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

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Vinyl siding defect recognition & diagnosis:

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.

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.

We also provide a MASTER INDEX to this topic, or you can try the page top or bottom SEARCH BOX as a quick way to find information you need.

Inspect Vinyl Siding for Damage: Examples of Bad Installation, Cracks, Leaks & Other Damage to Vinyl Siding

Horrible vinyl siding job in New York - many defects cataloged (C) Daniel Friedman

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While some vinyl siding on the home shown above has been replaced (darker siding at green arrow) this was one of the worst vinyl siding installation jobs I've seen.

At this New York hoome the siding has at some locations been installed using scraps (pink arrow), with gaps (black arrow), with lower corner trim on the outside rather than inside of the upper corner trim segment (leaky at pink arrow), buckling (tan arrow), with un-even, overlapped courses (blue arrow), perhaps where the siding was installed below a now-removed porch roof that has been left poorly-flashed as a possible wall leak (red arrow).

This article discusses vinyl siding inspection points, defects, and repair procedures.

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.

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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.


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 separate 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 healh risks, fire risks, and environmental concerns that 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 Friedmanh

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Shown above is a siding hook, also referred to in some manuals as a zip tool.

Figure 1-22: Vinyl siding profiles (C) Wiley and Sons, S Bliss

As Steve Bliss points out at VINYL SIDING LOCK & NAIL FLANGES, all vinyl siding panels have a locking tab at the bottom of each panel that snaps over the top tab of the panel below.

It'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.

Watch out: trying to tear off vinyl siding without unhooking the lower edge (buttock) of each siding course from the course below risks damaging more siding courses and increasing the cost of repair or replacement of the wall cladding. In fact, without a siding replacement tool such as Malco's Side Swiper SRT1 shown in our photo above, even if you can tear off the siding, re-hooking the bottom edge of the new siding section to the top of the course below can be almost impossible.

5 Steps in Using a Vinyl Siding Zip Tool or Un-Lock Tool

Below at left we illustrate how the vinyl siding hook can be used to "un-hook" the lower edge or "buttock" of vinyl siding in order to remove the siding for repair or replacement of damaged siding or to permit replacement of damaged corner trim or window trim or J-channel against which the vinyl siding is abutting.

How to use a vinyl siding hook to remove damaged vinyl siding (C) Daniel Friedman Names of the parts of a course of vinyl siding (C) adapted from Vinyl Siding Institute

At above right we illustrate the names for the parts of a course of typical vinyl siding. This illustration was adapted from the helpful vinyl siding installation manual provided by the Vinyl Siding Institute cited below.

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) (see REFERENCES) has a nicer handle that makes unlocking and re-locking of vinyl siding easier and less likely to be damaged.

  1. To use a siding unlock or zip tool, start removing siding by un-hooking the siding course immediately above the damaged siding.
  2. Simply insert the hook end of the tool into the locking flange in the buttock or lower edge of the vinyl siding (see sketches below).
  3. When the hook catches the up-facing lip of the siding buttock, pull downwards on the tool. The siding will un-hook from the top nailing flange of the siding course immediately below. This gives ready access to the nailing flange of the lower course.
  4. Use a small flat bar to pry out the nails in the nailing flange of the vinyl siding course to be removed. If the siding was nailed properly in its original installation the nails should not be tight against the siding or wall, so a thin flat bar will work nicely to remove them. Be sure that the butt of the flat bar presses against the nail flange or the wall sheating above the nail. Don't put the butt of the flat bar against the raised ridge of the nailing flange or you may damage it.

    If the siding panel being removed is very brittle or badly damaged such that its nail flange has been broken or can be broken away from the wall sheathing, you can opt to leave the nails in the wall: just remove any fragments of the old siding behind the nails and then drive the nail flush with the wall surface.
  5. Remove and replace the damaged vinyl siding.

Watch out: you may find that even if you are using stored "new old stock" vinyl siding from the original siding batch that was installed on the building the color of the new siding may not be a perfect match with the older siding remaining on the wall. Depending on the siding color and specific product, some sun-fading is normal. The photo of a horrible vinyl siding installation job shown below illustrates a color mismatch that was probably unavoidable. But the other bad siding work discussed starting at VINYL SIDING INSPECTION & REPAIR could have been avoided.

Horrible vinyl siding job in New York - many defects cataloged (C) Daniel Friedman

How to Remove & Replace Thick, Non-flexible Vinyl or Polycarbonate Siding Panels

CertainTeed and other manufacturers note that when removing thicker non-flexible vinyl or polycarbonate siding panels such as that company's Cedar Impressions Panel, to remove the old panels you will need to use a wood chisel to locate the locking tab of the old panel and to literally break it off.

The siding zip tool shown above won't work as the thicker plastic panels are not flexible enough to simply pull down and un-hook. The company provides a panel replacement kit that includes new cam clip and snap rivet fasteners to hold the replacement Cedar Impressions Panel in place. Or alternativel colored trim nails can be used to secure the new panel in place.

Where to Download Vinyl Siding Installation Manuals

Your local vinyl siding supplier or building supplier will be happy to give you the vinyl siding installation manual for the specific product you are purchasing, as everyone involved has an interest in a proper vinyl siding installation. If your supplier is out of manuals for their product just give the manufacturer a call or check their website for a down-loadable vinyl siding manual. Here are some sources of vinyl siding installation guides:

Reader Question: is it possible to avoid damaging vinyl siding when replacing broken corner trim?

Damaged vinyl siding corner trim (C) Daniel Friedman

29 October 2015 Tony Goszulak said:
Is it possible to not destroy the siding or trim corner when replacing the broken corner trim? The siding is existing and the corner was damaged next to a deck.



As a fellow whom I admire, instructor and home inspector Mark Cramer (Tampa) says: "... well, it depends"

Older vinyl siding may be quite brittle and hard to work-on without damage. Our photo above shows broken vinyl corner trim on a vinyl sided home in Glens Falls, New York. Your corner trim may look like that. The good news is that most vinyl siding can be removed, handled, or pieces replaced without breaking it.

  1. Work carefully using a special tool to unlock the clipped-together bottom edge of the siding. I have added a photo of the siding unlock tool into the article above.
  2. Then using a small flat bar or a pair of them, remove the siding nails holding the siding in place.
  3. Remove enough siding nails to remove or loosen the siding end enough to expose the nails holding the vertical vinyl corner trim in place.
  4. Remove and replace the corner trim as needed.
  5. Re-fasten and re-connect the siding.


Continue reading at VINYL SIDING BUCKLED WARPED or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.

Or see these

Vinyl Siding Articles

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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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