have a look at a concur on sovereign chemicals site. they fit in the loft and work opposite way to a dehumidifier by pushing air in and moisture out. find these work far better
something is wrong with that spec you dont inject when useing delta membrain. the membrain is basicaly a plastic sheet fixed to the wall and plasterd on but it needs a channel in the floor to drain any water away. take a look on sovereign chemicals web site
was the porch part of the original build or added at a later date. was it actualy built by the house builder. is it on the original plan. if not it may not have needed planing permision (ie) no building regs
if you have a welder put a dab of weld on screw head and build it up till you can get molegrips on.i found that it did not need to much as the heat had freed it