Photograph of - damaged vinyl siding Vinyl Siding Inspection & Diagnostic Guide; Vinyl Siding Repair Methods

  • VINYL SIDING INSPECTION & REPAIR - CONTENTS: How to inspect vinyl siding for damage or installation defects, photo guide to common defects in vinyl sided buildings. Improper installation details of vinyl siding or of vinyl siding F or J channel trim or corner moldings can cause or aggravate building leaks and even invite insect pests and structural damage.
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Vinyl siding defect recognition & diagnosis:

This article discusses common defects observed in vinyl exterior building siding, such as buckling, splitting, cracks, odors, and questions about the need for a vapor barrier behind vinyl siding and over building sheathing. Included are comments from several recognized building inspection and construction authorities.

Our page top photo shows wrinkled vinyl siding - often caused by heat exposure such as from a BBQ Grill - but in this location the pattern and size of the damage made us suspect that there was another cause.

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Inspecting Vinyl Siding for Damage: Examples of Leaks & Damage to Vinyl Siding

Article Series Contents

Impact Damage, Cracks, & Holes in Vinyl Siding

Most of the vinyl siding problems we see appear to be due to poor installation details, though on occasion we see cracks and breaks that may be blamed on older, more brittle vinyl products.

Damaged vinyl siding (C) Daniel Friedman Damaged vinyl siding (C) Daniel Friedman

Our photo (above left) demonstrates impact damage to vinyl siding, in this case just above the floor of an outside deck.

Our second vinyl siding damage (above right, courtesy of Carson Dunlop Associates) demonstrates an impact damage even to siding that made both a hole and a crack in the wall covering. With (often older-generation) more brittle vinyl wall siding products we often find impact damage and holes caused by stones kicked-up against the wall by a lawn mower or weed-wacker.

Vinyl Siding Gaps & Holes Caulked; Cracks at Vinyl Window Trim

Damaged vinyl siding (C) Daniel Friedman Damaged vinyl siding (C) Daniel Friedman

Our vinyl siding caulk photo (above left) shows a combination of improper trim installation, building leaks, caulk where it is not helping, and even the caulk was so sloppily applied that it didn't seal anything.

Our photo at above right shows cracking vinyl siding above a window corner - a bad place for a leak that can lead to building water entry, window damage, and even hidden mold.

Improper J-Channel in Vinyl Siding Cause Costly Building Damage

One of the most common vinyl siding installation mistakes (also found on aluminum sided buildings) is the improper cut and trim of the ends of horizontal J-channel used above windows and doors (shown at below-left), or improper termination of the bottoms of J-channel used along the sides of windows or doors (shown at below right).

Damaged vinyl siding (C) Daniel Friedman Damaged vinyl siding (C) Daniel Friedman

A simple error such as short-trimming of the J-channel and failure to provide proper water-directing bends can send water behind the J-channel and into the building wall and structure.

Vinyl siding J-channel end-treatment to avoid leaks (C) InspectApedia KGIn our photo at above left it looks like really sloppy J-channel work during siding installation, leaving a leak at the window sill. The required tab extension on the horizontal or upper J-channel is missing entirely, allowing J-channel rainwater to flow down behind the vertical J-channel along the window side.

In our vinyl siding J-channel photo at left it appears as if the window-top horizontal J-channel end cut tab was correctly cut and bent over the outside of the vertical J-channel running along the window side. A reader provided this detail during investigation of leaky vinyl siding that is illustrated and discussed at SIDING LEAK DIAGNOSIS & REPAIR.

[Click to enlarge any image]

Watch out: J-Channel errors can rot windows and doors: Our photo of improperly-cut J-channel trim around a window (above right) shows a more serious problem than may be immediately apparent. In Spackenkill, Poughkeepsie, NY we found an entire neighborhood of homes in which nearly all of the windows were rotted beyond repair due to this error.

Wind-blown rain sent inside the J-channel trim and into the window structure was the problem caused because the installer didn't follow the manufacturer's instructions. Properly the top J-channel is trimmed to include a tab bent over the vertical J-channel to route water outside, not inside the trim.
See Figure 1-25 in Best Construction Practices for details, and return here using your browser's "Back" button.

Here is what the Vinyl Siding Institute Advises about Installing J-Channel

J-channel is used around windows and doors to receive the siding. Follow the steps below when applying trim.

  • Cut and bend the tab of the top piece of J-channel down to provide flashing over the side J-channel. [This instruction pertains to J-channel run above windows and doors. Omission of this detail is a very common mistake that leads to leaks in and around windows - Ed.]
  • Fold the bottom end of the side piece of J-channel inward at the bottom of the window, to fit over the existing J-channel to prevent water from entering under the sill.
  • Cut the side J-channel members longer than the height of the window or door, and notch the channel at the top. Figure 33 [in the original document]. J-channel J-channel Window Head Flashing Figure 34.23
  • Miter cut the free flange at a 45° angle and bend the tab down to provide flashing over the side members (Fig. 34) [in the original document].

    A similar miter and tab may be provided at the bottom of the window, depending on the sill’s condition. The J-channel should fit snug to the window. 
    - The Vinyl Siding Institute, Website:, - retrieved 9 Feb 2015, original source:


Also see PEEL & STICK FLASHING MEMBRANES for products useful to seal around windows and doors before installing siding

Stains on Vinyl Siding

Details about stains on vinyl siding are now found in a separate article at VINYL SIDING STAINS

Algae growth on vinyl siding (C) Daniel Friedman

Common sources of stains on vinyl siding include formation of algae, fungus, lichens, dirt accumulation on damp surfaces, rain splash-up soil, even smoke from nearby barbecues or fires.

More about building wall stains can also be found in these companion articles:

Leaks From Vinyl Siding Bottom Edges; Breaks or Cracks in Vinyl Siding

Details about the causes of & cures for leaks in building siding are now

Damaged vinyl siding (C) Daniel Friedman

Vinyl Siding is Not Waterproof

Watch out: vinyl siding used on building exteriors is not nor is it meant to be a waterproof barrier. While the actual face of vinyl siding is waterproof, a vinyl sided building wall is by no means waterproof.

Openings at the lap joints of vinyl siding sections as well as drain openings provided along the bottom edge of most vinyl siding products let the wall system breathe and allow wind-blown rain that may enter the siding to drain out of it as well.

Loose Vinyl Siding: Blow-Offs, Fall-Offs & Nailing Defects

Below our photographs show what happens to loose, poorly-secured vinyl siding on a home. These pictures were taken just about a year apart. We had watched the loose buckling siding on this Poughkeepsie NY home for some time. Finally after a windstorm much of the gable end siding has simply been lost completely.

Vinyl Siding buckling & loose (C) Daniel Friedman Vinyl Siding buckling & loose (C) Daniel Friedman

Below are additional examples of poorly-attached siding (below left) and siding that was literally pulled off of the building when an adjoining stucture itself collapsed. The consequences of the failure at right were more serious than met the eye: this wide opening into the building wall allowed rain to soak the wall interior, leading to costly mold, rot, and insect damage to the structure.

Damaged vinyl siding (C) Daniel Friedman Damaged vinyl siding (C) Daniel Friedman

In our photo at above left demonstrates a loose siding panel that is inviting more serious wind damage. Our second photo (above right) demonstrates a combination of poor siding installation, improper lower-roof flashing, a home that sat for months unattended while wind, rain, and snow penetrated the structure. These are almost certainly construction and installation defects, not product defects.

Causes & Cures for Damaged Vinyl Siding: Bent, Buckled, Rippled or Sagging Vinyl Siding

Vinyl Siding buckling & loose (C) Daniel Friedman

Vinyl siding that buckles due to improper nailing (photo shown above left) is is not normally extremely wrinkled, and will be more wavy across longer horizontal runs of surface.

A Complete Guide to Causes of Rippled, Buckled, Bent Vinyl Siding is at:

Watch out: buckling vinyl siding at the bottom of a wall may indicate hidden structural damage or insect pest damage. Details are in the article cited above.

Detailed specifications for hanging vinyl siding to avoid buckling and blow-offs are found in this article:

Don't Bury Siding at Wall Bottoms - Insect Risk

As our buckled vinyl siding at ground photo (above left) and Carson Dunlop's photograph vinyl siding photo shows (below left), bringing vinyl siding down to ground contact or even below ground may please the architect or home owner's sense of aesthetics, but it is an engraved invitation to wood destroying insects to attack the structure.

Siding at ground (C) Carson Dunlop Associates Siding at ground (C) Carson Dunlop Associates

We like to see 6-8" of clear foundation wall between the bottom of wall siding and the top of the ground surface. Adding mulch as was done here, increases the invitation to termites.

Vinyl Siding / Plastic Odors, Emissions, Health Information

Watch out: Information about vinyl products (not just siding) that may produce odors or have other environmental concerns can be found at

How to remove vinyl siding: This Siding Hook is Key if you Need to Remove or Reinstall Part of a Vinyl-Clad Wall

Side Swiper vinyl siding replacement tool Malco (C) Daniel FriedmanhIt's not unusual to need to re-hook loose vinyl siding such as shown in our vinyl siding damage photo above, or to remove impact-damaged, heat damaged, or badly stained vinyl siding from a structure.

In fact we might try removing and re-nailing vinyl siding on a building wall that buckles every time the sun shines on it.

Brute force can un-hook vinyl siding in the middle of a wall from the course below and course above, in order to pull nails and take off a bad siding section.

But without a siding replacement tool such as Malco's Side Swiper SRT1 shown in our photo (left), re-hooking the bottom edge of the new siding section to the top of the course below can be almost impossible.

The hook on this tool is designed to loosen and then help re-lock the bottom edge of vinyl siding without cutting or damaging the siding.

A few home inspectors also carry this siding replacement tool to permit invasive inspection of a building wall - something not normally done during a visual home inspection for a purchaser.

A newer version of this tool, the Malco SideSwiperII (SRT2) has a nicer handle that makes unlocking and re-locking of vinyl siding easier and less likely to be damaged.


Continue reading at VINYL SIDING BUCKLED WARPED or select a topic from the More Reading links shown below.

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VINYL SIDING INSPECTION & REPAIR at - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

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