Roof truss bracing and strapping

[stuart45]

Roofs pitched with Fink trusses have sometimes suffered racking in the past, but older roofs that have stood the test of time should be OK without the diagonal bracing that was later introduced.
Ronny, it's probably that the timbers on a cut roof are thicker than the flimsy Finks, and they are also attached to the ridge board. Larger roofs are also likely to have purlins etc to add stability.

 

[pinenot]

Bye and large modern lightweight trussed roofs are built without a ridge board, cut or stick built roofs are braced via the ridge board and sometimes incorporate purlins.
Not all trussed roofs employ cross bracing and or wind bracing, the sarking providing all the bracing required...pinenot

 

[stuart45]

Not all trussed roofs employ cross bracing and or wind bracing, the sarking providing all the bracing required...pinenot

Sarking isn't normally used in England, but I'm guessing it's part of the Regs in Scotland?

 

[noseall]

The raised tie roof trusses we have just installed have 175 x 50 rafter chords whilst all the rest of the chords are 70 x 50.

Pretty chunky, heavy and braced to bu99ery.

 

[tony1851]

The raised tie roof trusses we have just installed have 175 x 50 rafter chords whilst all the rest of the chords are 70 x 50.

Pretty chunky, heavy and braced to bu99ery.

Do they have those glide shoes where they sit on the wall plate?

 

[pinenot]

Not regs but fairly normal, sarking can mean osb, ply or sawn 3/4" x 9" (just one spec) arch/se can specify differing.

 

[noseall]

The raised tie roof trusses we have just installed have 175 x 50 rafter chords whilst all the rest of the chords are 70 x 50.

Pretty chunky, heavy and braced to bu99ery.

Do they have those glide shoes where they sit on the wall plate?

Yes.

And they have been re-designed - thank goodness!

You once had to put just 1 fixing each side in the slotted part of the shoe, then you were expected to nail into the remaining holes AFTER the weight (roof tiles etc) was added to the roof, to allow for the push. This meant having to contort yourself into the eaves from inside and swing a hammer. Ridiculous.

Now the shoes come with all slotted fixing points, i.e. no single nail holes, so they can all be done prior to covering.

 

[RonnyRaygun]

Roofs pitched with Fink trusses have sometimes suffered racking in the past, but older roofs that have stood the test of time should be OK without the diagonal bracing that was later introduced.
Ronny, it's probably that the timbers on a cut roof are thicker than the flimsy Finks, and they are also attached to the ridge board. Larger roofs are also likely to have purlins etc to add stability.

Yeah, pretty obvious that the ridge board (and purlins if used) will stiffen up the structure nicely, especially once they are bearing onto the walls either side.
I've only ever done one building with a trussed roof and truss design is pretty specialist stuff anyway; beyond the scope of us average Joes!
Sometime you've got to ask a simple question to get an obvious answer...all adds to the knowledge bank!

 

[theoldun]

Sometime you've got to ask a simple question to get an obvious answer...all adds to the knowledge bank!

That answer earns respect Shogun.
Regards oldun

 

[catlad]

Just think Ronny how impressed your fellow accountants will be when you share your new found wisdom

 

[00]

Thanks for all the replies guys

I hadn't planned chevron bracing but my structure is just over 8x5m so perhaps I should.

I'm leaning towards getting an Structural Engineer to advise although I was hoping to avoid it (I had a builder who said they knew what to do as if it would be "standard", so thought it would be easy to find out)

I also want to try to keep the roof space as open as possible so people can still move around up there fairly easily - perhaps a SE can give me guidance on this also..