Fibre saturation point FSP
Fibre Saturation Point (FSP) relates to the moisture content (MC) of timber. Saturation Point (SP) may also be used with reference to other materials such as soil, but in both cases it refers to the point at which pores or cells are 'full' with water.
The FSP of timber will vary between species but it is normally accepted as averaging around 30%MC (moisture content), that being the percentage ratio of the wet wood to the theoretical weight of the dry wood. This level of MC is significant because it is considered to be the point of reasonable movement ie when wood that is significantly above this MC level dries its physical and mechanical properties change, which can lead to deformation.
Wood is hygroscopic so moisture levels can change in relation to the localised environment. As wood dries it shrinks, and as it absorbs moisture up it expands, the severity of which depends on the amount of moisture lost or gained. When wood is at the FSP of 30% further drying is less likely to cause significant deformation and it is therefore considered more stable or predictable in terms of being worked with.
The point at which timber stabilises in balance with the moisture of its own environment (which is normally below the FSP) is referred to as Equilibrium Moisture Content (EMC). This figure will vary depending on the species but more importantly with the moisture and temperature of the local environment, this hygroscopic characteristic of timber can be beneficial to internal environments when exposed internally. Fore more information see: Equilibrium Moisture Content.
[edit] Related articles on Designing Buildings
Featured articles and news
Investors in People: CIOB achieves gold
Reflecting a commitment to employees and members.
Scratching beneath the surface; a guide to selection.
ECA 2024 Apprentice of the Year Award
Entries open for submission until May 31.
UK gov apprenticeship funding from April 2024
Brief summary the policy paper updated in March.
For the World Autism Awareness Month of April.
70+ experts appointed to public sector fire safety framework
The Fire Safety (FS2) Framework from LHC Procurement.
Project and programme management codes of practice
CIOB publications for built environment professionals.
The ECA Industry Awards 2024 now open !
Recognising the best in the electrotechnical industry.
Sustainable development concepts decade by decade.
The regenerative structural engineer
A call for design that will repair the natural world.
Buildings that mimic the restorative aspects found in nature.
CIAT publishes Principal Designer Competency Framework
For those considering applying for registration as a PD.
BSRIA Building Reg's guidance: The second staircase
An overview focusing on aspects which most affect the building services industry.
Design codes and pattern books
Harmonious proportions and golden sections.
Introducing or next Guest Editor Arun Baybars
Practising architect and design panel review member.
Quick summary by size, shape, test, material, use or bonding..