What appears to be tile roofing is in fact metal roofing tiles. Even in 1910, considerations of weight and roof structure were important.
The metal tiles were innovative for their time, but it was a system that had some problems - no doubt why it never caught on and why we do not see much use of individual metal roofing tiles today, of the type used at the Hotel Stockton.
A field investigation of the Historic metal roofing system has revealed the following information that was used to develop the plan for rehabilitation and reuse of the tiles:
The metal tiles were designed to interlock. Each individual tile has a rise of 4 inches and an exposure width of 8 inches. The leading edge of one tile is designed to engage in a corresponding groove formed into the metal of the adjacent tile. The total engagement of two properly interlocked tile is 1/16 inch. This amount of engagement is not sufficient to reliably hold the tile edge, due to thermal expansion and contraction, which in the Stockton area is significant. The outside air temperature can range from below freezing to 110 degrees; the ambient temperature on the roof surface would have as much as a fifty percent greater range, due to solar radiation heating and night radiation cooling effects. The basic design of the original tile did not perform well relative to the engagement, as evidenced by later caulking of the joints, and surface nailing of the tiles. The nails installed later are all potential sources of leaks, as they are placed in the location where water runs (ie, at the ‘trough’ portion of the system, rather than at the ‘ridge’ of the tile. Nailing could not be done at the ‘ridges’ of the tiles since there was a gap below each tile at that location, due to the barrel classic mission shape.
The painting system used on the tile appears to be generally well adhered. The base metal is galvanized steel, of approximately 26 gage thickness. The galvanized coating appears to be in good condition where it has been exposed. There was some type of undercoating used (black in color) prior to applying the finish coating of reddish color paint. This undercoating is well adhered in most locations. Where paint has become dislodged, it appears to be as much due to foot traffic and the resulting bending and scraping of the tiles surface as actual weathering of the paint surface.
The tiles have been significantly dented and deformed due to foot traffic over the surface of the tiles over the years, and the relatively light gage of the metal that was used.. This denting and deformation has made each tile somewhat ‘unique’ in shape, and thus the interlocking of tile to one another using the original 1/16 inch engagement slot is problematic. It is unlikely that very many tile that are in existence are in their original shape and condition. Thus, after removal, reassembly of the tile as an interlocking system would likely be impossible. In addition, email contact with both fabricators and a contractor who worked with similar tile indicate that replication of the exact profile of these tile may not be possible, as there is no source that has been identified that could accomplish this due to the complex geometry.
There have been roof leaks over the years that have caused decay damage to roof sheathing and roofing framing. Repair of these substrate conditions requires removal of the roofing.
The original felt weather barrier under the metal tiles has deteriorated to the point where it is no longer functioning as a weather barrier. Water that gets below the tiles, from nails, tears, gaps, and holes, is prone to wet the wood and cause decay.
The original roofing had an unusual system for ventilating the attic. Holes were cut into the valley of the tiles, and rectangular rain leaders were soldered to the holes. The leaders went to a crudely fashioned metal trough concealed in the attic, which in turn led to a downspout. It appeared that due to pigeon entry into the attic spaces over many years, screening was later added to the holes. Air entered the attics through the holes, water entered also during rains, but was a ‘unwanted byproduct’ of the approach used and had to be disposed of. This approach led to leaks due to the water flow in the attic in a trough, accumulation of significant pigeon debris, and only small amounts of ventilation.
Based on the above facts and research, we have determined that the most feasible and historically appropriate approach to replication the character and exposed materials is to removed the existing roofing, repair and refurbish it, and reinstall it on 3/4 inch sleepers over a waterproof membrane. While the original tiles may shed much of the water, this approach allows water that does go past them to be shed from the roofing system by the membrane concealed below. It also allows a way to provide ventilation concealed below the tiles, without the elaborate and leak prone approach originally used.
Michael F. Malinowski AIA Architect
Michael F. Malinowski AIA Architect