Conscientious builders have known for many years that a pan flashing applied on the rough sill is a best-practice to collect and drain water that may leak through window or door frame joints or the flashing system above. Now pan flashings are a minimum code requirement.

The 2012 International Residential Code (IRC) R703.8 Flashing section goes further than the ’09 code and is pretty specific:  “…pan flashing shall be installed at the sill of exterior window and door openings. Pan flashing shall be sealed or sloped in such a manner as to direct water to the surface of the exterior wall finish or to the water-resistive barrier for subsequent drainage.” The code goes even further to prescribe flashing above the pan level: “Openings using pan flashing shall also incorporate flashing or protection at the head and sides.”

R703.8 has a few “outs” to the pan flashing. First, it defers to the manufacturer’s installation and flashing instructions. So if the manufacturer provides explicit instructions that don’t require pan or other flashing, then you would follow those instructions. However, most major manufacturers are on board with good flashing practices. Second, you can use an alternate “… design or method of a registered design professional.” Or third, flashing can be installed “in accordance with other approved methods.” An “approved method” in this case could be one that your local building official approves. So this could be a flashing system of higher or lower order than a pan-flashing method.

I can’t count the number of times window and door flashing processes have been covered in Fine Homebuilding and other construction magazines. It’s good to see the drumbeat of best-practice making its way into the code. It will be interesting to see what kind of inspection process code officials adopt to verify fenestration flashing.

Here are a few links to other Fine Homebuilding articles and videos on window and door flashing.

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