Selecting Tile For Indoor-Outdoor Use

Creating seamless transitions from indoors to outdoors can be aided by the right tile and paver choices.

authors Patrick O'Toole | December 3, 2021

BOLOGNA, Italy — The annual CERSAIE tile trade show is a good place to feel overwhelmed. This fall exhibitors in Italy put forth a dizzying array of new sizes, thicknesses, patterns, finishes, colors and styles. The same can be said of COVERINGS, the North American tile show held in Orlando last summer.

Cementum from Marazzi offers a concrete look in several shapes colors and thicknesses including 20 mm.

Porcelain tile, in particular, is a fast-growing category. It is a cousin to traditional ceramic tile, but it is harder, sturdier and better able to project colorful photo-realistic designs—from marble colors and patterns not found in nature to hyper-authentic stone, wood and concrete looks. It also costs about 60 percent more, on average, than its ceramic counterparts.

The higher cost owes to porcelain’s more stringent manufacturing process. Like ceramic tile, porcelain tile is made of clay, but it requires much higher temperatures and pressures. The result is an extremely durable product that is particularly well suited to indoor-outdoor flooring applications, particularly in climates with big temperature swings.

Porcelain is less apt to expand, contract or buckle due to extremes in temperatures or even snow and ice. Traditional ceramic tiles certainly work well outside; however, tile and paver setters must do more to address weather concerns.

Designers are increasingly seeking a seamless flow between indoor and outdoor spaces, particularly in places where large sliding and folding doors are pushed away to merge living spaces. Safety, durability and water resistance are key factors to consider when selecting a tile product that works well in a living room plus a few steps away on a lanai, patio or pool deck.

Panaria Ceramica’s Borealis line of wood-effect tiles are inspired by oak timber shades.

This article is therefore less about color and pattern and more about performance considerations. The images come from manufacturers who have recently highlighted their indoor-outdoor capabilities at either CERSAIE, which highlights Italian tile, and COVERINGS, which is a showcase for tile made in the U.S. and Spain, as well as Italy.

Slip Resistance, Thickness, Slope

REFIN Ceramiche’s Cortina line also offers wood effects in porcelain.

Porcelain tiles often come in glazed or unglazed versions. The unglazed version is a better choice for flooring applications, but a designer may select a glazed tile for inside and an unglazed tile for outside. Slip resistance is a major design consideration when specifying ceramic or porcelain tile in outdoor applications, particularly near a pool or hot tub. Manufacturers are responding by manufacturing the same tile size, pattern and color with different slip ratings—for example, an R9 rating for indoors and an R11 rating for outdoors.

Most designers and remodelers with experience know and understand the various rating systems for slip resistance. The Tile Council of North America references an ANSI standard for ceramic tile slip resistance. “ANSI A137.1–2012 standard, ceramic tiles selected for level interior spaces expected to be walked upon when wet must have a minimum wet DCOF AcuTest value of 0.42,” states the organization’s website,

R9 and R11 ratings are related to European standards for slip resistance, which is also expressed in DCOF or dynamic coefficient for slip resistance. The 0.42 DCOF rating cited above is based on a scale where a lower value is more slippery, and a higher value is more slip resistant.

Cotto d’Este’s Blend Stone line of porcelain tile shown with the Bocciardata finish, available in 14 mm and 20 mm thicknesses.

Ceramic and porcelain tiles are water resistant and offer more colors and patterns, but those properties tend to be slippery. So, it is important to look for higher DCOF or COF ratings in outdoor areas that are likely to be wet and walked on with bare feet. COF ratings in the range of 0.40 and 0.60 or higher are the best choice for ceramic or porcelain tiles.

Tile thickness for outdoor use is another key consideration. European manufacturers not surprisingly organize the thicknesses of their tiles in millimeters and centimeters. In the U.S., 0.25-inch tile is acceptable indoors, but outside tile should be 1.25 inches thick or more depending on factors like the weight of objects that will be placed on these surfaces.

European outdoor tile thicknesses are generally 2 centimeters, which is slighty more than 0.75 inches, 0.78 inches to be exact. They are also expressed as 20 millimeters, which is the same thickness as 2 centimeters. Thicker products are often 30 millimeters thick, which is 1.18 inches.

Gardenia Orchidea offers a line of outdoor tiles with metallic shades called Oxide. The iron shade is shown above. advises the following: “For covered exterior areas with minimal exposure to adverse weather, ½ inch, 3/8 inch and 5/16-inch tile can be specified. These thicknesses are also appropriate for applications in which they will not be expected to support heavy objects, like large appliances or vehicles. Two-centimeter pavers (0.78 inches) are recommended for uncovered exterior applications, inclement weather exposures, heavy-object support (including vehicles) and/or commercial foot traffic. Additionally, only 2-centimeter pavers should be used for raised pedestals installations, over flexible substrates or for installations set on sand, gravel or grass.”

In addition to the slip ratings and thicknesses, slope must be added to outdoor areas that are exposed to precipitation. Your tile professional should be consulted on the specification of outdoor tiles, that way all these considerations can be factored into a seamless indoor-outdoor look.

Ergon Engineered Stone’s Elegance Pro is a tile line that imitates sandstone and is available in seven colors and two thicknesses.

For more detailed outdoor tile design considerations, go to the websites for the Ceramics of Italy at or The Tile Council of North America at QR

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