trussed roof support for extension

[archie84]

hi. im gathering ideas for a extension were hoping to do. its on a dormer bunglo with attic trusses to the second floor. there at 600 centres with two areas doubled up for 1600 dormer windows at the front of the house.
the plan is to extend the upstairs floor to the wall plate giving us roughly around 1200 more in the rooms. remove the pitch ceelings and build a timbre framed flat dormer roof straight up off the wall plate to ceeling hight and clad the outside.
i assume that the only way the rest of the roof will stay up is if we run an rsj from one gable to the other.

something similar to this photo.

is there another way round this?

 

[bobsuerita]

It can be done the problem with attic trusses is there design the rafters are over sized to carry the floor joists through the uprights with gangnail plates so removing rafters for dormer would need work to the floor As well get a engineer

 

[archie84]

this photo is almost identical to what we have but without the uprights from the ceeling to the roof joists. the uprights that we have are put in afterwards and form no part of the integrity of the ceeling.

 

[bobsuerita]

if thats the truss design you have then your fine with what your intending without joist problems and yes you wil need a ridge steel
but an engineer will sort all that