Screwed & glued or just plain screwed? Your vinyl window installation

Home Inspector with Charles Buell Inspections Inc.


Lately I have been finding an epidemic of improperly installed replacement vinyl windows; or, if they are “properly” installed the installations are not working out as planned.

I am talking about windows where the old windows have been removed and new windows are installed in the same opening. 

Vinyl window with a flangeThere are correct ways and wrong ways to do this. 

There are ways to do it that are considered “best practice” and installations that are “less than ideal.”  These poor practices are a little bit more like trying to make a silk purse out of a sow’s ear as they say.

In homes where the siding runs right up to the window frame—as in older metal frame windows that have no wood trim around them—the siding must be cut back to allow for proper removal of the old window as well as to properly flash and attach  the new window in the old opening.

What I am seeing over and over is where the glass is removed from the metal frames and then the frames are collapsed so that the nail flanges can be withdrawn from behind the siding.  This accomplishes the desired goal of removing the window but also results in less desirable consequences.  The window wrap flashings and/or house-wrap will be trashed by the extraction process and gaps will be created in those protective materials that will be vulnerable to water intrusion after the new window is installed.  How can proper repairs be made to this damage without taking the siding off?

Once the old window is removed, the trick is to get the new window flanges back in behind the siding. 

This is where the magic comes in, because it essentially cannot be done.

The window installer simply scores the plastic nail-flange on the new window with a utility knife and snaps the flange off.  Even more magical is that there are actually vinyl windows that can be purchased that have no flange to begin with.  If you can buy windows without a flange that tells me there must be some magical way of sealing around them so that they do not leak.

Then again perhaps not.

Without a flange the new window can then be installed up against the interior trim.  Screws are then installed through the jambs of the window to hold the window in place.  The gap between the window and the original siding is then caulked; the installer collects his check and is off to screw and glue the next unwary client.

If you have ever visited the installation instructions of a window with a flange, you will see that it is actually quite a complicated process to install the window properly.  The window opening itself has to be sealed and wrapped with flashings.  These flashings, on all four sides of the window, are installed such that every layer overlaps the layer below it—including the house wrap.  A bead of caulk then gets installed all around the window and the window is set in the caulk and the flange is nailed.  After this another layer of flashings is installed—each layer lapping the layer below and the top layer goes under the building wrap across the top of the window.  The bottom flashing materials that runs behind the bottom nail flange is made to likewise lap over the top of the building paper/house wrap.

The gist of all of this, as you have probably gathered by now, is the idea that all layers of materials lap over the layers below it—all of which is finally lapped by the siding which, depending on the type, also laps each other.  In this way any water that finds its way into the wall structure can follow the surface of the house-wrap all the way to the bottom without getting into the wall structure.  At least this is the theory.  The resistance to water penetration with such an installation is great—even related to moisture vapor moving through into the home around the window as a result of negative pressure within the home.

So now we go and buy a window without a flange and install it in a manner that seemingly violates all of these protocols and then cross our fingers and hope for the best.  This might not be such a big deal in a house where the window is merely being fitted into an existing frame that is theoretically all flashed properly behind the wood window installation, but it is certainly less than ideal.

When the installation is done where the entire old window is removed and the new window is merely inserted and caulked, we are certainly asking for trouble down the road.  If the caulk is relied upon to keep water out, and the integrity of the house wrap and the flashings of the opening is questionable, all bets are off on keeping water out of the house structure long term.  This method of installation is far from “best practice.”

Proper installations typically requires either cutting the siding back so that the window can be installed with proper flashings and the nail-flanges intact, or the siding must be removed and then re-installed.  Obviously this ups the cost of the installation of your new windows.  Sometimes proper installation requires adjustments of the interior trim as well—thus further increasing the costs of the installation of your new windows.

In light of these considerations it is not hard to understand why some installers would take shortcuts—-why some homeowners would take shortcuts.  Add to this that if the windows are being sold as part of improving “energy efficiency” it may be necessary for the short cuts to be taken in order to meet the window seller’s claims of eventual “payback.”  Hopefully everyone knows by now that new windows will never pay for themselves in energy savings.  You change them out for comfort, sound control, because the original ones are no longer functional and energy efficiency in the sense that you will safe energy, not because they ever stand a chance of paying for themselves.

In doing research for this post I found it interesting that in some cases the window manufacturers seem to care less whether there is a flange or not and leave the weather-tightness to the installer.  While this seems contradictory to the lengthy “how-to-install” instructions that comes with the windows, one has to think about how many more sales of windows come into play when they don’t care how they are installed and hang the problems that develop with improper installation on the installer.  Of course logically it should be the responsibility of the installer—but I do think they are getting mixed messages.

Without proper flashings and nail flanges, we are relying on caulk alone to keep water out of the wall structure.  Even the best caulks don’t last as long as will be necessary to adequately protect the home.  Differing rates of expansion and contraction between the window and the siding materials will typically result in cracking of the caulk over time.  Cracks in the caulk mean that water will have a pathway into the home.  It also means that moisture will have a pathway to be drawn into the home when the home is under negative pressure.  That means moisture laden air will be drawn into the wall structure regardless of whether it is actual water or not—merely humid air can thus represent a problem.  Both scenarios are not good for the long term health of the home especially in really hot humid climates or really cold humid climates.  At one season or another, this is true of most homes in the US.

In this picture we can see paint failure and unevenness of the siding of the recently replaced window.  Elevated moisture was noted by moisture meter behind the siding in these areas of obvious damage.  The flange was not present and the jambs had been screwed in place.

Paint failure and moisture intrusion around a vinyl window

So how can you tell if your windows were installed without the flange?

If you have new windows and no changes to the siding were made—this might be one clue.

If you have new windows and no changes to the wood exterior trim were made—this would be another clue.  This next picture shows the original wood trim wrapped by new trim installed on top of the siding.

Original wood window trim wrapped with new trim

New windows with screws in the jambs would also be a good clue.

Typical screw in the jamb of a vinyl window where the flange has been removed 

If you can slip a knife into a crack between the siding/trim and the new window and you don’t hit the flange of the window within a 1-1/2”—this would be a good clue as well.  As in this three year old window in the next picture—where the caulk has already failed—the 3” knife at full depth along the side of the window should have hit the plastic flange before the knife got this far in.  This is clearly a window without a flashing and yet may be an approved installation according to the manufacturer of the window.  Is it “best practice?” Certainly not in my opinion.

Things that are cost effective in the short run are often not cost effective in the long run. 

Missing flange on a vinyl window

New wood trim around the windows is a pretty good clue that the flanges are in place but even this is no guarantee.  Trim installed on top of the siding is another clue that the flange might not be there.  This is not always true either however, because it is a common to find trim installed over the siding even when the windows are properly installed (I can argue that this is also less than ideal but that is a topic for another post).

Installation of windows without flanges has created enough window installation failure issues that some jurisdictions now require permits to install replacement windows and the windows have to be installed with proper flashing details.

Verification that the windows have been properly flashed and that the nail flanges are still in place is a good idea.  Windows installed without a flange are almost always, to some degree, going to be a gamble and vigilant maintenance of caulk seals will be essential.


By Charles Buell, Real Estate Inspections in Seattle


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Comments (41)

Harry F. D'Elia III
WEDO Real Estate and Beyond, LLC - Phoenix, AZ
Investor , Mentor, GRI, Radio, CIPS, REOs, ABR

Replacing windows is a very expensive item to have on the list. Warranty?

Aug 26, 2012 01:12 AM
Melissa Marro
Keller Williams First Coast Realty - The Marro Team - Orange Park, FL
Jacksonville Real Estate and Home Staging

What great guidelines and information. I'm definitely sharing this so buyers and sellers can be more aware. 

Aug 26, 2012 01:27 AM
Elite Home Sales Team
Elite Home Sales Team OC - Corona del Mar, CA
A Tenacious and Skilled Real Estate Team

I have a good friend who is a contractor and he will be replacing all his windows. Thanks for the info. I will give him the article.

Aug 26, 2012 01:40 AM
Gregory Bain
Mezzina Real Estate & Insurance - Little Egg Harbor, NJ
For Homes on the Jersey Shore

Always, well thought out good advice to those that can hear it. But, the cost of doing it correctly often makes the legitimate contractor too expensive for the uneducated home owner. Pay now or pay later. Re-Blogged.

Aug 26, 2012 01:47 AM
Chris and Dick Dovorany
Homes for Sale in Naples, Bonita Springs and Estero, Florida - Naples, FL
Broker/Associate at Premiere Plus Realty

Whats wrong with people.  Do they do this sub standard work themselves or hire handymen who really only know the basics.

Aug 26, 2012 01:50 AM
Jason Sardi
Auto & Home & Life Insurance throughout North Carolina - Charlotte, NC
Your Agent for Life

Buell - Way over my head but that is a good thing.  I know where to go to when I have questions about such things.  Kind of makes me wonder if it isn't a bad idea to hire an inspector if you do decide to replace your windows to avoid potential issues down the road.

Aug 26, 2012 05:19 AM
Charles Buell
Charles Buell Inspections Inc. - Seattle, WA
Seattle Home Inspector

Richie, glad to hear that---had another one today less than ideally done

Kristin, take lots of pictures :)

Harry, good question---these guys tend to go in and out of business over night

Melissa, thanks---and thanks for the reblog

Elite, let us know how it goes

Gregory, I think most people think short term

Chris and Dick, I am afraid that this is being done by "professionals" for the most part

Sardi, are you treading water again?:)

Aug 26, 2012 05:36 AM
Steven Cook
No Longer Processing Mortgages. - Tacoma, WA

Charles -- what a great, informational blog on windows.  It seems the only way one can possibly rely on the windows being installed properly, is if the manufacturer has its own crews that do the installation.  Even then, one might find some crews trying to shortcut the process so they can get more hung, and earn more income.

Aug 26, 2012 11:09 AM
Charles Buell
Charles Buell Inspections Inc. - Seattle, WA
Seattle Home Inspector

Steven, I think it would tak a lot of confidence in the person hired to end up with properly installed windows.  I think it would be very difficult for the average homeowner to have any clue as to what questions to ask.

Aug 26, 2012 01:15 PM
James Quarello
JRV Home Inspection Services, LLC - Wallingford, CT
Connecticut Home Inspector

Good post, but seeing screws in the jambs is common when replacement windows have been installed. It seems that a typical replacement window would disply these "clues" and be installed properly. 

Aug 26, 2012 10:48 PM
Charles Buell
Charles Buell Inspections Inc. - Seattle, WA
Seattle Home Inspector

Jim, very true---and they are not as much of a "meaningful" clue as to faulty installation when they are present and the original wood frames are still in place.  Their presence with no original frames is a bigger problem.  I still do not think that the screw and caulk approach is ideal----just not quite so much a concern when the original frames are still there.  It is interesting that no one would ever think (hopefully) of installing new windows in this fashion, so why does it all of a sudden become OK to retrofit windows in this fashion?

Aug 26, 2012 11:55 PM
James Quarello
JRV Home Inspection Services, LLC - Wallingford, CT
Connecticut Home Inspector

I understand the difference and will be more vigilant in the future. I do however have a hard time seeing the method of installing replacements as defective. It may be less than "ideal", but I can not recall finding issues with windows installed in this manner unless the installation itself was in some way defective, but then isn't that usually the case :)

Aug 27, 2012 12:02 AM
Charles Buell
Charles Buell Inspections Inc. - Seattle, WA
Seattle Home Inspector

Jim, I agree.  I wonder if this is something we are going to see down the road as being more of a problem as some of these replacement windows have more "history."  While there are caulks that are more durable than others, we all know how effective they hold up long term---especially when adhering to different materials.  It would seems that some sort of simple capping molding to bridge the caulked joint would be a huge improvement and would be closer to what exists in a normal wood window installation.  There is no question in my mind that the installations where they are not being installed inside the existing wood frames are not working.

Aug 27, 2012 12:17 AM

Well, if you install a retrofit on an existing good frame, I do not see a problem. Because that frame it is already relying on house wrap, caulking already anyways



Apr 30, 2013 08:05 PM
Terry Flannery

Great article and so true. We are a siding and window contractor in Washington state and we frequently find rot and mold issues from screw n glue window installs in high exposure areas. There is a new solution available to install replacement windows and integrate them to the existing building envelope without cutting back the siding. Check out the info and video here


Jan 13, 2014 01:49 PM

I just recently had a replacement window installed, to replace a vinyl window where the seals were bad. My home has vinyl siding. The new window does not have nail flanges. It was screwed into the window frame. The window was caulked on the inside, then a few lines against the wood framing of the window opening, then again on the outside between the new vinyl window and vinyl j-channel. The installer says we have nothing to worry about and my husband thinks I am completely insane. I don't know what to do, how long until it might leak? What are the true odds that it will? What can I do?

Apr 22, 2015 01:42 AM
Terry Flannery

Vinyl siding gets more water behind it then most other siding products so the odds of a leak are higher than most. i cant tell you when or if it will leak but if the caulking cracks or gets voids in it the potential is there. caulking is the only protection with this type of install.

Apr 22, 2015 04:08 AM
Charles Buell
Charles Buell Inspections Inc. - Seattle, WA
Seattle Home Inspector

Jhn, it is the connection between the vinyl and the wood that is the problem.

Terry, I will check out the link

Jen, whether it becomes a problem or not is related to a lot of considerations.  How exposed to the elements are the windows, are there big overhangs to protect them.  In multi-story buildings vapor drive due to stack effect is a consideration as water can be sucked past the windows.  Maintenace of the seals is critical.  With good caulk and great maintenance they should not be a problem in most instances.

Terry, agreed.

Apr 25, 2015 12:58 AM
Terry Flannery


Did you get a chance to check out the Rain Jacket Flashing System. . This is the best solution to integrate a replacement window to the existing building paper especially when the cladding is brick or stucco and cannot be cut back or removed. It also passes AAMA pressure tests.

Mar 01, 2016 02:28 PM
Charles Buell
Charles Buell Inspections Inc. - Seattle, WA
Seattle Home Inspector

Terry, I had not seen that system, and will be skeptical until proven otherwise.

Mar 02, 2016 01:38 AM