Wood adhesives/formaldehyde emissions and heavy timber construction

what types of adhesives are used in wood products and what are their characteristics

UF (urea-formaldehyde)

• used in interior panels

• not moisture resistant

• higher formaldehyde emissions

PF (phenol-formaldehyde)

• used in exterior grade plywood and OSB

• very moisture resistant

• low emissions

Isocyanate/Polyurethane adhesives

• used in OSB, LVL, and other engineered products

• no added formaldehyde

• strong, durable bonds

why is formaldehyde a concern in wood products?

it is a VOC (volatile organic compound) that can off-gas into indoor air

• UF-bonded products release more, especially when warm or humid

• emissions can cause irritation/health concerns

• regulations now limit emissions

what startegies are used to reduce formaldehyde emissions from wood products?

• using PF instead of UF

• Using NAF adhesives

• using ultra-low-emitting formaldehyde (ULEF) resins

• sealing exposed panel edges

• using products certified for low emissions

why are adhesives essential in engineered wood products?

they allow small wood pieces to be combined into large, strong, stable components

improve dimensional stabilitly

allow efficient use of wood fiber (less waste)

enable products like plywood, OSB, LVL, glulam

what defines heavy timber construction and what are its key characteristics

• large solid wood members (min sizes set by code)

• slow, predicatble charring (that protects structural core)

• limited conceled spaces (to reduce fire spread)

• noncumbustible exterior walls

• wood decking (used for floors/roofs)

why does heavy timber construction perform well in fire?

mainly bc of its predictability:

• large wood members char on the outside

  • this slows down heat penetration

  • the structural core remains strong for a long time

• heavy timber does not collapse suddenly like unprotected steel

what are the minimum size requirements for heavy timber members?

• columns must be large enough to resist fire/structural loads

• beams and girders must meet minimum thicknesses

• floor decking must be thick enough to char without failing

• roof decking has slightly reduced minimums bc roof loads are lights

Pros and Cons of heavy timber construction

pros:

• excellent fire resistance

• aesthetic appeal

• sustainability

• good sturctural performance

• fast erection

cons:

• requires large, high-quality lumber

• more expensive than light-frame wood

• connections must be carefully detailed for fire

• limited concealed spaces make MEP routing harder

• building height and area limits

what is mass timber and how does it differ from traditional heavy timber

mass timber

• engineered wood panels and members like

  • CLT (cross-laminated timber)

  • glulam

  • nail-laminated timber (NLT)

  • dowel-laminated timber (DLT)

differences:

• heavy timber = solid wood members

• mass timber = engineered, layered, or laminated components

  • allows for:

    • taller building

    • larger spans

    • more predicatble performance

    • better use of smaller lumber pieces

what is CLT and what are its advantages

CLT = cross-laminated timber

• made of layers of boards stacked crosswise and glued

• provides 2-way structural action

• very dimensionally stable

• excellent fire performance

• can replace concrete slabs in many buildings

• enables tall wood buildings

how are heavy timber and mass timber connected?

steel plates

bolts

dowel-type fasteners

concealed connectors for fire protection

traditional joinery

fire resistance strategies for mass timber

• char layer protects core

• oversizing members to allow sacrificial char

• encapsulation with gypsum board

• limited exposed areas