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IS 401:2001 is the Indian Standard (BIS) for preservation of timber. This code covers the recommended practices for the preservation of timber. It classifies timber based on natural durability and treatability, providing guidelines for selecting appropriate preservative types, treatment methods, and retention levels to protect wood from decay, fungi, marine borers, and insect attacks.
Specifies methods and good practices for the preservative treatment of timber to protect it against decay, insects, and marine borers.
! Timber must be properly seasoned (barked and dried) prior to preservative treatment to allow adequate penetration, except for specific diffusion processes.
! Heartwood is generally highly resistant to preservative penetration; therefore, treatments primarily aim to thoroughly protect the outer sapwood.
! Refractory timbers (species that are hard to treat) may require incising (making shallow cuts) before pressure treatment to ensure sufficient preservative absorption.
BS 8417:2011+A1:2014BSI (British Standards Institution), United Kingdom
HighCurrent
Preservation of wood. Code of practice
Provides a comprehensive code of practice for wood preservation based on a formal 'Use Class' system.
AWPA U1-22AWPA (American Wood Protection Association), USA
HighCurrent
Use Category System: User Specification for Treated Wood
Defines treatment requirements based on a 'Use Category System' that links end-use exposure to preservative retention and penetration.
AS/NZS 1604.1:2021Standards Australia / Standards New Zealand
HighCurrent
Specification for preservative treatment - Part 1: Sawn and round timber
Specifies requirements for preservative-treated timber using a 'Hazard Class' (H1-H6) system for different service conditions.
EN 335:2013CEN (European Committee for Standardization), Europe
MediumCurrent
Durability of wood and wood-based products - Use classes: definitions, application to solid wood and wood-based products
Defines the 'Use Class' system for exposure conditions, which underpins all other European timber preservation standards.
Key Differences
≠IS 401 uses descriptive categories for end-use (e.g., 'timber in contact with ground'), whereas modern international standards (BS 8417, AWPA U1, EN 335) use a more structured numerical 'Use Class' or 'Hazard Category' system (e.g., Use Class 4 for ground contact).
≠IS 401 prominently features and specifies Copper Chrome Arsenic (CCA) preservatives for a wide range of applications. Many international standards heavily restrict or ban CCA for residential and consumer applications due to health and environmental concerns, promoting alternatives like ACQ (Alkaline Copper Quaternary) and Copper Azole.
≠While IS 401 focuses primarily on the net retention of preservatives (kg/m³), international standards like EN 351-1 and BS 8417 place equal or greater emphasis on specifying and classifying the depth of preservative penetration into the sapwood.
≠International standards are often more explicit in their requirements for quality control schemes, third-party verification, and branding/marking of treated timber to ensure traceability and compliance.
Key Similarities
≈All standards share the fundamental objective of extending the service life of timber by protecting it from biodegradation by fungi, insects, and marine borers.
≈The primary methods of treatment, including non-pressure (brushing, dipping) and pressure processes (Full-cell, Empty-cell), are described in a similar manner across IS 401 and international standards.
≈A core principle in all standards is the requirement for timber to be properly seasoned to a suitable moisture content before pressure treatment to ensure effective preservative uptake.
≈All standards categorize preservatives into basic types, such as oil-borne (e.g., Creosote) and water-borne (e.g., CCA and its alternatives), and specify them based on the exposure risk.
≈The principle of increasing preservative retention and penetration requirements with increasing biological hazard (e.g., interior dry vs. ground contact vs. marine use) is a common thread throughout all the codes.
Parameter Comparison
Parameter
IS Value
International
Source
Moisture content before pressure treatment
Not more than 25%
Generally below Fiber Saturation Point (approx. 25-30%)
AWPA U1
Min. CCA retention for general ground contact (e.g., posts)
12 kg/m³
6.4 kg/m³ (UC4A - General Use Ground Contact)
AWPA U1
Min. Creosote retention for marine piles (severe exposure)
320 kg/m³ (Creosote-fuel oil 50:50)
320 kg/m³ (Creosote)
AWPA U1
CCA retention for interior timber (not in contact with ground)
4 kg/m³
2.5 kg/m³ (UC2 - Interior, dampness possible). CCA use is highly restricted.
AWPA U1
Hazard classification for exterior, above-ground timber
Described as 'Timber for external uses... not in contact with the ground'
Use Class 3
BS 8417 / EN 335
Hazard classification for timber in marine environments
Described as 'Timber for marine constructions'
Use Class 5
BS 8417 / EN 335
⚠ Verify details from original standards before use
Key Values4
Quick Reference Values
Class I Timber DurabilityAverage life > 120 months
Class II Timber DurabilityAverage life 60 to 120 months
Class III Timber DurabilityAverage life < 60 months
Ideal moisture content before pressure treatment15% to 25%
Tables & Referenced Sections
Key Tables
Table 1 - Natural Durability of Timbers
Table 2 - Treatability of Timbers
Table 3 - Recommended Practice for Preservation of Timber