There’s a new type of flashing for window sills on the market now. It’s the Rissan 430 grey corner from Siga, which is a piece of pre-formed flashing tape that fits perfectly into the corners of door and window rough openings. I was lucky enough to get several Siga tapes and tools donated for my basement renovation and have been really impressed with them.* I’ll cover the full window flashing and air-sealing process in another post. Today, though, I want to focus on this one piece.

Standard method for flashing sills

Window flashing has come a long way in the past couple of decades. It used to be just wrapping the rough opening for the window with the water-resistive barrier (WRB). Then came the flashing tapes. Often they’re poorly applied and not integrated properly with the WRB.

The photo above shows flashing tape over the sill and up the jamb a little ways. Some builders stop there with the sill flashing and put the WRB over it and then some flashing tape up the jambs.

But the problem here is that empty square you see where the tape goes from horizontal to vertical. At the upper left of that square, water can get into the rough opening.

There are better ways

To avoid the empty square, we need to do some tape origami. That’s what Minnesota home builder Randy Williams did in the photo below. It takes extra time to do the fancy cuts and then apply the tape so it lies flat.

Another way to go here would be to use a liquid-applied membrane. You could use only that material to flash the whole window, and it can work well. Or you can do a hybrid flashing system with tape and liquid-applied membrane. That’s what the builder did in the photo below.

DuPont saw an opening in this market and came up with a method that uses a single piece of tape to span a corner with complete continuity. That’s their FlexWrap bending around the corner in the photo below.

Huber Engineered Woods has a similar product called Stretch Tape.

All of these methods and products have their pros and cons, but all can work well when used properly.

The Rissan 430 grey corner

Now, let’s talk about the new kid on the block: the Rissan 430 grey corner. John Rockwell, a Siga rep, brought me a box full of Siga goodies the week before last. Unfortunately, we weren’t ready to install the windows when he was here. Then last week, Connecticut home builder Ben Bogie came down to Atlanta to help me get my four windows installed.

After building and installing the window bucks, we applied the sill and corner flashing. Rather than write about the process here, I’ll let you watch Ben in action. The video below shows the start-to-finish installation of one of the Rissan 430s in a sill corner.

Maybe you didn’t time it in the video, but it took Ben only about a minute and a half to install one corner. And it’s easy to install it with no wrinkles or other defects that can cause leaks. Builder Randy Williams wrote about the Rissan 430 in his blog and said this: “I found the [Rissan 430] installs easier than other sill protection systems, there was no bunching of the tape in the corner and no ‘fish mouths’ to direct water behind the tape, which can be common with other systems.”

If I were a builder, the Rissan 430 as well as Siga’s other products would be a staple in my flashing toolbox most likely. Check out the Rissan 430 at the Siga website, and look at their other products while you’re there. If you’re looking for high-performance materials for air and water control layers, Siga is one of the best places to go.

*Full disclosure: Siga supplied the sealing tapes and tools used to install my windows.

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Allison A. Bailes III, PhD is a speaker, writer, building science consultant, and the founder of Energy Vanguard in Decatur, Georgia. He has a doctorate in physics and is the author of a bestselling book on building science. He also writes the Energy Vanguard Blog. For more updates, you can follow Allison on LinkedIn and subscribe to Energy Vanguard’s weekly newsletter and YouTube channel. Images courtesy of manufacturers, except where noted.