I'm currently doing a loft conversion at a liveable spec. Beams are in incl ridge 2 at 205 and ridge at 152. roof is 3m centre top inside pitch and each side pitch length is 4.5m. Inside of loft is 4.8 m side to side ( beams run along this length) and front to back is 7m. The bottom steels are set to take a 4.8 8x3 C24 at 400 centres (mid ******* council requested due to length of span. I am bolting with m12 coach bolts washer plates spring washer nuts and sprocket spikes 3.6 6x2 C24 timber butted over ridge steel and continuing down 300 past the 6x2 C24 upright off each side steel beam. Also 6x2 brace horizontal 1cm below ridge beam. These are all running at 600 centres (8 of as 4.8m distance). The roof outer is felt and Marley wavey concrete tile. Finally my question is are the 6x4 c24 sistered beams to roof sufficient at 600 centres. Council did not know and requested 400 centres which is far more effort to complete. My engineer reports was only for steels and joints. Can anyone advise what they feel is correct before I try and look for an engineer to show on paper to council what is ok here. I have overkilled the ask detail hopefully to explain the setup.