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Designing Fire and Acoustic Rated Systems

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Designing Fire & Acoustic Rated Systems In Residential Buildings


Detached housing

Designing Fire & Acoustic Rated Systems

Attached housing

Apartments


Designing Fire & Acoustic Rated Systems

1. Fire separation in residential construction

− Overview − Timber systems − Junction detailing − What to do / What not to do

2. Building with Timber in Bushfire-prone Areas


– Multi

– Residential

– Timber

– Frame

– Construction

M

R

T

F

C

MRTFC - Overview


• MRTFC deals with:

– Class 1 buildings (houses or dwellings attached side by side)

– Class 2 buildings (flats and units above one another as well as side by side)

– Class 3 buildings (residential parts of hotels, motels, accommodation for students, aged and disabled)

• Performance criteria in these classes focuses on:

– Fire resistance

– Sound resistance

MRTFC and Performance Requirements


• In Class 2 and 3 residential buildings there is extensive use of “Sole occupancy units” (SOUs). This separates buildings into manageable units and provides protection to “other property”:

– A SOU is a part of a building that is occupied by one owner, lessee or other occupant

– SOUs must be designed to restrict fire and sound from affecting adjoining SOUs

SOU Concept


• The National Construction Code (BCA) requires protection to be provided at the boundaries between compartments or SOUs

• The walls, floors and ceilings bounding compartments are constructed to meet “Fire Resistance Levels” (FRLs) to prevent spread of fire

• FRLs are expressed in minutes as follows:

FRL: 60 / 60 / 60 structure integrity insulation

• Columns have a FRL of 60/-/- or 120/-/- etc as they are not barriers

• Partition walls are the exact opposite: barriers but non-loadbearing so typically have a FRL of -/30/30 or -/60/60

Measuring Fire Resistance Levels


• Focus is on fire/sound wall separation i.e.: – Minimum FRL 60/60/60 – Walls must extend from ground to the underside of a non

combustible roof – No shared space between dwellings e.g. no shared roof

cavity – No structural members crossing the separating wall (except

roof battens 75mm x 50mm max.) – Each dwelling must have independent access to the road or

open space

Class 1 Buildings (e.g. attached dwellings, townhouses)


• MRTFC details focus on meeting the combined requirements of fire, sound and structural requirements for designated wall, floor and ceiling elements in Class 1, 2 and 3 buildings

• A systems approach is used to meet needs which can be broken up into: – Wall framing systems – Floor/ceiling framing systems

• Each system uses a number of common concepts to maintain continuity at intersections between elements and at penetrations, including: – Fire resistant joints – Cavity barriers – Fire stops

General Framing Requirements


• The system features two stud walls with a separating cavity

• Load Bearing frames are typically made from 90x45 timber framing

• The frames can be prefabricated as required

• The system is easy to handle and erect on-site

• Insulation is used extensively between studs or in the cavity

• It must be non-combustible (BCA Requirement)

• Fire grade plasterboard is built up in layers to meet fire requirements

• Fibre cement sheet can be used in combination with plasterboard

• Other cladding or linings can be used over these components

Double Stud Walls


Double Stud Walls


Depending on the type of construction, fire rated walls may need to continue through the roof and eaves cavities. In these areas: – walls must

extend at least to the underside of the roof

– walls may be single skin (not double) because sound resistance isn’t required in the roof or eaves areas

Treatment of Roof and Eave Cavities


• Floor/ceiling systems are required between sole occupancy units (SOUs)

• These systems consist of floor coverings, platform flooring, floor joists, sound insulation, resiliently mounted ceiling battens and ceiling linings

Floor/Ceiling Systems (e.g. Used in apartments)


Floor/Ceiling Systems


• Timber joists dictate the load and spanning capacity of the floor

• Non-combustible sound insulation is placed within the joist depth

• Resiliently mounted ceiling battens are fixed transversely to the joists to isolate sound from the structure above

• Plasterboard is fixed to the sound resilient supports. A build up of layers is used to achieve sound and fire requirements (fire grade board required)

Summary of Floor/Ceiling System Components


Floor/Ceiling Systems

FRL Rw+Ctr

51 19 mm pbd

floor 60/60/60

90/90/90

120/120/

120 90

53

90 90

90

51 60/60/60

90/90/90

120/120/

120

FRL Rw+Ctr

19 mm pbd

floor

51

90

53

51

60/60/60

90

51

120/120/

120

90/90/90

60/60/60

Rw+Ctr

19 mm pbd

floor

FRL

53


• Care must be taken to ensure weak spots don’t occur at the interfaces between systems (e.g. intersections and penetrations)

• Methods of doing this include:

– Fire resistant joints

– Cavity barriers

– Fire stops at gaps and

penetrations (caulking)

Continuity of Systems


• Fire resistant joints are used at intersections between floor/ceiling elements e.g. where one element has a lower FRL than the other.

• Some structural framing remains protected by the plasterboard and by the slow charring of the other framing at the junction.

Fire Resistant Floor Junctions

In the event of

a fire, the floor

joist can

rotate without

affecting the

fire rated wall.


• Needed at intersections between wall/wall elements such as when one element has a lower FRL than the other

• The joint is made by adding extra pieces of timber to the joint between the elements

• The extra timber adds fire resistance because when it burns it forms an insulative char layer on the surface – this slows burning in the core of the timber and in doing so provides fire resistance for a period of time

• In general, the more pieces of timber added to the joint, the longer the joint will last.

• In some cases light gauge steel angles are also used to slow char at corners

Fire Resistant Wall Junctions


• Cavity barriers restrict the passage of flame, smoke and gasses in cavities that bypass wall/floor/ceiling intersections

• Typical example: intersection between a wall separating SOUs and a non-fire rated external brick veneer wall

• Cavity barriers can be made by:

– timber battens

– appropriate sheet linings

– moisture repellent mineral wool

– Light gauge steel profiles

Example prior to brick veneer being laid

Cavity barrier

using sheet

lining

Cavity Barriers


Use fire shafts as a means of

avoiding services in fire/sound rated

walls

Fire Rated Shafts


What not to do!

Suspended slab above a basement car

park. Penetrations through the suspended

slab with many oversized fire collars.


What to do!


What not to do!

Hole in wall dividing two SOU’s - GPO

without protection behind.


What to do!

Fire rated wall box – up to 2 hours

protection.


What not to do!

Down lights in ceiling within the SOU - no

protection of the penetration behind the

light fittings.


What to do!

Lightweight intumescent down light covers

for fire-rated ceilings – up to 2 hours

protection


What not to do!

Service cabinet – no protection in the ceiling

space.


What to do!

Run services is a dedicated

shaft.


• Protect the timber with plasterboard

Alternative Method


• Timber can be effectively used in buildings that are exposed to fire.

Conclusions

• The key to the correct use of timber is the detailing in accordance with relevant Australian standards and industry manuals (e.g. Technical Guides).

FRL Rw+Ctr

51 19 mm pbd

floor 60/60/60

90/90/90

120/120/1

20 90


• WoodSolutions Technical Guides

• Improvements include details for columns in walls and improved junction details

• Available for free by registering at www.woodsolutions.com.au

More Information

http://www.woodsolutions.com.au/


Building with Timber in Bushfire-prone Areas


Devastating Victorian Bushfires – Black Saturday February 7, 2009


AS 3959—2009

Australian Standard®

Construction of buildings in

bushfire-prone areas

AS

3959—

2009

• Published 10 March 2009

• Enacted in Victorian Building Regulations – 11 March 2009

• 108 Pages (1999 edition was 31 pages)

• Extensive options and construction and two methods for assessment

Modes of Fire Spread


Bushfire Attack Level (BAL)

Description of predicted bushfire attack and levels of exposure

Construction Objectives

There is insufficient risk to warrant specific construction requirements.

Ember attack Average heat flux to cause

annealed glazing to fail

Increasing levels of ember attack and burning debris ignited by windborne embers together with increasing heat flux.

Screened annealed glass (screens assumed to cut

radiation by 50%)

Increasing levels of ember attack and burning debris ignited by windborne embers together with increasing heat flux.

Unpiloted ignition of timber (US reference – timbers ignite

between 25 to 35 kW/m2)

Increasing levels of ember attack and burning debris ignited by windborne embers together with increasing heat flux with the increased likelihood of exposure to flames.

Occasionally within flame (limit to knowledge available)

Direct exposure to flames from fire front in addition to heat flux and ember attack.

Building within flame (unknown territory )

Bushfire Attack Levels & Corresponding Construction Objectives

BAL–LOW

BAL–12.5

BAL–19

BAL–29

BAL–40

BAL–FZ


Typical Radiant Heat Intensities &

Phenomena

kW/m2 Phenomena

4 Pain to humans after 10 to 20 seconds

10 Pain to humans after 3 seconds

13 Ignition of timber after a long time (piloted)

25 Ignition of timber after a long time (non-piloted)

38 Ignition of black drill fabric after a long time (non-piloted)

42 Ignition of cotton fabric after 5 seconds (non-piloted)

45 Ignition of timber in 20 seconds (non-piloted)

Reference: AS3959-2009 Appendix G – Table G1


Building Requirements

AS3959 specifies building

requirements for each BAL

The aim is to prevent

embers, radiant heat and

flames breaching the

building’s envelope


Lightweight Timber Options

External wall Cladding – full wall height

BAL–LOW Traditional timber framing and lightweight

cladding materials.

BAL–12.5

BAL–19

Bushfire-resisting timber or timber species

listed in E1

BAL–29 Bushfire-resisting timber and sarking

BAL–40

BAL–FZ

FRL of 30/30/30 required – moisture-resistant

(M-R) fire grade plasterboard/timber systems.



Windows

BAL–LOW All timber window frames.

BAL–12.5

BAL–19

Bushfire shutters and all timber frames or

External mesh screens and all timber frames or

Frames with bushfire-resisting timber or

timber species from E2.

BAL–29 Bushfire shutters and all timber frames or

frames with bushfire-resisting timber.

BAL–40 Bushfire shutters and all timber frames or

tested windows to AS1530.8.1.

BAL–FZ Bushfire shutters and all timber frames or

tested windows to AS1530.8.2.

Note: There are also requirements to screen openable parts

of windows (up to BAL-29) and entire window

assemblies (BAL-40).


Timber Species Options

Bushfire-

resisting

timbers

Blackbutt, Kwila (Merbau), Red Ironbark,

River Red Gum, Silvertop Ash, Spotted

Gum and Turpentine

Timber

species* from

E1: density

750kg/m3 or

greater include:

All BRTs above also: Box(s) [Brush, Grey,

Coast Grey, Yellow], Grey Gum, Grey

Ironbark, Jarrah, Kapur, Karri, Kempas,

Keruing, Manna Gum, Messmate,

Mountain Grey Gum, New England

Blackbutt, Southern Blue Gum, Sugar

Gum, Sydney Blue Gum , Stringybark(s)

[Brown, White, Yellow ]

Timber

species* from

E2: density

650kg/m3 or

greater include:

All species from E1 (above), also: Alpine

Ash, Blackwood, Mountain Ash, Shining

Gum, Slash Pine, Southern Blue Gum,

White Cypress

Doors & Windows,

decking, external wall

cladding, subfloor:

bearers, joists &

supports BAL: LOW,

12.5, 19 & 29

Note: Fire retardant

treated timber can

also be used.

External wall

cladding, decking

BAL: LOW, 12.5, 19

Doors & Windows

BAL: LOW, 12.5, 19


For a timber clad wall in BAL–40 and

BAL–FZ, use a wall with a Fire

Resistance Level (FRL) of 30/30/30

(structural adequacy / integrity /

insulation).

This can be achieved with the use of

moisture resistant fire grade

plasterboard and external timber

cladding.

One layer of 16 mm moisture resistant

fire grade plasterboard provides a FRL

of 60/60/60.


Fire Rated Wall Systems


BAL–FZ Metal Roof Solution

15mm T&G

plywood

Timber fascia

(no requirement

on timber species

or density) 16mm moisture

resistant fire

grade

plasterboard

75mm

50 50

40mm

max.


Shutter Systems (BAL−40 & BAL−FZ)

www.wildfireprotection.com.au

Timber Window (BAL−FZ)

& Shutter Systems (BAL−FZ) www.paarhammer.com.au

Window Options (Examples for BAL−40 and BAL−FZ)

Window and Door Systems (BAL−40)

www.miglas.com.au

Timber Window & Door

Systems (BAL−40) www.stegbar.com.au


Fire retardant systems – coatings and impregnation

Building Protection Options (Examples)


The BushFire Loch

roof sprinkler systems

Building Protection Options


More Information

• WoodSolutions Technical Guide #4

• Available for free by registering at www.woodsolutions.com.au

http://www.woodsolutions.com.au/


woodsolutions.com.au The knowledge building website.

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