Timber Tops for Concrete Slabs
Design considerations of timber or plywood tops for concrete slabs
The design of timber tops for concrete slabs requires consideration of certain aspects.
Slab condition aspects for design of timber tops for concrete slabs
In Australia, concrete slab on ground accounts for about 75% of the primary floor surfaces in new domestic structures. Because of the blandness of the bare concrete surface, it is inevitably covered with other more attractive material, particularly in the living areas of the house.
Plywood flooring over battens on concrete
One way of installing a floor over concrete is to fix battens to the concrete, then attach plywood flooring over the battens. This system requires greater floor to ceiling height than attaching the plywood directly to the concrete.
Plywood flooring attached directly to concrete
When headroom is at a premium, the only possible solution to installing a plywood floor over concrete is to fix the plywood directly to the concrete slab.
Plywood Bracing
Plywood bracing - introduction and advantages
Historically, residential and other low rise buildings in Australia have regularly suffered wind damage. The personal and community costs, emotionally and economically, have been enormous. Wind damage is universal throughout Australia. Although the problem of wind design has been well accepted, in the tropical cyclone prone areas of Australia, wind damage from local thunderstorm or downburst activities cost millions of dollars annually. The latest version of the wind loading code AS1170 Part 2 - 1989 recognises this situation.
Plywood wind bracing – standard solutions
The standard plywood bracing solution provides a simple yet safe method of designing wind bracing to suit a large proportion of low rise timber framed structures in Australia. This solution is the method used in Australian Standard AS1684 National Timber Framing Code.
Plywood wind bracing – engineered solutions
The Engineered Solution provides building designers, architects, building technologists and engineers with a method of designing optimal plywood bracing for a timber framed building.
Materials specification for plywood bracing
Plywood bracing panels must comply with the requirements of AS/NZS2269-1994 Plywood - Structural and be branded with the PAA / JAS-ANZ Product Certification brand stamp.
Plywood Wind Bracing - Timber Framing Specification
Timber wall framing must comply with AS1684-1992 National Timber Framing Code or Framing Manuals produced by bona fide timber organisations.
Additional installation requirements for plywood bracing panels
Additional installation requirements are common to:
Standard Bracing Solutions
Engineered Bracing Solutions
Wood and its origins
Laminated Veneer Lumber - External Applications
It is not recommended to use LVL in outside applications or those permanently exposed to the weather or a high level of moisture.
Laminated Veneer Lumber - Handling and Storage
To maintain LVL in good condition during storage, the products should be stacked on a level base clear of the ground and well protected from the weather.
Applications
Standards governing plywood sheeting
All plywood used in residential flooring, bracing, webbed beams or non trafficable roofing should comply with Australian Standard AS/NZS 2269 Plywood - Structural and be branded with the PAA Product Certification stamp for structural plywood.
Design and selection of plywood flooring
Floor live loads for a wide range of buildings and occupancies are given in Appendix B of AS 1170-1989 "SAA Loading Code - Part 1: Dead and live loads and load combinations". The loading requirements of the Building Code of Australia are deemed to be satisfied by using this code.
Australian Standards and Quality Assurance for plywood external cladding
Plywood can be used as an attractive and economic exterior cladding for residential, commercial, industrial and rural buildings.
Plywood webbed beams
Box and C-section beams built with timber flanges and plywood webs are stable, lightweight and cost effective, particularly as lintel beams, rafters or purlins. These fabricated beams are viable alternatives to large section timber, which is becoming difficult to obtain in suitable quality and length.
Plywood roofing
Structural plywood is approved for use as non-trafficable roofing in AS1684.
Structural plywood can be surfaced with a wide range of water proofing membranes, ranging from felt and tar, used in the USA for industrial buildings, to fibreglass reinforced roofing shingles. Fibrous cement shingles and timber shakes are also suitable. Recommendations of the surfacing product manufacturer must be strictly adhered to.
Plywood external cladding
A wide range of plywood products exist that can be used as external cladding. For maximum efficiency plywood can be used for wall bracing as well as cladding. All plywood external cladding must be treated against fungal attack.
Materials handling applications of plywood
PAA Product Certified structural plywood is well suited to applications in materials handling and transport. Structural plywood has physical and structural characteristics that are an advantage in materials handling applications such as pallets, containers and transport cases.
Structural Components from Plywood
Only plywood produced under a recognised quality scheme such as PAA Product Certified plywood should be used for structural components as the permanent Type A bond and standardised basic working stresses specified in AS/NZS2269 are essential for reliable design. Standard section properties, basic working stresses and elastic moduli are contained in AS1720, AS2269 and the article "Structural Plywood".
Applications of plywood on the construction site
Structural and exterior plywoods have many applications on the building site.
Products & Characteristics
Product Certification and Quality for Plywood
The Plywood Association of Australia (PAA) Product Certification Scheme, which commenced as a process based quality control program in 1963, is now in use industry wide.
Standards for Plywood.
PAA members manufacture plywood to the following Australian Standards under an industry wide total product certification scheme.
The characteristics of structural plywood
Structural plywood can be worked with conventional wood working tools. It can be cut, drilled, bored, planed and sanded with ease.
Marine plywood
Marine Plywood manufactured to AS/NZS2272 has a permanent Type A phenolic bond. It is manufactured from selected species based on density, bending strength, impact resistance and surface finishing characteristics.
Exterior Plywood
Exterior plywood is non-structural plywood suitable for exterior door skins, hoardings, signs and cladding. No stress grades are applied to exterior plywood.
Interior plywood
Interior plywood is a non-structural appearance grade suitable for internal wall panelling, furniture and fittings, interior door skins and ceiling lining.
Plywood in Concrete Formwork
Plywood possesses properties that are excellent for concrete formwork. Plywood characteristics relevant to formwork design such as strength and stiffness to weight ratio, dimensional stability, ease of working and impact resistance are detailed in the PAA publication "Plywood in Concrete Formwork".
Overlaid plywood
Plywood is often overlaid for protection against weather and wear. A variety of overlay materials can be effectively combined with plywood.
Preservative treatment of plywood
All timber products decay under certain conditions. For example, if the moisture content is high enough, the area confined and unventilated, and the temperature conducive, fungi can cause decay in most timber species.
Fire And Flame Resistance of Plywood
There are two ratings applied to buildings with regard to response to fire.
Fire resistance level: This can apply only to a total building element e.g. a fire door or a wall or roof system. A product cannot be fire rated.
Early Fire Hazard Indexes: These are a measure of a product's surface characteristics relating to spread of flame, heat evolved, smoke emission and ignition.
The types and sizes of plywood panels
The four standardised types of plywood produced in Australia are:
structural plywood produced to AS/NZS 2269; marine plywood produced to AS/NZS 2272; exterior plywood produced to AS 2271 and interior plywood produced to AS 2270.
The other standardised glue laminated veneer product is structural laminated veneer lumber (LVL). It is produced to AS 4357. A complete description of the characteristics of each of the products is contained in publications available from the Plywood Association of Australia (PAA).
Laminated Veneer Lumber (LVL)- Introduction, products and applications
Laminated veneer lumber (LVL) is manufactured from veneers which are rotary peeled then dried. They are laminated together under high temperature and pressure using a phenolic adhesive.
Plywood bond types
Australian Standards define and specify tests for four types of glue bond:
Type A bond; Type B bond; and Type C and D bonds.
Plywood face grades
Plywood can be ordered with face veneers suitable for the intended application.
Storage and fixing of plywood
Plywood should always be stored in a dry shelter protected from sunlight. Panels should be stored flat. Do not lean panels against a wall or the side of the rack for long periods.
Finishing of exterior plywood
PAA Product Certified plywoods with S, A or B grade face veneer quality have a surface designed to provide a suitable substrate for a high quality finish when appropriately sanded. Structural plywoods normally possess a C or D quality face veneer that is not designed to provide a high quality paint substrate. Structural plywood is available with A and B grade face veneers on special order.
Finishing of interior plywood
Under normal protected interior conditions, type D or C bonded plywood will give long term durability without preservative treatment. Before finishing ensure that the plywood is dry (below 12-15 percent moisture content) and the surface to be painted is clean, smooth and wax free.
Thermal Properties of Plywood
The average coefficient of thermal expansion for structural plywood is approximately 4.5 x 10-6mm/mm/°C. This compares with 11 x 10-6mm/mm/°C for steel.
Flooring
Structural Plywood Specification – Residential Flooring
All PAA T&G plywood panels are manufactured to AS/NZS2269-1994 "Plywood - Structural", and must be stamped with the PAA Product Certification stamp.
Installation of Plywood Residential Flooring
Sub-floor beams and joists must be sized and installed in accordance with AS1684 "SAA National Timber Framing Code".
Wet area plywood flooring in residential uses
Tongue and Groove (T&G) structural plywood can be used in potentially wet area rooms, such as bathrooms or laundries, providing an impervious surface, and a floor system that can be suitably graded to a waste as required by state authorities.
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