Sheet metal Because sheet metal is installed first, it is critical to the complete tile assembly. Setting up the proper elevations for the full tile assembly should be done prior to any metal installation. Sheet metal should be installed at all deck transitions. Since the sheet metal contractors are not familiar with the waterproofing requirements nor are they responsible for the tile elevations, it is critical that they be given direction. All of these transition details can be prefabricated prior to installation in the field. The architect will usually specify soldered corners on all prefabricated items.
The waterproofing manufacturers, since they do not sell nor do they warrant the metal, require that the installation at least follow SMACNA (California Association of Sheet Metal and Air Condition Contractors, National Association) guidelines. For our applications on an exterior deck, the nailing patterns are minimum 3in. on center in a staggered pattern with a minimum 4 in. overlap between metal pieces. All overlap joints must have sealant (a single component urethane is recommended) between the laps.
The metal laps should always follow the same lapping procedure as you would use with sheathing membranes on walls. Since some decks have the slope built into the framing you want to start at the lower end and lap over the lower pieces as you would do with shingles.
When deciding how large the prefabricated items should be, the following rules of thumb should be followed. The horizontal legs on the deck should always be at least 4 inches. Manufactures of waterproofing materials recommend at least 4 inches of metal exposed for an attachment. The vertical leg should be a minimum of 6 inches up the wall. Many of the failures found in new construction are because there was very little overlap at the sheathing paper to flashing detail.
All too often the stucco contractor, without direction, has set his weep screed too low which causes the tile contractor to compromise his minimum mortar bed thickness or his slope to drain. A two piece deck to wall metal is preferred over a one piece flashing detail because of its flexibility with regard to elevation. A one piece deck to wall has the stucco termination built in at a fixed distance off the deck. Once this one piece is set, the elevation maximum is now set because you cannot float any higher than the stucco termination.
Actually, it can be floated higher and we see this done all too often. If you did float higher than the stucco termination the water would have no way of exiting the stucco and would be forced to exit the stucco and into the wall. If the L flashing or deck to wall flashing, the first component of a two piece flashing system, is used, the tile setter can float his mortar bed or mark his elevation so that the stucco contractor can set his weep screed after the proper elevations have been set. It is also a good idea to let the stucco contractor know not to put the weep screed to close to the deck as this will cause you a problem when you are caulking your expansion joint at the perimeter.
The industry has found many leaks occurring where a deck to wall flashing and drip edge termination begins. In figure # 7 you will see a typical drip edge termination piece. This piece is designed to eliminate any lapping or corner to stucco interface weaknesses. It allows for plenty of room for not only the drip edge and deck to wall to overlap but for the stucco or siding lapping over as well.
The post collar in figure # 8 is designed so the post can be cerf cut to accept a short flange placed into the cut and caulked. This design was created to minimize the chance of water getting between the metal and the post.
Figure # 10 is a door saddle. Door openings are the single greatest source of failures. Doors are not designed to be waterproof and they are not warranted as such. This door saddle is designed to prevent water intrusion regardless of the door system.
The following are the most common sheet metal details found on exterior deck applications:
1. Outside corner
2. Inside corner
3. Overflow scupper
4. Standard scupper
5. Standard Drip edge
6. Reverse Drip Edge
7. Drip to wall termination
8. Post collars
9. Standard L metal deck to wall flashing
10. 2 Piece Door Saddle