In rock climbing, “trad” is short for traditional. For climbers the designation of “trad” means purity: no drilling is done, the anchors are set into cracks and rely on the skill of the installer to save them from a fall. In the case of roofing: traditional roofing means no modern solutions like manufactured components, sealants, or other temporary products. When we design a traditional roof, the goal is to make it permanent. A roof should last the entire lifespan of a building. A temporary roof has to be re-roofed multiple times during the life-cycle of the building at considerable cost each time. It is better to invest upfront, and make the roof as durable as the rest of the exterior finishes.
Classically there are a few materials which have proven track records of protecting buildings for multiple centuries: Slate, Tile, and Copper.
Material selection is the easy part. The custom builder, the preservation architect, and the institutional project manager, often wisely selects these materials for historic projects. The problem with selecting these great materials in America: There is no group that juries members who practice the trade, and there is no governing body that sets standards for proper work or curriculum for study. Most of the “new” roofs you see constructed of these great materials are relying on modern (disposable) products to ensure they actually function. Further, there is no legal structure for recourse. If you commission a “historical” roof, and the company selected shows up, does a great job, leaves it looking good (from the ground): this leaves most in the market with the impression they are getting a good service, and a permanent roof. However with properties changing hands so often, the new owner, or the owner in 50 years is going to have a time-bomb on their hands when the temporary sealants, solder and other questionable techniques start to show their inferiority.
This is the status of most homeowners and institutions that have historic roofing, either original or re-commisioned at some point in history; they inherit all the problems and defects caused by poor training, no oversight, and no standards. Many of these defects don’t show up until the poor design has been through many decades of service. In my travels inspecting historic roofs all over the country and the Caribbean, I have seen very few examples of historic work done properly in metal. We did have some great slating traditions that made it over from the old country, and there is a solid heritage in the northeast of very well made slate roofs. This issue was brought to light with Joe Jenkins: in the Slate Roofing Bible. This book is the best source for knowledge on the history of slate roofing and following Joe’s instructions laid out in this reference will produce excellent results.
Where the Slate Roof Bible falls short: is the history and heritage of metal roofing, and the metal flashing associated with most slate and tile roofs.
The goal of the trad roofing guild, is to establish an institution similar to a bar or medical board: to set standards for authentic and permanent metal roofing, and provide a source list of those trained and competent to produce roofs up to guild standards.