Preserving the Clay Tile Roof on Your Historic House | Wisconsin Historical Society

Guide or Instruction

Preserving the Clay Tile Roof on Your Historic House

Preserving the Clay Tile Roof on Your Historic House | Wisconsin Historical Society
EnlargeClay tile roof

Clay tile roofs are one example of a roof material that has a life span of 100 years. Source: Phil Thomason.

If your historic house has a clay tile roof, you have one of the most beautiful and long-lasting roofs in Wisconsin. However, your clay tile roof will not reach its long-term life expectancy if it has damage that is not addressed promptly. Clay tile roofs can suffer damage from storms, fallen tree limbs or poor-quality flashing.

You should hire an experienced professional to make repairs to your clay tile roof. When you consult with a clay tile roof professional, you will be able to make better decision if you understand how your roof was installed and what types of repairs are possible.

Clay Tile Roof Longevity

Clay tiles were manufactured in various colors, shapes, textures and sizes. They were made in a multitude of styles from French to Spanish barrel. By the late 1800s, most clay tiles were made by machinery. The tiles were fired in very hot kilns to make them harder and more durable, and they could be glazed or colored.

On most clay tile roofs, the openings in the ridge caps, the edges along valleys and the areas along the first course (row) of tiles were usually filled with mortar that was colored to match the tiles. The mortar prevents wind-driven rain, sleet and snow from getting under the tiles. It also prevents bats and other small animals from nesting in the crevices.

Most clay tile roofs in Wisconsin were installed on new houses built from the late 1800s through about 1930. Clay tile roofs in Wisconsin can last 100 to 150 years. Therefore, many clay tile roofs have reached or are reaching the end of their functional life. The longevity of your clay tile roof will depend on:

  • How the tiles were fastened to your roof.
  • How steep your roof is.
  • How well your roof was originally flashed.
  • Whether your roof has been maintained over the years.

The surface of clay tiles that are exposed to frost over a long period of time will begin to show scaling. Environmental pollution can also discolor clay tiles. In some cases you will be able to clean off this discoloration with a mild detergent and a stiff nylon brush. If the soot and grime do not come off easily, you may want to just live with this aged look.

Clay Tile Repair and Replacement

You must decide whether to repair or replace your entire clay tile roof by assessing the condition of your tiles. Good clay tiles will look solid with no scaling or cracks. Clay tiles whose surfaces show scaling are at the end of their life. If less than 20% of your clay tile roof is damaged or worn out, you can hire a professional to replace individual tiles on your roof. New clay tiles are installed in two ways:

  • Fastening the new tile in place by a nail with copper flashing installed over it.
  • Hanging the new tile in place with copper straps hooked under the butt edge of the tile.

If 20% or more of your clay tile roof is damaged or worn, you will have to replace your entire roof and all the flashings. Your clay tile roof is a character-defining feature of your historic house, so your best choice is to replace your damaged clay tile roof with a new clay tile roof. However, if your original roof was not clay tile, you should not install a clay tile roof on your house.

New Clay Tile Selection

Clay tiles have increased in popularity due to the preservation movement. As a result, new and very good salvaged tiles are available that will closely match the size and appearance of your original tiles. When you are selecting new clay tiles for your roof, buy tiles that were manufactured in the United States. Although tiles imported from Mexico, South America, China and other areas can be excellent quality, they will not closely match the size, color and texture of your original tiles. Always order more tiles than you need so you have a supply for later use.

The color of your new tiles might not completely match your original tiles. If you must replace individual tiles in an area of your roof that is visible from the public right-of-way, you could take tiles from less-visible areas of your roof to repair the more visible section of your roof.

Clay Tile Installation

When your roofer is installing a clay tile roof on your historic house, you should make certain your roofer follows these installation practices:

  • Use copper or stainless steel nails. Your roofer should install slate with copper or stainless steel nails. The original nails used to install your clay tiles can create a maintenance issue. Steel, cut or square nails used in the late 1800s rust and fail the most. Your clay tiles should have been installed using nonferrous metal nails like copper. If the nails holding your clay tiles are failing and your tiles are still in good condition, a clay tile professional can remove the nails and reinstall the tiles.
  • Install appropriate flashing systems. Most clay tile roofs were installed with copper or lead-coated copper flashings. Your roofer should use only one type of flashing metal. Differing metals that come in contact can create galvanic action — an electric current that will erode the weaker of the two metals. Make certain your roofer uses copper sheets that are not less than 16 ounces. A 16-ounce copper sheet is a one-square-foot sheet of copper that weighs 16 ounces. The higher the number of ounces, the thicker the copper will be. In valleys and other high-water areas, your roofer should use 20- or 24-ounce copper. Your roofer should also install rubber membranes at all eaves and in all valleys, and copper W-valley flashing over the rubber membrane.

The information presented here is not intended to provide comprehensive technical advice or instructions on solving historic preservation issues. Any information contained or referenced is meant to provide a basic understanding of historic preservation practices. Read full disclaimer.