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Julie Root
Senior Member
Username: julie_root

Post Number: 31
Registered: 02-2004
Posted on Tuesday, December 06, 2005 - 12:51 pm:   Edit PostDelete PostPrint Post

I am working on a public school in LA. Due to the newest energy codes in CA we have to specify a low-e dual glazed in order to meet the District's requirement of exceeding T24(the energy code) by 20%.

The District is having a tough time getting their arms around this issue mainly because the District's Maintence and Operations has a problem with dual glazing because it takes longer to get replacement glass when a window is broken.

I understand both sides. I have two questions.

Does anyone have experience with conviencing a Owner's M&O side that dual glazing is harder to break than single glazing?

Does anyone know of resources regarding intrustion strageties that are aesthetically appealing (i.e. not security bars or wire)? We have tighly spaced mullions (10" o.c.) at the ground floor.

We are also looking into laminated glass for the exterior lite and we are doing a life cycle cost to show how much addition energy they will be paying for with single glazing.

Any other thoughts on the subject are welcome.
Curt Norton, CSI, CCS
Senior Member
Username: curtn

Post Number: 100
Registered: 06-2002
Posted on Tuesday, December 06, 2005 - 12:58 pm:   Edit PostDelete PostPrint Post

Do the window sizes vary or are there typical sizes?

How about providing extra stock of a few sets of glazing that would be available in case of breakage. More could be ordered as the supply gets low.
John Bunzick, CCS, CCCA
Senior Member
Username: bunzick

Post Number: 440
Registered: 03-2002
Posted on Tuesday, December 06, 2005 - 01:29 pm:   Edit PostDelete PostPrint Post

You discussed dual-glazed windows. In the case of true dual-glazed products (as opposed to insulated glass units), each lite is installed in the window separately. If one lite breaks, you are only replacing that one lite.

However, in LA with low-e glass, I'm thinking what you are proposing is insulated glass units. IG units are no less likely to break than monolithic glass unless you use a stronger lite of glass as part of the IG. Laminated glass is actually quite a bit weaker than ordinary annealed glass at the same thickness, although if it breaks it will stay in the frame. Tempered glass is about twice as strong as annealed for a given thickness.

Tempering glass and fabricating IG units have longer lead times than just cutting annealed, but there are probably local fabricators who can respond reasonably quickly to a single replacement. Some types of vacuum deposition low-e coatings, however, may not be available from local fabricators due to the necessary equipment investment. Shipping these products damages the coating. Some newer low-e coatings, however, have been developed that can be shipped. PPG among others makes such a coating. Curt's idea of having some extra stock of IG units, or even sash if they're operable, in the event of damage is a good one.

Alternatively, a pyrolitic-low-e coating could be investigated to determine whether it can give you the needed SHGC for your locale. These can be readily shipped. Another option for low SHGC is the solar selective tints that are available from many manufacturers. They are typically very pale blue or green and can be laminated and tempered like untinted, but probably would not need to be coated to get the necessary SHCG.

As to preventing intrusion, with 10 inch-spaced mullions, it seems like you've got part of your work done already. If you were to use an impact-resistant outboard lite (tested for large missle impact in hurricane zones), it would be extremely difficult to break the glass and remove it from the frame to get inside. The glass may crack, but they would be unlikely to get inside. For this small an opening, even tempered, especially a bit thicker than typical, would pretty difficult to break. However, it is the highly localized stress from a sharp-pointed impact that breaks it most easily (i.e. a rock). I think stopping intrusion will be easier and cheaper than preventing breakage.

There are a wide range of cost implications for each of these options. I suggest you talk to a competent glass fabricator to get a handle on them.
J. Peter Jordan
Senior Member
Username: jpjordan

Post Number: 157
Registered: 05-2004
Posted on Tuesday, December 06, 2005 - 01:57 pm:   Edit PostDelete PostPrint Post

In an urban area such as Los Angeles where there are probably a number of fabricators, I don't think there will be much of a turn-around problem with getting replacements. It is a little more complicated since someone will have to come out and measure the window and then get the measurements to the fabricator (wireless e-mail). The lite is fabricated and then brought to the jobsite for installation. Monolithic glass can be measured, cut on the jobsite, and then installed.

I would think it would be prudent to consider a standing contract with 1 or more fabricators which specifies 24-hour turnaround (less maybe?). This will probably apply to laminated glass as well.

M&O units sometimes have difficulty understanding that code compliance may not be an option. They may have to come up with new procedures for dealing with this issue.
Anne Whitacre, CCS CSI
Senior Member
Username: awhitacre

Post Number: 271
Registered: 07-2002
Posted on Tuesday, December 06, 2005 - 04:09 pm:   Edit PostDelete PostPrint Post

one thing you can do is make sure you are using fully annealed glass for all lites that aren't tempered. there are also clear vandal resisting films that can be applied to the lites.

I also agree with Peter -- have the owner buy a few double-glazed units for their maintenance stock, and then because of your location and the number of local fabricators this should not be an issue. the smaller units are also easier to replace than larger ones.
Curt Norton, CSI, CCS
Senior Member
Username: curtn

Post Number: 101
Registered: 06-2002
Posted on Tuesday, December 06, 2005 - 04:27 pm:   Edit PostDelete PostPrint Post

Depending on what high performance glass you chose, the outboard lite may require heat strengthening. Special coatings, tempering and heat strenghtening can all make getting replacement units time consuming.

Ordering multiple units at a time would also be more cost effective. (to replace the extra stock as it is depleated)

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