Sacrificial timber
The term ‘sacrificial timber’ refers to timber in a structural assembly that is intentionally oversized in order to enhance its fire resistance. Timber burns at a regular and measurable rate, so exposed timber sections can be designed with an additional 'sacrificial' element (ie increased width and/or depth) that will char slowly and protect the inner, structural timber from fire damage.
Sacrificial timber can be a design solution if a solid timber member is to be exposed – either fully or partly – or if full fire resistance cannot be provided by plasterboard (or other) fire insulating materials.
The outer surface of a timber element will typically char in a fire, with temperatures in excess of 350°C necessary for flaming to occur. The charred portion of the timber then acts as an insulator and, although some will be irreparably damaged (or ‘sacrificed’), the core timber retains its stability and structural integrity.
The density, and therefore the charring rate, of the timber element will determine the required quantity of sacrificial timber. BS EN 1995-1-2:2004 provides charring rates for different timber materials for the purposes of informing initial design.
Notional charring rates (the charring rates apply to each face exposed to fire):
MATERIAL | CHARRING RATE ßn (mm/min) |
Softwood timber | 0.8 |
Softwood glulam and laminated veneer lumber (LVL) | 0.7 |
Hardwood timber and hardwood glulam | 0.55 |
For example, if a softwood element is exposed on all four of its sides to 20 minutes of fire:
2 x 20 x 0.8 = 32 mm
The width and depth of the element would require 32 mm of sacrificial timber.
[edit] Find out more
[edit] Related articles on Designing Buildings Wiki
Featured articles and news
Not buildings. Happy holiday from DB.
Improving government projects with data and AI
Enabling better outcomes, efficient modern delivery and influential leadership on government projects.
BSRIA Living Laboratory Innovation Challenge
Final days for submission, closing March 29.
Windows, their frames, forms, factors and functions.
The hidden subtleties of U-Value calculations
Different contexts and what to include as variables.
A brief run down with related articles.
Electrical sector calls for safer public EV charge points
Serious concerns about electrical safety in the public domain.
Building Blocks manifesto presented to parliament
Architects Declare call in for support of five critical policies.
The four elements of project management with APM
Analysis, expectations, collaborative communication and partnerships.
City of London launches Heritage Building Retrofit Toolkit
Empowering owners to initiate necessary adaptations.
Guidance on RAAC in listed buildings
Published by Purcell, endorsed by IHBC, SPAB and C20.
Learning from the past.
Reluctance to hire people with criminal convictions revealed
Employing People with Criminal Convictions Report.
Tackling unconscious bias; Women's History Month
Personal reflections, as the last week of March approaches.