I'm working on trying to find a solution for an above average height glass rail (or wall) that is going on top of a hi-rise building in Ft. Lauderdale, FL. The owners are wanting the glass panels to be 7'2" tall OA with 14" buried into a knee wall and secured with steel mounts and bolts. So 6' will be exposed. An engineer I spoke with said that at this height, due to the strict HVHZ codes and wind load pressures, that we will need to have gaps in between the panels to decrease the pressure. He recommended 6" gaps if the panels are 6' W and 4' gaps if 4'W. While this makes sense to me the owners are adamant that all the glass is butted together with no gaps as there is a Penthouse patio below. Do you recommend I just tell them this is how is needs to be to pass code or do you know of an alternative solution that may work? I've attached their rendering and I added in the light gray lines to help them at least visualize how it may look with the gaps.
JLC-1
May 20, 21 12:16 pm
tell them they're going to save 8% in glass with the gap, that should do the trick. I don't see it as a code issue, but structural integrity of glass panels, they're basically rigid flaps and can/will break in a type 4 hurricane. (we've had to go to laminate glass for simple 3' railings) bonus question, who's going to clean this glass wall from the outside?
James Petty
May 20, 21 1:33 pm
You need the gaps between glazing to allow each panel to act independently in wind loads and help relieve some of the stress. This is very normal. See above from Top of the Rock. As JLC-1 mentioned, they'll save X% on glazing today, and a lot more on repair later when the butted glazing breaks.
t a z
May 20, 21 2:30 pm
I don't think the gap can exceed 4" per code to work as a guardrail
Also have a look at "The Edge." Just like "Top of the Rock" it has tall glass barriers as part of an outdoor observation deck. Gap from photos online looks pretty tiny.
Also a fully grouted continous base shoe detail will be more efficient for the glass than point supported if you have the depth.
t a z
May 20, 21 2:42 pm
Base shoe construction photos here for scale before the pavers are in:
Laminated glazing will get you the Hurricane rating. Wind load will drive the overall thickness requirements.
natematt
May 21, 21 1:27 pm
Hurricane or not, laminated would be typical for this application anywhere. I've done a couple of these elsewhere that required triple lamination only a few stories up. I'd presume that with a strong enough glazing assembly this would be doable, but then again maybe not? Are there ANY examples in that area?
It could be much more complicated than that though, does this require an NOA?
t a z
May 21, 21 2:06 pm
Yeah, you're probably right. While technically feasible, it may be too cost prohibitive in terms of compliance testing and materials.
I can't think of any particular FL examples.
natematt
May 21, 21 5:25 pm
The gaps are common for glass guardrails of this type seemingly everywhere, even if they are smaller gaps, I know of several in my area on skyscrapers, that have like 1" gaps. I've always thought this was more about cleanliness, since you don't have to worry about alignment as much...
I wonder if you can get around this by using a top-rail, i know that's often preferable per code, and may be preferable aesthetically vs large gaps
OP should really just get the code section from the engineer, what's the point of asking this question if it's actually a strict code requirement?
t a z
May 24, 21 5:46 pm
If you have a top rail you can engage multiple panels in resisting point and impact loads.
t a z
May 24, 21 5:55 pm
You're right as well, the minimum gap is more about visual consistency and installation tolerances. Big giant chucks of glass are hard to space perfectly. Serviceability (deflection) needs to be checked, but for a straight wall runs only the corners are potentially an issue depending on the detailing.
Wood Guy
May 20, 21 8:24 pm
Can you offset the panels so they are in alternating planes?
Koww
May 21, 21 2:53 pm
just add more layers of glass.. easy peasy
Finjohn
May 24, 21 3:43 pm
It turns out that they are fine with 4" gaps. We will add something like perforated rubber or plastic in the gaps which will allow air to get in but keep debris from going through the gaps. Thanks for all your great replies. I appreciate it.
archanonymous
May 24, 21 6:06 pm
Maybe consider perf metal - something more durable and able to be coordinated with adjacent finishes? (I hope you don't have too much plastic and rubber on the rooftop). Also be advised that even very open perforations result in something like 50% of wind load/ pressure as a solid thing. It isn't like the wind just flows right through because there's some holes.
I'm working on trying to find a solution for an above average height glass rail (or wall) that is going on top of a hi-rise building in Ft. Lauderdale, FL. The owners are wanting the glass panels to be 7'2" tall OA with 14" buried into a knee wall and secured with steel mounts and bolts. So 6' will be exposed. An engineer I spoke with said that at this height, due to the strict HVHZ codes and wind load pressures, that we will need to have gaps in between the panels to decrease the pressure. He recommended 6" gaps if the panels are 6' W and 4' gaps if 4'W. While this makes sense to me the owners are adamant that all the glass is butted together with no gaps as there is a Penthouse patio below. Do you recommend I just tell them this is how is needs to be to pass code or do you know of an alternative solution that may work? I've attached their rendering and I added in the light gray lines to help them at least visualize how it may look with the gaps.
tell them they're going to save 8% in glass with the gap, that should do the trick. I don't see it as a code issue, but structural integrity of glass panels, they're basically rigid flaps and can/will break in a type 4 hurricane. (we've had to go to laminate glass for simple 3' railings) bonus question, who's going to clean this glass wall from the outside?
You need the gaps between glazing to allow each panel to act independently in wind loads and help relieve some of the stress. This is very normal. See above from Top of the Rock. As JLC-1 mentioned, they'll save X% on glazing today, and a lot more on repair later when the butted glazing breaks.
I don't think the gap can exceed 4" per code to work as a guardrail
Also have a look at "The Edge." Just like "Top of the Rock" it has tall glass barriers as part of an outdoor observation deck. Gap from photos online looks pretty tiny.
Also a fully grouted continous base shoe detail will be more efficient for the glass than point supported if you have the depth.
Base shoe construction photos here for scale before the pavers are in:
https://ny.curbed.com/2019/3/1...
Laminated glazing will get you the Hurricane rating. Wind load will drive the overall thickness requirements.
Hurricane or not, laminated would be typical for this application anywhere. I've done a couple of these elsewhere that required triple lamination only a few stories up. I'd presume that with a strong enough glazing assembly this would be doable, but then again maybe not? Are there ANY examples in that area?
It could be much more complicated than that though, does this require an NOA?
Yeah, you're probably right. While technically feasible, it may be too cost prohibitive in terms of compliance testing and materials.
I can't think of any particular FL examples.
The gaps are common for glass guardrails of this type seemingly everywhere, even if they are smaller gaps, I know of several in my area on skyscrapers, that have like 1" gaps. I've always thought this was more about cleanliness, since you don't have to worry about alignment as much...
I wonder if you can get around this by using a top-rail, i know that's often preferable per code, and may be preferable aesthetically vs large gaps
OP should really just get the code section from the engineer, what's the point of asking this question if it's actually a strict code requirement?
If you have a top rail you can engage multiple panels in resisting point and impact loads.
You're right as well, the minimum gap is more about visual consistency and installation tolerances. Big giant chucks of glass are hard to space perfectly. Serviceability (deflection) needs to be checked, but for a straight wall runs only the corners are potentially an issue depending on the detailing.
Can you offset the panels so they are in alternating planes?
just add more layers of glass.. easy peasy
It turns out that they are fine with 4" gaps. We will add something like perforated rubber or plastic in the gaps which will allow air to get in but keep debris from going through the gaps. Thanks for all your great replies. I appreciate it.
Maybe consider perf metal - something more durable and able to be coordinated with adjacent finishes? (I hope you don't have too much plastic and rubber on the rooftop). Also be advised that even very open perforations result in something like 50% of wind load/ pressure as a solid thing. It isn't like the wind just flows right through because there's some holes.