Thank you @toddinmn. I understand that the awning windows might need to be tempered given their height from the floor. But not the picture window. The contractor also told me that the requirement for tempered windows is not Building Code in my area. He said Marvin and Pella are asking for it (the two brands he carries).

When I looked for pros and cons of tempered glass windows, each result mentioned the possibility of spontaneous breakage. In particular, if you have direct sun on part of it, so sun is heating that section, but not on another, then breakage can result which would not happen with regular glass. This window faces SE, but part of it has trees shading it, and the rest gets unobstructed direct SE sun. Or, over the years the frame may experience some bending or flexing which would cause tempered glass to break but not regular glass. It is a large window.

In certain and very few instances it could happen but is very rare. I have never replaced tempered glass because of this, only due to impacts from break in.

If tempered glass breaks, you end up with little chunks of glass, if regular glass breaks, and someone is near it, the glass is in shards, and someone could be seriously hurt. I would want the tempered glass, especially in a window that low down.

I suspect the requirement for tempered glass in the fixed window is dictated by code. If so, any debate is moot point. The 2021 International Residential Code (IRC,) which forms the core of most statewide building codes, requires glass to be tempered (safety glazing) as noted in section R308.4.3

R308.4.3 Glazing in Windows

Glazing in an individual fixed or operable panel that meets all of the following conditions shall be considered to be a hazardous location:

1. The exposed area of an individual pane is larger than 9 square feet (0.836 m2).
2. The bottom edge of the glazing is less than 18 inches (457 mm) above the floor.
3. The top edge of the glazing is more than 36 inches (914 mm) above the floor.
4. One or more walking surfaces are within 36 inches (914 mm), measured horizontally and in a straight line, of the glazing.

@cat_ky As I said in my OP and my follow-up comment, I had expected that the awning windows need to be tempered given their height from the floor. Again, my concern is about the possibility of spontaneous breakage in a window as large as this picture window is, and given its exposure to full sunlight on part of it, and shade on the other part.

I'll attach a couple screenshots that list the risks of tempered glass. Furthermore, Marvin has a carve-out in its warranty for a tempered glass window. It does not have the coverage of the Marvin warranty. Instead it has the coverage of the glass manufacturer, which is Cardinal Glass, and which only provides a one-year warranty on its tempered glass. So if the tempered glass has spontaneous breakage more than 1 year out, I am on the hook for a very costly replacement.

@Charles Ross Homes Our local Building Code only has the requirements you listed #2,3,4. I expected that the 2 awning windows need to be tempered. My concern is the large picture window and the risk of spontaneous breakage. Marvin is requiring it - not my local code - yet Marvin won't warranty it.

This portion of the code causes much confusion. Your awning windows may not need to be tempered. Read the language carefully. To be considered a hazardous location, all of the listed conditions must apply--not one or two, but all.

Manufacturers may limit production of large windows to tempered glass only. The glass is typically warranted by the glass manufacturer--not the window manufacturer.

The Awnings are under 9 square feet and should be exempt. The picture is over 9 square feet and the bottom edge of glass is within 5’ from the floor , therefore not exempt.

You could shorten the window so it is higher then 5’ or put in another window below it that is less than 9sf and tall enough so that other is more than 5’ off the floor or any combination of windows so the panes are less then 9 sf.

In the end tempered glass is pretty tough, these type of occurrences are rare, Marvin uses Cardinal glass which has a very good reputation for quality control.

@aem04,

most of your concerns about tempered glass vs annealed glass are due to a misunderstanding of the differences between the two products. In real world, tempered glass is actually recommended over annealed for many of the potential problems that you are worried about. Tempered glass is NOT more prone to breakage than annealed, in fact it's actually significantly less prone to breakage.

HHG is a Chinese glass company, and while not a knock on them per se, the list of potential "problems" that you posted is more like that they are covering their a$$ in case anything happens rather than a comprehensive list of actual things you need to be concerned about.

Thermal stress..... As you mentioned in a couple of your posts, thermal stress breakage typically occurs when the glass surface is exposed to direct sunlight but part of the glass is shaded at the same time.

Despite the general conception that glass is a very good conductor of heat, it really isn't and it is possible to have a significant difference in temperature between the shaded and unshaded portions of the glass.

Every one degree difference along the border between the hot glass and cooler glass adds 50psi of stress to the glass. If the temperature difference within the glass along the hot and cold border exceeds about 40 degrees or 2000psi, annealed glass is going to break while tempered glass won't even notice. This is the primary reason why oven doors or gas fireplace doors use tempered glass and not annealed. Annealed breaks MUCH easier than tempered when exposed to temperature variations.

Numbers 4, 7, 8, 9 in the examples that you posted are all basically the same thing... install is right and it doesn't break, install it wrong and breakage can happen.

Number 5 and 10 are both about manufacturing defects. Nickel sulfide inclusions are a thing and tempered glass does break from it, but not if the glass was manufactured in North America. Don't know what other "manufacturing defects" they are addressing since their comment is very vague.

And impact... tempered glass is considered to be safety glass because of how it breaks and not because it is four times stronger than annealed. That said, although tempered glass can be broken from an impact, it's still at least four times stronger than annealed glass.

As Charles Ross posted, the awning windows probably don't need to be tempered and technically the big one probably doesn't either, at least per code, but there is no way I personally would not temper the big one for safety AND strength. It is better than annealed for your situation.

Per Todd's comment on five feet above the floor, that only counts when the window is adjacent to an operable door... warning copy paste below:

R308.4.2 Glazing adjacent to doors. Glazing in an individual fixed or operable panel adjacent to a door shall be considered to be a hazardous location where the bottom exposed edge of the glazing is less than 60 inches (1524 mm) above the floor or walking surface and it meets either of the following conditions’

1. Where the glazing is within 24 inches (610 mm) of either side of the door in the plane of the door in a closed position.

2. Where the glazing is on a wall less than 180 degrees (3.14 rad) from the plane of the door in a closed position and within 24 inches (610 mm) of the hinge side of an in-swinging door.

Honestly, you are really overthinking this thing. If you want the awnings to be tempered then get them tempered, but trust the people who make the windows, and accept that tempered glass in the big window is a very good idea. They really are concerned about your safety and that's why they want to temper it.

" Again, my concern is about the possibility of spontaneous breakage in a window as large as this picture window is "

Not an issue. Oberon covered it all well above but we use glass way larger than that every day and all tempered glass everyday commercially and honestly I have heard of 2 pcs maybe that spontaneously broke in the 10 years.

Spontaneous breakage chance would be about you winning the lottery chance. Yes, it happens to someone. But not to you. Your oven door has a higher chance of shattering than does a window, because it goes through heat cycles. And that is still very very rare.

Thank you all for your advice on this tempered glass picture window. I can't tell you how much it has helped me, and I hope it helps anyone on here in the future with the same questions. @oberon476 your detailed explanation taught me a lot, much appreciated.

I've now received from the contractor a contract for me to sign with all the Marvin Ultimate specs for the tempered glass picture window and the 2 awning windows which are not tempered glass. One thing specified there has given me pause. Note that the current 35-year-old picture and awning windows are dual-paned non-tempered glass. The biggest issue I've had with them the last couple years is severe cold infiltration in the winter. That is because the aged frames are rotting, and the seals between the dual panes have failed around the edges. We've needed a space heater just to be able to sit in that room during the winter.

The contract specifies for the 2 awning windows (not tempered glass): "IG - 3/4" - 1 Lite". Is that dual pane? And for the 9' x 5' picture window: "IG - 1 Lite 1/4" Tempered". Sounds like not dual-paned? That concerns me. My intention in spending this amount of money is to improve quality-of-life in this room so that it is comfortable and livable. It's not an easy expense for us, so I am hoping you guys will fill me in on whether there will significant improvement in cold infiltration or not.

Yep, they are both dual pane.

IG stands for Insulating Glass which is the industry term for multi-panel glass units.

There should also be a reference in the paperwork to LoE coating and argon between the lites of the IGU (Insulating Glass Unit).

If you are dealing with a salesperson, they should be explaining all this to you.

Curious why you are going with the Ultimate? While it is a gorgeous window, it's also one of the more expensive windows that you are going to find on the market.

Since you said in your original post that cost didn't matter, I didn't even think about it, but in your last post you said that "this is not an easy expense...". Have you looked at other, less expensive, options from Marvin in their Essentials and Elevate fiberglass lines?

Thanks for your reply @oberon476. I'll address each of your points:

IG stands for Insulating Glass which is the industry term for multi-panel glass units.

That is good to hear. I think I was concerned by the 1/4" measurement for the picture window rather than the 3/4" I expected. Why is it only 1/4"?

There should also be a reference in the paperwork to LoE coating and argon

Yes, it says "Low E2 w/Argon" for each window. I didn't mention it because I didn't have a question about it.

Curious why you are going with the Ultimate?

I have been changing all the 1990 windows in my home gradually over the last 12 years. I originally chose Marvin Ultimate 12 years ago, and since then have replaced all my windows with the Ultimates. While they were expensive, it was not as bad pre-Covid. This window unit of picture/awnings is now the only one left to be changed. And since these are so large, and on the front of the house, it would be glaring if they did not match the rest of the windows. Also, the Ultimates have been great performers, all look exactly as the day they were installed, and I have been very happy with them.

Since you said in your original post that cost didn't matter...

I said that in reference to tempering the window - i.e. my concern was not about the amount of the upcharge added to temper the window vs not tempered. My concern about the risk of spontaneous breakage outweighed the cost of the upcharge.

Having said that, the overall cost of this 9'x5' picture window and two awning windows is quite high. As mentioned, my fear is of paying such a large amount if additional comfort and better quality of life from it will be minimal.

Because of the overall size, each individual piece of glass is 1/4" thick. Most likely the overall IGU (insulated glass unit) makeup is 1/4" glass / 1/2" air space (with argon gas) / 1/4" glass for a total of 1" overall thickness which is std for picture windows from Marvin in the Ultimate series I do believe..

@aem04, makes sense on the Ultimates. Glad that they have worked out so well for you.

Per argon and Low-E, I was asking because they would not be available unless you had a dual pane (or triple) glass assembly. Argon obviously because its a gas infill in the space created between multiple lites and while there are types of Low-E coatings than can be used with a single lite, they are much less common than the type that you have that must be enclosed in the space created between two lites as well.

Honestly, I was also a little puzzled by the "IG - 3/4" - 1 Lite". Is that dual pane? And for the 9' x 5' picture window: "IG - 1 Lite 1/4" Tempered"., as well. While manufacturer's codes can sometimes be confusing to people not familiar with them, and while I would be curious to see the actual paperwork, there wasn't the slightest doubt that you were getting dual pane windows.

I think that mwm's reply makes a lot of sense.

@millworkman and @oberon476 thank you for that helpful info. Mwm, glad to know about the 1/4" meaning. Oberon I should have realized about the Argon in the specs that must mean the picture window is dual pane!

There were also these performance specs provided:

- for the 9'x5' picture window with tempered glass: U-Factor 0.27, Solar Heat Gain Coefficient 0.35, Visible Light Transmittance 0.6, Condensation Resistance 58

- for each of the two 4'x'2 awning windows (non-tempered): U-Factor 0.3, Solar Heat Gain Coefficient 0.29, Visible Light Transmittance 0.49, Condensation Resistance 56