Building contractors can cut corners, we all know this, whether you’ve heard it through the grapevine or experienced it first-hand. The fact is, if you take short cuts when manufacturing or erecting a roof truss, it’s bound to fail sometime in the future. No one wants to think they could potentially be living under a ticking time-bomb.
While we can’t stress the importance of this enough, it’s vital to have an engineer inspect the final installation, but if you can’t get one to come to the building site, here are some tips on how to spot a truss that’s bound to cause a headache in the future.
Joins That Fit
Most of our chords, webs, and web runners (timber lengths) are cut out utilising an electronic cutting machine that ensures all the lengths are exactly according to plan. But for those who don’t have access to this high-tech machinery, they rely solely on human craftsmanship.
While there are loads of skilled woodworkers in South Africa, the fact is most of the labour force is unskilled. And utilising untrained workers can mean your truss is more susceptible to errors. Take a close look at whether the joins fit, that there aren’t marked gaps in between the joins, that they line up to their surfaces, and that the whole structure is identical to the other trusses.
Surfaces need to be flush, otherwise load bearing areas of the structure will eventually give in and cause chaos in the future.
If you’ve ever wondered what the metal sheet that joins truss lengths together is called, it’s a gusset plate. Gusset plates are the general term, and there are more specific names, but we’ll get there. These are crucial to any truss project. A gusset plate consists of two sides, a flat surface with loads of nails sticking out the other side that you hammer into the timbers to join them together.
These gusset plates should be mounted flat and securely. If the gusset does come too lose in the future, it can mean a catastrophic failure of the entire structure. There are no substitutes for this fitment technique.
An example of someone cutting a corner will be if a contractor decides to sandwich the joins with plywood and screws. This is genuinely a shocking shortcut as this hack has no real structural holding power, and will come loose if not replaced quickly with a proper gusset.
Gusset plates are the glue that keeps trusses together.
This attention to detail should be extended to all joining gusset plates, such as the wall plate, splices (just in case the timber isn’t long enough), and nail plates (usual gussets).
There’s a reason why trusses aren’t built from ply board, chipboard, and dare we say it pallet pine, it’s because those woods are not strong enough. You need dense pine that can take the designed roof weight. If there is a difference between the timbers, it can mean a shortcut or weaker, weathered wood.
Making sure that all the chords have the same timber also means that you can be sure they’ll age at the same rate. That’s if you live long enough to see the need to replace the trusses in your roof.
It’s the details that matter when inspecting a truss. You wouldn’t sit on a chair with exposed nails, cracked legs, or rickety; it’s the same principle when it comes to reviewing a truss.
If there is anything that looks unfinished and poorly done, raise a flag and ask questions. While we believe we’ve seen it all, we’re still surprised by how many ways there are to construct a lousy truss.
Do yourself a favour and call a professional to construct your trusses.