Are my loft joists strong enough?

[Ricardus]

Forgive me if this has been asked before, but I couldn't find it on a brief search.

I'd like to board & insulate my loft with a view to a conversion in the (dim distant lottery winning) future, but I'm worried the joists aren't man enough for the job.

My loft has 100mm x 35mm wide joists running front-to-back with 570mm between the joists. The roof has W shaped trusses made out of the same size wood.
I'm no builder but it looks a bit weedy to me, although until last week, there was a 3'x2' cold water tank sitting right in the middle on a timber frame spread across three of the joists.

 

[masona]

I take it you have gang nail trusses, if so, read here and scroll down to section 3:2 or page 52

 

[Ricardus]

I take it you have gang nail trusses, if so, read here and scroll down to section 3:2 or page 52

Yep, fig 68 with water tank on Fink Trusses is exactly what I had until last week when the new combi was installed.

But does this mean my loft beams can take a decent load or not?

 

[masona]

Can you do a photo or drawing?