Have you noticed brown stains, bubbling paint, or soft wood around your windows or doors, and aren’t sure what’s causing it? Worried that improper flashing is hiding rot beneath your siding?
If so, you’re not alone, and your concerns are valid. At RoofSmart, we’ve helped countless Seattle homeowners who thought their siding was installed correctly… until years later, when water damage, rot, or mold proved otherwise.
All siding should be expected to “leak” in the Seattle area. It should be installed to allow it to drain and dry out.
On multiple occasions, we’ve helped customers replace entire walls because the rot was so extensive, so we know how important z flashing is in a rainy area like Seattle (and which ‘alternatives’ for z flashing to avoid).
In this article, we’ll explain:
- What z flashing is and why it matters
- How poor installation can ruin your siding (and home)
- What happens when flashing is skipped or replaced with caulk
- How to make sure your contractor is actually qualified
Whether you’re in the middle of a siding project or dealing with a mystery leak, this guide will help you get answers and avoid expensive mistakes.
What is z flashing, and how does it prevent leaks in my siding?
Before breaking down what z flashing is, I will give you a quick overview of the most common components of a siding assembly and where to find them. Check out this photo that breaks it down:
Z flashing is the standard type of flashing used when installing windows and doors on any home. It gets its name from its shape, which looks somewhat like the letter z:
Image from TrexSeal
The flat part of the z flashing sits on top of the door so that the long, tall part is against the wall. This helps protect the door or window from water getting in. The bottom folds over the edge of the door or window top so that water is directed out to the ground.
Z flashing is used to prevent leaks at horizontal breaks in your siding. Even if water gets behind the siding, a flashing is designed to direct water from behind the siding and out to the ground. In some cases, the middle section of the z flashing is even angled to naturally direct water downward.
Seattle’s building code requires flashing above exterior windows and doors. Z flashing meets the flashing code requirements that describe what can be used above exterior doors and windows.
How is z flashing installed?
The z flashing is layered in with the sheathing paper and other siding pieces to add extra protection against leaks.
Here’s what it looks like installed:
After this step, your contractor will install the underlayment flashing, typically FortiFlash or Vycor 6” self-adhered butyl tape, then a siding board over the top of the z flashing.
That way, even if water gets behind the siding and drips down, your windows and doors will be protected because the water can drain back out, and never hits your wood subwall.
A key step here is making sure that the siding is installed slightly above the top of the window or door, not right on top of it. There should be a little gap because that is where the water collected by the z flashing will drain out. And it should *not* be caulked.
If no gap is left, then there was essentially no point in even installing the z flashing because water will be stuck behind the siding anyway.
What happens when z flashing isn’t installed properly on Seattle homes?
Your contractor should never skip out on installing z flashing, especially in a constantly rainy place like the Seattle area. There are no alternatives that adequately protect your roof.
If your contractor wants to avoid installing z flashing and suggests other alternatives, that’s a red flag. Using other alternatives is pretty much guaranteeing your roof will leak in the rainy Seattle weather.
For example, I cannot emphasize enough how bad of an idea it is to not use z flashing and then just caulk it. Too many contractors think that sealing holes or gaps off with caulk is good enough to prevent leaks or other issues.
What it actually does is trap water in the siding. Z flashing is supposed to redirect water that gets into the siding back out. But with no flashing in place and the exit point caulked over, the water stays in the siding.
This causes:
- Rotting wood
- Mold
- Structural damage
Rotting wood is a pain to deal with and an expensive issue to fix. The big problem with a siding leak is that it stays hidden for a long time. The siding will look fine, but underneath it, the wall is rotting and beginning to crumble.
We’ve seen this happen on countless occasions. Recently, we had a customer who had windows with no z flashing that we sealed in with caulk. After years of leaking, here’s what we found when we pulled off the siding:
Unfortunately, the whole wall looked like this and needed to be replaced. The longer your leak is hidden, the worse the damage will be.
Here’s another example from a recent job we did:
Again, this customer hired a contractor who skipped out on z flashing and just caulked around the windows. After 10 years of leaking, this is what we found underneath the siding.
The real bummer is that a fair amount of our customers were using a (supposedly) reputable contractor. They thought their home was in good hands, but they ended up paying the price (tens of thousands of dollars) 10+ years down the line.
How do I make sure my siding contractor is qualified?
To prevent hiring a company that will skip steps and cause damage to your home, make sure you do research on each of your options.
Check out the company’s website and social media to see if they’ve posted pictures of siding jobs they’ve done. You want to make sure you have proof that they’ve successfully done whatever kind of work you want them to do on your home.
You can also look them up to verify that they’re licensed in your area, and read reviews about the company on multiple different websites. For more tips on making sure your siding contractor is qualified, read our article “Is Your Seattle Roofer Actually Good? Here’s How to Tell Before It’s Too Late”.
Even though that article is about Seattle roofers, the tips can still be used to evaluate any kind of contractor anywhere in the world.
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