The Three Things a Cladding Spec Must Lock
A wood cladding specification has to define the assembly, the material, and the review process in one coordinated package, because a gap in any one shows up on the finished wall. Architects who spec only the species, and leave the assembly and submittal process implied, are the ones who find problems after the first bundles open on site.
The WoodWorks technical resources for commercial and multifamily construction land on the same idea: exterior wood is a system. The species sets the durability ceiling, but the assembly and the install decide whether the wall reaches it. For the assembly side, our guide on rainscreen systems for commercial cladding covers the cavity and drainage detailing any species leans on.
Define the Material in Real Terms
A material definition that says "premium grade" tells the supplier nothing. The spec has to state species, grade, grain orientation, moisture content, and profile geometry outright. Each of these drives how the wall looks and how it behaves.
- Species and category: state whether the project wants a modified wood (Accoya, Thermory, or Abodo Vulcan), a tropical hardwood (Ipe, Cumaru, Sapele, Teak), or a domestic species (Western Red Cedar, Cypress, White Oak). Modified products are also the only category that carries a real manufacturer warranty, so if a warranty is required, the spec has to point at a modified product.
- Grade: use real grading language. For cedar, separate clear vertical grain (CVG) from select tight knot (STK), since they read completely differently on a facade. For hardwoods, reference the relevant NHLA grade or an architectural grade defined by sample.
- Grain orientation: vertical grain or quartersawn stock moves less than flat grain and holds a finish longer. Call it out where stability matters.
- Moisture content: state a target MC and an acclimation requirement. Installing wood outside its equilibrium range is a leading cause of post-install movement. See our moisture content guide.
- Profile geometry: define face width, reveal, and tongue or rabbet dimensions, and hold a milling tolerance across the order.
Lock the Profile and Fastener Method Together
The profile and the fastener method are one decision, because shiplap and tongue-and-groove do not take the same fastening. Spec one without the other and it turns into a fight during shop drawings.
| Profile | Fastener method | Notes |
|---|---|---|
| Tongue-and-groove | Hidden, blind-nailed or clipped through the tongue | Keeps the face clean; required for concealed fastening |
| Shiplap | Face fastened with visible stainless fasteners | Cannot be hidden-fastened on an exterior wall |
| Clip-system profile | Proprietary metal clip in a milled kerf | Requires a profile milled for that specific clip, not standard T&G |
Every fastener on exterior wood should be stainless steel or hot-dipped galvanized to keep corrosion staining off the face, and all cladding goes over furring strips regardless of profile so the wall can drain and dry. When a grooved profile is used, the groove faces down to shed water. Our furring and ventilation guide details the cavity requirements.
Require a Mockup and Define the Submittal
A physical mockup approved before material release is the single most effective safeguard on a large wood facade. Samples, finish schedule, fastener type, and rainscreen detailing all get reviewed and signed off before the bulk order ships, not after the first bundle is open.
The submittal package should require species and grade samples, the actual profile milled to the specified tolerance, the finish system on the actual species, and the fastener and clip components. Reviewing those against the design intent catches substitutions early. A lower-cost species or a look-alike profile changes shrinkage, finish behavior, and fastener holding, so substitutions get judged against the approved mockup, not waved through on a spreadsheet.
Single Source, Fire Assembly, and Certification
Specifying the whole cladding package from one supplier keeps grade, color, and milling consistent across all elevations, which is hard to recover once the facade is split between vendors. On a multifamily building running thousands of board feet across several elevations, lot-to-lot grade variation and color drift between sources jump right out.
The spec also has to line up with the fire requirement. Many multifamily facades require Class A flame spread per ASTM E84, established at the assembly level and confirmed with the authority having jurisdiction. Our guide on commercial exterior wood cladding and fire code covers the compliance paths. Where institutional or public funding applies, the spec should also require FSC or PEFC chain of custody; see our FSC certification guide. Because J. Gibson McIlvain mills cladding profiles in-house, it can produce submittal samples and mockup material to the exact specified grade, profile, and tolerance, then ship the released order nationwide from the same source.
"The specifications that go smoothly are the ones that define grade in real language, set a moisture target, lock the profile to the fastener method, and require a mockup before we ship a single bundle. When all of that is written into one section, the species almost takes care of itself. The jobs that struggle are the ones where the drawings say premium wood siding and assume everyone fills in the rest the same way."
Brett Miller, President, J. Gibson McIlvain Company
How J. Gibson McIlvain Would Build the Specification
Helping write a multifamily cladding specification, for J. Gibson McIlvain, means turning design intent into a buildable lumber order. The team starts from the code envelope and the assembly, then defines the material in real grading terms, then coordinates the profile with the fastener and clip system. Because the company mills profiles in-house and ships nationwide, West Coast included, a single specification can cover an entire project with consistent grade, color, and milling tolerance across every elevation.
The team's strongest push is to approve physical samples, a profile mockup, and finish samples before release. That one step heads off most of the substitution and consistency problems that surface on large facades. It also hands the architect and owner a shared reference for the finished wall, which protects everyone when questions come up during construction.
Specification and Procurement Checklist
| Spec item | Why it matters |
|---|---|
| Species and category | Sets durability and whether a warranty is possible (modified products only). |
| Grade in real terms | CVG vs STK for cedar, NHLA or architectural grade for hardwoods, not "premium." |
| Moisture content and acclimation | Prevents post-install movement; specify target MC and acclimation time. |
| Profile geometry and tolerance | Holds reveal and fit consistent across the order. |
| Profile and fastener pairing | T&G for hidden fasteners; shiplap for visible; clips need clip-specific profiles. |
| Mockup before release | Catches substitutions and sets a shared visual reference. |
| Single source | Keeps grade and color consistent across elevations. |
| Fire assembly and certification | Class A where required; FSC or PEFC on public and institutional work. |
Where Specifications Usually Fail
- Grade by adjective: "premium" or "high quality" is not a grade. Use CVG/STK or NHLA/architectural grade defined by sample.
- No moisture-content requirement: wood installed outside its equilibrium range moves after install regardless of species.
- Profile without fastener method: shiplap cannot be hidden-fastened; only T&G can. Resolve it in the spec, not in shop drawings.
- No mockup: without an approved mockup, substitutions and color drift show up too late.
- Split supply: multiple sources produce visible grade and color variation on a continuous facade.
Ordering Information to Resolve Before Pricing
- Code envelope: construction type, fire-separation distance, required flame-spread class.
- Material: species, grade, grain orientation, moisture-content target.
- Profile: face width, reveal, T&G or shiplap, clip compatibility, milling tolerance.
- Process: mockup scope, submittal requirements, finish samples.
- Logistics: single-source confirmation, total square footage, delivery sequence, lead time.
Related J. Gibson McIlvain Guidance and Next Steps
Frequently Asked Questions
What should a multifamily wood cladding specification include?
It should define three things in one coordinated package: the wall assembly (rainscreen cavity and fire-rated detailing), the material (species, grade in real terms, grain orientation, moisture-content target, and profile geometry), and the review process (mockup approval and submittal requirements). It should also lock the profile to the fastener method, require stainless fasteners, and tie the package to a single source so grade and color hold across elevations. Naming the species alone is not enough.
How should grade be specified for wood cladding?
Use real grading language rather than adjectives like "premium." For cedar, separate clear vertical grain (CVG) from select tight knot (STK), since they look entirely different on a facade. For hardwoods, reference the applicable NHLA grade or an architectural grade defined by an approved sample. Grade specified by sample and by recognized grading rules removes ambiguity and gives the supplier an enforceable target.
Why require a mockup before releasing the cladding order?
A physical mockup approved before release is the most effective safeguard on a large wood facade. It lets the architect and owner confirm species, grade, profile, finish, and fastener detailing against the design intent before thousands of board feet ship. It also creates a shared visual reference that catches substitutions early, since a lower-cost species or look-alike profile can change shrinkage, finish behavior, and fastener holding.
Does the profile choice affect how cladding is fastened?
Yes. Tongue-and-groove profiles allow hidden fastening, blind-nailed or clipped through the tongue, which keeps the face clean. Shiplap on an exterior wall has to be face fastened with visible stainless fasteners and cannot be hidden-fastened. Clip systems require a profile milled specifically for that clip rather than a standard T&G. Because of this, the profile and the fastener method are one decision that should be resolved in the specification.
Can a lumber supplier provide mockup and submittal samples for a multifamily spec?
Yes. A supplier that mills in-house can provide species and grade samples, the actual profile milled to the specified tolerance, and the finish system on the real species for mockup and submittal review. J. Gibson McIlvain mills profiles in-house, holds FSC chain-of-custody certification, and ships nationwide, so the approved mockup and the released order come from one consistent source.
Sources and Standards Referenced
- WoodWorks - Commercial and multifamily wood construction resources
- National Hardwood Lumber Association - Hardwood grading rules
- ASTM - E84 surface burning characteristics
- Forest Stewardship Council - Chain of custody certification
- PEFC - Programme for the Endorsement of Forest Certification
- American Wood Council - Wood construction standards
