When considering the job that our prefabricated trusses do and the ease of their installation it can be easy to overlook the important responsibility that bracing undertakes. Bracing ensures that trussed rafters maintain a rigid, secure and stable roof structure. If the bracing provided is not used entirely, positioned incorrectly or not securely fixed, it can result in a distortion or failure of individual trusses or in a worst case scenario - the whole roof so it’s safe to say they’re pretty important!
Bracing can be used temporarily for safety whilst erecting the trusses, for stability on a permanent basis (to keep the trusses in place) or to combat wind where bracing can transmit wind forces to suitable load bearing walls.
The Timber We Use For Bracing
When it comes to stability bracing we supply rough sawn timber which is 100 x 22mm in size. This is in line with requirements stated by Eurocode and is perfect for the job it needs to do. For the trusses themselves we use TR26 stress graded timber which is kiln dried and planed all round.
The Main Types Of Stability Bracing That We Use At MRT
Regardless of the type, it’s important to note that any stability bracing is always nailed to the underside of the rafter so that you have a smooth surface to lay your roof tile of choice onto.
Longitudinal Bracing- These run continuously straight through parallel trusses along the entire length of the building. Where necessary, bracing is lap jointed over at least 2 trusses. A top tip of ours is to ensure that you leave a 25mm gap between the end of the longitudinal bracing and the rafter so that the diagonal brace can be secured.
Rafter Diagonal Bracing- Extends the full length of the truss from the apex (top of the truss) to the wallplate (not from the overhang/ soffit) and must have firm contact with the wallplate at approximately 45 degrees to the ridge (the line formed by the truss apexes).
This is especially important to install with attic and raised tie trussed roofs. It should NOT be omitted in any circumstance. You will need to batten out the room and skeiling areas to allow for the fixing of the plasterboard.
If you’re in Scotland, sarking is fixed directly to the top of the roof trusses meaning the rafter diagonal bracing may be omitted. If you’re elsewhere in the UK, please inform your designer as this adds extra loading onto the trusses which needs to be accounted for.
Chevron Bracing - On occasions where this type of bracing is needed it usually covers a minimum of three truss webs (half way to the apex of the truss) at approximately a 45 degree angle.
Ceiling Bracing- This is only specified on our designs when no plasterboard is directly fixed to the underside of the trusses.
Bracing Layouts For Different Types Of Trusses
Although there are three main types of bracing, their layouts (the way we set them out) can vary depending on a number of factors such as the size/ span of the truss, the type of truss and the number of webs in the truss. We could go on but we think you catch our drift!
I guess you could say that our main message here is that all of the bracing that we supply with your trusses should be USED – every last timber! No waste do you hear us? The reason for this is that the bracing forms a significant part of the calculations that we provide to assure the integrity of your roof design. These are the same calculations that you can use towards passing building regulations so it really is vital that all bracing is installed to coincide with our guidelines.
You could be reading this and have just received an order of trusses from us or you may be soon expecting your delivery. Either way, if you need help with bracing then we have a variety of installation guides to walk you through properly bracing your roof to suit whichever type of truss you have.
To be more specific, we can give you a quick and easy-to-follow guide for the following truss types and bracing layouts:
We hope this article helped you to decipher your way through the complexity and importance of bracing when it comes to installing your trusses in a structurally sound manner! The documents linked above can be used as an additional guide but don’t forget – you will always be provided with a bracing plan unique to your project that we have designed for you. It will look something like this:
We will also provide you with each truss profile showing the placement of each type of bracing too which will look like this:
In mainland UK on trussed rafters and engineering joists.
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