Rain should run off the roof and into the gutter.
Step flashing protects the gap where roofs meet walls by weaving into the roof shingles. At the bottom of the roof, water needs to be directed away from the wall or you'll get a cascade of moss, mold, and rot.
If not directed away, water can pour into walls behind the siding cut that points up the roof rake.
The bottom piece of step flashing can be bent in such a way that it deflects water away from the side wall and into a gutter. You can also buy preformed kick out flashings.
How spending 10 bucks could have saved $1,000 or more:
Deflecting the water away from the wall is even more important when there is a window at the base of the roof rake, which ensures a huge water problem (#bugsmoldrot) sometime in the future.
Flashing that prevents water from entering wall cavities is required by the IRC, yet many, many roofing jobs do not include kickout flashing.
But let's not beat up on roofers—even the best roofers cannot overcome bad design:
Does it really take a village to stop rot?
Sooooo, today, our village is going to visit a few ways to do kickout flashing right:
- A good way (from Building America Solutions Center)
- A slightly better way (don't cut the step flashing)
- And an über way (from Hammer & Hand a general contractor specializing in high performance building with offices in Portland, OR and Seattle, WA—where it gets rainy sometimes).
First, the good way from Building America:
Water Managed Roof Assembly
"Step and kick-out flashing at all roof-wall intersections extending >= 4 inches on wall surface above roof deck and integrated with drainage plane above."
Four steps to step flashing:
A. Install roof felt prior to step and kick-out flashing.
B. Install step and kick-out flashing to extend at least 4 inches above the roof deck along the wall.
C. Install roofing shingles and building wrap over flashing.
If installing a metal and rubber membrane roof, install continuous flashing instead of step flashing.
A better way: don't cut the flashing
Kickout flashing is typically made by cutting and bending a piece of step flashing.
But you can skip the cutting part and jump right to the bending part which eliminates a cut in your flashing:
Don't cut it and overlap the flaps of metal, twist the flashing with needle nose pliers and then flatten the twist with a vice.
Or vice grips.
You can also spend the $20 on a preformed kickout flashing (let me Google that for you).
Now that we have covered good and better, let's look at the über way:
Hammer & Hand has a Best Practices Manual for employees and subcontractors to follow ensuring minimal construction defects and comfort issues.
Hammer & Hand's method incorporates liquid applied membrane and flashing tape to seal the house wrap at the roof/wall intersection.
On the roof, a strip of peel and stick membrane bridges the roof/wall connection before roofing felt and step flashing goes down.
All of this happens before the house wrap goes on. Not how it is *usually* done.
Incidentally, the products that H&H specify are
After the step flashing and roofing has been installed, peel and stick goes over the top of the flashing and house wrap slip over the peel and stick above the roof and the house wrap below.
—Note: These illustrations are drawn by me, Dan Morrison. If you are Sam Hagerman, Dan Whitmore, or any other Hammer & Hand representative and you notice that I got something wrong, please let me know,