plate

Hi All, I have a first floor extension similar to the one in the photo below, but about half the span (~3.3m span with two columns). The photo shows that they used a steel beam with a plate welded to the underside, but installed the beam to carry the outer leaf rather than the inner one...

I'm arranging a washing machine cable to exit a bathroom, thru an interior brick wall, to a FCU on the far side. Outside zone 2. Is there a 'pass tru' wall plate available for the bathroom side, maybe with a single gang back box, to tidy it up. Rather than just having the washing machine cable...

I need to put a stud wall on an old conc. car port floor that will have a 1200 membrane laid over it. Are a few holes in the membrane considered to be that much of an issue? I see youtube stud wall videos but nothing showing a sole plate being fixed down with a membrane below it? Thanks, Dain