Composite board materials compared

Key issues

Composite timber products have many advantages over ordinary timbers:

• They can utilise smaller dimensions of timber as the raw material, but can be manufactured to create large dimension composite beams and sheets, etc.

• Less timber overall is required to make products which are lighter and stronger than timber. Lower quantities and smaller sizes of timber means less pressure on native forest timber

Concerns:

• Binding resins are the prime concern. Most boards use toxic resins though alternatives are beginning to appear.

• Much of the timber content originates from non-sustainable sources. FSC products are still difficult to obtain.

Types of composite boards:

1 Fibreboards

Fibreboard, sheet material made from glued and pressed softwood dust or chips or in the case of strawboard, well, straw. Fibreboard is commonly used throughout the building construction industry. Fibreboard is strong and has a stable, smooth and scratch-resistant surface. Because fibreboard is usually made from waste produced during wood processing, it is an efficient use of forest resources. Fibreboards usually rely on their inherent resins to bond though conventional medium density fibreboard (MDF) contains urea-formaldehyde or phenol-formaldehyde, which off-gasses into interior air. Some non-formaldehyde MDFs are available but some like diisoynate resins can cause asthma during manufacture.

Softboard / medium board / hard board
	High natural content
	Can use recycled / waste wood (but check!)
	Non-toxic (no resin binders)
	Some boards use materials from renewable resources (eg flax)
	May use wood from non FSC sources

Strawboard
	Recycled and recyclable agricultural waste
	Very low embodied energy at factory gates
	Renewable resource
	100% natural content (straw produces its own binding resin)
	When used as a partitioning component it reduces the amount of timber needed
-	One Canadian product uses MDI resin as a binder (non formaldehyde)
	Imported to the UK primarily from Europe - increasing embodied energy
	Susceptable to fungal decay but can be treated with boron compound before installation
	Heavy, needs special skills. Need to be stored dry to prevent swelling

Medium Density Fibreboard (MDF)
	Can use recycled / waste wood (but check!)
	High natural content
	Most MDFs use toxic resin risking formaldehyde off-gassing
	Dust produced in sawing MDF is a lung irritant.
	Most use wood from non FSC sources

2 Particleboards

Particleboard is made from chips of timber bonded with urea formaldehyde resins bonded to form boards (sheets) by applying mechanical pressure and heat. They have a low strength and stiffness, good fire resistance and air tightness. OSB is bonded largely using the more stable phenol formaldehyde.

Chipboard
	Some chipboard uses recycled wood (but check!)
	Reuseable but difficult to remove without damage
	High embodied energy
	Likely to use wood from non FSC sources
	Toxic resin risks formaldehyde off-gassing
	Large quantities of VOCs released as part of the manufacturing process

Oriented Strand Board (OSB)
	Some chipboard uses recycled wood (but check!)
	Reuseable
	High embodied energy
	Likely to use wood from non FSC sources
	Large quantities of VOCs released as part of the manufacturing process

3 Ply-based boards

• Conventional plywood is made of thin veneers of wood that are bonded together with formaldehyde resins. Its strength is derived from gluing an odd number of sheets of veneer with the grain of adjacent sheets at right angles to each other.
• The majority of hardwood plywood are composed of a core layer faced with higher quality woods using urea-formaldehyde (UF) glue.
• Softwood plywood is used for exterior and structural applications (walls, floors, roofs), and its adhesive consists of phenol formaldehyde (PF) resin. PF, a more expensive, water-resistant glue, offgasses at a relatively slower rate than UF glues.
• Blockboard is constructed from softwood timber core strips of up to 30mm wide, which are glued between outer veneers whose grain runs in the opposite direction.
• Laminboard is constructed in a similar fashion as blockboard but the core strips are not more than 7mm wide. It is a finer quality timber board with a better finish than blockboard.

Plywood
	FSC sources available
	strength
	high natural content
	diisoynate resins when used in plywood are non off-gassing (but harmful in manufacture)
	High embodied energy
	Likely to use wood from non FSC sources
	Toxic resin risks formaldehyde off-gassing

Blockboard / Laminboard
	High embodied energy
	Likely to use wood from non FSC sources
	Toxic resin risks formaldehyde off-gassing

4 Cement-bound boards

Wood wool mixed with Portland Cement in ratios varying from 30-70 to 50-50. Can use a chemical accelerator for setting.

Wood – cement particleboard / woodwool cement slabs
	Can use recycled / waste wood (but check!)
	Relatively high thermal mass
	High embodied energy (the cement content)
	Classed as hazardous waste
	Probably uses wood from non FSC sources

We would specify:

First choice:• Fibreboards (mediumboard is a good substitute for plywood for structural sheafing – though it lacks high moisture resistance) • Bitumen impregnated fibreboard
Second choice: • Particleboards – bonded with non-formaldehyde resins
If you have to use ply: • Check that the wood is FSC sourced and the bonding uses non-formaldehyde resins
'Greenwash' alert: • Look out for FSC sourced outer veneers sandwiching cores from non-sustainable sources - laminate flooring is a good example.

Composite board products:

• L681 Insulation
• FSC Board suppliers - a list of suppliers of ply, mdf, chipboard, OSB etc.

Further information:

TRADA: www.trada.co.uk/