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Looking to put insulation, plasterboards on the garage ceiling and some down lighters,
Not a massive amount of heavy stuff is currently stored there (primarily boxes etc).
There are 5 joists, joist size approx 6m X 7.5cm x 4cm, distance apart from joists approx 56cm , garage size wall to wall 5.6 X 2.6)

I would put loft boards that spam across 2 joists and meet in the middle of the centre joist (2 loft boards across)

There are two pieces timber that travel laterally at the top and bottom of the garage and was wondering if they serve a purpose or they can be removed (it would be harder to board it along with them in place and in my eyes the loft boards that would be screwed there probably serve the same purpose?

Pictures of diagonal truss in question below :

Bottom:

Top:

If something needs to be in place what is an alternative to have that doesn’t travel laterally i.e (can I put a horizontal piece of timber across like the ones in the middle

In terms of reinforcement:

Initially I was going to sister the joints but they are too long and cant find made to order so now would add herringbone struts

pic below:

and would also add joist hangers

Finally any other recommendations would be very welcome