Loft advice needed

[martlewis]

About to add extra insulation to the loft so while I'm at it I'm hoping to lay some flooring and build some storage shelves. It's a completely open space but with a large joist laid across the the top of other joists diagonally corner to corner. Any idea why? Was going to increase space for insulation by laying larger fists next to the existing ones but this is causing a problem. Any thoughts?

 

[Doug B]

The timber is usually attached to the joists below, there are several ways that this is done but it is there to give rigidity to the joists.

 

[blackrodd]

You don't say how old the building/roof is, or if its a cut or truss roof.
Some pics would be good.

Regards Rodders