Stone-coated steel roofing tile systems require a minimum 4/12 roof pitch (about 18.4 degrees) for Tefute Classical, Bond, Shingle, and Wood-Shake profiles per the FL31708-R6 installation manual [S5]. Exposed-fastener steel shingle systems such as TAMKO MetalWorks accept roof slopes from 3 inches per foot up to vertical application [S6].
Three installation families dominate the alloy steel roofing category: batten-mounted (raised fastener rows over counter-battens), direct-to-deck bend-up (panels fastened through the headlap and pressed up at the upslope edge), and direct cut-and-tuck (panels interlocked without a separate batten strip), as catalogued in the Westlake Royal Unified Steel resource library [S2]. All three are documented in vendor PDFs published 2023-2025 and remain the basis of 2026 code-approval submittals [S1][S3].
Pitch, Substrate, and Code Approval Constraints
Tefute stone-coated steel tiles are evaluated by ICC-ES for thermal/moisture protection, fire resistance, wind-uplift, and weather resistance, and qualify as a Class A roof assembly when installed to manufacturer spec [S5]. The minimum 4/12 pitch threshold is a hard limit; lower-slope applications fall outside the tested assembly and will not carry the manufacturer's limited warranty [S5]. Local building codes always override the manual, and code approvals carried in the Westlake Royal library include FL27408-R4, NOA 24-031801, NOA 25-031801, CAL Fire 21-003, CCMC 14112-R, CCMC 14113-R, and TDI RC-226 / RC-99 [S2].
Fire-retardant plywood is explicitly NOT an approved decking substrate for stone-coated steel tile [S5]. The deck must be cleaned, levelled, and squared, with all existing roofing stripped to the sheathing; fastener pops and damaged sheathing must be corrected before underlayment is laid [S5]. TAMKO MetalWorks similarly requires a code-compliant roof deck, and its application instructions limit use to roof slopes of at least 3 inches per foot (approximately 14 degrees) up to vertical [S6].
Underlayment and Battens
Underlayment for stone-coated steel systems must comply with local Building Code requirements and is typically a high-temperature, self-adhered membrane or 30/90 lb felt over the entire deck [S5]. The batten, where specified, is a horizontal counter-batten strip (commonly nominal 1x2 or 1x3 lumber) fastened to the deck and used to key the panel sidelap and headlap. The PINE-CREST Shake and BARREL-VAULT Tile profiles both ship with separate batten and direct-to-deck install guides in English and Spanish [S2].
Direct-to-deck bend-up and direct cut-and-tuck methods eliminate the batten and reduce total roof stack-up by roughly the batten thickness (typically 19 to 38 mm), which simplifies flashing transitions at eaves and valleys [S1][S2]. Trade-offs: direct-to-deck methods demand tighter deck flatness tolerances because the panel sits directly on the sheathing, and any waviness in the substrate will telegraph through the finished roof. The bend-up nose is then pressed and fastened so the next upslope course locks over it without a separate cap [S1].
Fastener Selection and Saltwater Environments
Westlake Royal publishes a dedicated Tech Bulletin on panel fasteners in saltwater environments, treating coastal exposure as a separate specification class from inland installs [S2]. Unified Steel also publishes a separate Steel Screws brochure and a Compatibility and Cutting tech bulletin covering blade types, snips, and saw choices that do not contaminate the AZ-150 or Galvalume coating [S2].
For exposed-fastener systems like TAMKO MetalWorks, fastener count, washer seating, and torque are controlled by the application instructions and must hit the embossed fastener targets on each shingle; under-driven or over-driven fasteners cause panel distortion and capillary leak paths [S6]. McElroy Metal's metal roof installation manual adds that when replacing stainless steel, the finish, alloy type, and temper must all be matched to the original, because mixing 300-series and 400-series stainless in the same runoff path drives galvanic corrosion [S4].
Re-Roofing Over Existing Shingles
Westlake Royal dedicates a Tech Bulletin to installing panels over existing roofs, covering tear-off vs overlay decision points, extra load on the truss system (stone-coated tile weighs 1.4 to 1.6 kg per panel depending on profile), and fastener pull-out in old sheathing [S2]. Tefute is stricter: it recommends removing existing roofing down to the deck before installation, and warns that failing to do so may void the manufacturer's warranty and may violate local building code [S5].
Tear-off is the conservative answer on residential work, and is mandatory when the existing roof is more than one layer, when sheathing condition cannot be verified, or when the total weight of the overlay would exceed the truss design load. If a re-roof is approved over a single existing layer, the deck still must be cleaned, levelled, and squared to the same standard as a new-deck install [S5].
Wet-Install, Solar, and Eave Details
Westlake Royal ships three narrowly-scoped bulletins that often get ignored: Installing Panels When Wet, Installing Solar Systems, and Optional Eave Riser Details [S2]. Each addresses a known field failure mode: wet-install deck moisture gets trapped under the panel and corrodes the coating from below; solar mounts concentrate point loads on the panel and need blocking or L-foot adapters that match the profile rib; eave risers stop wind-driven rain from being pushed back under the bottom course.
Compatibility and Cutting is the most-cited bulletin in the Westlake library because it tells the installer which saw blades, shears, and nibblers leave the AZ coating intact and which generate enough heat to damage it [S2]. The Cool Roof tech bulletin is paired with the Cool Roof Brochure and lists the Solar Reflectance Index (SRI) values that satisfy California Title 24, Part 6 reflective-roof requirements [S2].
Comparison: Three Install Methods on Five Decision Criteria
On a typical residential re-roof in 2026, the choice between batten, direct-to-deck bend-up, and direct cut-and-tuck breaks down over five criteria. (1) Minimum pitch: batten 3/12, direct-to-deck bend-up 3/12 to 4/12 depending on profile, direct cut-and-tuck 4/12 (matches the Tefute Class A tested assembly) [S2][S5]. (2) Total stack-up height at the eave: batten adds 19 to 38 mm; the two direct methods add zero. (3) Deck flatness tolerance: batten forgives up to 6 mm deviation over 1.2 m, direct methods require 3 mm or less. (4) Wind-uplift rating path: batten systems carry the higher FBC 1504.3.1 / 1504.3.2 numbers for HVHZ; direct-to-deck relies on the headlap fastening schedule only. (5) Installed labour: batten adds one day of carpentry per 30 m of eave, direct-to-deck trades that day for tighter layout discipline [S1][S2][S5].
For buyers comparing roll-formed alloy steel coil stock against alternative panel substrates, the same five criteria apply: pitch, stack-up, tolerance, wind rating, and labour. The wider the deck tolerance and the lower the pitch, the more a batten system earns its keep; on a clean new-deck build at 5/12 or steeper, direct-to-deck wins on speed and on the linear-guide of trim compatibility across the Unified Steel accessory suite [S2].
Failure Modes and When to Replace, Not Repair
Three failure modes force panel replacement rather than spot repair: coating breach larger than a 25 mm circle (weld-through, deep scratch, or stone-coat loss exposing the AZ-150 substrate), panel deformation beyond memory (the steel will not spring back when walked on), and fastener back-out in more than 10% of panels in a single course [S1][S5]. The Compatibility and Cutting bulletin and the Saltwater Environment fastener bulletin together define the inspection thresholds for warranty-claim adjudication [S2].
For decision tracking into the next code cycle, watch for revisions to FBC 1523.6.5.2.4 (HVHZ) and to the Florida product approval FL27408-R4 in the Westlake Royal approvals list [S2]. Specifiers sourcing titanium-alloy standing-seam alternatives for high-corrosion coastal sites should also compare the McElroy Metal installation manual's stainless matching rule against the Westlake fastener bulletin, since the two documents use slightly different alloy nomenclature for the same 300-series hardware [S2][S4].
For related coverage, see Handheld DMM Sizing and Selection: A Spec-First Guide.