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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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.
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.
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.
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.
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).
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.
In 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.
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: http://www.vinylsiding.org/Email: firstname.lastname@example.org, - retrieved 9 Feb 2015, original source: http://www.vinylsiding.org/wp-content/uploads/2015/01/I1_Vinyl_Siding_Installation_Manual_English.pdf
See VINYL SIDING INSTALLATION for details.
Also see PEEL & STICK FLASHING MEMBRANES for products useful to seal around windows and doors before installing siding
Details about stains on vinyl siding are now found in a separate article at VINYL SIDING STAINS
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:
Details about the causes of & cures for leaks in building siding are now
at SIDING LEAK DIAGNOSIS & REPAIR
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.
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.
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.
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.
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.
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.
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.
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.
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
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Shown above is a siding hook, also referred to in some manuals as a zip tool.
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.
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.
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.
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.
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.
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:
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.
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