Linear Drain System Specification 101 for Accessible Bathrooms and Wet Rooms

Streamlined shower design feature offers sophistication and sanitation
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Sponsored by Infinity Drain
By Kathy Price-Robinson

Specifying A Linear Drain System Based on Function

Which linear drain system is best for a given project? This is based on whether it is a barrier-free bathroom and which waterproofing technique the installer will be using.

Traditional versus Modern Waterproofing

The difference between traditional and modern waterproofing methods is being able to tile directly on the waterproofing membrane (instead of having a secondary mortar layer), which saves floor height in installation and can be beneficial in designing barrier-free and curbless showers.

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The difference between traditional and modern waterproofing methods is being able to tile directly on the waterproofing membrane (instead of having a secondary mortar layer), which saves floor height in installation and can be beneficial in designing barrier-free and curbless showers.

Traditional North American waterproofing methods require multiple levels of installation, skill sets, and limited square footage. The traditional method for installing a tiled shower begins with the installation of a mortar bed that is sloped to the weep holes in the clamping floor drain. A waterproofing membrane, typically referred to as a pan liner, is subsequently placed over this "pre-slope" and clamped into the drain.

Regionally Specific Waterproofing Methods

Pan liners may consist of metals such as lead and copper, or plastics such as polyvinyl chloride (PVC)and chlorinated polyethylene (CPE). In the Northeastern part of the United States, lead or copper pans are still a popular way to waterproof a shower.

In some regions of the country, specifically in Southern California, installers also employ hot mop systems that involve applying layers of asphalt and roofing felt to build up a pan liner. Pan liners are carried up to a height of at least 3 inches above the finished height of the curb and must not be penetrated by any fasteners. Pan liners are not designed to allow for the direct application of ceramic or stone tile.

Membrane and Pan Liner

The most mainstream way to waterproof a shower, and what most showers in the United States utilize, is the vinyl pan liner or rubber liner. This method uses a thick yet flexible membrane to create an envelope on the shower floor and up a small portion of the walls. It is almost like wrapping a present or doing origami.

There are two types of linear drain systems that are a good fit for showers with traditional waterproofing methods: site-sizable linear drains and fixed-length linear drains.

Site-Sizable Linear Drain Systems

Site-sizeable linear drains work with the standard installation using a shower pan liner and a clamping floor drain to connect to the waste line.

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Site-sizable linear drains allow for more flexibility during installation.

This system is sold as a complete kit, and modifications can be made to the length and outlet placement on-site. This provides ultimate flexibility in making the drain work for the site-specific conditions. It also allows the drain to be sized on-site for a perfect wall-to-wall installation. In theory, a linear drain does not technically need to go from one wall to the opposite wall. However, wall-to-wall installations look more pleasing to the eye. And functionally, it allows a true one-plane floor pitch with no water pooling in the corners of the shower. This also creates complete water removal when placed along the threshold of the shower with no curb or barrier.

In this system, channels are constructed of stainless steel or PVC and utilize a neutral pitch (meaning a flat-bottom channel). Because the outlet is located on-site, the channel cannot come pre-pitched. It is a common misunderstanding that the channel for a linear drain system requires a drastic pitch to get the water headed toward the outlet. Water is always looking for its low point or level—that is the outlet. Through capillary action, as the channel fills with water, it pulls itself down the waste line. What is left in the channel are water droplets held on via surface tension.

Consider a site-sizeable linear drain installation with a PVC channel. This ‘sandwich’ style of installation is characterized by the waterproofing being ‘sandwiched’ by the two mortar layers. Thus, a secondary mortar bed must be installed to provide load distribution and a bonding surface for the floor tile. Pea gravel is placed around the clamping floor drain’s weep holes to prevent blockage before installing the secondary mortar bed. This installation can be summed up as a ‘sandwich’ style of install: Mortar, waterproofing membrane, mortar. The mortar is the bread of the sandwich, and the waterproofing membrane is the meat.

Site-sizeable linear drains may be available with either a PVC or stainless steel channel. Some local municipalities such as New York, Chicago, and San Francisco require all-metal plumbing components. In these cases, the all stainless steel site-sizable linear drain is the appropriate option.

Fixed-Length Linear Drain Systems

The second type of linear drain that works with traditional waterproofing and a clamping floor drain is a fixed-length linear drain system.

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Shown is the construction assembly for a fixed-length linear drain system.

This is a set-size, set-outlet-location linear drain system, which means there is no on-site flexibility. This could be a limitation or hindrance in a custom home or high-end renovation. But for new construction or large multifamily or hospitality projects where speed of installation is a priority, fixed-length systems can be a good option. Depending on the manufacturer, the outlet is either centrally placed or offset.

Fixed-length linear drains have pre-pitched channels because the outlet location is predetermined. The illustration shows a fixed-length drain side detail. Notice the use of the clamping floor drain and sandwich-style installation. The channel comes in one welded piece instead of components like the site-sizeable model. Channels are constructed of either PVC or stainless steel depending on the manufacturer, and most companies offer a custom fabrication service if needed.

Challenges with using a fixed-length drain system include achieving a perfect wall-to-wall installation and being able to adjust to normal construction tolerances. If the wall or outlet location is off by any amount, the specified drain may no longer fit the space.

These are drains that work with traditional waterproofing techniques. However, modern waterproofing techniques call for different types of linear drain system solutions.


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Originally published in June 2020