mud bed shower construction. TriForms are fully compliant with both the International Plumbing Code and Universal Plumbing Code, the standards used by plumbing code authorities across the US and Canada.


1. A TriForm sized for your project
2. A linear drain assembly in the style that suits your preference and in the depth range for the thickness of the tile or stone you plan to use
3. A TriForm waterproofing kit
4. Additional reinforcement tape, corners, and waterproofing compound, depending on the size of the shower you build and its complexity (built-in bench, niches, bump-out walls, etc.).


TriForm thickness at edges: 7/8"

TriForm composition: Fiberglass, resin, and steel reinforcements.

Slope gradient: Pitches vary in slope, though all pitches are equal to or greater than 1/8" per foot (complies with all applicable codes for a pre-fabricated, structural shower plumbing fixtures).

Structural: Yes, for spanning properly sized joists 16" on-center.

Weight load capacity:
560 lbs. on joists and blocking
1,100 lbs. with joists and blocking and "- thick plywood underneath (call ARC for more information)

Stress capacity: 4,000 pounds-force per square inch

Support requirements:
Installation requires completely supporting the entire perimeter of the TriForm and the drain trough. Any cuts or notches made in the former must be supported. Support can be achieved with joists and supplemental 2 x 6 or 2 x 8 blocking.

Custom fitting:
TriForms can be cut to length (do not cut closer than 4" from perimeter of the drain trough). Use a fine-toothed metal-cutting blade in a circular saw (the cut will go through steel reinforcement tubes near the outer edges of the former).

Drill anywhere in a former around the rim and in the flat drainage area. Use a twist drill bit designed for metal, and countersink each hole to bed screw heads slightly below the surface of the TriForm. Installation screws are used in addition to construction adhesive (on wood) or thinset mortar (on concrete).

Waste capacity:
The drain trough contains three locations for 2 diameter waste line connectors. Each connector is capable of handling a water flow rate of approximately 8 gallons per minute (Note: A typical shower head generates 1.5 to 3 gallons per minute).