Structural Plywood: Bonding, Fire and EPD Data for Designers

Structural plywood is the layered, cross-bonded wood panel used for floor and roof decking, wall sheathing and as a stiffening element in construction.^[1][10] Several makers publish both a declaration of performance and a verified EPD for it.

This profile sets out what four EPDs, three declarations of performance (DoP) and the standards catalogue pages we could read say about it, and where they stop. All figures come from manufacturers' documents unless a source says otherwise.

What is structural plywood and how is it made?

Veneers, cross-lamination and glue

Metsä Wood's EPD describes its spruce plywood as 3 mm rotary-peeled softwood veneers, cross-bonded with weather- and boil-resistant phenol-formaldehyde adhesive, in thicknesses of 9 to 30 mm.^[1] WISA's DoP covers structural birch plywood with crosswise veneers, 6.5 to 50 mm thick, from 5 plies at 6.5 mm to 37 plies at 50 mm.^[6] Latvijas Finieris describes overlaid birch plywood glued with weather- and boil-proof phenol-formaldehyde or lignin-phenol-formaldehyde resin to EN 314 class 3 (exterior), and says bonding with melamine-urea-formaldehyde resin to EN 314 class 1 is also possible.^[3] San Giorgio's raw birch plywood is glued with phenol resin.^[4]

The EPDs print the adhesive content in different ways, so the shares below are ours, calculated from each EPD's own content table, and are not comparable line for line. Metsä Wood: phenol-formaldehyde adhesive 5 % of the product, 23 kg per m³.^[1] WISA: adhesive resin 48.4 kg plus hardeners and fillers 9.4 kg in 680 kg, which is 7.1 % and 8.5 % (48.4 ÷ 680 and 57.8 ÷ 680).^[2] Latvijas Finieris: resins 45.8 kg plus hardener 17.2 kg in 715 kg, which is 6.4 % and 8.8 % (45.8 ÷ 715 and 63.0 ÷ 715).^[3] San Giorgio: adhesive 88.26 kg in 720 kg, which is 12.3 % (88.26 ÷ 720).^[4] Layup differs too: at 9 mm the Metsä DoP lists 3 plies, while the WISA and Finieris DoPs list 7.^[5][6][7]

WISA's documents name an adhesive resin and phenolic coatings but not the resin chemistry.^[2][6] None of the documents we read names polyurethane adhesive for structural plywood.

Which standards apply?

All three DoPs cite EN 13986:2004+A1:2015, the standard for wood-based panels in construction, with AVCP system 2+.^[5][6][7] The Estonian catalogue page gives its scope as unfaced, overlaid, veneered or coated panels for structural and non-structural use in dry, humid and external conditions, and for floor, roof and wall decking, and lists plywood among the covered panel types together with LVL, OSB, particleboard and fibreboard. It is listed under Regulation (EU) 305/2011, valid from 6 October 2015.^[10]

EN 636:2012+A1:2015 sets the plywood requirements for general-purpose and structural use in dry, humid or exterior conditions and gives a classification based on bending properties. Its catalogue page states that its clause 4 values are product properties and not design characteristic values; those come from EN 12369-2 or from the manufacturer's own testing to EN 789 and related methods.^[11] EN 12369-2:2011 gives characteristic values for plywood complying with EN 636, for panels with five or more layers and 6 mm or more overall thickness, a ratio of cumulative veneer thickness in alternate directions of no more than 2.5, and wood species with a mean density above 350 and up to 750 kg/m³. The catalogue marks that 2011 edition as withdrawn from 1 October 2025 and lists EN 12369-2:2025 as valid from that date; we did not read the 2025 edition's scope.^[13] EN 314-2 specifies bonding classes of veneer plywood by end use.^[12] The standard texts are paid and we did not read them.

The three DoPs describe the EN 636 classes in slightly different words. Metsä Wood's EN 636-2 S covers internal structural use in dry conditions and internal or protected external use in humid conditions.^[5] WISA lists EN 636-1 for internal dry use, EN 636-2 for protected external use in humid conditions, and EN 636-3 for external use with coating and edge sealing.^[6] Latvijas Finieris lists EN 636-1 S for internal dry use, EN 636-2 S for internal use in humid conditions and EN 636-3 S for protected external use in limited wetting conditions above ground.^[7] We show both without deciding between them; the DoP supplied with the panels governs.

How does structural plywood perform?

Strength, stiffness and density

The table lists values as printed in each DoP, for two thicknesses. Parallel (∥) and perpendicular (⊥) refer to the grain direction of the face veneer. The spruce and birch panels have very different layups and densities, and the DoPs state their basis in different ways, so the table shows what each document declares, not which panel is stronger for your application.

One calculation shows why the grain direction matters. For the Metsä spruce panel at 9 mm, the perpendicular bending strength is 3.0 N/mm² against 22.9 parallel, so the panel is about 7.6 times weaker across the face grain (22.9 ÷ 3.0); at 18 mm the ratio is 1.7 (21.5 ÷ 12.3). The two birch DoPs show smaller ratios at 9 mm (1.7 for WISA, 46.4 ÷ 27.4; 1.4 for Finieris, 52.1 ÷ 36.7). The Metsä DoP also declares point-load capacities and impact classes for floor and roof panels (its Annexes 1 and 2); the WISA DoP lists point-load strength and impact resistance as NPD (no performance declared).^[5][6]

Reaction to fire

The three DoPs print the same structure of classes under EN 13501-1. For a panel of at least 9 mm mounted without an air gap the class is D-s2,d0 (Dfl-s1 for floorings); the Metsä and WISA DoPs specify that this applies directly on a class A1 or A2-s1,d0 product of minimum density 10 kg/m³ or on at least class D-s2,d2 products (of density 400 kg/m³ or more in the Metsä DoP), while the Finieris table states only "without an air gap". With a closed or open air gap of no more than 22 mm behind the panel the class is D-s2,d2 at 9 mm; with a closed air gap, D-s2,d1 from 15 mm; with an open air gap, D-s2,d0 from 18 mm. For any other use the class is E, from a minimum thickness of 3 mm in the Metsä and Finieris DoPs and 4 mm in the WISA DoP.^[5][6][7] Latvijas Finieris also declares Cfl-s1 and Bfl-s1 classes for named overlaid floor products on stated substrates, citing classification reports.^[7] Metsä Wood's EPD lists a FireResist variant with a fire retardant, but we did not open a class for it.^[1]

Moisture, bonding and durability

Metsä Wood's DoP declares bonding class 3 (exterior) and biological durability use class 2 for its uncoated panel, and its EPD states service classes 1 and 2 under EN 1995-1-1, with a 100-year service life that can be used in calculation if the panel is installed according to instructions.^[1][5] The WISA DoP declares bonding class 3, use class 2 for uncoated panels and use class 3 for coated and edge-sealed panels; its EPD says plywood is mainly used in dry or moderately humid conditions and gives a minimum 100-year service life if installed properly and moisture exposure is low or moderate.^[2][6] Latvijas Finieris declares bonding class 3 and use class 2 for uncoated or overlaid panels, and use class 3 for overlaid panels with protected edges.^[7] Metsä Wood's EPD gives a moisture content of 7 to 9 % as delivered from the mill; the Finieris EPD gives 9 ± 3 % during storage at 20 °C and 65 % relative humidity, and its DoP footnotes the same 9 ± 3 % to its EN 636 strength classes.^[1][3][7] The service lives are manufacturers' statements; none of the documents gives an independent field measurement.

Formaldehyde and emissions

Each DoP declares formaldehyde release class E1.^[5][6][7] The WISA and Finieris DoPs add compliance with Commission Regulation (EU) 2023/1464.^[6][7] Metsä Wood's EPD states that its spruce plywood, tested to EN 717-1 (a chamber method, per its catalogue page), emits approximately 0.018 ppm, against the E1 requirement of 0.100 ppm that the EPD states.^[1][14] WISA's EPD says its plywood has an M1 emission classification from the Building Information Foundation RTS, depending on the product.^[2] The Finieris EPD lists CARB Phase 2 and TSCA Title VI among its certifications, and San Giorgio's EPD states compliance with CARB Phase 2 and TSCA Title VI and prints "ULEF" in its technical table.^[3][4] We did not open any emission test report, certificate or label registry, and none of the documents we read cites EN 16516.

What do the four EPDs show?

All four EPDs were opened as registry pages and PDFs on EPD International and use EN 15804+A2 with the wood c-PCR (EN 16485). They differ in product, density, system boundary and data year, so the results are separate rows and are not comparable; each EPD itself sets conditions for comparison, including identical functions and declared units and equivalent system boundaries.^[1][2][3][4]

Three reading notes. First, the negative A1–A3 totals come from counting the tree's biogenic carbon uptake as a negative term in the production stage. Each EPD models that carbon leaving the product system in module C3 at end of life, which is why the C3 column is large and positive; we show both and do not net them, and Metsä Wood's EPD states that once the material is disposed of, biogenic carbon is released back to the atmosphere.^[1][2][3][4] Metsä Wood adds that carbon stays stored as long as the plywood is in use and that reuse and recycling prolong storage; its EPD also gives a recycling scenario, in which C3 is +751 and module D is −732 kg CO₂e per m³.^[1] San Giorgio's EPD gives alternative scenarios in which A1–A3 is unchanged (−724) and C3 is +546 with 100 % recycling or +1,600 with 100 % incineration.^[4] Second, the fossil term is the part that does not depend on that accounting: +202 (Metsä), +360 (WISA), +370 (Finieris) and +382 (San Giorgio) kg CO₂e per m³ at A1–A3, but because the densities differ from 460 to 720 kg/m³ and the products include different films and coatings, these figures are not like-for-like. As a check on one EPD, Metsä's three terms add up as +202 − 724 + 3.24 = −518.8, matching its stated −519.^[1]

Third, we found inconsistencies inside the documents. The Finieris EPD prints biogenic carbon in raw plywood as 323 kg C (−1,185 kg CO₂e) on one page and 311 kg C (−1,139) on another, with 3.1E+02 in its table, and a table note says biogenic characterisation factors were set to zero although the table carries a −1.1E+03 value.^[3] The San Giorgio EPD states a 65 % recycling and 35 % incineration end-of-life scenario on one page and a scenario "with 46 % of wood recycling" on another, and the water-deprivation row of its 100 % incineration table repeats the GWP values.^[4] The registry pages list PCR 2019:14 version 1.3.4 for the WISA and Finieris EPDs, while the PDFs print 1.2.5 and 1.3.3.^[2][3] The WISA EPD gives the DoP code on the CE marking as WISA007CPR, while the DoP we read is numbered UPM007CPR.^[2][6] We quote the values as printed and flag them rather than correct them. The WISA PDF is a revision dated eleven days before we read it; its version history describes that third version only as an update of the EPD owner.^[2]

Which forest certificates do the documents state?

Metsä Wood's EPD states that its Suolahti mill and its wood supplier Metsä Forest hold PEFC and FSC chain-of-custody certificates, and prints licence codes (FSC-C014476 and FSC-C209093; PEFC/02-31-03 and PEFC/02-31-381). It also states that the PEFC logo means all wood is legally harvested and at least 70 % comes from certified forests.^[1] The WISA EPD ticks "FSC and PEFC CoC" without a certificate number.^[2] The Finieris EPD lists PEFC/12-44-007 among its certifications and does not list FSC.^[3] San Giorgio's EPD says its wood is sourced under FSC and PEFC chain of custody, and its website gives FSC-C100309 and ICILA-PEFC-COC-004711 and states that products are available as certified only on customer request.^[4][9] We did not check any of these in the FSC or PEFC databases, so we cannot say which products carry which claim. Ask for the certificate and the claim on the invoice for the lot you buy.

What happens at end of life?

The EPDs model burning or recycling, not reuse. Metsä Wood treats the product as secondary fuel in its main scenario and gives a recycling scenario separately; WISA assumes 100 % energy recovery; Finieris follows the energy-recovery scenario in EN 16485; San Giorgio assumes chipping for recycling plus incineration.^[1][2][3][4] The adhesive stays in the panel (about 5 to 12 % by our calculation above), and Metsä's EPD describes preservative and fire-retardant variants, which affect what recycling or burning is appropriate. We found no document in this research that reports reuse of structural plywood from buildings.

Does the Metsä spruce product still exist, and what could we not open?

Metsä Wood's spruce plywood page, read on 19 October 2026, states that spruce plywood products have been officially phased out and are no longer in production; the page is undated, and the site navigation labels the product discontinued. The Suolahti mill page on the same site still lists a spruce plywood capacity of 160,000 m³ a year, and the EPD registry still shows the EPD as valid to 2029.^[8][1] We treat the spruce EPD and DoP as documents about a product that the manufacturer says is no longer made, and we did not find structural spruce plywood documents from another maker.

We could not open Metsä Wood's spruce plywood product datasheet (the link returned a sign-in page), any Metsä Wood birch plywood DoP or EPD, a WISA datasheet, or a San Giorgio DoP or CE declaration; the San Giorgio EPD and website do not state CE marking or structural strength values, so we do not describe its panels as structural plywood. We did not open FSC, PEFC, M1, CARB or TSCA certificates, test reports or registries, or the full texts of the standards.

How does it compare with OSB, CLT and LVL?

The EN 13986 catalogue page lists plywood, OSB and LVL as panel types within one standard, and Metsä Wood's EPD names Kerto LVL, birch plywood and spruce plywood as its main products.^[10][1] None of the documents we read compares plywood with OSB, CLT or LVL on strength, carbon, durability or cost, so we make no comparison. For the structural timber elements we have profiled, see cross-laminated timber and glulam.

When to specify it, and when not

It suits

• Decking, sheathing and bracing where design values are needed. The Metsä, WISA and Finieris DoPs give strength and stiffness values by thickness; Metsä's DoP states its values are for structural calculations with EN 1995 (Eurocode 5), and the WISA and Finieris DoPs refer to EN 1995-1-1 for kmod and kdef.^[5][6][7]
• Dry interiors and protected humid conditions. All three DoPs declare bonding class 3 and cover EN 636-2 use; the fire table allows D-s2,d0 for 9 mm and thicker panels on suitable substrates.^[5][6][7]
• Where self-weight matters. Metsä Wood's EPD describes its spruce panels as light. The spruce DoP declares a density of 460 kg/m³ against 680 (WISA) and 715 (Finieris average) for the birch panels, so on a per-m³ basis the birch panels are about 1.5 times heavier (680 ÷ 460 = 1.48; 715 ÷ 460 = 1.55). Metsä Wood says it no longer produces the spruce panel.^{[1][5][6][7][8]}
• Exposed or coated use when the specification names the right product. WISA and Finieris describe EN 636-3 use for coated or overlaid panels with protected edges, and San Giorgio's EPD describes its film-faced panels as for external use, with flooring and formwork among the applications; we read no DoP for San Giorgio, so its panels have no declared structural class here.^[4][6][7]

It may not suit

• Where the panel is permanently wet or exposed with raw edges. The Metsä DoP stops at EN 636-2 and use class 2; the birch DoPs reach use class 3 only for coated and edge-sealed panels. We found no document that supports unprotected ground contact or immersion.^[5][6][7]
• Where a spruce structural panel is wanted from the one maker we read. Metsä Wood's own site says it has stopped producing it.^[8]
• Where an assembly needs more than Euroclass D. The panels are combustible; classes above D appear in the DoPs only for specific floor products on stated substrates, and assembly fire resistance is a design question the documents do not answer.^[5][7]
• Where very low emissions are specified in the brief. The documents declare E1 and name other labels, but we did not read the reports or the labels' limits; ask for the specific certificate for the grade and thickness.^[5][6][7]
• Where carbon is judged by the A1–A3 total alone. The EPDs' negative totals depend on biogenic carbon accounting and are returned in C3 under each EPD's own scenario; the fossil term, the data year and the product (film-faced or not) differ.^[1][2][3][4]

Against named alternatives

The research supports only a limited comparison. The panels in the DoPs have a declared thermal conductivity of 0.12 W/(m·K) (spruce) and 0.17 (birch); none of the documents discusses thermal bridging. The CLT and glulam profiles on this site give their own declared values; we did not find a source that compares them with plywood on a like-for-like basis. Climate-specific guidance is not given in the documents we read, apart from the manufacturers' statements on humid and moderately humid conditions above.

Suppliers whose documents we read

Frequently asked questions about structural plywood

The bottom line on structural plywood

Structural plywood is well documented where makers publish a DoP and an EPD: design values by thickness, bonding class 3, Euroclass D and E1 formaldehyde are all on paper. What the paperwork does not settle is the chemistry of some adhesives, the certificates behind forest claims, durability in service and the like-for-like carbon comparison between products. Ask each supplier for the current DoP for your thickness and use class, the EPD with its boundary and data year, and the registry entry for any certificate it cites.

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