Barrett also described water coming up through the floor plate suggesting that there was damage to the bottom of the ship from the berg's ice shelf.
Further more, a first class passenger said the their cabin was flooding from water coming up through the sink plumbing which was also connected to the bottom of the ship.
Water did not spill over from one boiler room into the next. This is a nice but wrong explanation in the movies. Boiler Room No. 5 was filling already from the damage on the starboard side coal bunker. Leading Stoker Barrettt who was in BR 5 gave the time he left as about 1.10 a.m. when the BR started to flood which was more the failure of a coal bunker door which hold the water back in the coal bunker and was not designed to withstand such water pressure.
Barrett used the escape ladder which lead to the port side of E Deck and he was clear that water did not spill over.
The difficulty of making the uptakes watertight was one of the reasons given for not continuing them further up.
I seem to remember that one of the firemen said the water came in from above, either a bulkhead collapsing (unlikely as it was made to resist the maximum height of water) or via one of the openings above.
There was no plan to make the "uptakes" watertight. There high of the bulkheads were directed by the BOT.
I do not know of anyone mentioned it. Maybe you can share it if you find it.