SPECIFICATION FOR CLASSIFICATION OF TIMBER (IS: 399)

CLASSIFICATION OF TIMBER

POSITION BASIS:



a) Standing Timber

It means that a living tree

b) Rough Timber

forms a part of the felled tree.

c) Lumber

Lumber are logs of timber sawn into planks, posts,

etc.

MODULUS OF ELASTICITY BASIS:

The species of timber recommended for constructional
purpose are classified as:-

Group A

Modulus of elasticity in bending above 12.5 kN/mm2

Group B 

Modulus of elasticity in bending above 9.8 kN/mm2
and below 12.5 kN/mm2

Group C

Modulus of elasticity in bending above 5.6 kN/mm2
and below 9.8 kN/mm2.

AVAILABILITY BASIS:

According to availability, timber can be of three

grades, namely X, Y and Z.

Grade A

Most common, 1415 m3 or more per year

Grade B

Common, 355 m3 to 1415 m3 per year

Grade C

Less common, below 355 m3 per year

This is based upon the figures supplied by the forest departments.

DURABILITY BASIS:

Test specimens of size 600 × 50 × 50 mm are buried

in the ground to half their lengths. The condition of

the specimen at various intervals of time are noted

and from these observations their average life is

calculated. Timbers are classified based upon such

observations as of:

 

a)High Durability: Average life of 120 months and

over.

 

b)Modrate Durability: Average life of less than 120

months but of 60 months or more.

 

c)Low Durability: Average life of less than 60

months.

SEASONING CHARACTERISTICS BASIS:

Timbers are classified depending upon their behaviour

to cracking and splitting during normal air-seasoning

practice under three categories.

a) High Refractory: are slow and difficult to season

free from defects.

b) Moderate Refractory: protection is given against

rapid drying.

c) Low Refractory: These can be rapidly seasoned

free from defects.

TREATABILITY BASIS:

This classification is based upon the resistance offered by the heartwood of a species to preservatives under a working pressure of 1.05 N/mm2 as:

(a) Easily treatable.

(b) Treatable but complete preservation not easily

obtained.

(c) Only partially treatable.

(d) Refractory to treatment.

(e) Very refractory to treatment, penetration of

preservative being practically nil from the

sides and ends.