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7/30/2019 Step-By-step Guide to Specifying Timbers
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STEP 1:SO YOU WANT TO USE TIMBER
Basically, you want timber or mainly two purposes, i.e., or structural uses; and
aesthetic purposes (e.g., urniture and other decorative uses).
I you are looking or structural timbers, then go to Step 2 .
I you are looking or timbers or decorative purposes, then skip to Step 4 .
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In the usage o timber or structural purposes, the strength properties o the timber
are o prime importance. The strength required o a timber varies, depending on
the load that the structure is expected to carry. Obviously, the heavier the loading,
the stronger the timber required. The strength properties o most o the commontimbers have been studied and based on conventional standards, the timbers have
been grouped into Strength Groups, as shown below: -
The more common timber construction applications are listed in Appendix 1, alongwith the strength requirement o the timbers.
STEP 2: STRUCTURAL TIMBERS-STRENGTH CONSIDERATIONS
Decide on the strength requirement o your particular application by reerring to Appendix 1 .
Go to Step 3 .
Strength Group A Extremely Strong
Strength Group B Very Strong
Strength Group C Strong
Strength Group D Weak
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By reerring toAppendix 2 , speciy the species o your choice (i you decide to usesingle
species) or the correct Strength Group (i you decide to use the
End-Use groupingconcept).
Decide whether you wish to use single species or End-Use groups
Now skip to Step 5 .
STEP 3: SPECIFIC TIMBERS VS. END-USE GROUPS
There is a question o whether you wish
to recommend a specic timber or the
job in hand (e.g., Kapur or roo trusses),
or a mix o timbers, each capable oullling your needs. The advantage
o choosing a single species is that
consistency is assured (or as assured as
timbers can be). Balanced against this is
that speciying single species will tend to
exhaust the species quickly and drive up
the price o that particular species. Also,
this is inecient utilisation o the orest
resource.
Thereore, as ar as possible, try to speciy
timbers that are capable o doing the
job as an End-Use group. The timbers in
each End-Use group have been screened
or their properties vis--vis the job in
hand. Thereore, it does not matter i any
one o the group members is supplied or
a mixture o members is supplied, as each one o them is capable o doing the job.
Speciying End-Use groups will bring down the cost o the project as now the supplier can supply a
mixture o species in lieu o the more expensive timbers. There will be less delay too, or now the suppliers
can make up the supply with a mixture o species instead o waiting to collect enough quantity o a
particular species or delivery. End-Use groups or the more common usage o timber have been compiled
by the Forest Research Institute Malaysia, and urther inormation on these End-Use groups can be
obtained rom them or the Malaysian Timber Council.
Ater determining the strength requirement o your application, you can now decide on the
timber you need by reerring to Appendix 2.
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STEP 4: TIMBERS FOR DECORATIVE PURPOSES
Speciying timbers or aesthetic purposes is very much an
individuals choice, dictated by taste and artistic inclinations.
Timbers are selected based on their decorative characteristics.
However, it must be noted that considerations must be given to
aspects such as colour matching; nishing and natural deects.
Very oten, your choice is limited to a ew truly decorative timbers,
and the specications are thereore species-oriented.
Go to Step 5 .
Speciy timbers that have the decorative
characteristics that you want.
Include a clause on colour consistency
(or stained to give a uniorm colour).
Speciy the fnishing you want, e.g., planed; moulded;
coated with plastic; special fnishes (speciy type o paints i
necessary).
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STEP 5: DURABILITY
CONSIDERATIONS
Decide whether you need durability or not,
based on the hazard that the structure is
expected to ace during service.
I you do, go to Step 6 .
I you do not need durability,
then skip to Step 9 .
Timber is subject to attacks by biological agencies
such as ungi and insects, especially termites.
While some timbers are more durable than others,by and large, all timbers will succumb to attacks
under the right conditions. These conditions
include the presence o moisture, and insect
inestation, especially the possible presence
o termites. The conditions under which your
structure is installed will dictate the amount o
hazard that the timber will ace during service.
I your application is expected to last, then
durability becomes an important consideration.The choice then is to either use naturally
durable timbers or, i they are not available (or
too expensive), have the timbers treated with
preservatives.
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STEP 6: HAZARD TYPES
Reer to Appendix 3 to decide whichhazardtype applies to your applicationGo to Step 7 .
The hazard aced by timber in service varies in accordance with the degree o
activities o the wood destroying agencies. For instance, timber under cover
will ace less hazard than timber exposed to the elements. The various service
conditions have been grouped or their degree o severity in terms o hazard
aced by timber in service. The hazard types are described in the table ound
in Appendix 3.
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Decide whether you require preservative treatment
or your timber. I you do, go to
Step 8 , i not, skip to Step 9 .
Reer to Appendix 2 or timbers requiring
preservative treatment.
STEP 7: NATURAL DURABILITY VS ARTIFICIAL DURABILITY
As mentioned in Step 5 earlier, timber varies in its resistance
to attacks by biological agencies. Some species are more
durable than others. In act, some timbers are so durable, that
they do not need any preservative treatment, e.g., Teak andBalau. However, other than this handul o naturally durable
timbers, all other timbers should be treated with preservatives
to enhance their service lie-span.
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Add a clause requiring pressure
impregnation methods or treating
your timber.
There are many chemicals available in the market that are used to protect timber.However, or a timber structure to be properly protected, the treatment should
last or a long t ime and i possible, permanently. The only way to achieve this is to
select chemicals that are capable o permeating into the timber in a permanent
manner. Furthermore, many o the chemicals available in the market tend to
break down with time and thereore their protection value will reduce as time
goes on.
The most widely used preservative chemical or timber in the world today is CCA,
which is short or a mix o water-borne inorganic salts o Copper, Chromium,
and Arsenic. CCA is perect in that when impregnated into the wood, it is chemically bonded onto
the wood matrix and thereore will not leach out o the wood, imparting a permanent protection to the
timber. Commercially, CCA is pressure-impregnated into the timber. The down side o using CCA is
that it is considered as environmentally unriendly by many countries. Various substitutes have been
developed to replace CCA but none o them has proven to be as ecacious as CCA.
Another pressure-impregnation method available is LOSP (Light Organic Solvent Preservatives). This
method uses a mixture o solvent-borne chemicals (usually an organo-tin and an insecticide).
Both methods have their advantages and disadvantages, and the choice is very much dependent onthe needs o the application. Table 1 lists out the comparative characteristics o CCA and LOSP.
The preservative loading required varies with the degree o hazard to which the timber is exposed.
Obviously, the greater the hazard, the greater the amount o preservatives needed. Appendix 4 lists out
the preservative loading required or the various hazard classes.
STEP 8: PRESERVATIVE TREATMENT
Preservatives are chemicals that are introduced into the t imber to prevent
attacks by biological agencies. In order to ensure proper protection o the
timber, the chemicals must be well and truly impregnated into the timber. The
only way to ensure this is to use pressure-impregnation methods when treating
timbers. Merely brushing, spraying and dipping the timber with preservatives willnot impart an ecient protection to the timber. Thereore, it is wise to insist on
the pressure-impregnation method when treating your timber.
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Speciy the preservative loading required
or your application, with reerence to
Appendix 3 .
Table 1: Comparison between CCA and LOSP
Go to Step 9 .
Please note that LOSP is not recommended or applications that are in contact with the ground.
CHARACTERISTICS CCA LOSP REMARKS
SOLVENT WATER WHITE SPIRIT THE WATER IN CCA WILL WET THE TIMBER
AND THUS SUBJECT THE TIMBER TO
DIMENSIONAL MOVEMENT UPON DRYING,
WHILE LOSP WILL NOT WET THE TIMBER AS IT
HAS NO WATER.
COLOUR GREEN COLOURLESS CCA WILL IMPART A GREEN COLOUR TO THE
TREATED TIMBER, WHILE LOSP ALLOWS THE
ORIGINAL COLOUR OF THE TIMBER TO SHOW
THROUGH.
FIXING METHOD CHEMICALLY BONDED TO NOT CHEMICALLY BONDED, CCA AFFORDS A MORE PERMANENT
THE CELL WALLS OF THE AND CAN BE LEACHED OUT OF BONDING WITH THE WOOD. LOSP TENDS
WOOD. THE WOOD. TO LEACH OUT OF THE TIMBER,
ESPECIALLY WHEN IN CONTACT WITH THE
GROUND.
EFFECTIVENESS EFFECTIVE AGAINST VERY NOT SUITABLE FOR TIMBERS IN CCA IS A BETTER CHOICE FOR OUTDOORS
HAZARDOUS CONDITIONS CONTACT WITH THE GROUND. APPLICATION.
EFFECT ON METAL MILD CORROSIVE EFFECT ON NO EFFECT ON METAL. CARE SHOULD BE TAKEN WHEN USING CCA
FASTENERS METAL FASTENERS WHEN IN WET OR HUMID ENVIRONMENT.
WET OR UNDER HUMID
CONDITIONS.
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As wood is a hygroscopic material, it will absorb and/or give up moisture to the surrounding atmosphere
to achieve a moisture equilibrium. During the process o absorbing and losing water, the wood will swell
and shrink, causing dimensional changes that may compromise the structure. For example, foor boards
that are installed wet will shrink upon drying and you will nd gaps between the boards. On the otherhand, swelling will cause stuck drawers and sticky doors. In principle, it is advisable to have the timber
at the approximate moisture content as the ambient environment in which it is installed to prevent any
dimensional movement.
As a guideline, the moisture content o the outdoor environment in Malaysia is approximately 19% while
in an air-conditioned room, the m-c drops down to around 12%. It ollows that wood that has been dried
by leaving it exposed to the outside environment,
will not be drier than 19% m-c, no matter how long
it is let there. I and when such timber is installed
in an air-conditioned room, the wood begins todry out and in the process will shrink and develop
dimensional movement.
I your application is outdoors and exposed to
the elements, then it is perectly sae to use
wet timbers. However, i the job is within an air-
conditioned environment, then it is advisable to use
timber that has been dried down to approximately
12%. And the only way to dry timber down tolower than 19% is to dry it articially in a kiln,
hence, kiln-dried timber.
STEP 9: MOISTURE CONTENT
Reer to Appendix 4 or the m-c o
timber required or various applications.
Add a clause on having your timber kilndried i your application is exposed to
air-conditioned environment.
You should by now have covered the most
important aspects of specifying timbers for
your project. If you have any further queries
on the use of timber, please contact the
Timber Industries Development Division ofthe Malaysian Timber Council at
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Appendix 1: Strength Groups o Timbers and Their Applications
APPLICATION STRENGTH GROUP* STRENGTH GROUP**
Structural Components
i. COLUMNS, BEAMS, BEARERS, STUDS, JOIST, TIES & STRUTS A & B SG1, SG2, SG3 & SG4
ii. FORM WORK A, B & C SG1, SG2, SG3, SG4 & SG5
Roofng
i. RAFTERS, TIES, STRUTS, PURLINS & BRACING A & B SG1, SG2, SG3 & SG4
ii. BATTENS A, B & C SG1, SG2, SG3, SG4 & SG5
Staircase
i. STRINGERS, TREADS, TRIMMER BEAM & HANDRAIL A & B SG1, SG2, SG3 & SG4
ii. BALUSTRADES A, B & C SG1, SG2, SG3, SG4, SG5 & SG6
Flooring
i. FLOOR BOARDING & PARQUETRY A & B SG1, SG2, SG3, SG4 & SG5
ii. SKIRTINGS A, B & C SG1, SG2, SG3, SG4, SG5 & SG6
Walling
i. WALL, PARTITION, FRAMING & EXTERNAL WALL BOARDING A, B & C SG1, SG2, SG3, SG4, SG5 & SG6
ii. INTERNAL WALL BOARDING, SLATE SCREENS A, B, C & D SG1, SG2, SG3, SG4, SG5, SG6 & SG7
iii. FACIA BOARDS A & B SG1, SG2, SG3 & SG4
Ceiling Frames
i. COVER BATTENS TO JOINT OF CEILING SHEETS A & B SG1, SG2, SG3 & SG4ii. CEILING STRIPS AND SOFFIT BATTENS A, B & C SG1, SG2, SG3, SG4, SG5 & SG6
Door & Window Frames
i. DOOR, WINDOW AND VENT FRAMES, INCLUDING THEIR STOPS AND GROUNDS A & B SG1, SG2, SG3 & SG4
ii. DOOR LEAVES, WINDOW AND VENT SASHES A, B & C SG1, SG2, SG3, SG4, SG5 & SG6
Furniture
i. BUILT-IN FITTINGS, FURNITURE GENERALLY AND WORKSHOP FURNITURE A, B & C SG1, SG2, SG3, SG4, SG5 & SG6
ii. SCIENCE LABORATORY TOPS A & B SG1, SG2, SG3 & SG4
Beading Fillets & Edgings Generally A, B & C SG1, SG2, SG3, SG4, SG5 & SG6
* The strength groups mentioned here are based on Engku Abdul Rahmans
(1988a,b) classication wherever possible. For timbers that have not been
classied by Engku Abdul Rahman, their strength grouping is based on
Burgess (1958).
** Malaysian Standard Code o Practice or Structural Use o Timber (MS
544:Part 2:2001).
16
(Engku Abdul Rahman,
1988a,b)
(MS 544:Part 2:2001)
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Appendix 2: Strength Grouping o Timbers
* Commercially available
Source: Malaysian Standard Code o Practice or Structural Use o Timber (MS 544:Part 2:2001).
Appendix 3: Hazard Types and Required Treatment
HAZARD TYPE DRY SALT RETENTION REQUIRED
(kg/m3 (Ib/t3)
Mild Interior timber not used in contact with the ground 5.60 (0.35)
Moderate Exterior timber not used in contact with the ground 8.00 (0.50)
Severe Exterior timber used in contact with the ground 12.00 (0.75)
Very Severe Timber used in constant contact with resh water 16.00 (1.00)
Extremely Severe Timber used in marine environment 24.00 (1.50)
Requiring Treatment
SG2 SG3 SG4 SG5 SG6 SG7
DEDARU KELAT BERANGAN BABAI BAYUR ARA
KEMPAS* KEMBANG SEMANGKOK* DEDALI MALABERA DAMAR MINYAK BATAI
MERBATU* KULIM* DERUM BALEK ANGIN BOPENG DURIAN* GERONGGANG*
MERTAS PAUH KIJANG KAPUR* BINTANGOR* JELUTONG* LARAN
PENYAU KASAI* BRAZIL NUT JONGKONG PELAJAU
PERAH KERUNTUM DARK RED MERANTI KASAH PULAI*
PETALING MEMPENING GERUTU* LIGHT RED MERANTI* SESENDOK*
RANGGU MERANSI KEDONDONG* MACHANG* TERENTANG*
RU MERANTI BAKAU* KELEDANG* MEDANG*
SURIAN BATU MERAWAN* KERUING* MELANTAI*
TUALANG* MERPAUH* KETAPANG MERSAWA*
NYALIN KUNGKUR SENGKURAT
PERUPOK RUBBERWOOD* TERAP*
PUNAH* MELUNAK* YELLOW MERANTI*
RENGAS* MEMPISANG*
SIMPOH* MENGKULANG*
NYATOH*
PENARAHAN*PETAI
RAMIN*
SENGKUANG
SEPETIR*
TETEBU
WHITE MERANTI*
Naturally Durable
SG1 SG2 SG3 SG4 SG5
BALAU* BELIAN BEKAK* GIAM* TEMBUSU
BITIS MATA ULAT* DELEK MALABERA
CHENGAL* KEKATONG* KERANJI* MERBAU*PENAGA RESAK*
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APPLICATION MAXIMUM M-C AT TIME MAXIMUM M-C AT
OF INSTALLATION FOR NON TIME OF INSTALLATION
AIR-CONDITIONED APPLICATIONS FOR AIR-CONDITIONED
APPLICATIONS (KILN-DRIED)
Structural Components
I. EXTERNAL-COLUMNS, BEAMS, BEARERS, STUDS, JOINTS, 30% (THICKNESS EXCEEDING 100MM) N.A
TIES & STRUT 25% (THICKNESS NOT EXCEEDING 100MM) N.A
ii. INTERNAL 19% 12%
Roofng
i. RAFTERS, TIES, STRUTS, PURLINS & BRACING 25% N.A.
ii. BATTENS 25% N.A.
Staircase
i. STRINGERS, TREADS, TRIMMER BEAMS & HANDRAILS 19% 12%
ii. BALUSTRADES 19% 12%
Flooring
i. FLOOR BOARDING & PARQUETRY 19% 12%
ii. SKIRTINGS 19% 12%
Walling
i. WALL, PARTITION, FRAMING 19% 12%
ii. EXTERNAL WALL BOARDING 19% N.A.
iii. INTERNAL WALL BOARDING, SLATES & SCREENS 19% 12%
iv. FACIA BOARDS 19% N.A.
Ceiling Frames
i. COVER BATTENS TO JOINTS OF CEILING SHEETS 25% N.A.
ii. CEILING STRIPS AND SOFFIT BATTENS 19% 12%
Door & Window Framesi. DOOR, WINDOW AND VENT FRAMES, INCLUDING THEIR 19% 12%
STOPS AND GROUNDS
ii. DOOR LEAVES, WINDOW AND VENT SASHES 19% 12%
Furniture
i. BUILT-IN FITTINGS AND FURNITURE GENERALLY 19% 12%
ii. WORKSHOP FURNITURE 19% 12%
iii. SCIENCE LABORATORY TOPS 19% 12%
Beading Fillets & Edgings generally 19% 12%
Appendix 4: Moisture Content (M-C) o Timber or Various Applications
(In Tropical Conditions)
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Head Ofce
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MALAYSIA
Tel: 603 92811999
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London, SW1H9HP
UNITED KINGDOM
Tel: +44 207 2228188
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P.O. Box 62476, Dubai
UNITED ARAB EMIRATES
Tel: +971 4 3326998
Fax: +971 4 3326889
E-mail: [email protected]
www.mtc.com.my