Most standing seam content treats seam height as a look. It is a look, but it is also a coverage width, a panel count, a clip count and, in two Florida counties, the difference between a permittable roof and a rejected submittal. We stock all six combinations, so here is the decision with the real numbers behind it.
The short answer: spec 1.5 in. by default. It reads better from the street, it puts the seam further above the water plane, and every 1.5 in. profile we carry is HVHZ approved. Spec 1 in. when coverage width and panel count are doing the talking, which on a large simple plane in SL100 is a real saving, or when you want aluminum mechanical lock, where M100 gives up nothing in coverage.
What seam height actually changes
The seam is the raised vertical rib between pans. Its height sets three things.
- Appearance. A 1.5 in. seam casts a deeper shadow line and reads as a stronger horizontal rhythm from ground level. On a low, wide Florida house where the roof is a large part of what you actually see, that is a design decision, not a detail.
- Height above the water plane. The pan carries the water and the seam sits above it. More height is more margin, which is why taller seams are the conventional answer on lower slopes and in driven rain.
- Coverage width. The taller the seam, the more of the coil goes into standing the seam up rather than covering roof. This is where the money is, and almost nobody quantifies it.
Coverage width, and what it does to your panel count
Every figure below is the maximum coverage from the signed Florida Product Approval for that exact panel.
| Profile | Attachment | Seam height | Max coverage | Material | HVHZ |
|---|---|---|---|---|---|
| SL100 | SnapLock | 1 in. | 17 in. | 24 ga steel | Yes |
| SL150 | SnapLock | 1.5 in. | 16 in. | 24 ga steel | Yes |
| NS100 | NailStrip | 1 in. | 16 in. (24 ga), 15.75 in. (26 ga) | 24 or 26 ga steel | No. Outside HVHZ only |
| NS150 | NailStrip | 1.5 in. | 15.5 in. | 24 ga steel | Yes |
| M100 | Mechanical lock | 1 in. | 16 in. | 0.032 in. aluminum | Yes |
| M150 | Mechanical lock | 1.5 in. | 16 in. | 24 ga steel or 0.032 in. aluminum | Yes |
Two things jump out of that table.
First, the SnapLock pair carries a real coverage penalty for the taller seam. SL100 at 17 in. covers 6.25 percent more roof per panel than SL150 at 16 in. Take a plain gable with two planes, each 60 ft along the eave by 20 ft up the slope. At 17 in. that is 43 panels per plane, 86 for the roof. At 16 in. it is 45 per plane, 90 for the roof. At 15.5 in. on NS150 it is 47 per plane, 94 for the roof. Clips, seam footage and the time to set each panel all scale with that count, and 94 panels is roughly 160 more linear feet of seam than 86.
Second, the mechanical lock pair carries no coverage penalty at all. M100 and M150 are both 16 in. maximum. If you are already accepting the labor of field seaming, the 1.5 in. M150 costs you nothing in panel count over the 1 in. M100. That makes the M100 versus M150 decision purely about material, appearance and load rather than about coverage.
Load ratings do not simply rise with seam height
This is where the generic advice breaks down. A taller seam is not automatically a stronger assembly. An approval rates a specific panel with a specific clip at a specific spacing, and the numbers do not line up in a tidy row.
- SnapLock at 24 in. clip spacing: SL100 rates 67.3 psf, SL150 rates 86 psf. The 1.5 in. wins.
- SnapLock at 6 in. clip spacing: SL100 rates 131 psf, SL150 rates 116 psf. The 1 in. wins.
- NailStrip, top rated method: NS100 in 24 ga rates 153.5 psf, NS150 rates 116 psf. The 1 in. wins, and by a wide margin.
- Mechanical lock, top rated method: M100 rates 101 psf, M150 in 24 ga steel rates 131 psf. The 1.5 in. wins.
So the honest statement is that seam height and rated capacity are correlated at loose spacing and not correlated at tight spacing, and the only way to know is to read the method table on the approval for the exact panel and gauge you are quoting. Verify the current revision at floridabuilding.org before submittal.
One more point that gets misused constantly: these are allowable loads with a factor of safety of 2.0 already applied. They are not ultimate values and they are not the maximum design pressures published for exposed-fastener panels like 5V crimp. Comparing across those two kinds of number is meaningless, and a plans examiner will notice.
In the HVHZ, 1 inch narrows your options
The High Velocity Hurricane Zone is Miami-Dade and Broward counties only. Inside those two counties a panel must hold an approval that specifically covers the HVHZ, and there is no engineering workaround.
At 1.5 in., all three attachment methods are available to you: SL150, NS150 and M150 are all HVHZ and Miami-Dade approved. At 1 in., two of three are: SL100 and M100 hold it, and NS100 does not, in either 24 ga or 26 ga. That is the single most consequential fact on this page. If a Miami-Dade or Broward job wants a clip-free nailstrip install, it has to be NS150 at 1.5 in. We will not quote NS100 into those counties at any price.
Outside the HVHZ all six are permittable subject to the site wind calculation, and NS100 in 24 ga becomes genuinely attractive: the fastest install in the line and the highest allowable load we publish.
Cost: where the difference actually shows up
Per square foot of finished roof, the two seam heights are close on material. The gap opens up in three places.
- Panel count. Narrower coverage means more panels for the same roof. More panels means more clips or more flange fasteners, more linear feet of seam, and more time setting panels.
- Trim. Ridge, hip and eave details are cut to the seam profile. A 1.5 in. seam needs deeper closures and taller trim legs, and mismatched trim is one of the more common reasons an order sits at fabrication. Order trim with the panel from accessories, in the same gauge, finish and color run.
- Waste. Because panels are fabricated to exact length by our Florida fabrication partners and delivered crated, there is no end-lap allowance and no stock-length remainder to write off. The waste math is driven by the plane widths, not by how long the run is. That is the whole point of crated delivery.
Which to spec
Work it in this order.
- County first. Miami-Dade or Broward and you want nailstrip? It is NS150. Everything else is open.
- Exposure second. Within sight of salt water, aluminum with a PVDF finish, which points at M100 at 1 in. or the aluminum M150 at 1.5 in.
- Then the plane. Big, simple, unbroken planes reward the wider panel, so SL100 at 17 in. earns its keep. Cut-up roofs with a lot of hips, valleys and dormers do not, because the coverage advantage disappears into offcuts.
- Then the look. If the client is choosing on how the roof reads from the street, 1.5 in. is the answer and the panel count is the price of it. Say so plainly rather than absorbing it in the bid.
For the full picture on gauges, finishes, warranty terms and how to read an approval, start with our standing seam guide for Florida contractors, and if the attachment method is still open, the SnapLock, NailStrip and mechanical lock comparison works through that decision. When you have the county and the profile, run the job through Instant Metal Quote for a material list, or send plans to our sales desk and we will work the seam height with you against the actual planes.
