Can Water Get Behind Vinyl Siding? | Quad Cities Guide

Why Isn't Vinyl Siding Completely Waterproof?

Vinyl siding panels overlap and interlock rather than being permanently sealed together into one solid exterior membrane.

That design allows the siding to expand and contract as temperatures change.

It also means that during severe wind-driven rain, some incidental moisture can reach the area behind the panels.

Suburban Construction's existing guidance explains that this is expected behavior for the material. The wall system behind the siding is designed to provide the secondary water-management protection.

Read: Is Vinyl Siding Waterproof?

What Actually Keeps Water Out of the Wall?

Think about the exterior as several layers working together.

A good siding system assumes some water may reach the drainage plane and gives that water a controlled path back outside.

Darin Wilson: Follow the Water Path

Darin Wilson is Vice President and Co-Owner of Suburban Construction and helps guide the company's exterior remodeling operations and quality standards.

His approach to suspected water problems is especially useful because the place where a homeowner sees the symptom is not always the location where the water entered.

“Hidden water damage is rarely diagnosed by looking at one siding panel. We follow the water path and look closely at windows, roof intersections, flashing, housewrap, penetrations, and the sheathing underneath.”

— Darin Wilson, Vice President

That is an important distinction. A wet area below a window may begin at the window head. Damage near the bottom of a wall may originate several feet higher. Water can travel along flashing, framing, sheathing, or housewrap before becoming visible.

Read the Hidden Water Damage Behind Vinyl Siding Guide

Where Does Water Commonly Get Behind Siding?

The middle of an undisturbed siding panel is often not the most vulnerable location.

Pay closer attention to transitions and openings such as:

• Above and below windows
• Around exterior doors
• Roof-to-wall intersections
• Lower ends of rooflines
• Deck and porch connections
• Exterior faucets
• Electrical boxes
• Exterior lights
• Dryer vents
• Bathroom exhaust vents
• HVAC penetrations
• Chimneys
• Inside and outside corners

Every opening through the siding is also a place where the water-management system needs to be properly detailed.

Windows Are One of the Most Important Inspection Areas

Windows interrupt the drainage plane of the wall.

That means the flashing around the window needs to work with the housewrap so water is directed outward instead of into the wall cavity.

A window can look perfectly normal from the outside while concealed flashing behind the siding is missing, damaged, or installed in the wrong sequence.

If water staining repeatedly appears below a window after storms, the area deserves closer investigation.

Roof-to-Wall Intersections Can Be Another Trouble Spot

When a lower roof terminates against a taller siding wall, large amounts of rainwater can be concentrated in a relatively small area.

Proper flashing needs to direct that water away from the wall.

Problems in these areas can allow moisture to travel behind the siding and affect sheathing below the roofline.

Can Water Get Behind Siding During a Heavy Storm?

Yes.

Wind changes the way rain strikes the exterior.

Instead of falling primarily downward, rain can be driven horizontally and upward into small gaps and transitions.

That is one reason Quad Cities homes need more than the visible siding panel to protect the wall.

A properly installed wall assembly should be prepared for wind-driven rain rather than assuming every drop remains on the outer surface.

What Does Housewrap Do?

Housewrap or another approved water-resistive barrier provides an important secondary drainage plane behind the siding.

It needs to be installed with proper overlaps and integrated correctly with flashing.

Suburban Construction's siding installation process includes installing a quality weather-resistant barrier and properly integrating it around windows, doors, and other exterior penetrations.

Read: Does House Wrap Matter Under Vinyl Siding?

What Happens if the Housewrap Is Missing?

Then incidental moisture has less protection between the siding and moisture-sensitive wall materials.

That can increase the risk of repeated wetting of:

• Wood sheathing
• Framing
• Exterior insulation
• Window openings
• Door openings
• Interior finishes

The same concern exists if housewrap is present but torn, reverse-lapped, poorly taped, or incorrectly integrated with flashing.

Can Water Become Trapped Behind Vinyl Siding?

It can when the drainage system is poorly detailed.

Problems may occur when:

• Housewrap overlaps are reversed.
• Flashing directs water inward instead of outward.
• Drainage openings are unintentionally sealed.
• Too much caulk traps water.
• Exterior penetrations are poorly detailed.
• Sheathing is already damaged.

The goal is not to prevent every molecule of moisture from ever reaching the space behind siding. The goal is to prevent water from becoming trapped where it can damage the wall.

Don't Try to Fix Everything With Caulk

When homeowners see a gap, the natural reaction is often to fill it with sealant.

Sometimes sealant is exactly what the detail requires.

Other times, indiscriminately applying caulk can interfere with drainage.

Suburban Construction's hidden-water guidance makes an important point: caulk cannot recreate missing flashing or rebuild a damaged drainage plane.

Flashing and layering manage water. Caulk is a supporting detail—not the entire system.

How Can You Tell if Water Is Causing Damage?

Hidden moisture does not always become obvious immediately.

Warning signs can include:

• Musty odors
• Water stains on interior walls
• Peeling or bubbling paint
• Soft drywall
• Swollen trim
• Loose siding
• Soft exterior trim
• Repeated moisture below windows
• Recurring problems after storms

These symptoms can also have other causes, so they should be investigated rather than treated as automatic proof that the siding installation has failed.

Can the Siding Look Fine While the Wall Is Wet?

Yes.

That is one of the difficult things about hidden water damage.

The siding panels may still appear straight and undamaged while moisture is affecting sheathing behind a window, roofline, deck connection, or exterior penetration.

The condition of the visible siding does not always tell you the condition of the wall underneath.

Can Water Damage the Sheathing?

Repeated wetting can damage moisture-sensitive sheathing materials.

Once siding is removed, possible signs include:

• Dark staining
• Swelling
• Soft areas
• Delamination
• Rot
• Deterioration around fasteners

The source of the water should be corrected before damaged material is replaced and the wall is covered again.

Should You Put New Siding Over a Moisture Problem?

No.

New siding can make a house look dramatically better, but it cannot cure an existing moisture problem underneath.

Suburban Construction specifically advises homeowners to correct moisture and insulation problems before covering the wall with new siding.

Read: Can Vinyl Siding Cover Existing Moisture Problems?

What Happens During a Suburban Construction Siding Replacement?

One advantage of a complete siding replacement is the opportunity to inspect the concealed wall.

Suburban Construction's installation process includes removing the old siding and evaluating what is underneath before installing the new exterior system.

That process can include:

1. Removing the existing siding.
2. Exposing and inspecting the sheathing.
3. Identifying damaged or deteriorated areas.
4. Repairing appropriate damaged materials.
5. Installing or correcting the water-resistive barrier.
6. Integrating flashing around windows, doors, and penetrations.
7. Installing the new siding system.
8. Completing trim, sealing, cleanup, and final inspection.

Review the Suburban Construction Siding Installation Process

Should Old Siding Be Removed?

Removing existing siding provides much better access to inspect the sheathing, housewrap, flashing, and insulation underneath.

That does not mean every siding-over-siding installation is impossible, but homeowners should understand what information remains hidden when the original exterior stays in place.

If moisture is one of your concerns, the ability to actually inspect the wall becomes especially valuable.

What Should You Do After a Major Storm?

After significant wind-driven rain or hail, walk around the house and look for changes.

Pay particular attention to:

• Loose siding
• Missing panels
• Broken corners
• Damage around windows
• Damaged roof-to-wall flashing
• New interior stains
• Soft exterior trim

Photograph anything unusual. If the symptom repeatedly appears after storms, that timing can provide an important clue when diagnosing the problem.

Questions to Ask if You Suspect Water Behind Your Siding

The Bottom Line: Can Water Get Behind Vinyl Siding?

Yes—and a properly designed siding system anticipates that possibility.

Vinyl siding sheds most exterior water, while the housewrap, flashing, sheathing, drainage details, and installation behind it provide the additional protection needed when incidental moisture gets past the panels.

The real concern is water that cannot drain or water that reaches vulnerable materials because the underlying wall system is missing, damaged, or incorrectly installed.

As Darin Wilson emphasizes, don't diagnose a moisture problem by staring at one siding panel. Follow the water path and evaluate the entire exterior system.