The Case of the Do Not DIY Door

Question:

Good Morning Glass Detective,

I am preparing to replace the glass only in an old aluminum sliding door. The frame is not thermally broken, however, the glass is insulated. The outside-to-outside dimension of the aluminum slider extrusion is 1”. I am guessing that the glass panes are 7/16” with 3/16” airspace, leaving 1/8” for rubber gasket. Does this sound reasonable? The daylight dimension of the glass is 44 3/8” x 74 3/8”.

Thank you for your time.
Dave
Queenstown, MD

Answer:

Dear Dave,

Thank you for making contact with the Glass Detective regarding your patio door glass issue and in particular, how to size or measure (for ordering purposes) the correct glass. To start, let’s give you some basic information about patio doors and the glass used therein. Here we go: Over the past 40 or so years there have been numerous companies that have come in and gone out of the patio door manufacturing business. These various manufacturers all pretty much made the same basic door and, for the past few decades, they have almost all been glazed with insulating glass units using tempered glass. Perhaps 95% or more of the doors produced are glazed with tempered glass. These doors have been manufactured using wood, aluminum, bronze, stainless steel, vinyl, and fiberglass.  Because a multitude of manufacturers and a variety of products have been used to make these doors, there is no consistency in how the glass units get installed.

First off, I always recommend that glass be replaced professionally by a reputable glass shop or window and door dealer in your area. They will be able to take accurate measurements and recommend replacement options. This is not something that should be DIY’ed. That being said, the following is for informational purposes only so that you may have a better understanding of the process.

There are two primary methods for installing a piece of glass into a patio door frame.  The first is what we will call the “wrap-around” method.  In this approach to installing a piece of glass into the door frame, the frame comes completely apart.  It is typically screwed together or clipped together in some fashion at the four corners of the door.  When the screws or clips are removed, the frame comes apart into four pieces and, obviously at this point, the glass is out of the frame.  Sometimes there is a wrap-around gasket that is part of this type of frame, or it might be glazed using a sealant or some kind of gasket strips.  The best way to measure the glass for this type door frame is to take the existing frame apart, measure the exact dimensions (and thickness) of the original glass, and then order an appropriated size replacement piece of glass.

Naturally, you would most likely want to put the frame and glass back together and use it temporarily while you are waiting for the replacement glass unit to arrive.  This approach could be problematic if the original glass is already broken because tempered glass can explode and fall out of the opening when it is broken.

If it’s an insulating glass unit in the patio door, hopefully only one lite would be broken and you can still use the above approach.  If both lites of the tempered glass unit are broken, you can still get the glass size by taking the frame apart and measuring the insulating glass spacer that would be in the frame.  The tempered glass at the perimeter of the unit usually sticks to the spacer sealant making it easy to see how much larger the glass was than the spacer frame.

The other commonly used approach for installing glass into a patio door incorporates a removable stop or molding which appears to be a part of the door frame itself.  These removable stops can be popped off allowing for an accurate measurement of the glass unit in the door.  Commercial sliding doors typically are glazed in this manner.  I also have observed some wooden patio doors that are manufactured in such a way that the frames wrap around the glass but are glued or pressed together in a manner that it is quite difficult to get apart for measuring or replacement purposes.  In these cases, you will most likely have to order a new patio door with the glass already glazed into it.  This type of door is rare, but I have seen them.

In your email to the Glass Detective, you ask how much to add (for the glass size) to what you have measured as the “daylight” opening.  Depending on the manufacturer of the patio door, your add-to-daylight dimension could be anywhere from 5/8-inch to one-inch.  You also state that you are guessing at the glass thickness and the allowance for the rubber gasket that is apparently part of the glazing system.  I don’t think you should guess at anything.  Unless you are experienced with this kind of work, the job could be difficult enough without guessing at the sizes or thickness. Virtually all professional glass shops today use an infrared device for measuring glass thickness which not only provides them with the overall thickness of the glass unit, but also with the thickness as the individual glass pane and the thickness of the air space between them.  The most modern of these glass measuring devices will even indicate if there are any coatings (such as low-E) on any of the glass surfaces.  Assuming that the patio door is next to a patio fixed glass panel, you are most certainly going to want to match the glass coatings if there are any.

I’ve now been in the glass business for over 44 years and I have seen a number of DIY projects involving patio doors that have turned into a disaster.  A good glass shop not only will handle the job professionally, making sure that the glass is appropriate and installed properly, but can also clean, adjust and lubricate (or replace) the door rollers as necessary. And if you’re lucky enough to have a standard size piece of glass in your door, the job will be less expensive than you think.  I have long thought that glass replacement of any kind should not be a DIY project for anyone except an individual experienced in measuring, handling, and installing glass.  This is perhaps not what you wanted to hear from the Glass Detective, but I truly believe that my advice relative to using a glass professional to handle your project is appropriate.  I wish you good fortune with your project and thank you once again for making contact with the Glass.com Glass Detective.