Metal roof deck fastener patterns determine whether your building's roof stays attached during a hurricane. In Broward County, where design wind speeds reach 170-180 MPH and uplift pressures exceed 120 psf in corner zones, the difference between a 36/7 and 36/9 screw pattern can mean the difference between a roof that holds and one that peels away.
Every screw in a metal roof deck serves as a mechanical tension link between the deck sheet and the structural support below. When hurricane winds create negative pressure on the roof surface, each fastener must resist its tributary share of that uplift force without pulling through the deck or pulling out of the support.
Wind uplift on a metal roof deck creates a suction force measured in pounds per square foot (psf). The total force on each deck panel equals the uplift pressure multiplied by the tributary area each fastener serves. A 36-inch wide deck panel on 5-foot joist spacing with a 36/7 pattern puts each screw responsible for approximately 2.6 square feet of deck area. At 60 psf field zone uplift, each screw must resist about 156 lbs — well within the 285+ lb allowable pullout capacity of a #12 screw in 22-gauge deck.
The calculation changes dramatically in corner zones. At 120 psf uplift, that same 156 square inches of tributary area demands 312 lbs per screw — exceeding single-fastener allowable values and requiring either denser patterns (36/9), thicker deck (20-gauge), or reduced support spacing. This is why Broward County engineers specify different fastener patterns for each roof zone, and why getting the zone boundary dimensions correct is as critical as selecting the right screw.
The notation system for metal deck fastener patterns uses two numbers separated by a slash. The first number (36) indicates the deck panel width in inches — standard 1.5-inch B-deck is manufactured in 36-inch wide sheets. The second number indicates the total fasteners per support per panel width. A 36/7 pattern places 7 screws across each 36-inch panel at every support location: one in each of the 6 valleys (flutes) plus one at the side-lap overlap. The 36/9 pattern adds two additional fasteners — typically at the high ribs or doubled at the side-laps — increasing the attachment density by 29%.
Less common patterns include 36/4 (every other flute, used only for low-wind field zones not applicable in Broward), 36/5 (alternating with side-lap), and 36/11 (maximum standard density before requiring double-row attachment). For Broward County HVHZ projects, you will most commonly encounter 36/7 as the minimum field zone pattern and 36/9 for perimeter and corner zones, with some corner zone designs requiring 36/11 or staggered double-row patterns.
Proper sequencing of deck installation, fastening, and inspection in Broward County follows a strict order. Each phase depends on the previous one passing inspection before proceeding.
The Broward County deck inspection (Phase 4) is the critical hold point. Inspectors walk the deck and verify fastener patterns at randomly selected joist lines, check screw engagement depth, confirm side-lap spacing, and compare installed patterns against the sealed engineering drawings. Covering deck with insulation before passing this inspection results in mandatory removal of insulation for re-inspection — a costly delay that adds 3-5 days and $8,000-$15,000 to a typical commercial project.
ASCE 7-22 divides every roof into three wind pressure zones. Each zone requires progressively denser fastener patterns as uplift pressures increase from center to edge to corner.
FM Global wind uplift classifications define the minimum fastener density and deck gauge combinations. Each rating level corresponds to a tested uplift capacity in psf, and Broward County projects must match or exceed the calculated design pressures in every zone.
| FM Rating | Uplift Capacity | Pattern (22-ga) | Pattern (20-ga) | Side-Lap Spacing | Broward Zone Use |
|---|---|---|---|---|---|
| FM 1-60 | 60 psf | 36/4 | 36/4 | 36 in. OC | Not permitted in HVHZ |
| FM 1-90 | 90 psf | 36/7 | 36/5 | 24 in. OC | Field zone (non-HVHZ) |
| FM 1-120 | 120 psf | 36/9 | 36/7 | 12 in. OC | Field (HVHZ), Perimeter |
| FM 1-150 | 150 psf | 36/11 | 36/9 | 12 in. OC | Perimeter (HVHZ), Corner |
| FM 1-180 | 180 psf | Double-row | 36/11 | Every support | Corner zones (HVHZ) |
Notice the efficiency gain from using heavier gauge deck: a 20-gauge panel can achieve FM 1-120 with only a 36/7 pattern (the same pattern that gives 22-gauge deck FM 1-90). This is because thicker steel provides higher pullout resistance per screw, meaning each fastener carries more load. On large Broward County commercial projects, the marginal cost of upgrading from 22-gauge to 20-gauge deck ($0.15-$0.25/SF) is often offset by reduced fastener labor in perimeter and corner zones — particularly on buildings with high perimeter-to-area ratios like strip malls or L-shaped structures.
Not all self-drilling screws perform equally in metal deck substrates. Pullout capacity varies significantly between manufacturers, screw diameter, thread pitch, and the gauge of steel being penetrated.
Allowable Stress Design (ASD) values represent the working capacity after applying a safety factor of 3.0 to ultimate test values. When an engineer calculates the required uplift resistance per screw in a given zone, they compare that demand against the ASD pullout value — not the ultimate value. If the demand per screw at a 36/7 pattern is 290 lbs in the perimeter zone but the #12 Tek screw only provides 282 lbs ASD in 22-gauge deck, the designer must either switch to a 36/9 pattern, upgrade to #14 screws, specify 20-gauge deck, or use Hilti fasteners with their higher tested values.
Broward County structural plan reviewers verify these calculations by cross-referencing the specified screw manufacturer's ICC-ES evaluation report (ESR) against the calculated demand. Using a generic "self-drilling screw" specification without a specific ESR number is grounds for plan rejection.
Steel deck gauge is the single most influential variable in fastener pullout capacity. Thicker material grips screw threads more effectively, and the difference is not linear — upgrading from 24-gauge to 20-gauge nearly doubles per-screw pullout values.
Side-lap fasteners serve two critical functions: they prevent differential movement between adjacent deck sheets under uplift, and they transfer horizontal diaphragm shear forces across sheet joints. Both functions demand specific spacing based on the FM rating and wind zone.
Side-lap screws must engage both deck sheets with a minimum of three full threads exposed below the bottom sheet. Under-driven screws that strip the threads or over-driven screws that dimple the deck beyond 1/16 inch are rejected during Broward inspections. The most common field error is using #10 screws where #12 are specified — the visual difference is subtle but the shear capacity difference is roughly 20%. Inspectors often carry thread gauges to verify screw diameter at random side-lap locations.
The structural member supporting the deck determines the maximum achievable pullout capacity per fastener, regardless of screw size or deck gauge.
On Broward County metal building projects with cold-formed purlin framing, the purlin-to-rafter connection is often the weak link in the uplift load path — not the deck fastener itself. Engineers must verify that the purlin clip angle or direct bolted connection can transfer the cumulative tributary uplift from all deck fasteners between purlin supports. A common error is designing the deck fastener pattern to resist 120 psf uplift while the purlin clip is only rated for 800 lbs — insufficient when a single purlin at 5-foot joist spacing supports 30 linear feet of deck edge at the building perimeter.
Broward County's High Velocity Hurricane Zone extends along the coast where design wind speeds reach 170-180 MPH under ASCE 7-22. Metal deck fastener patterns in these areas exceed standard FM Global minimums.
Where non-HVHZ areas can use FM 1-90 in the field zone, Broward HVHZ requires FM 1-120 minimum. This bumps the field pattern from 36/7 to 36/9 on 22-gauge deck, adding approximately 2 screws per support per 36-inch panel — roughly 0.4 additional screws per square foot.
Corner zones in HVHZ frequently require FM 1-150 or FM 1-180 ratings. At these levels, standard screw patterns cannot achieve adequate capacity in 22-gauge deck. Solutions include upgrading to 20-gauge deck, reducing joist spacing to 3.5-4 feet, or specifying double-row fastening with staggered screws at 6-inch intervals along supports.
HVHZ projects receive approximately three times the inspection scrutiny compared to non-HVHZ areas. Deck fastening requires a dedicated inspection before insulation, and Broward HVHZ inspectors verify screw counts on a minimum of 20% of all joist lines — randomly selected at time of inspection, not pre-announced.
Every screw used in HVHZ metal deck attachment must have a current ICC-ES evaluation report (ESR) documenting tested pullout values in the specified deck gauge. Generic "self-drilling screw" specifications are rejected during plan review. The ESR number must appear on the sealed engineering drawings and match the product delivered to the jobsite.
The most expensive error in metal deck fastening is using the field zone pattern across the entire roof and then discovering during inspection that perimeter and corner zones are under-fastened. Retrofitting a 36/9 pattern over an existing 36/7 requires drilling new holes in the deck — holes that weaken the deck section and may require a structural re-analysis. The cost-effective approach is marking zone boundaries on the deck with spray paint before any screwing begins, then working from corners inward with the densest patterns first.
Screws placed too close to the edge of a deck flute or too near a sheet end can pull through under load, even if the pullout capacity into the support is adequate. AISI S100 requires a minimum edge distance of 1.5 times the screw diameter (approximately 5/16 inch for a #12 screw) and an end distance of 3 times the diameter. On 1.5-inch B-deck with narrow flutes, centering the screw in the valley becomes critical — a 1/4-inch offset can reduce pullthrough capacity by 30%.
Deck fastener pullout values published in ICC-ES reports assume the screw penetrates a support member of specified minimum thickness. If the engineer specifies #12 screws based on pullout values in 1/4-inch steel (open-web joist chord) but the actual support is a 16-gauge purlin, the pullout capacity drops by 35-45%. On Broward County projects where the structural frame is pre-engineered by one firm and the roof deck is detailed by another, this disconnect between assumed and actual support gauge is a frequent source of inspection failures.
Technical answers to the most common questions about metal roof deck screw patterns, pullout values, and Broward County requirements.
The 36/7 pattern means a 36-inch wide metal deck panel secured with 7 fasteners per support — one in each valley (flute) of the deck profile. For standard 1.5-inch B-deck with 6 flutes, this puts a screw in every flute plus one at the overlap. This is the most common field zone pattern in Broward County for wind uplift ratings up to FM 1-90. The 36/7 pattern provides approximately 2.33 fasteners per linear foot of support.
The 36/9 pattern adds 2 additional screws per support compared to 36/7, placing fasteners in every flute plus additional screws at the high ribs or side laps. This increases the pullout capacity per support by roughly 29% and is required in perimeter and corner zones where uplift pressures in Broward County can exceed 90 psf. The 36/9 pattern is standard for achieving FM 1-120 ratings on 22-gauge deck.
In 22-gauge (0.0295 in.) steel deck, #12 Hilti S-MD screws achieve approximately 850-950 lbs pullout in laboratory conditions, with allowable design values around 285-320 lbs after safety factors. Standard #12 Tek screws from manufacturers like Buildex achieve roughly 780-880 lbs ultimate pullout, with allowable values around 260-295 lbs. Actual field values depend on installation torque, hole condition, and whether the screw penetrates a joist flange or web.
Yes, deck gauge significantly impacts fastener capacity and required patterns. Thinner deck (24-gauge at 0.0239 in.) has lower pullout resistance per screw — roughly 30% less than 20-gauge (0.0358 in.) — requiring more fasteners or tighter spacing to achieve the same uplift rating. In Broward's HVHZ areas, 22-gauge is the practical minimum for most commercial roofs, and 20-gauge deck may be specified for corner zones where 36/9 patterns alone cannot meet the required uplift resistance.
Side-lap fasteners connect adjacent deck sheets at their overlapping edges between supports. FM Global requires side-lap screws at a maximum of 36 inches on center for FM 1-60, 24 inches for FM 1-90, and 12 inches for FM 1-120 and above. In Broward County corner zones, side-lap fasteners may be required at every 12 inches — effectively at each support location. Side-lap screws are typically #10 or #12 self-drilling TEK screws and must engage both sheets with a minimum of 3 exposed threads beyond the bottom sheet.
Deck-to-joist connections fasten metal deck to wide-flange steel beams or open-web joists, where the screw penetrates the top chord or beam flange (typically 1/4 inch or thicker steel). This provides high pullout values — often 1,200+ lbs ultimate per fastener. Deck-to-purlin connections attach to cold-formed Z or C purlins (typically 14 to 18 gauge), yielding lower pullout values of 600-900 lbs per screw. Purlin connections often require denser fastener patterns to compensate for the thinner substrate, and Broward inspectors verify the support member gauge during deck installation inspections.
Yes. Broward County's High Velocity Hurricane Zone encompasses coastal areas where design wind speeds reach 170-180 MPH. While FM Global 1-90 may satisfy field zone requirements in non-HVHZ areas, Broward HVHZ typically demands FM 1-120 minimum in field zones and FM 1-150 or 1-180 in corners. This often means 36/9 patterns in the field (where 36/7 would normally suffice) and double-row fastening or reduced support spacing in perimeter/corner zones. All fastener patterns must be shown on sealed engineering drawings reviewed by the Broward County Building Division.
Roof zones follow ASCE 7-22 Component and Cladding zones. Zone 1 (field) covers the interior roof area; Zone 2 (perimeter) extends inward from the roof edge a distance equal to 10% of the least horizontal dimension or 40% of the roof height (whichever is smaller, but not less than 4% of the least dimension or 3 feet); Zone 3 (corner) occupies the square formed where two Zone 2 perimeter strips intersect at roof corners. In Broward, wind uplift pressures can be 2.0 to 2.8 times higher in corner zones versus field zones, which is why fastener patterns escalate dramatically from field to corner.
Get zone-specific uplift pressures, fastener pattern designations, and pullout capacity verification for your Broward County metal deck roof project. ASCE 7-22 compliant calculations in minutes.
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