An envelope shower base (also known as an “envelope cut” shower floor) is a technical tiling method used to create a sloped shower floor using tiles that are larger than 4 inches instead of the traditional small mosaics.
Historically, bowl shaped shower floors required small tiles (typically 4 inches or smaller) because these mosaics could easily conform to the “bowl” shape needed for drainage. The small tile size eliminates the risk of lippage – which is where edges of an adjoining tile is higher than its neighbor. This made for a smooth shower floor that drains properly. An envelope base bypasses the 4 inch tile size limitation by cutting large tiles into specific geometric triangles that slope independently toward the drain.
How It Works
The technique is named after its appearance, which often resembles the back of an envelope.
- The Geometry: Installers map lines from the four corners of the shower floor to the four corners of the drain.
- The Cuts: Large tiles of any size are cut along these diagonal lines to create grout joints which point to the drain.
- The Slope: These triangular pieces are set on the four distinct flat planes, each pitching downward toward the drain to ensure proper water flow. If your shower floor has more than 4 sides, you will have more flat planes.
Key Benefits
- Modern Aesthetics: It allows for a seamless visual flow by using the same large-format tiles on both the bathroom floor and the shower base.
- Easier Maintenance: Because it uses large tiles, there are significantly fewer grout lines compared to mosaic floors, reducing areas where mold and mildew can accumulate.
- Curbless Design Compatibility: This method is frequently used in barrier-free (curbless) showers, providing a sleek, high-end look while maintaining the accessibility required for aging-in-place or wheelchair access.
Installation Options
- Custom Field-Built: Professional installers create a custom slope using a drypack sand/mortar bed, then template and cut the tiles on-site. This takes considerable skill and experience to accomplish.
- Pre-manufactured Foam: Some manufacturers offer pre-sloped Styrofoam pans designed specifically for envelope drainage, which can be easier for DIY enthusiasts to install but they must be an exact fit for the size, shape, drain type, and drain location otherwise the envelope shape will not fit your shower.
- Custom Made Foam: Starting around $25 per square foot, ordering a custom made foam base on line is easy and will fit your jobsite perfectly. Using a manufacturer such as Built With Foam that is UPC certified will guarantee the slope of the shower floor meets industry standards for proper drainage.
Limitations
- Envelope shower bases do not eliminate the need for the proper slope on a shower floor which must be between 2% and 4% for residential showers. The slope requirements may necessitate the installation of a second floor drain, the use of a linear drain, or moving the location of a drain to a more central location. A custom foam shower base manufacturer will be able to help you in determining the best drain type and location for your situation.
- Since these are floor tiles, they MUST have the proper slip resistance. The slip resistance rating is always shown on the box exterior when selecting tile.
- For showers with more than 4 sides, deciding which corner of the drain each flat plane points to can be a design issue.
