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.

There 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is where the glass is removed from the metal frames and then the frames are collapsed so that the nail flanges can be withdrawn from behind the siding.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.

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.

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

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.

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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