Installing Posts For Decks And Verandahs With Heavier Loads + Installing Membranes For Tiled Decks
preservative treated. Refer to ‘Construction Timbers in Queensland’ for suitability www.daff.qld.gov.au.
Preservative treatment for posts in the ground and framing on the ground, shall be to hazard level H5. Preservative treatment for framing more than 150 mm above ground should be H3.
• adequate ventilation
• access for future maintenance and termite control.
• constructed from naturally termite-resistant timbers, in accordance with Appendix C in AS 39660.1, or
• constructed from preservative-treated timber in accordance to Appendix D of AS 3660.1; or
• have a termite barrier to protect the primary building elements installed in accordance with AS 3660.1.
Primary building elements include framing members, floor (decking boards), stairways and ramps, i.e. elements that take part of the building load. Where installation of a termite barrier according to AS 3660.1 is chosen as the method to provide protection, AS 3660.1 requires attachments to buildings, such as decks, to be separated at least 25 mm from the building. Where this can’t be achieved, the termite barrier must be extended to include the deck.
Termite protection can be achieved by placing all posts that support the deck framing on galvanised metal stirrups that have at least 75 mm clearance above the finished ground level:
fasteners are not suitable due to early breakdown of the plating.
Footings for supporting posts are usually designed in two ways. The most common method is concrete footings with galvanised stirrups embedded or fixed in the footings to support the posts. An alternative method is to support the deck post by embedding the post directly into the concrete footing. When this method is used, care is required to use no-fines concrete, have adequate concrete under the post and slope the top of concrete footing away from the post.
The design of footings is outlined in AS 2870 or AS 1684. Usually, the soil classification and expected loads on the deck are required to be known. Decks designed to AS 2870 and AS 1684 are for decks used for housing with average loads and ground conditions. If these conditions are not met (e.g. the deck needs to support a spa or the deck is to be tiled), the design needs to be considered by a structural engineer.
As shown above, posts are usually connected to concrete footings via a stirrup. They are generally preservative-treated softwood (H3 hazard level) or natural above-ground durability Class 1 or 2 timber species.
The span tables within AS 1684 have the required timber sizes for posts (that table is available here). These are dependent on the deck area, roof area (if any), post height and stress grade of the timber selected. Common cross-sectional sizes for posts vary, but usually start at 88 mm and upwards. Minimum sizes for posts are also governed by the distance between the ground and the underside of the bearers. The maximum height of a deck above the ground for a given post dimension is 15 times the face width of the post.
Deck posts need to be braced and AS 1684 has various bracing methods. These methods are either cross bracing between posts or as a cantilever timber stump.
Be safe. If there appears to be anything suspicious about the stability of a deck or balcony, avoid the area, and get the structure inspected by an expert. An expert can help to diagnose a problem and provide advice on fixing the problem.
All decks and balconies:
- Check that the structure is properly fixed to the main building. Use a pushing and pulling action on the main supporting beams or joist to check for signs of movement.
- Think about the number of people and objects on a deck or balcony. Large loads placed on a deck regularly or on special occasions may exceed the load that the deck or balcony was designed to hold.
- Think about the safety of children and visitors. Do not let people climb on the balustrades or handrails of decks. They may not be designed to withstand that load and may lead to falls from elevated heights, resulting in serious injury or death.
- Check for signs of rot, corrosion, looseness or instability.
- Stairs, handrails and balustrades should be securely fastened at all points. Pay particular attention to balustrades that are fixed to the balcony’s top surface and not fixed directly to the main supporting structure.
- Look for signs of sagging or loss of tightness where wire balustrading has been used.
- Check the timber for signs of decay, rot or insect attack. For example, is the timber spongy when probed with a sharp object?
- Look for signs of bending, warping, sagging and splitting. Pay close attention to beams that span long distances without any supporting posts and columns.
- Check to see if the timber needs a reapplication of stains, oils or paints, remembering different timbers may need different treatment.
- Check bearers and joists are adequately supported.
- Check all connections for signs of deterioration, such as beam to post connections, and for any loose or rusting fixings.
- Check for loose decking boards or flooring.
- Look out for signs of deflection or leaning.
- Check for the presence of spalling, where chunks of concrete flake off or crack.
- Examine the underside and edge of the balcony for rust stains or exposed steel reinforcing.
Installing A Membrane For A Tiled Deck
Waterproof decks and balconies are defective if the waterproofing system is not installed in accordance with the manufacturer’s installation requirements.
Decks and balcony freeboard outside windows and doors: Waterproof decks and balconies are defective if they do not have a drainage system sufficient to withstand wind-driven water surging from the deck or balcony that complies with the Building Code of Australia and AS 4654.2.
Ponding on waterproof decks and balconies Waterproof decks and balconies are defective if water ponds (with the exception of residual water remaining due to surface tension) or does not drain to the outer edge or a stormwater inlet.
Decks and balconies that are required to be waterproofed are defective if they are not provided with adequate drainage and provision for overflow.
Prior to installing the membrane the Tiler will check the edges to ensure they're square and as sharp as they should be and will provide the correct drainage and where, after membrane installation, water may pool and adjust that surface tension.
A protective barrier to prevent accidental falls is usually comprised of handrails, infill and posts that support it. A balustrade may be made from many materials including timber, metal, glass etc.
A beam supported by a wall, piers or posts that in turn supports joists or other framing.
A covering of a frame that provides protection from the weather and is usually not load-bearing.
A horizontal framing member that is supported on or by bearers, ledgers or other structural members that in turn supports floor or ceiling linings such as decking boards.
A member that is attached to a house frame. It is designed to support a deck and transfers the weight of the deck to the house foundation.
A structural component, such as a beam or column, or part of an assembled structural component.
Products And Tools To Help You Get It Done
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Trigger with variable speed control by dial.
Spear & Jackson Box Level Pack: $49.00
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Stanley 57 Pce Screwdriver Set: $25.00
• Standard & Phillips™ head screwdrivers. • Multi-bit screwdriver & assorted bits. • 1/4" drive sockets (Metric/AF).
Stanley Fatmax 8m Tape Measure: $27.90
• 8m x 32mm or 8m/26' x 32mm.
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Johnson Brothers Mitre 10 Trade Centre at Mona Vale - everything you need under one roof.
Johnson Brothers Mitre 10 New Store
73 Bassett Street
Mona Vale - Online Store: Jbhmv.Com.Au
Products advice is available from the trained friendly staff at Narrabeen, Mona Vale and Avalon Johnson Brothers Mitre 10.
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