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
Renovating Union Chain Bridge.
AI tools for planning, design, construction and management
A long, continually expanding list, any more to add?
Robots in the construction industry
From cultural characterisations to construction sites.
Empowering construction with AI integration
New horizons with a human touch.
A Better Hiring Toolkit for construction
Tooling up to hire under best practice standards in the sector.
Recharging Electrical Skills in Wales
Step by step collaborative solutions.
Ireland budget announcement 2025
CIOB responds with positivity, criticism and clarity.
The continued ISG fall out, where to go?
Support for ISG contractors, companies and employees.
New HES national centre for traditional building retrofit
Announced as HES publishes survey results which reveal strong support for retrofit.
Retrofit of Buildings, a CIOB Technical Publication
Expected to become one of the largest activities in the global construction industry.
Scope determination appeals and the Building Safety Act
Process explained following release of appeals guidance.
The ECA industry focus video channel
Keeping update with the industry session by session.
Over 25 recorded informations sessions freely available.
AT Awards 2024 ceremony East London October 25th.
Revisiting the AT community at the 2023 awards evening.
The Community Housing Fund and built affordable homes
CLTN reviews the impact of the Fund and calls for extension.
The grading system of the Regulator for Social Housing
A background, an explanation and ten recent enforcements.
Construction, repair and maintenance. Book review.
Putting new life into a city with a 1900 year history.
BSRIA Briefing 2024: Sustainable Futures speakers
Redefining Retrofit for Net Zero Living 22 Nov.