 An eave closure or birdstop to keep out birds is notably absent from the replacement tile in the center of the bottom row. Photo: NPS files. |
Field and Specialty Tile. The tiles that cover the majority of the flat
surface of the roof are called field tile. Some roof shapes, particularly
conical towers or turrets, require tiles of graduated sizes, and some shapes
or patterns of field tile also require specially shaped finish tiles to
complete the roof covering package. Other uniquely-shaped tiles were made
to fit odd-shaped spaces and places including dormers and valleys, roof
hips, rakes, ridges and corners. There are also finish tiles that fulfill
certain needs, such as eave closures or clay plugs called "birdstops."
These are intended to keep out snow and rain, and birds from nesting in
the voids under the bottom row of curved tiles. Different patterns and
designs can also be created by combining, or mixing and matching flat tiles
with dimensional tiles.
Tile Colors. A terra cotta red is the color most commonly associated
with historic clay roofing tiles. The reddish color comes from clay with
a large percentage of iron oxide, and there are many variations of this
natural color to be found in tiles ranging from deep reddish browns to softer and paler oranges and pinks. Lighter buff and beige
colors, as well as black, also appear on traditional tile-roofed buildings.
Buff-colored tiles were made from nearly pure fire clay, and pouring manganese
dissolved in water over the tile before firing resulted in smoke brown
or black glazed tiles. Toward the end of the 19th century the popularity
of colored glazes for roofing tiles increased, and their use and the range
of colors continues to expand today.
Most historic glazed roofing tiles
are in fairly natural hues that range from reds and browns and buffs, to
blacks and purples, blues (often created with smalt, or powdered blue glass),
and a wide variety of greens (usually created with copper slag). There
could be a considerable range in the colors of tiles that were baked over
a wood fire because the temperature within the kiln was so uneven; tiles
closest to the fire cooked all the way through and turned a darker red,
while tiles farthest from the flames were likely to be smoke-stained, and
lighter orange in color.
"The Preservation and Repair of Historic Clay Tile Roofs" an Historic Preservation Brief
