Reprinted from Western Roofing magazine September/October 2007.

 

 

No Slope Too Steep

Tile Offers Options for Most Steep Slope Roofing Applications

by Richard K. Olson, technical director, TRI

 

(Editor’s Note: Richard K. Olson is technical director for the TRI. The association represents industry professionals involved in the manufacturing and installation of concrete and clay tile roofs in the U.S. and Canada, and works with national, state, and local building officials to develop installation techniques, codes, and standards for better roofing systems. Olson can be reached at rolson@tileroofing.org.)

 

 

With this issue of Western Roofing magazine focused on steep slope roofing materials it seems only appropriate to help our readers understand what the steep slope definition really is. According to most of our TRI “ask the expert” e-mails, our consumers presume that steep slope is just as it sounds a roof that has a roof slope of 7:12 and greater. We are constantly asked why our tiles cannot go on traditional lower sloped roofs like other roofing materials.

•               Roof slope is properly defined by the codes, not by perception. While at times it may seem like proper roof pitch is arbitrarily created by the manufacturer, it is in fact, specified by the building codes. Roof slope is defined as the vertical rise of the roof plane. It is easily measured as the inches of rise in a 12” horizontal measurement. The codes further provide only two categories of roof slope, low slope (flat), and steep slope.

                  In the case of the majority of southwestern home designs this will generally fall between 4:12 and 7:12. And in the newer architectural styles we are finding even greater slopes of 7:12 and over as designers try to make the roof a more focused feature of the home to accommodate the higher cathedral interior areas. As we increase the roof slope it will continue to become more visible from the street.

•               So what are the minimum slopes for concrete and clay tiles? For tile, like other steep slope roofing materials, codes define the minimum roof slope of 2.5:12 for proper installation. The reason for this is that when tiles are properly installed, the actual angle of the tile as it sits on the next course of tile below can actually be about 10° of slope or less, depending upon tile profile. Below this slope, tile can in some cases become almost dead flat, thus compromising the system’s natural water-shedding capabilities.

                  So for those tiles installed on roof slopes from 2.5:12 to less than 3:12, both the codes and industry require special underlayment considerations to provide a proper water shedding system. The roofing contractor must first install some form of a “built-up” roofing membrane (three-ply minimum) applied per code requirements or a code-approved alternative. This will provide a long-term substrate that can handle any water that might pass through to the underlayment at these low slopes.

•               We want to use concrete or clay tile on our flat roof patios, carports and front door overhangs. With today’s design professionals trying to maximize the full architectural value of roof tiles, we’re also seeing increased interest in utilizing those special roof areas in non-occupied spaces. While these fall below the minimum for tile installations they still can offer that great look of tile. The designer will have to make sure (if building codes require) that there remains a complete roof system underneath the tile, which is then treated as a decorative element. While tiles installed on these almost dead flat installations may not be visible from the street, they can offer added “aesthetic” benefits, especially when viewed from an upper story, or if the house is set lower than the street.

                  For these installations we also have to look at how these tiles are installed and fastened. Patio covers, for example, are not necessarily required to fully shed water and are not code-defined “occupied areas.” Since these applications are there more for appearance and shade, the tiles are generally installed over plywood or just battens. In these areas the use of nails requires that the contractor consider ways to avoid having the tips of the nails (called shiners) show through the bottom. By nailing at slight angles or using a slightly thicker batten the nails can be carefully hidden in these critical areas.

•               But what about the steeper slopes for tile? We have talked about the lower-slope parameters, but what about really steep slopes. Roof tiles can be installed to roof slopes greater than 24:12. In the Moderate Climate Installation Guide TRI provides the industry code approved information for installing all tiles for all roof slopes. In the case of roof tiles that are designed with anchor lugs that protrude on the under side of the tile, there are special allowances that are summarized in table 1b of the Moderate Climate Installation Guide. These anchor lugs become part of the fastening system and when installed on battens on roof slopes from 4:12 thru 5:12 do not require any additional fasteners except at the roof perimeters. As a roofing material we have seen tiles used on roof slopes up to 24:12 on a regular basis and even greater in some special applications. For the installation of tile on roof slopes greater that 24:12 there will be additional requirements to help hold the tiles in place since the tiles are becoming somewhat vertical. •••