Hanging heavy bag from Garage roof

[JP_]

Surely the joist hangers would go onto the wall plates in the event that there isn't sufficient space to get them in atop the wall plates

yes, that is what I meant - you said it better!

 

[JP_]

I don't quite understand you. Are you saying get some very long joists in to go across the rafters from left side of the garage to the right and fix them down then fix the bracket to the top of the joists? and if not feasible use smaller pieces and joist hangers?

Yes, long joists, like the bottom ones there now, but it will be much bigger and not support anything above, just for the bag. I don't know how to calculate the size, so just go big!

 

[Deleted member 174758]

Be doubly amazed then because they are also designed to take a snow load of 60kg/m² which is similar to tile loads

A quote from a technical paper (called "The Seven Deadly Sins of Trussed Rafter Construction") on Fink truss roofs: "Typically the bottom chord of a truss is designed for a superimposed load of 0.25 kN/m2 which the author often refers to as empty cardboard boxes loading."

So whilst the top of a Fink truss frame is designed specifically to carry the load imposed by the roof cladding, snow and wind, the bottom chord is designed to carry only a thin skin of plasterboard and little more. Not surprising when you consider that the bottom chords on this roof are 75 x 38mm (3 x 1.5in) on about a 4.1m (13.4ft) span (based on those blocks being 340mm long blocks)

There are exceptions to this, where the builder has specified that the bottom chord be capable of supporting a load, but that does need to be specified at time of manufacture

 

[JP_]

Makes sense - the bottom bit is only really there to stop the top bits going sideways.
I had my extension done with trusses (7m wide, 7m long) and the smaller builder did walk around on them, but said it was still a bit hairy!
They ended up putting in a solid internal wall so the who thing was also supported on that - as I asked them to board it for storage.
They don't make houses like they used to!

 

[Deleted member 174758]

If you ever see a truck delivering them you'll maybe notice that they are invariably carried apex downwards because as one SE put it "Sort of like an eggshell they are stronger in one direction". The preference is also to crane them in place these days rather than manually handling (at least where I've worked) as doing that means there is less chance of damaging the all important bottom chord or the nailer plates

 

[Dereekoo]

A quote from a technical paper (called "The Seven Deadly Sins of Trussed Rafter Construction") on Fink truss roofs: "Typically the bottom chord of a truss is designed for a superimposed load of 0.25 kN/m2 which the author often refers to as empty cardboard boxes loading."

So whilst the top of a Fink truss frame is designed specifically to carry the load imposed by the roof cladding, snow and wind, the bottom chord is designed to carry only a thin skin of plasterboard and little more. Not surprising when you consider that the bottom chords on this roof are 75 x 38mm (3 x 1.5in) on about a 4.1m (13.4ft) span (based on those blocks being 340mm long blocks)

There are exceptions to this, where the builder has specified that the bottom chord be capable of supporting a load, but that does need to be specified at time of manufacture

I'm thinking those blocks are 440 long so span nearer 5m?

 

[withers]

Yes, long joists, like the bottom ones there now, but it will be much bigger and not support anything above, just for the bag. I don't know how to calculate the size, so just go big!

Now I think I know what you both mean, thick heavy duty joists NOT rafters fixed to the top of the piece of wood resting across the top of the wall above the window running in parallel to current rafters.

And if the joists do not fit, use joist hangers attached to the wall

The fixing holding up the bag is fixed to the joists hanging down, any impact from the bag is sent into the joists and at most directly into the wall and not the roof structure

I have created a diagram of how I imagine it, this is a view if you were looking at it from the ceiling looking down, let me know if it makes sense or not.

 

[withers]

I'm thinking those blocks are 440 long so span nearer 5m?

If you are referring to the rafters in my garage yes the garage is just shy of 6M long (back of garage to garage door)

Just to add they appear to be extended further down using those metal plates that hold the rafters together

 

[Dereekoo]

If you are referring to the rafters in my garage yes the garage is just shy of 6M long (back of garage to garage door)

Just to add they appear to be extended further down using those metal plates that hold the rafters together

Completey disorientated, what is width of garage?

 

[withers]

Completey disorientated, what is width of garage?

Actually just got floor plans up the garage 2.59m wide by 5.39m long

So the rafters are very likely 5m total.