NCC 2019 Volume One
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Specification C1.13a Fire-protected timber
1. Scope
This Specification contains requirements for fire-protected timber and procedures for determining the time at which the temperature at the interface between the protection system and the timber is exceeded.
2. Requirements
2.1
General requirements
Intent
To specify the protection requirements for fire-protected timber.
Where fire-protected timber is used, it must be provided with protection so as to achieve the FRL required of the building element.
In addition, the timber must have either of the following:
- a non-combustible fire-protective covering which achieves a resistance to the incipient spread of fire of not less than 45 minutes when tested in accordance with Section 4 of AS 1530.4 (see Clause 2.1(a)(ii)(A)); or
- at least two layers of 13 mm thick, fire-protective grade plasterboard fixed in the manner required to achieve the required FRL of the element (see Clause 2.1(a)(ii)(B)).
Figure Spec C1.13a Fire-protected timber
The covering required by Clause 2.1(a)(ii) part or all of the system used to protect the timber in order to achieve the required FRL of the building element.
Clause 2.1(a)(ii)(A) separates the testing requirements into two sub-clauses; Clause 2.1(a)(ii)(A)(aa) for horizontal elements and Clause 2.1(a)(ii)(A)(bb) for other elements.
For testing of horizontal elements, the test must be conducted in accordance with Section 4 of AS 1530.4. The resistance to the incipient spread of fire is deemed to have failed at the time when the maximum temperature recorded by thermocouples located on the unexposed face of the element lining exceeds 250°C.
The requirements for the testing of other than horizontal elements are contained in Clause 2.1(a)(ii)(A)(aa). For the purpose of measuring temperatures in accordance with this Clause, thermocouples complying with clause 2.2.3.1 of AS 1530.4 shall be positioned at the following locations:
For wall systems and the like:
- Five thermocouples shall be evenly distributed to monitor the temperature on the unexposed surface of the fire-protective covering at the centre of the specimen and at the centre of each quarter section.
For column systems and the like:
- Thermocouples shall be positioned at all locations considered to be critical on the unexposed surface of the fire-protective covering.
For all systems:
- For timber framed systems, padded thermocouples shall be located in a clear space on the unexposed face of the fire-protected covering and shall not be located at the timber interface.
- For monolithic timber systems, thermocouples (without insulating pads) shall be located at the interface of the fire-protective covering and the timber.
- The thermocouples shall not be located closer than 200 mm from any joint in the fire-protective covering.
- Where the fire-protective covering is not in contact with the monolithic timber, the surface of the timber is deemed to be the interface.
- The acceptance criterion is the minimum time at which the unexposed face of the fire-protective covering or interface exceeds a maximum temperature of 250°C.
The testing must be carried out in accordance with the Standard Fire Test, or an equivalent or more severe test on the timber element with the proposed non-combustible fire-protective covering fixed in a representative manner and confirmed in a report from an Accredited Testing Laboratory.
2.2
Massive timber
Intent
To specify alternative protection requirements for fire-protected timber which is massive timber.
Fire-protected timber which is massive timber need not comply with Clause 2.1 if it complies with Clause 2.2. Compliance with Clause 2.2 is achieved when all of the following is applied:
- the element is protected to achieve the required FRL (see Clause2.2(a)(i));
- a non-combustible fire-protected covering is applied to the timber which achieves either of the parameters specified in Table 1 (see Clause 2.2(a)(ii)); and
- cavities within the fire-protective covering, if present, are filled with non-combustible insulation (see Clause 2.2(a)(iii)).
The covering required by Clause 2.2(a)(ii) may form part or all of the system used to protect the timber in order to achieve the required FRL of the building element.
The option provided under Clause 2.2(a)(ii)(A) requires a test to be carried out on a representative specimen. Refer to Clause 3 for test procedures.
Under Clause 2.2(a)(iii) the fire-protective covering may be fixed to timber battens so long as any cavities are filled with non-combustible insulation.
2.1 General requirements
(a)
Fire-protected timber must—
(i)
utilise a non-combustible fire-protective covering fixed in accordance with the system requirements to achieve an FRL not less than that required for the building element; and
(ii)
have a non-combustible fire-protective covering fixed in accordance with system requirements—
(A)
to achieve a resistance to the incipient spread of fire of not less than 45 minutes when tested in accordance with—
(aa)
for horizontal elements — Section 4 of AS 1530.4; and
(bb)
for other elements — the relevant test procedures from Section 4 of AS 1530.4 applied to the element lining; or
(B)
which consists of not less than 2 layers of 13 mm thick, fire-protective grade plasterboard.
(b)
For the purposes of (a), the non-combustible fire-protective covering provided under (a)(ii) may form all or part of the non-combustible fire-protective covering provided under (a)(i).
2.2 Massive timber
(a)
Fire-protected timber, where the timber is massive timber, need not comply with Clause 2.1 if the fire-protected timber—
(i)
utilises a non-combustible fire-protective covering fixed in accordance with system requirements to achieve an FRL not less than that required for the building element; and
(ii)
has a non-combustible fire-protective covering fixed in accordance with system requirements—
(A)
(B)
not less than that specified by Table 1; and
(iii)
has either—
(A)
any cavity —
(aa)
between the surface of the timber and the fire-protective covering; or
(bb)
between timber elements within the fire-protective covering,
filled with non-combustible insulation; or
(B)
no cavity—
(aa)
between the surface of the timber and the fire-protective covering; or
(bb)
between timber members within the fire-protective covering.
(b)
For the purposes of (a), the non-combustible fire-protective covering provided under (a)(ii) may form all or part of the non-combustible fire-protective covering provided under (a)(i).
Table 1 Interface temperature and minimum fire protective grade plasterboard thickness
Application
Time – without timber interface exceeding 300°C (mins)
Minimum thickness of fire-grade plasterboard (mm)
Inside a fire-isolated stairway or lift shaft
20
13
External walls within 1 m of an allotment boundary or 2 m of a building on the same allotment
45
2 x 13
All other applications
30
16
3. Determination of time the timber interface temperature exceeds 300°C for timber at least 75 mm thick
Determination of time the timber interface temperature exceeds 300°C for timber at least 75 mm thick
3.1
Form of test
Intent
To provide a test procedure for massive timber.
Clause 3.1 specifies the testing requirements for fire-protected timber. Clause 3.1(a) requires the test to be in accordance with the Standard Fire Test, or to apply an equivalent or more severe test method. The Accredited Testing Laboratory must also provide a report to confirm the time at which the timber interface temperature exceeded 300°C.
The remaining Clauses are specific requirements on how to conduct the test. Clause 3.1(b) requires the test specimen to incorporate representative joints used in the proposed system. The locations where interface temperatures are measured during the test is specified by Clause 3.1(c). The final sub-clause, Clause 3.1(d), specifies the method of measuring the temperature; which is in accordance with AS 1530.4.
3.2
Smaller specimen permitted
Intent
To allow a smaller test specimen to be tested.
Clause 3.2 permits the Accredited Testing Laboratory to conduct a test using a smaller test sample than that required by Clause 3.1, provided:
- the specimen is not less than 1000 mm × 1000 mm and is representative of the proposed construction;
- the fire resistance has already been determined by a full scale test in accordance with AS 1530.4; and
- the Accredited Testing Laboratory defines the limitations of the tested material, i.e. the size limitation to which the actual system can be constructed.
3.3
Acceptance criteria
Intent
To specify the acceptance criteria of the test.
Clause 3.3 specifies that the acceptance criteria is the time at which any of the thermocouples (specified in Clause 3.1) exceeds 300°C during the test.
3.1 Form of test
(a)
Tests must be carried out in accordance with the Standard Fire Test, or an equivalent or more severe test, on the timber element with the proposed non-combustible coverings fixed in a representative manner, with the time the timber interface temperatures exceeded 300°C confirmed in a report from an Accredited Testing Laboratory.
(b)
If a fire protection system incorporates joints, the test specimens must incorporate representative joints.
(c)
Interface temperatures must be measured over the following features by a minimum of two thermocouples:
(i)
At joint positions in the protection systems.
(ii)
At least 200 mm from any joint.
(iii)
At service penetrations.
(iv)
At any other locations where, in the opinion of the Accredited Testing Laboratory, the interface temperature may be higher than the above positions.
(d)
The temperatures must be measured in accordance with Appendix C1 and Section 2 of AS 1530.4 as appropriate.
3.2 Smaller specimen permitted
An Accredited Testing Laboratorymay carry out the test specified in Clause 3.1 at pilot scale provided—
(a)
a specimen (which must be not less than 1000 mm x 1000 mm) adequately represents the proposed construction in the building; and
(b)
the fire resistance of the specimen has already been determined in a full scale test performed in accordance with AS 1530.4 to demonstrate adequate retention of the fire protection system in conjunction with the timber elements being protected; and
(c)
the results of the test do not apply to construction larger than limits defined by the Accredited Testing Laboratory conducting the pilot examination.
3.3 Acceptance criteria
The time the timber interface temperature exceeds 300°C must be taken as the minimum time any of the thermocouples specified in Clause 3.1 exceeded 300°C.