Timber Building Materials: A Guide to 7 Documented Options

What "timber and wood" means in this guide

The grouping is ours, not a standard, a certification or a performance claim. It collects the seven profiles we have published under the Timber and wood family. They are not interchangeable products: CLT and glulam are engineered structural timber; thermally modified wood is ordinary timber modified by heat for stability and durability; acetylated wood and furfurylated wood are solid softwood modified chemically (with acetic anhydride and furfuryl alcohol), and for each the documents we found come from one maker (Accsys and Kebony); charred wood is timber whose surface has been burned, which research describes as a one-sided thermal modification; and reclaimed wood is timber used again.^{[2][3][4][8][9][10][1]} Other timber products have no profile yet, and this guide adds no facts of its own: every figure comes from the linked profiles, each of which lists its primary sources.

Wood fibre insulation, also made from wood, sits in our bio-based guide and has its own profile, wood fibre insulation; it is not compared here.^[7][6] Exposed CLT interiors are covered in a separate article, Mass Timber Interiors: What to Specify When Exposed CLT Is the Finish.^[5]

Timber and wood at a glance

The tables repeat what each profile states, with its units, standards and test conditions; each row links to the profile that lists the primary sources. Nothing is converted or averaged. The columns are not like-for-like, because the documents come from different manufacturers, programmes and years.

(a) Structure and engineered timber

The glulam profile calls glulam a structural material, not an insulant, and the CLT profile says a panel alone needs a separate insulation layer in an envelope.^[2][3] Values are manufacturer-declared and differ in density and moisture basis.

(b) Thermal modification and reuse

Table (b) mixes a manufactured product with a recovered one, so its columns do not line up: the thermally modified wood row rests on an association handbook and four EPDs (three of them supply its per-m³ carbon figures), the reclaimed wood row mainly on one US study and a UK interview study. On grading, the reclaimed wood profile says the general grading standards do not apply to reclaimed timber, while Norway has published a visual grading standard for reused spruce and pine (NS 3691-3:2025; catalogue entry read, standard not read).^[1]

(c) Chemical modification and charring

Table (c) shows three different cases. The acetylated and furfurylated wood rows each rest on one maker's documents (Accsys, Kebony), several of which are out of date or differ from one another, so the cells keep each document's date and standard; the charred wood row rests on three manufacturers' documents, two EPDs and peer-reviewed studies, and the profile calls the independent evidence thin.^[8][9][10] Durability classes (EN 350), reaction to fire (EN 13501-1 or ASTM E84) and EPD programmes are different declared units and standards, so they are shown separately and not compared.

How to choose between timber materials

This section sets out the conditions and trade-offs each profile states, then the constraints that cut across them. It ranks nothing and names no product to buy.

By application

Structure. The CLT profile lists Stora Enso's uses as internal and external walls, floors and roofs; at Brock Commons, 5-ply CLT floor panels sit on glulam columns on a 2.85 × 4.0 m grid and act as two-way slabs, which removes load-carrying beams.^[2] The glulam profile covers beams, columns and long spans, with maximum lengths of 27 m (42 m custom) for Hasslacher and under 55 m for Rubner, a note that transport and crane access usually decide the real limit, and curved and 3D-curved components from Rubner.^[3] In our reading, the profiles describe CLT as a panel for walls, floors and roofs and glulam as a linear member. Thermally modified wood is not structural, and its profile points to glulam or CLT for structure.^[4] Accsys's documents give DIBt-approved strength classes C22 and C16 for acetylated wood in stated section sizes under static or quasi-static loads, but nothing for large spans, and the profile found no sourced comparison with glulam or CLT; for furfurylated wood it found no structural grading.^[8][9] Reclaimed timber for structure is possible but uncommon: in the UK study only one participant gave an example, and the profile advises planning an audit before demolition, a grading route and a buyer early.^[1]

Cladding and exterior timber. The thermally modified wood profile lists exterior cladding first among its uses: the handbook recommends only Thermo-D for cladding and decking under prolonged wetting, a minimum thickness of 19 mm for outdoor wall and ceiling cladding, and a surface treatment for weather-exposed use, and it does not recommend the wood for contact with soil or water.^[4] The CLT documents limit use to service classes 1 and 2, and the CLT profile says to check the class definitions against site conditions; the glulam profile reports service classes 1 to 3 on one EPD and says detailing must keep the product dry on site.^[2][3] The reclaimed wood profile lists cladding among supplier products but has no durability or moisture measurements.^[1] Accsys states EN 350 durability class 1 for acetylated wood, with a warranty of 25 years in ground or fresh water that does not cover marine organisms, and says no finish is needed for longevity and stability; ICC-ES evaluates it for ground contact under US codes.^[8] Kebony's Clear datasheets state use class 3 (outdoor, above ground), and its documents say the board turns silver-grey outdoors and that oil, stain or paint reduces the greying; the SINTEF approval and the decking guide say not in contact with soil, and the profile found no document comparing furfurylated wood with other timbers under the same test.^[9] Charred timber suits appearance-led ventilated facades with access for touch-up, because the manufacturers describe periodic oiling and expect soot erosion or flaking; the profile found no use-class or durability statement for a charred product, so soil contact, immersion or a required durability class are not supported by its sources.^[10]

Interiors and exposed timber. For indoor cladding, ceilings, saunas and furniture the handbook's use-class table recommends Thermo-D or Thermo-S, and the handbook gives minimum thicknesses of 14 mm for indoor wall and ceiling cladding and 26 mm for floorboards.^[4] For exposed CLT, our article reports that KLH, Stora Enso and a Swedish industry guide each define their own surface-class limits, so a class name alone does not fix the appearance; KLH states that cracks and joints form as the panel dries and cannot be prevented, and names an ideal air humidity of 40 to 60 %.^[5] For visible glulam, surface quality is a specification choice (Hasslacher EPD).^[3] How much exposed timber a building may have depends on its fire design and national rules, which the article did not read.^[5] The acetylated wood documents cover cladding, decking and joinery, and the profile notes that uncoated boards bleach and then grey; the furfurylated wood profile lists cladding, decking and roof boards; the charred wood profile describes it as suiting dark, textured surfaces on facades and interiors where the client accepts that the surface changes.^[8][9][10]

Reuse. The reclaimed wood profile reports that the benefit depends on what would otherwise happen to the old wood: with standard GWP accounting reuse beat new wood in the base case, but could be worse if all the old timber were burned to displace coal or natural gas, and in the UK 65 % of waste wood (a 2023 figure cited by the authors) already goes to biomass. Old timber may carry lead-based paint or past preservative treatments, so the profile asks for the building's origin and treatment history.^[1]

Fixings and compatibility. The acetylated wood guide strongly recommends stainless steel or equally corrosion-resistant fixings because of the acetic acid left in the wood, advises against ordinary or galvanised steel and asks for a compatibility check of sealants and adhesives with their suppliers.^[8] The furfurylated wood profile gives stainless steel A4 or A2 only, with A4 near the coast, and notes that galvanised or ferrous metal stains the wood dark; Kebony's user guide says Kebony Character must not be processed further, while the SINTEF approval says processing weakens the protection, and we show both documents without deciding.^[9]

By constraint. Fire, moisture and durability class, certification, carbon and documents are set out in the next section.

What cuts across the seven profiles

Fire and charring

Reaction to fire (a Euroclass) and fire resistance are different questions. The CLT profile says the material is combustible, so the question for a designer is how a layered panel chars and whether the bonded layers stay together.^[2] Euroclass D-s2,d0 is declared in all three CLT documents and in the Hasslacher and Rubner glulam EPDs; the charring rates in table (a) are declared for two different products and adhesives, so we show both without comparing them.^[2][3] The glulam profile notes that national annexes can change the design values of EN 1995-1-2, and the CLT profile cites a 2021 review (abstract only) finding natural-fire charring rates and zero-strength layers higher than common guidance, with delamination able to cause secondary flashovers in small enclosures.^[3][2] According to the 2017 Brock Commons project factsheet, published by a provincial forest-products market agency and so a promotional source, the CLT and glulam were fully encapsulated in three to four layers of Type X gypsum board; we cite it as a description of that project's choice, not as evidence of fire performance.^[2][5] For thermally modified wood, the handbook says the wood has a smaller fire load and lower smoke production than standard timber, but that these factors may not be used directly in fire design, and it requires application-specific fire planning.^[4] For reclaimed wood, whether the EU default class can be used is a question for a fire engineer.^[1] For acetylated wood, Accsys's documents differ by date: Euroclass D in the 2020 guide (a property of the whole cladding system), Class E for 19 mm tongue-and-groove boards over a ventilated 40 mm cavity and Class D in some build-ups in the January 2026 guide, and Class D or E in the August 2025 datasheet; the profile read no classification report.^[8] Kebony's Clear cladding declarations of performance state D-s2, d0 with an open air gap behind, while the class B-s1, d0 claimed for retardant-treated profiles rests on a report the profile did not see.^[9] For charred wood no Euroclass was found, and the independent studies in table (c) show no systematic gain from charring, so the profile treats the char as a finish, not as a fire treatment.^[10]

Moisture

The CLT documents deliver panels at 12 ± 2 % moisture (Stora Enso, KLH) and limit use to service classes 1 and 2 of EN 1995-1-1; the glulam profile reports delivery at about 12 ± 2.5 % (Hasslacher) and use in service classes 1 to 3, except glued solid timber (classes 1 and 2). We show both as the documents state them: they are different products from different manufacturers.^[2][3] Water vapour resistance factors are given as ranges: KLH declares μ 300 (dry) to 46 (wet) for CLT and Mayr-Melnhof 20–50, a disagreement the CLT profile flags; Hasslacher gives μ = 50 (dry) to 20 (wet) for glulam and Rubner lists 20–50.^[2][3] Thermally modified wood has lowered equilibrium moisture content and reduced swelling, but at a cost in strength (table b), and reclaimed wood has no measured moisture data in its profile.^[4][1] Acetylated wood is documented at 3 to 5 % equilibrium moisture content with 0.7 % radial and 1.5 % tangential dry-to-wet change (Accsys data sheet); furfurylated wood at a maximum tangential swelling of 4 % against 8 % for untreated wood (Kebony Clear datasheets), or about 6 % for Character in the user guide, measured differently; for charred wood the figures are laboratory results on spruce and beech, with cupping toward the charred face described in the sources.^[8][9][10]

Certification and chain of custody

The registry checks in the CLT, glulam, thermally modified wood and reclaimed wood profiles were made on 7 and 8 October 2026, and those in the acetylated, furfurylated and charred wood profiles on 14 October 2026. The CLT profile found Stora Enso Wood Products' FSC licence C125195 valid, while Mayr-Melnhof's EPD states mainly PEFC-certified spruce, which it treats as a company claim.^[2] The glulam profile found Moelven's FSC listing but notes that the EPD names a different address from the valid entry, so it advises confirming that the valid entry covers the glulam you specify; PEFC claims were not checked.^[3] For thermally modified wood, HJT-Holz's EPD states that its wood comes from PEFC- or FSC-certified forests, a company statement.^[4] For reclaimed wood, an FSC Recycled claim rests on FSC-STD-40-007; the profile says it tells you the supplier followed that classification, not that the wood has a structural grade or is free of treatments, and none of reSAWN's 11 product entries is labelled FSC Recycled.^[1] For acetylated wood, the SCS listings of Accsys's two EPDs show validity to 2031, the Cradle to Cradle certificates expire on 1 and 7 November 2026, and FSC certificate CU-COC-807363 shows as valid.^[8] For furfurylated wood, the two EPDs are listed as valid to 2027, the Nordic Swan licence copies end 30 September 2026 and the SINTEF approval ended 1 October 2025, with Kebony's FSC and PEFC certificate copies not checked in the registries.^[9] For charred wood, the SuMPO and International EPD System entries were found, and PEFC and FSC statements on company pages were not checked against certificates.^[10]

Embodied and biogenic carbon

Where a profile reports a negative A1–A3 total, it attributes the figure to stored biogenic carbon, counted as a negative biogenic term under EN 15804+A2.^[2][3][4] The tables show the fossil and biogenic parts alongside wherever the profile states them, never netted, and the amounts the EPDs model returning at end of life: in Thermory's pine EPD, C3 adds +740 kg CO₂e per m³, almost all biogenic, under a scenario of 82 % recycling and 18 % energy recovery, and HJT-Holz models incineration, with C3 at +767.^[4] The figures are not a ranking: the glulam profile says the three EPDs differ in density, product mix, background database and rules for biogenic carbon (and that Moelven's own A1–A3 rows add up to about −691, not the stated −674, so it uses only stated totals), and the thermally modified wood profile says EPDs from different programmes may not be comparable.^[3][4] Reclaimed wood has no EPD, and its 2013 US study reports fossil CO₂ and energy, not an A1–A3 figure; the profile says the benefit depends on what would otherwise happen to the old wood.^[1] The acetylated wood EPDs declare positive totals (+259 to +524 kg CO₂e per m³, with fossil +1,060 to +1,280 and biogenic −816), which the Kingsport EPD's interpretation attributes to acetic anhydride production, steam and electricity, and Kebony's EPDs give −1,080 (Clear decking) and −715 (Character cladding) with fossil +401 and +328 alongside and C3 at +1,030 and +1,060; the Accoya totals do not equal the sum of their printed components, as the profile notes.^[8][9] For charred wood, Yakiwood's EPD gives −659 per m³ (fossil +117, biogenic −787) and Nakamoto Zourin's gives 3.4 kg CO₂e per m² of board for an intermediate product, so the two are not comparable; the profile quotes only Yakiwood's A1–A3 figures because that EPD's module D values appear inconsistent, and does not net the negative total because the same EPD assumes 90 % of the wood is incinerated at end of life.^[10] By our count, five of the seven profiles (CLT, glulam, thermally modified, furfurylated and charred wood) report an EPD with a negative production-stage total, and five (CLT, glulam, thermally modified, acetylated and furfurylated wood) report EPDs that model the biogenic carbon returning at end of life.^{[2][3][4][8][9][10]}

Emissions and documentation

Emission evidence is uneven: KLH and Mayr-Melnhof declare formaldehyde class E1 for CLT, Mayr-Melnhof's EPD summarises two chamber tests and Hasslacher reports a 28-day EN 16516 test of glulam (TVOC 271 µg/m³), while the thermally modified wood profile found no current emission label for a product and the reclaimed wood profile names lead-based paint as the documented hazard.^[2][3][4][1] The acetylated wood profile found a 2015 EPD statement of low emissions (M1) but did not see a test report or M1 certificate behind it and a vinegar smell on freshly cut boards (a manufacturer statement); Kebony's safety data sheet names wood dust as the main hazard and the profile found no emission test report; for charred wood no VOC or PAH emission data was found.^[8][9][10] Taken together, the bottom lines ask for different documents (our summary): the current declaration of performance, the ETA annexes and the fire test that matches your project (CLT); the current EPD, the declaration of performance for your strength class and the registry entry for any certificate cited (glulam); the modification temperature, the EN 350 class of the exact product, the current EPD and the fire test for your build-up (thermally modified wood); origin, treatment history and certificate numbers (reclaimed wood); the batch's durability documentation, the current EPD and certificates, the fire test for your build-up and the fixing specification (acetylated wood); the current EPD, the declaration of performance for your profile, the fire report for your build-up and the Nordic Swan licence status (furfurylated wood); and the char depth, the finish, the fire classification report for your build-up, the current EPD and the maintenance regime (charred wood).^{[2][3][4][1][8][9][10]}

The 7 profiles

• Cross-laminated timber: A solid-wood panel of at least three layers of boards glued at right angles, with declared Euroclass D-s2,d0, λ 0.12 W/(m·K) and use in service classes 1 and 2 only.^[2]
• Glulam: Structural timber made from kiln-dried softwood laminations glued with the grain parallel to EN 14080, in strength classes from GL20h up to GL36h.^[3]
• Thermally modified wood: Ordinary timber heated in a kiln with steam to at least 160 °C, with no added chemicals, for cladding, decking and interiors but not for load-bearing structures.^[4]
• Acetylated wood: Solid wood reacted with acetic anhydride; the documents are Accsys's, which state EN 350 durability class 1 and recommend stainless steel fixings, and whose fire classification differs between its 2020 and 2026 guides.^[8]
• Furfurylated wood: Softwood impregnated with furfuryl alcohol and cured inside the wood; Kebony's documents state Euroclass D-s2, d0 for Clear cladding, while several certificates and approvals have lapsed or differ between documents.^[9]
• Charred wood: Solid wood whose surface has been burned to a char layer; the profile found no Euroclass report for a product and reports independent studies showing no systematic gain in flammability or decay resistance.^[10]
• Reclaimed wood: Timber recovered from old buildings, piers or other structures and used again; its profile says current grading standards do not apply to it, notes a 2025 Norwegian standard series on evaluating reclaimed wood that it did not read, and takes its carbon figures from one 2013 US study.^[1]

Related: bio-based materials. Our bio-based guide covers twelve other profiles, including wood fibre insulation, and notes that mass timber is outside it.^[7]

Further reading. Our article Mass Timber Interiors: What to Specify When Exposed CLT Is the Finish sets out what manufacturers' documents and research bodies state about leaving CLT visible as a wall, ceiling or floor finish.^[5]

Frequently asked questions about timber building materials

About these data

Every figure on this page comes from the linked profiles, each of which lists the primary sources behind its numbers. This guide adds no measurements and no sources of its own, and counts across profiles are ours. Where the profiles state different bases or disagree (service classes, vapour resistance ranges, charring rates of two products, Accsys's fire documents of different dates, Kebony's two declarations of performance), the page shows both. Registry statuses and validity dates are as each profile reports them on its own checking date: confirm them on the registry before specifying.