Why Do So Many Newly Built Homes with Panel Siding Leak?

Did you buy a newly built home expecting it to be worry-free, only to hear that new construction homes in Seattle are developing siding leaks just a few years later? Are you concerned that hidden installation shortcuts behind your panel siding could be allowing water to rot your walls long before you notice there's a problem?

Most homeowners assume a brand-new home should be built to modern standards and protected from water intrusion for decades. Unfortunately, that's not always the case.

At RoofSmart, we've repaired numerous new-build homes where panel siding began leaking because the flashing installation was skipped, put in incorrectly, or replaced with cheaper alternatives. Since these leaks occur inside the wall, the damage often goes unnoticed until mold, rot, or structural deterioration has already become extensive (and expensive) to repair.

In this article, we'll explain why so many new homes with panel siding develop leaks, how h flashing is supposed to be installed, the warning signs that water is getting behind your siding, and what you can do to protect your home from costly hidden damage.

What causes panel siding to leak?

Panel siding is supposed to be installed with a special type of flashing called h flashing. If the installers skip it, install it incorrectly, or use the wrong kind of flashing, then your siding is very likely to leak:

• Missing flashing: Installing siding with no flashing in a rainy area like Seattle is a disaster waiting to happen. Water will get behind the panels and stay there, causing mold and rot in your walls.
• Incorrect Installation: Misaligned seams or improper layering allow water penetration. If your contractor isn’t paying attention to instructions, it can be easy to make a mistake that leaves a gap for water to get in. For example, we recently replaced a few walls for a customer with this issue. Their wall had h flashing, so everything looked normal, but it was not installed properly, so the siding was actually leaking. The OSB behind the siding was completely rotten:

• Cheaper Alternatives: Simple metal strips are ineffective at keeping water out. Nails are placed on the metal strip in the gap between panels, meaning that there are a bunch of holes right where all the water is being directed. This is an example from a different customer with panel siding who did not have h flashing. As you can see, the area all around the metal strip is rotten:

A lot of homeowners do not realize that there is a problem with the flashing on their wall, so they don’t expect to have any problems. The bummer about siding leaks is that they can easily be hidden within the wall for a long period of time, so you don’t realize there is a problem until extensive damage is done.

And this is the same problem you have with roof leaks. People think the shingles look fine when it's really all rotten because of condensation or leaking. So it's actually harder to tell in a wall because, in a roof, if the water drips down to the ceiling, you'll see it. But in the wall, you don't see it until it's really bad. Often, you don't notice until you lean against it.

There are a few signs that you can look for to see if the panel siding on your home is leaking. Take a look at this image as an example:

• Popping Nails: There's a lot of moisture in the wood, so the nails aren't biting the way that they would normally bite. And then when the sun hits it and it gets hot, now it all flexes, and the nail just works its way out.
• Panel Flex: You can also see that the panel is cracking and looks like it's flexing because the panel is trying to move.
  

  Common Causes of Panel Siding Leaks on New Homes

  
  

  Problem	What Causes It	Warning Signs	Recommended Solution
  Missing H flashing	Installer skips the required flashing between panels	Hidden leaks, rot behind siding	Install proper H flashing with flashing tape and drainage layers
  Incorrectly installed H flashing	Flashing isn't layered correctly or seams are exposed	Water intrusion despite flashing being present	Remove and reinstall siding using manufacturer installation guidelines
  Metal strip used instead of H flashing	Builder uses a cheaper alternative	Nail holes in water path, premature leaks	Replace with manufacturer-approved H flashing
  Missing flashing tape	Nail heads and seams remain exposed	Water enters behind flashing	Install continuous flashing tape over flanges and seams
  Improper panel alignment	Gaps or uneven joints between panels	Water infiltration and panel movement	Reinstall panels with proper spacing and alignment
  Poor drainage design	Water has no escape path behind siding	Moisture trapped inside walls	Build a drainage plane that directs water out
  Hidden moisture	Water becomes trapped behind siding	Mold, rot, deteriorating sheathing	Remove damaged materials and correct waterproofing
  Popping nails	Wet sheathing expands and contracts	Nail heads backing out of siding	Repair moisture damage and secure siding properly
  Cracked or flexing panels	Swollen wall sheathing pushes against siding	Visible bowing or cracking	Repair the wall assembly and reinstall panels
  Builder shortcuts	Cost-cutting during installation	Premature siding failure	Hire an experienced siding contractor familiar with proper flashing methods

  
  

  How is h flashing installed with panel siding?

  Proper installation of h flashing means layering everything properly to create a drainage system that assumes water will get behind the siding and channels it out.

  Here are all of the components:

  First, you need to install the plywood, then put a layer of underlayment on top of that. This creates your base for layering all the components using the following steps:

  1. H-Flashing: Flange is nailed to the wall.
  2. Flashing Tape: Covers the flange and nail heads for extra waterproofing.
  3. Panel Pocket: Receives the siding panel.
  1. Hem: A small curl at the pocket's edge creates a small bump that keeps sending the water down the drainage channel.
  4. Continuous Layers: Flashing tape runs continuously across horizontal seams for full protection

   

Here’s an example of what this looks like with one piece of siding installed:

The siding is installed up against the h flashing. You can see the flashing tape on the other side that has been applied over the edge of the h flashing.

This process is continued for both the vertical and horizontal flashing installations:

Following this layering process with h flashing will ensure that water cannot get trapped behind the panels. You have to assume that water will get behind the panels and give it a path out.

This gives the water an easy path to follow to drain, and even if it gets behind the siding, it can still get out. You want to have a place for the water to be able to get out. That's the bottom line.

This wall is now protected from leaks and rot.

Why are so many new-build homes missing h flashing?

Panel siding is chosen because it’s fairly easy and quick to install compared to other options. To make it cheaper and faster, some contractors skip the h flashing or use a different type of flashing.

Since the average homeowner doesn’t know what goes into installing siding, they are drawn to the lower price. While this might save money initially, it also means that your siding is vulnerable to leaks. Replacing rotting wood and installing new siding can easily cost tens of thousands of dollars.

So even though it costs a little bit more up front to properly install h flashing, it ends up saving you money in the long run and prevents a lot of hassle.

Will a rainscreen prevent my siding from rotting?

As you've seen, many panel siding leaks don't happen because the siding itself is defective. They happen because critical flashing details are skipped or installed incorrectly. When water gets behind the panels and has nowhere to drain, it can quietly rot your sheathing, framing, and insulation long before you notice any visible signs of damage.

Installing h flashing correctly is one of the most important steps in preventing these hidden leaks, but it's only one part of a complete wall assembly.

Some homes are also incorporating rainscreen systems, which create an air gap behind the siding to help water drain away and allow the wall to dry more effectively. A rainscreen can provide another layer of protection against the moisture problems that are so common in Seattle's wet climate.

Read our article “Will Installing a Rainscreen Prevent Siding From Rotting?” to learn how rainscreens work, when they're worth installing, and whether they can help protect your home from the hidden rot and water damage that affect so many new-build homes.