as I understand it, the fire risk from windows is mostly from the glass breaking. This link has lots of information about home hardening I’m including the link to the page that discusses windows.

https://www.firesafemarin.org/home-hardening/windows

"Our contractor tells us that only vinyl windows meet Title 24 unless we spend 4-5X the $"

He may be correct and he may be incorrect. Personally I would not take him at his word. I would contact a local well reviewed and reputable window and door store and solid local lumberyard and work on the window package pricing with them. Is there a reason you have to use your contractor for the windows? Is there certain brands only that he will use? Typically fire rated will require steel (and be expensive in any brand) and I am on the east coast and not familiar enough with T24 to offer much more advice.

Do you have photos of your house showing current style of windows? Why do you need new windows? Yes, vinyl replacement windows can be the cheapest way to go, but 4 to 5 times the cost for something else isn't my experience. Title 24 is not very restrictive as far as windows go. I agree with millworkman's take: find a local vendor and start from there.

I believe the current Title 24 codes require the maximum U-factor for windows be 0.30 and the maximum SHGC be 0.23. Assuming you are not doing other upgrades to the house, your windows will have be at those values. If your replacements windows are casements, there are aluminum windows that have those values. Pretty much all european style aluminum casement windows meet Title 24. Some regular aluminum casements meet those requirements as well. For example, Fleetwood 450-T line works. You should talk to a shop specializing in windows and doors to find out details as the pros suggested. It is difficult to tell if the 4-5x estimate is correct without comparing actual quotes. We had dealt with the same issues but we are doing a full renovation and the windows can have higher values if other areas of the home have energy improvements.

For anyone following this post, I want to report back. I was disturbed by the pressure on the part of the contractor to put vinyl windows in our authentic MCM. (our house was damaged in the CA wildfires.) The vinyl would lower the value of our house, which had original aluminum windows, though single pane. He kept insisting we would not pass energy inspection with aluminum of any sort to meet CA's title 24. There was no room in the house for compensating insulation, etc. It took me two days to realize he had in hand an official energy report, done by an engineer, that had never been given to me. The energy report had done an analysis of the house with vinyl windows, which obviously the contractor or the architect, anyone but me, had decided on for me. Someone finally told me to ask for that report. I called the engineer and he said, no problem, you can have aluminum windows, and he just rewrote the report so the new HVAC we are getting anyway compensated. It's hard to believe I had to have such a huge and upsetting wrangle --I feel like I am being kept at arm's length from the project and I have to be hypereducated to advocate for myself when it is my house and I am paying for this work, albeit some is an insurance settlement.

@Pamela,

Just to be clear, the title 24 report does not care what kind of window will be used. It only specifies the U-factor and SHGC. What are the numbers on your report? Please keep in mind, you will still need to find aluminum windows that have those performance numbers. Depending on what those values are, your choices may be limited if you are looking for double pane aluminum windows.

@lc, I think we are okay. The u-factor of the thermal break windows we are getting range from .39-.29 --average around .35 and the engineer used a u-factor of .48 for the calculations. None of these windows have a .48. He then gives us a compliance margin based on the proposed design of 147.33 --which is an improvement of 2.7 percent over the standard. This is based on an HVAC with a split AC, which I think is what does the trick here --but we are getting an entirely new HVAC, anyway. There are many numbers in this report, which is about 25 pages, but that is the summary. What else should I be looking for. And btw we live in a community of MCMs and they all have aluminum windows --I can't believe ours is the only house in the neighborhood that must have vinyl.

Millworkman --Yes, this is an "insurance company" job. We had to go that way to be able to complete the work for the payment we had. (Windows are on my dime though because most of the replacements are in the unburnt part of the house, so i don't get it.) I also hired a very experienced contractor to watch over the insurance company, MY advocate sided with them on the vinyl windows, so!! I think Title 24 has just filled these folks with an abundance of caution. As it turns out, our HOA does not even allow vinyl windows. Part of it is having people involved who know nothing about the MCM. Our house is authentic and 70 years old. We've tried to preserve whatever features we could. A big problem is, we are not there --we have been across the country and unable to be on site because of covid. Finally we've gotten our vaccines and are heading out to LA in a few weeks to supervise this project ourselves to the end. This was my husband's parents' house --it was caught up in the wildfires end of 2019, my father in law died, and this valued house became ours. All our work on its behalf has been remote.

Got yeah, sorry to hear, and good luck. Interesting that the HOA doesn't allow vinyl yet no one on site picked up on that. Scary.

@Pamela,

The performance numbers you quoted seem amazingly high to me. We couldn't pass title 24 if our windows averaged anything even close to 0.4 U-factor even with all the other improvements: new HVAC, new roof, new insulation, etc. Maybe you don't have a lot of windows. What is the glazing percentage on your report? Your report should be titled certificate of compliance - residential performance compliance method. The standards version should be compliance 2019.