How do I add a joist?

[justanotherguy]

I'm putting in a megaflo tank, which will be 300kg when full. Structural engineer advised putting in a few extra joists.

I cut one to length, and even diagonally between two existing joists it won't go in.

The only option I think is to make a single joist out of two shorter joists that overlap, and are then bolted.

Question is, to support a ceiling, and a moderate amount of attic storage (boarded out), how much do I need to overlap?

Or am I going about this completely the wrong way?

The existing joists are 4.17m at 0.3m centres, one end on a wall plate, the other resting on outside wall.

 

[Chukka63]

can you not use joist hangers which are cut into each wall.or use 1 joist hang and just cut one onto a supporting wall??

 

[justanotherguy]

can you not use joist hangers which are cut into each wall.or use 1 joist hang and just cut one onto a supporting wall??

I don't think so, not if I want them to be level with the rest of the joists.

If I did, I'd have to cut into the wall plate, which isn't really an option.

Plus I can't come in from above, as the cylinder is already in place.

 

[Chukka63]

one end on a wall plate, the other resting on outside wall.

not sure why u cant fit 1 joist hanger into the outside wall and cut an angle (presumably) on the other end to match roof pitch.slide joist onto wall plate and locate in hanger.

hard to picture with no photos or being on site

 

[justanotherguy]

This is the problem - I can't get it on to the wall plate from below.

I've cut it to the right length, but that means the wall plate is in the way, unless I drop it down from above, which I can't, because the tank is already in place.