Flashing is metal that is used to protect various junctions on your house’s exterior from water getting inside the house structure. It takes many shapes. Typically it can be seen above window and door trim. When used there it is called drip cap. It is also seen where T-111 siding is stacked vertically, and it is called z-bar flashing there. Where siding ends at a roof surface, you will see step-flashing. In the following pictures you will see both step-flashing and z-bar flashing. The customer had called me because there was a water leak from the roof into the garage. I went up on the roof to take a look and discovered that there was a 1×4 trim board at the bottom of the siding, along the roof, and it was not protected by z-bar flashing. Where the siding contacted the 1×4, water would run into that junction and go behind the 1×4 and leak into the garage. Along the way it would of course wet the wall framing, the roof framing, the roof plywood, and the drywall in the garage below. Over time those things would rot, causing an expensive repair job to be required. My customer did well to call me before that happened!
So without further ado…
Here, you can see the absence of metal between the 1×4 and the clapboard siding. There is step-flashing behind the 1×4 – that is visible, but no z-bar flashing sitting on top of the 1×4. Time for an important note:
As long as there is physical contact between molecules of “matter”, water will travel from one molecule to the other. This is how sap rises up a tree, how kerosene rises up a wick, and how water will run behind this 1×4. If water will go up, then going laterally is a snap!
Here’s what z-bar flashing looks like: (I just sketched it on my pad, uploaded a picture of it)
Here it is plainly visible that the z-bar flashing will direct any water that runs down the clapboard to continue its merry way down the 1×4 as well, courtesy of the flashing. This sketch is an “exploded” side view. Normally those two boards are nailed to the sheathing. Duh, right?
Here we see water staining and deterioration of the flashing, a big nail and the hole it made through the flashing (that’s normal), but we also see water staining ABOVE the step flashing in a couple spots. That’s where the water got behind the step-flashing and dripped into the garage below. By the way, I forgot to tell you, that flashing behind the 1×4 that is now visible after pulling the 1×4 away from the sheathing, is step-flashing. It goes behind the clapboard vertically, and it goes under the shingle horizontally. Every shingle gets its own piece of step flashing, because every shingle has a junction with the siding and therefore needs the protection from a piece of flashing. You’ll see this in the next couple shots:
First, my sketch of a piece of step-flashing. There are various sizes, but I use the 8″ x 8″ version. It’s folded in half by a machine and sold at Home Depot and Lowe’s and other lumber yards.
So… Starting at the bottom, we put one piece under each shingle.
We do that all the way up the roof. In the picture below, I’m almost half way up the slope.
We go all the way up the roof and then do the other side as well. In the pic below we can see really well how the step flashing is under each shingle and together they act sort of like feathers on a duck, overlapping each other to make sure water runs off (or down is more like it). This is how we protect that junction of siding and roof.
When we get to the top, where the two slopes meet at the ridge, we cover the two runs of step-flashing with two custom pieces of flashing and then – drumroll, please – we install the z-bar flashing behind the clapboard in preparation for re-installing the 1×4’s.
It’s important that there be an “evaporation gap” between the 1×4 and the shingles so that water doesn’t take advantage of the contact and run up backside of the 1×4, like sap up a tree. So I ran the 1×4’s through the table saw, removing 3/4″, and re-installed it. Recycle!
It’s a good thing to see flashing on your house. It’s visible proof that water is staying out (as well as bugs, wood rot, mold).
Doesn’t that look better than these pictures down below, of the original condition, where there’s no z-bar flashing, no visible step-flashing, no evaporation gap?
A common problem in many siding/roof junctions is the bottom step-flashing not dumping its water onto the roof or the ground, but rather dumping it behind or under something. If there’s rotted siding or trim below, that is often the problem.
Here’s a picture of that:
First, a shot of the flashing stopping short, and there’s a hole in the wall where water goes behind the siding. Damage to the siding is visible.
In this next shot, I added a piece of flashing under the one that was dumping water into the hole in the siding, to get water past the hole and outside the siding.
And finally, I added a piece of flashing – a diverter – to divert water into the gutter, rather than have it run down the surface of the siding.
Call me to fix your flashing problems, as I have a LOT of experience doing it.