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  • By Mark Meshulam

    Vinyl windows, also known as PVC (polyvinyl chloride) windows or uPVC (unplasticized PVC) are a ubiquitous part of the residential window landscape, and not only that, there are a lot of them out there.

    There are many satisfied vinyl window customers and I have seen many good installations, however there can also be problems with vinyl windows. Some problems are common to all windows, others stem from the unique properties of PVC. Some problems occur in the window itself, some come from the way windows are installed or joined to one another or to adjacent materials.

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    What is PVC / Vinyl?PVC used in windows
    PVC is a thermoplastic polymer constructed of repeating vinyl groups (ethenyls) having one of their hydrogens replaced with a chloride group. That’s it! Grab a tweezers and make some yourself. Seriously, folks, PVC is the third most widely produced plastic and is expected to exceed 40 million tons by 2016.

    PCV is made up of 57% chlorine by weight. The remainder is the petrochemical ethylene. Windows and plumbing pipes are made from rigid, or unplasticized PVC, also called “rigid PVC” or “uPVC”. Shower curtains, IV bags and sex toys are made from plasticized PVC due to their need for flexibility.

    Properties of PVC
    The good news about vinyl as a window material

    Section through vinyl double hung window frame sill. (1)frame jamb (2) insulated glass (3) operable sash (4) lift rail (5) sill insert (6) frame sill (7) insect screen (8) screen frame (9) screen track.

    Section through vinyl double hung window frame sill. (1)frame jamb (2) insulated glass (3) operable sash (4) lift rail (5) sill insert (6) frame sill (7) insect screen (8) screen frame (9) screen track.

    • Generally, PVC has better resistance to thermal conductivity than thermally broken aluminum.
    • The color of the product is inherent in the material, so if the window window frame is scratched, you still see the same color. This is great if you like white windows because the vast majority of vinyl windows are white.
    • PVC is a thermoplastic and can be fused at frame corners. If the frame extrusions are designed so that sill, jamb and head are similar to one another, they can be mitered and fused. First the window frame parts are cut at a miter (45 degrees), then the cut ends are pressed against a hot metal plate to melt the ends. Then the ends are pushed together to form a (usually) watertight corner. The aluminum and wood window guys haven’t figured out how to melt and fuse corners with their materials yet.

    Properties of PVC
    The bad news about vinyl as a window material

    • PVC is not as rigid as wood or aluminum. Generally, PVC is used only for relatively small windows as a result. It can be fitted with internal metal frame stiffeners.
    • PVC is a thermoplastic with a relatively low melting point, about 212°F (100°C). It begins to soften 149°F (65°C). If any part of the vinyl window frame heats up too much, it can bend and then “take a set”.
    • PVC has a greater coefficient of thermal expansion than does wood, aluminum or glass. This means it shrinks and grows more with changes in temperature. One of the worst areas where this can have an effect is at the glazing area, where the glass engages into the sash or frame. Glazing sealants can shear because the PVC is moving against the relatively stable glass. Leaks around the glass can result.
    • PVC is a little tricky for sealant adhesion – sometimes caulk doesn’t stick to it. When working with any substrates, and especially PVC, you must do adhesion tests two weeks before doing the work.

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    Here are some problems I have seen with vinyl windows.The numbering does not reflect frequency of the problem, but rather an attempt at creating the illusion of organization.

    1. Water leaks through window frame joinery
    Back in the day before vinyl window manufacturers found out how well the fused corners worked, they simply screwed and sealed the frame corners together. To make things worse, the corner joinery was in some cases not conducive to effective sealing. Add in the problems with sealant adhesion, and you have a leak at the bottom of the window, allowing water into the building. You can determine if your vinyl windows have this problem by performing water testing.

    Water damage beneath leaking vinyl window frame. Leaks rusted out the steel opening liner, then went on to attack the wood.

    Water damage beneath leaking vinyl window window. Leaks rusted out the steel opening liner (left), went on to attack the wood (right), ran down inside the wall and destroyed a wood floor.


    Top left: Two older style vinyl windows being pulled apart at the stacking mullion. The joinery is
    2. Water leaks through glazing
    Because vinyl changes in dimension with changes in temperature much more than glass, long term movement can shear glazing sealants and bring about glazing leaks

    Because vinyl changes in dimension with changes in temperature much more than glass, long term movement can shear glazing sealants and bring about glazing leaks


    Thermal movement of PVC is seven times that of glass. As the temperature changes, the PVC often slides against the glass. This can puts stress and wear on the glazing sealant, which might be only 1/16″ thick, eventually shearing it. I have seen vinyl window sash overflow with a light water spray.


    3. Water leaks through trims attached to PVC windows
    Trims could be mullions, brick-mold or capping. Generally, these elements must be continuously sealed to the window at the exterior plane. At the interior, screws driven into wet areas of the window will produce leaks and should be avoided.
    Left: Vinyl window mullion is split open revealing an aluminum stiffener and an absence of sealant between the H-section and windows. This assembly leaked. Right: New assembly has sealant present between H-section mullion and adjacent windows at exterior plane (inset)

    Left: Vinyl window mullion is split open revealing an aluminum stiffener and an absence of sealant between the H-section and windows. This assembly leaked. Right: Looking down on the top of a pair of windows mulled together. New assembly has sealant present between H-section mullion and adjacent windows at exterior plane (inset-sealant location indicated by arrows)

    Gaps between brick mold and window must be sealed continuously

    Gaps between brick mold and vinyl window must be sealed continuously

    When vinyl windows are replaced, thin aluminum sheet metal known as capping is formed on site and applied to the perimeter of the window. Left: Capping peeled away to reveal wood far behind so that capping is not supported. This capping was held in place with a face-nail. Right: New capping being installed so that its contour is visible. Outward bend in capping makes a good caulk joint design very difficult.

    When vinyl windows are replaced, thin aluminum sheet metal known as capping is formed on site and applied to the perimeter of the window. Left: Capping peeled away to reveal wood far behind so that capping is not supported. This capping was held in place with a face-nail. Right: New capping being installed so that its contour is visible. Outward bend in capping makes a good caulk joint design very difficult.


    Too often, installers do not understand that water must drain from the top of the steel lintel - the angle that holds up the brick above. So, they clad the lintel with capping so that water goes into the window system, where it is uncontrolled and eventually becomes a rusty leak. At left, the installer is removing the flimsy capping

    Too often, installers do not understand that water must drain from the top of the steel lintel - the angle that holds up the brick above. So, they clad the lintel with capping so that water goes into the window system, where it is uncontrolled and eventually becomes a rusty leak. At left, the installer is removing the flimsy capping. At right, steel lintel is revealed. Caulk joint above the lintel on the brick confirms that drainage area of lintel was buried beneath the capping.

     

    4. Bowing or bending of vinyl frame or sash members
    Due to their inherent flexibility, framing members should be shimmed and fastened well. Even if this is done, framing members that span a distance should be observed for excessive bending. Such bending will often result in reduced performance as can be seen in the photo below.

    The meeting rail of a vinyl double hung window bows in excess of 1/16

    The meeting rail of a vinyl double hung window bows in excess of 1/16

    A bowed meeting rail is not just a visual issue. It results in a misalignment between the lower and upper sash. In this picture, the misalignment is fully 5/32

    A bowed PVC meeting rail is not just a visual issue. It results in a misalignment between the lower and upper sash. In this picture, the misalignment is fully 5/32


    5. Poor component tolerances
    In vinyl windows, just like any other manufactured product, the parts need to fit. Sadly, this does not always happen. Window manufacturers use “cutting formulas” to tell them the cut length of each part of a window, given the window’s overall size. In a simple double hung window there can easily be almost 30 parts that all must be cut to the proper length in order to work well. Sometimes there can be an error in the cutting formula. If assemblers on the plant floor are not vigilant, poorly fitting components can be released to the public, resulting in degraded quality and reduced performance.

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    The horizontal parts on this lower sash are too short, resulting in a large gap between the side of the vinyl sash and the adjacent frame. The weatherstrip is supposed to be compressed 30%. Instead it is uncompressed and has a nearly 1/8

    The horizontal parts on this lower PVC sash are too short, resulting in a large gap between the side of the sash and the adjacent frame. The weatherstrip is supposed to be compressed 30%. Instead it is uncompressed and has a nearly 1/8

    6. Poor serviceability
    Double hung windows utilize a pair of spring-loaded balances that assist in reducing the amount of force need to raise the sash, and to hold the sash in its raised position. It is not uncommon for this balance to fail and require replacement. Sash balances should be easily replaceable, but on one of the jobs pictured here, one would need to cut the frame in order to replace the balance.

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    7. Insulated glass seal failure
    Seal failures occur in vinyl windows, just as they occur in wood and aluminum windows. Often, this is due to the long term presence of water in the area beneath the glass.

    Insulated glass seal failure in vinyl window

    Insulated glass seal failure in vinyl window


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    25 Comments

25 Responses to “Leaks and Problems with Vinyl Windows”

  1. Rafael Pérez Molina

    Another big issue I perceive on PVC windows is cristalization due to UV exposition. It would be interesting to know your point of view about it.

  2. Mark – Here is an interior shot of a vinyl window where the little window drain slots couldn’t keep up with the rain. I had about 1,000 of them on this project that were suspect. Some of these windows we could “port out” and increase the flow, but a few were too warped to be dependable even with adequate drainage and had to be replaced.

    Also, I included some photos of the rear hatch glass that exploded in my little electric car. The factory didn’t want to warrant it because, “One had never failed before due to a defect”. I said, “Well you got one now!” Look at my notes and you can see the defect clearly. After their engineers looked at this, I got my $700 piece of glass replaced under warranty…

    I have an 70+ window residential project starting shortly. New home, hand made wood windows, reverse slopes, no weather strips, literally sheets of water entered at some locations during a bad storm – Lots of interior damage.

    John McReynolds, CGR GMB
    Home Defect Analysis & Solutions
    Comprehensive Claims Solutions, Inc.
    Houston, Texas 77080
    leak at bottom of pvc window

    leak at bottom of pvc window

  3. We are saving up this year, so as to not have to face another winter with jack frost blowing threw our home. Time to replace all the windows!

  4. “One had never failed before due to a defect”. I said, “Well you got one now!”

  5. Thanks Mark. I enjoy reading your materials, very interesting and informative. Keep up the great work.
    Regards,

    (architect/attorney)

  6. Hello,
    You are providing some great advice on the website with regard to the water issues. The one thing that I noticed with regard to the ice damming, that was over looked is the root cause of ice damming.
    It is caused by the heat from the house melting the snow at the roof interface and forming ice at other parts of the roof that are cold, typically by the gutters or exterior edges.
    This problem is typically a roof ventilation issue.
    This also can be indicative of other problems such as insulation properties being lessened through condensation on the roof, roof rotting out and ice piercing the roof membrane.
    We are currently introducing roof vents into the chicago area that are designed especially for flat roofs. We have seen a lot of issues with flat roofs lately in buildings that are a few years old. Most times it is due to the impermeable moisture barriers being penetrated too often with can lights, speakers and other in ceiling holes, allowing interior moisture into the attic that ends up condensing in summer when the ac chilled air meets the super heated moist air. Leaking can lights are the normal result.
    In winter the moisture turns to ice if not eliminated and can compress the insulation.
    Check out our vents at http://www.ventilation-maximum.com/English/index.html
    We are the supplier in the US from the midwest to the west coast.
    Thank You
    Ventaroof LLC
    312-753-9199

  7. This is great information about vinyl windows. It shows how important it is to get windows and service that is guaranteed. If you need vinyl window repair or replacement in your home, stop by clearchoicewindowsofutah.com and contact us for a quote.

  8. Very informative info, Mark.

    Please check out this window made in Indiana. Alum. exterior with a vinyl interior married with urethane foam.

    http://www.stjamescompany.com

  9. window pvc is leaking from bottom onto sill leaking at bottom where 2 windows are attached together example { ! }{ ! }
    ___“____

    “(leak on sill)

    any ideas thank you very much

  10. Hi! I was googling water leaks, and stumbled across your site. Wow, lots of great information! I just noticed water damage to the wood trim and drywall on the bottom, interior corner of my daughter’s double hung vinyl windows. There is also a small spot of soggy drywall on the ceiling below these windows. I’m obviously concerned, and am planning to go back to both my window, and siding contractors to fix the source of the problem. Unfortunately I don’t even know where to begin figuring out where the water is coming from. It’s definitely an outside problem as there is no plumbing on that side of house. Any suggestions as to the source? I’d like to be informed prior to talking to the contractors so they’re not “fixing” the wrong (read easiest, cheapest) thing. Thanks for you site and feedback!

  11. Window leaks are a high priority problems. Left unattended, leaks through windows or walls can cause extensive and expensive water damage.

  12. Vinyl windows are one of the most durable, easily maintained windows you can choose when upgrading the windows on your home.

  13. If you have vinyl windows, please take a moment to join our “Rate Your Vinyl Windows” survey. It’s at the bottom of Leaks and Problems with Vinyl Windows.

  14. UPVC windows are good alternative for old ordinary windows as they are thermal resistent. You have also added some cons of UPVC which I found informative, thanks for sharing.

  15. Mark,

    Great site, lots of great information. Just built home in SE WI. Many of my windows have condensation although I have humidity down to 40%. But now I’ve noticed I have several windows that area leaking air where the sash at top of bottom window meets the middle (locking area) on both sides. How do I fix that. The windows are supposedly Windgate by Alliance and have a 5 year warranty. Trying to get builder, installer, etc., to respond is a joke.

    Ron

  16. We do not have condensation, but my how the windows whistle when the wind blows from certain directions. The air leak we are having is at the top of the window. Any suggestions to fix it?

  17. Nice site analysing upvc issues. Many are poorly fitted. I had all my patio doors/windows leaking water and found an easy way to fix them so I made a video that may be of interest to others with water leaks. See here:
    http://youtu.be/AhU_9ME311s

    Regards Jon

  18. What I am having a problem with is crank out vinyl windows and we have some heavy winds that have bent the vinyl frame where the crank is and so this area is bent out. Now we have not as good seal on the window.

  19. Replacement windows without exterior perimeter flashing are an irresponsible product. There is no way to effective seal water out. Relying on caulking means it is only a matter of time before water infiltration occurs.

  20. I just got new vinyl windows, and there are screw tips protruding between glass panes, on left side of each window.. There are two screws, one 1.5″ from the top and another one 1.5″ from the bottom. I thought that there should be nothing protruding between panes, as windows are supposed to be sealed. Is is a defect and will it present a problem with condensation? Protruding tip is about 0.25″ long… Is it normal? Windows were installed a week ago. Thanks!

  21. Hi Vera,
    Can you send a few pics of this to me at mark@chicagowindowexpert.com?
    Thanks, M

  22. This sounds like permanent damage and may warrant getting a new sash.
    M

  23. Assuming the windows that whistle are operable, you may need to add a thicker weatherstrip or some sort of additional latch that closes the top corner more tightly.
    M

  24. Hi Ron,
    If possible, send a few pictures to mark@chicagowindowexpert.com and I will try to help.
    M

  25. I had 2 custom made (language from contract) Vinyl Double hung windows, 2 full grids 6/6, wide flat, 1 mull 2 metal rips costing me $1 328 dollars installed in my condo 7/7/14. The window is leaking. The caulking/sealant is caving/sunk in at the bottom, especially at the left corner. I called the contractor and the man who installed the windows is coming out tomorrow morning to look at it and put more caulking/sealant in where it is wet and caving in. Do you think this is going to fix the problem? I really don’t know what to do. I’m a librarian and the best I could do was google the internet and I found your website, which is excellent. Help me with some advice as to what to do or say tomorrow, please. Thanks for listening, Sincerely, Linda T.

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Another view of stress waves emanating from the nickel sulfide inclusion. The stress waves are in the shape of four teardrops pointing to one another, converging at the nickel sulfide inclusion. The small teardrops aim toward the glass surface, where the localized stress was quickly relieved as the fracture made its way to the surface. The taller teardrops stretched their way along the length of the fracture.
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