I have a 1979 brick and tile two floor semi with 'fink' roof trusses. There are 11 trusses at approx 600mm centres. The trusses are made of 34mm timber with nail plates where the timbers join as well as part way along the joists. Their other dimensions are - rafters 117mm wide - joists 97mm wide - internal 'W' support timbers 58mm wide. The trusses are approx 2.00m from top to bottom. The roof ridge is parallel to the front and back of the house. The internal floor dimensions of the house are approx 7.80m front to back by 5.90m. There are two partition walls on the top floor running parallel to the ridge (i.e. at right angles to the trusses). One is approx 2.40m from the back of the house and the other is 3.60m from the front of the house. I want to knock down and rebuild this second wall so that instead of being 3.60m from the front of the house it is 4.50m from the front of the house. The joists below the partition walls also run parallel to the partition walls. I don't believe that either of these partition walls is load bearing but would appreciate some advice.
They may be still load bearing as the 1st floor joists may be bridged to take any weight but if you can situate the new wall in line with a joist then you should be ok. You may need to support the roof until the wall is back in place, you should consult a joiner first.