Lap joints in flashing

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Author Message Robin E. Snyder Senior Member Username: robin Post Number: 511 Registered: 08-2004 Posted on Wednesday, February 26, 2014 - 05:47 pm:    This particular situation is a sill, about 16 inches deep with sheet metal flashing. How are the laps typically handled? Butyl tape? Rivets? The SMACNA manual seems vague and only says "4 inch lap". J. Peter Jordan Senior Member Username: jpjordan Post Number: 688 Registered: 05-2004 Posted on Wednesday, February 26, 2014 - 06:54 pm:    It depends on the material. You won'd do the same thing for copper that you would for aluminum that you would for galvanized steel that you would for stainless steel... Also depends on vertical or horizontal. It depends on how much they should move. Moving joints may require sealant (I prefer silicone), but butyl may be OK. In some cases a lap with some sort of bayonet connection and cleats may be sufficient. Robin E. Snyder Senior Member Username: robin Post Number: 512 Registered: 08-2004 Posted on Wednesday, February 26, 2014 - 07:20 pm:    sorry...galvanized steel J. Peter Jordan Senior Member Username: jpjordan Post Number: 689 Registered: 05-2004 Posted on Thursday, February 27, 2014 - 11:01 am:    If this is an exposed vertical application, you can simply lap the material. Lapping with a sealant would be better. You will be primarily depending on the material's shedding water. Detailing a clip/cleat or some sort of bayonet joint will provide a measure of mechanical security. On a horizontal situation (e.g., a coping), you will probably want to design some sort of expansion joint that will prevent water from moving sideways to compromise the flashing. and to guard against ponding water. Brian E. Trimble, CDT Senior Member Username: brian_e_trimble_cdt Post Number: 71 Registered: 08-2005 Posted on Thursday, February 27, 2014 - 03:27 pm:    If this is flashing under a brick sill, then I usually tell people to overlap with two lines of sealant to seal it together. If there were more good sheet metal workers there would be crimped edges and soldered joints (depending on the metal), but I just don't see that happening too much any more. Of course, I'd also tell you not to have ANY laps and try to go with a single sheet, but I'm not sure the length of your sill. John Bunzick, CCS, CCCA, LEED AP Senior Member Username: bunzick Post Number: 1560 Registered: 03-2002 Posted on Thursday, February 27, 2014 - 04:38 pm:    I would use a cover-plate, or an under-plate, with two lines of sealant or adhesive gasketing. Laps will often not work well when there is more than one bend in the profile because the two pieces will not be able to nest perfectly tightly. If the design can stand it, an actual seam is better.