Our customers often ask what are the most important things to know when erecting trusses for their homes. It’s a fair question because truss building is a specialised craft that requires expert planning and production. While you can purchase your own gusset plate* (*the metal roof plate) from a local DIY store, let’s just say we would highly recommend leaving the whole process to the professional craftsmen as a poorly erected truss is dangerous. That being said, if you’re in the market and want to know what’s going on before you swipe your credit card for the final payment, here are the top three things you need to know about trusses.
What’s the quality of the wood?
Like anything in life, a product is only as good as the materials used to create it – the same is true for trusses. While the price might affect what quality and thickness of wood you choose, try to budget so you can get the thickest gauge of timber. If you’re really on a shoestring budget, insist the best quality is used for the top and bottom chords, as these beams will take most of the strain – in “non-building jargon’” these are the frame. All timber used must be SABS approved and graded.
Check to see if beams are straight, and if they are bent make sure they flatten out when under weight. This means you need to make sure the concave surface is facing down, otherwise, it’ll bend more under the roof’s weight. However, you really want flat timber.
The gullets should also be looked at before letting the builders lift their hammers. While it is highly unlikely a contractor would use ungalvanized parts, we’d recommend double checking. There is no specific tip for telling the difference between galvanised and zinc plated pieces, the metal does take on a marble look when treated properly – also, it shouldn’t rust. So, if there’s any hint of rust, it’s not treated correctly.
How is the final product put together?
Now that you’ve inspected the parts, it’s time for the contractors to assemble the pieces. Make sure that you’ve gone through the process of having the dimensions set-out by a professional roof design program; we use Roofcon licenced software. All our Truss Members are cut with an imported SPIDA COC machine for the most accurate cuts possible.
Once the crew have measured, cut, and assembled the trusses, you’ll need to make sure that it’s been put together correctly. Be wary of large gaps between chord surfaces. If there are noticeable spaces between timbers, don’t use them. It’s frowned upon to use nails to fasten most woodworking jobs together, but for trusses it’s ok. If you’re up to the challenge, you can try and pry a nail from the timber with a hammer for extra quality control – if it does slide out you have a problem, but that’s very unlikely.
Grab a measuring tape and your truss plan, and double check the measurements. While the expression goes, “Measure twice, cut once”, it should be, “Measure constantly like a paranoid person – cut – and then measure again”. Make sure to check that the trusses are the correct size before they are shipped out of the yard. Also, remember to check the pitch, as cutting timber at an angle is a task that can easily result in a mistake. The degree angle should be on the plans and most smartphones come with a leveller app (please note, these aren’t very accurate). While this might seem excessive, remember that once the trusses leave the yard you won’t be able to adjust them on site.
Watch how they are mounted
Let’s make this clear. No one should ever cut pieces off a truss. If they do, the structural integrity of the truss will be compromised. Erecting a truss is a labour intensive job, and lifting them into place should be done by an experienced carpenter team or even a crane or forklift, dependant on the size. Keep an eye out for whether the truss is supported at its joints when being moved into place. Remember, the more extensive the span you’re covering, the more people you’ll need to reduce stress on the structure.
Once it’s in place make sure that it is anchored onto the load-bearing walls properly, these aren’t always the outside walls, ask an architect to help you check.
But if you’re ever in doubt, make sure to call in a professional for a second opinion.