Loft Boarding advice

[Kevlav]

Hi,

I am looking to board my loft for storage but suspect the ceiling joists might sag with the additional weight. I was thinking of building a new floor frame with bigger joists resting on supporting walls so the existing ceiling joists where not taking any additional weight but unfortunately the upstairs walls that the existing ceiling joists rest on do not go all the way to the ground (build across 1st floor joists). Looking around on different loft boarding companies sites I see a number suggesting building a frame and hanging it from the roof purlins like below pics. My question is would this method of hanging from the purlins for additional support be adequate? I could also support the party wall end of the floating frame with joist hangers fixed to the wall.

 

[Leofric]

Depends on the size and span of the purlins ,loadings etc - one for a structural engineer isn't it ?

 

[cdbe]

I built a similar platform in my loft but as I had a load bearing spine wall it was only the 2 outer ends hanging off the purlins, exactly as in the diagram above. This was only a temporary measure (mainly to raise the floor above the insulation and has now been replaced by new loft floor joists) and I kept all the heavy stuff over the central wall.
In your situation, if I could get them in there and I had 2 gables, I'd do as you suggest and joist hang some timbers between the walls. I would also say that (within reason) it doesn't matter too much about the size of them as you don't need to worry to much about deflection. Mine was something ridiculous like this and although temporary did the job, albeit with a bit of bounce!

Looking at my scribble above I would hazard an unqualified guess and say that if you only hung off the purlins at the ends close to the gables rather than the centre then there's practically no additional loading on the purlin?

 

[Kevlav]

After doing a bit more digging about in the loft I have come up with what I think may be a better solution. This would be built above the existing ceiling joists and none structural walls (red) so nothing would be touching them.

Please excuse my art work hopefully it illustrates what im looking at doing.