Tie downs is a generic term used to describe various methods of securing a structure in position to prevent potential storm damage. This can range from the most rudimentary brackets such as triple grips designed to secure your patio roof rafters to a support beam through to cyclone rods which are designed to anchor your roof structure through your wall frames to the concrete footings below. In days gone by the installation of tie down brackets was very basic with the majority of the house components simply secured with nails. When inspecting some of the old Brisbane colonial houses I am often amazed that they haven’t lost a roof or been blown apart during significant storm periods.
Whilst it is not a requirement to continually upgrade to the current building code there are some triggers during a renovation process that would necessitate upgrading being undertaken. For example, under current building guidelines if you were to completely remove the old galvanised iron roof sheeting from a house and replace it with new Colorbond roof sheeting the requirement is to undertake some upgrading of the original roof structure to minimise the risk of potential storm damage. This would involve the installation of tie down strapping to the ends of the rafters to try and prevent wind uplift etc. It should however be noted that this can usually only be undertaken when the roof sheeting has been removed. It is often too difficult to install the tie down strapping to the end of the rafters when the roof sheeting is secured. So when you next get your roof sheeting replaced ensure that the quote includes some degree of roof upgrading.
On older generation houses you will notice that the tie down brackets that secure the house to the stumps are relatively intermittent and predominantly only installed to the external perimeter of the house. Modern construction requires tie down brackets or adequate fixings from the posts directly to the house bearers. Having your house adequately secured to the supporting stumps is imperative unless you want to take off like the Wizard of Oz house during a cyclone.
Generally speaking cyclone rods are designed to secure the very top wall plate (top of your wall frame) to a concrete slab or to the supporting bearer structure under your house and is in turn secured to your stumps. These cyclone rods are specifically designed to minimise the risk of your house blowing apart during extreme wind conditions. It is however imperative that the cyclone rods are correctly installed. On a recent Brisbane building inspection in Mount Cotton the carpenters had secured the cyclone rods to timber blocking that was glued to the underside of the chipboard flooring. Subsequently given extreme conditions the timber blocking would have simply pulled through the floor structure.
Rafter Tie Downs
When constructing a patio roof for example it is common to use various types of rafter tie downs (metal brackets) such as triple grips or rafter hangers. These are a very effective method that adequately secures rafters in position. It is however imperative that adequate nails are used to secure the rafters in position. Generally speaking a minimum of four nails to either side of a joist/rafter bracket is required.
So the next time you’re talking to a tradie regarding some alterations or your building inspector, when he mentions tie downs you will know exactly what he’s referring to.