How can I find out if a thick and solid internal wall can be removed without floor above collapsing?

This sounds really dangerous. Keep away from it. Call a structural engineer immediately. I know of a very similar situation where the wall fell through the floor and ceiling below and ended up as a huge pile in the lounge/kitchen. Fortunately no one was in the house at the time .. and they probably would not be there now had they been underneath the wall. However there may be a perfectly feasible solution which is supporting things. Get on the phone... now!

I totally agree with the other builder. Get an engineer to look at it immediately it sounds dangerous.

This is very dangerous and must be assessed by a structural engineer as soon as possible. Your life is at stake and your home too. Whilst there is a cost involved make sure you are speaking with a member of the Institute of Structural Engineers and is someone who has the qualifications to make the right assessment and give you the correct advice. Please don't delay. If you don't know who to call we can give you some suggestions of qualified firms/individuals if that would help. If so do get in touch. We are here to help.

Hi, The best option is to ask a structural engineer. There could be many things. Is the solid wall being supported on a beam? It should be a steel beam or a lintel underneath, depending on the span of the opening below. Regarding the first floor wall that has been replaced with a stud wall, you need to know how was the stud wall built. Stud walls can also be load-bearing depending mostly in the distance between studs, the section of the studs, if ply has been applied to both sides, etc. Two things are clear: 1. You cannot remove a wall without knowing if it is load-bearing or not. 2. If the first-floor wall is supported on a beam or not. If the answer is not, that is a dangerous situation.