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
One of the most impressive Victorian architects. Book review.
RTPI leader to become new CIOB Chief Executive Officer
Dr Victoria Hills MRTPI, FICE to take over after Caroline Gumble’s departure.
Social and affordable housing, a long term plan for delivery
The “Delivering a Decade of Renewal for Social and Affordable Housing” strategy sets out future path.
A change to adoptive architecture
Effects of global weather warming on architectural detailing, material choice and human interaction.
The proposed publicly owned and backed subsidiary of Homes England, to facilitate new homes.
How big is the problem and what can we do to mitigate the effects?
Overheating guidance and tools for building designers
A number of cool guides to help with the heat.
The UK's Modern Industrial Strategy: A 10 year plan
Previous consultation criticism, current key elements and general support with some persisting reservations.
Building Safety Regulator reforms
New roles, new staff and a new fast track service pave the way for a single construction regulator.
Architectural Technologist CPDs and Communications
CIAT CPD… and how you can do it!
Cooling centres and cool spaces
Managing extreme heat in cities by directing the public to places for heat stress relief and water sources.
Winter gardens: A brief history and warm variations
Extending the season with glass in different forms and terms.
Restoring Great Yarmouth's Winter Gardens
Transforming one of the least sustainable constructions imaginable.
Construction Skills Mission Board launch sector drive
Newly formed government and industry collaboration set strategy for recruiting an additional 100,000 construction workers a year.
New Architects Code comes into effect in September 2025
ARB Architects Code of Conduct and Practice available with ongoing consultation regarding guidance.
Welsh Skills Body (Medr) launches ambitious plan
The new skills body brings together funding and regulation of tertiary education and research for the devolved nation.
Paul Gandy FCIOB announced as next CIOB President
Former Tilbury Douglas CEO takes helm.