Alternative Types of Roofing – Clay Tile – Part I

Today we start looking at the topic that we consider really exciting because it takes us to different parts of the world and on a virtual tour through history. Roofs have been in a Central part of building structures, and even before the dawn of civilization.

The common types of contemporary roof systems are single ply polymer or standing seam metal flat or low-slope roofs and asphalt shingles or slate tiles at higher slope roofs.  There are many other type of roof materials though.  In this series we will look at terracotta tiles, thatch roofs, corrugated metal roofs, and green roofs.  It will be a very exciting learning experience.

We start this multipart series by looking at terracotta clay tile roofs.   The outline of the first part of the series follows below and in todays article we will be looking at sections 1-3:

  • The History of Clay Tile Roofs
  • Clay Tile at Mansard Roofs in Washington DC
  • Limited Spans and the Impact of Structural Roof Capacity 
  1. The Overlapping Concentric Nature of Roofing 
  2. The Reversibility of Clay Tile
  3. Upkeep, Care and Maintenance of Washing DC Historic Roof
underside of terracotta tile roof
Looking at the top side of the roof, the aesthetic is relatively common and familiar in most parts of the world with types of historic construction.


The history of clay tile roofs

The history of clay tile roofs in Spain and Latin America goes back centuries. Introduced by the Romans and refined by the Moors, terracotta roofing tiles became integral to Spanish architecture. The Mediterranean-style, blending Roman, Moorish, and Gothic elements, embraced these tiles for their durability and insulation against the Iberian Peninsula’s hot climate. 

As Spanish settlers explored the Americas, the Mission style in regions like California showcased the continuation of this tradition. In Latin America, during the colonial period, Spanish architectural styles spearhead regionally, with cities like Mexico City displaying colonial buildings featuring distinctive red clay tile roofs.

clay tiles
The underside of the Terracotta tile roof is almost like a mirror image, butnhere you can see the supporting purlins and exposed tops of each tile.

Clay Tile at Mansard Roofs in Washington DC

Over time, the use of clay tiles adapted to local styles, incorporating influences from indigenous cultures spread up into the north of Mexico into areas that are today part of the USA.    Today you can see many examples of terracotta tile used at mansard roofs here at the historic rowhomes of Capitol Hill and Washington DC.  However, aside from mansard roofs, and very particular Spanish or Mediterranean-style designs, terracotta tiles are a bit rare as the main roofs in Washington, DC.  Terracotta tile is a relatively dense and heavy roof material and requires more structural support than the typical alternatives.

The Washington DC rowhome mansard roofs are relatively small and limited in size. They have some of the highest pitch angles and slope of any roofs in the city.   The detail of the slope and limited size is directly related to why terracotta tile roofing is an acceptable candidate for these mansard roofs and found there much more commonly than in other types of main building roofs.

Limited Spans and the Impact of Structural Roof Capacity

The limited size of the mansard roof means that there are limited spans from the ridge to the eave of the roof. 

In the next section of this article we’re going to talk about the difference a slope makes on the structural load or capacity at the end of the field of the roof, but here, it’s a  somewhat different principle.  This principle is more intuitive.  If a structural element has a lesser span, the structural capacity increases in a nonlinear way.    Especially, structural member, or support, of shorter flexural span has a much higher capacity.   For example, a roof rafter made of a wooden 2×12 would be two inches wide by twelves inches in height.  That board can support way more than 10 times the load of a board of the same height and width if the other board has 10 times the length. This is an example on nonlinearity in structural capacity.

terracotta flatroof tiles
Unlike panelized materials, a significant amount of intermediate support is required to support the extra weight of terracotta roof tiles.

High Vertical Slopes Shift the Load Away from Intermediary Support

Effectively, a lesser structural bearing load is applied to the intermediary supports or structure of a roof system when a roof has a higher degree of slope or pitch.   You can understand this concept by visualizing a flat deck, whether it be a floor deck or a roof deck, Any point within the field of the roof.   This structural engineering principle is essential to understand the required amount of support, there’s a major difference between a relatively high slope roof and a relatively low slope roof.

Looking at a wide view under the roof system, you can see the structural backbone of the roof.

roof struts frame
In the picture below you van see the greater expanse of the roof struts frame.

In the next upcoming article we will pick right back up on this topic and discuss the concentric nature of roofing laps and why laps are needed in roofing and we will talk about the unique reversibility of clay tile.  

On Key

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