Sistering a joist - a few questions

Hi,

I want to reinforce an existing timber beam by sistering it to another piece of timber. Having searched the forum, and elsewhere online, i still have a few questions.

First, I can only access the existing beam from one side. So:

1. Is it OK to reinforce the existing beam from just one side?

2. Assuming i reinforce using timber, can it be fixed with coach screws, with timber connectors between the two beams?

3. If so, how far should the screws penetrate into the existing joist?

4. I seem to recall that the screws shouldn't be in the middle of the beam, but closer to one edge. The top or the bottom edge?

More generally:

5. How important is it to have the sistered timber also bear on the wall? Opinion on this seems to differ. It might be possible to do, but will be much more work that having the new timber simply stop flush with the wall.....

For background, based on timber-span loads, this is probably not strictly necessary, but i am keen on a "belt-and-braces" approach. Specifically, the current joist measures 65mm x 95mm and spans a distance of almost 4 metres. Crucially, along its length the joist is supported by four vertical beams, each measuring roughly 100mm square and resting on the solid floor below. Bearing onto the main joist are the first-floor floor-bearing joists, 450 mm apart.

I want to remove one of the vertical timbers that provide intermediate support, creating an unsupported span of 1650mm.

Apologies for writing so much - feedback very welcome!!!

Crawf