Glass for skylights

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Author Message Jerome J. Lazar, RA, CCS, CSI, SCIP Senior Member Username: lazarcitec Post Number: 1022 Registered: 05-2003 Posted on Tuesday, December 17, 2013 - 03:15 pm:    This query pertains to a South Florida project with a large custom skylight. Typically we specify laminated glass to meet impact requirements of the building code, but the Design Architect is asking for Insulated Lam Glass as that is what he is used to in Northern climates. Are their any advantages of using Insulated laminated glass in Southern Skylights? Lynn Javoroski FCSI CCS LEEDŽ AP SCIP Affiliate Senior Member Username: lynn_javoroski Post Number: 1731 Registered: 07-2002 Posted on Tuesday, December 17, 2013 - 06:05 pm:    Is there an advantage to insulating anything in southern climates? (Rhetorical question). I might even want to go with a translucent insulating laminated glass! Ron Beard CCS Senior Member Username: rm_beard_ccs Post Number: 411 Registered: 10-2002 Posted on Tuesday, December 17, 2013 - 10:22 pm:    ....or tinted or reflective insulating glass units. Laminated insulating glass is standard practice in the Mid-Atlantic states. What is the standard glazing for curtain walls in South Florida? As a side topic, presently are all states enforcing fall-protection over skylights? "Fast is good, but accurate is better." .............Wyatt Earp J. Peter Jordan Senior Member Username: jpjordan Post Number: 656 Registered: 05-2004 Posted on Wednesday, December 18, 2013 - 07:29 am:    Are the AHY requiring laminated lites for both inner and outer lites? I would assume the would require the laminated lit on the inside lite. This means that the outside lite could have a low-e coating on the 2nd surface. This improves the solar heat gain coefficient as well as the U-value. I would assume that you couldn't get the SHGC you need without such construction. Guest (Unregistered Guest) Unregistered guest Posted on Tuesday, December 17, 2013 - 09:29 pm:    What am I missing here? Wouldn't one want to "automatically" insulate for interior cooling loads? Jerome J. Lazar, RA, CCS, CSI, SCIP Senior Member Username: lazarcitec Post Number: 1023 Registered: 05-2003 Posted on Wednesday, December 18, 2013 - 08:26 am:    In South Florida skylights must be impact resistant, therefore the laminated lite is the outer lite and because its an over head glass system, the lower lite is laminated as well. I am waiting to hear from the Mech Engineer whether Insul Glass was included in the energy calcs. If not than the client wants to know if there are any other advantages in using insulated glass in this application. J. Peter Jordan Senior Member Username: jpjordan Post Number: 657 Registered: 05-2004 Posted on Wednesday, December 18, 2013 - 10:04 am:    If both lites are laninated, you can use a pyrolitic low-e coating from Pilkiington on surface 4. You can improve the thermal performance slightly with a low e coating on surface 5 or 8. If you want to use a sputter coating, berufy that the one you want can be fabricated into a laminated lite. Dave Metzger Senior Member Username: davemetzger Post Number: 483 Registered: 07-2001 Posted on Wednesday, December 18, 2013 - 12:04 pm:    I'd be careful about using a sputter coating on surface 8; if a coating must be used on an exposed surface, it's better to use a pyrolytic coating. Sputter coatings are OK on surfaces 4 and 5 (with laminated lites for both inner and outer lites) or surfaces 2 and 3 (for a non-laminated outer lite). "Berufy"? Is that Texas dialect? J. Peter Jordan Senior Member Username: jpjordan Post Number: 658 Registered: 05-2004 Posted on Wednesday, December 18, 2013 - 01:04 pm:    Dave is the second to comment on "berufy" (an iPad thumb correction of "verify"); maybe I should add that to my Texas dictionary (yes, you need a separate dictionary in Texas where "awl" is the petroleum product you get out of the ground. Verify if the sputter coating you want can be used in a laminated fabrication. In this design, you may be stuck using the pyrolitic coating if you want one at all. For all you guys who work on stuff north of I-10, yes there are energy requirements that have a requirement for a U-value that would require a low-e coating. Usually, that is driven by the SHGC, and since almost any low-e coating will drop the U-value from about 0.47 to 0.25-0.29, you get improvement in that area as well. In our area, you can get the SHGC required by default (0.25) by using very dark gray glass (PPG's GrayliteŽ II High Performance Tint) without the low-e coating, but very few designers want their glass that dark. The U-value stays at 0.47/0.50. On every other product I can think of, you need a low-e coating. In Jerome's case, you could get a SHGC of 0.21 by using the Graylite in the assembly without using the low-e coating. Again, you won't see very much improvement in the U-value without the low-e coating (tint has nothing to do with U-value), but you may not need it. I would, however, be very surprised if the designer would go for the dark glass (visible light transmission would be about 7 percent). ken hercenberg Senior Member Username: khercenberg Post Number: 656 Registered: 12-2006 Posted on Wednesday, December 18, 2013 - 01:14 pm:    My guess would be that the architect thinks you need laminated glass for both lites being in a hurricane zone. Outer lite laminated to withstand missile impact; inner lite to meet typical Code requirements. If Code only requires inner lite to be laminated in order to meet missile impact requirements, tempered should be fine at the outer lite. I have to presume that any of the large skylight companies down there can tell you what they usually do. It's been a few years but as I recall all the skylights I've done in Southern Florida were single pane laminated designed for missile impact. Seems to me that the outer lite was pretty darn thick, perhaps 9/16 inch with a 90 mil interlayer. Thinking more about this, wouldn't you have to use something listed by the County? Here's one by Super Sky: http://www.miamidade.gov/building/library/productcontrol/noa/12102306.pdf. I'm amazed that they would permit heat strengthened glass instead of fully tempered. I thought that was a building code requirement. Jerome J. Lazar, RA, CCS, CSI, SCIP Senior Member Username: lazarcitec Post Number: 1024 Registered: 05-2003 Posted on Wednesday, December 18, 2013 - 06:21 pm:    FINALLY HEARD FROM MECH, NO INSUL GLASS REQUIRED FOR ENERGY COMPLIANCE...KEN, THE TOTAL THICKNESS OF LAM GLASS IS TYP 9/16-INCH THK W/1/4-INCH THK INNER LITE AND 1/4-INCH THK OUTER LITE SANDWICHED BETWEEN 0.060-INCH PVB INTERLAYER PER NOA. ken hercenberg Senior Member Username: khercenberg Post Number: 659 Registered: 12-2006 Posted on Wednesday, December 18, 2013 - 08:16 pm:    I guess we went for overkill using the 90 mil, or maybe I'm just getting senile and we ran with NOA accepted 60 mil. Either way, glad you got the answer. Good luck with the architect. Chris Grimm, CSI, CCS, SCIPa, LEED AP BD+C, MAI, RLA Senior Member Username: tsugaguy Post Number: 310 Registered: 06-2005 Posted on Thursday, December 19, 2013 - 08:01 am:    Are we talking small missile impact (a metal ball if I recall correctly) or large missile (an 8 foot long 2x4" piece of lumber)? Check IBC to be sure but I think the former is for below 30 feet, an elevation at which above that there is less likelihood of tree branches blown at your glazed opening in a hurricane. It would seem a good idea to insulate for holding in the precious A/C $ but perhaps this makes the skylight framing too bulky and costly so someone has decided to use trade-off method in ASHRAE 90.1 rather than prescriptive method for U value? This is all just going out on a limb in case it helps make sense of what you are hearing from the engineer. Check what the actual local requirements are of course. Good to also talk to a reputable glazing fabricator and skylight manufacturer.