We need to have installed a new physical roof on our home due to the short life of the existing flat roofs that are leaking. Since the kitchen roof is flat and actually drains towards a 2nd floor room, we decided to replace it now and also expand the kitchen by 5 feet into an existing storage...

I have an older home, with a low basement, I want to increase the ceiling height as much as possible. the area is about 10'w x 12'l, it presently has 2 X 8 wood joist. how can I sister , or use metal angle or channel, so I can reduce the size of the existing joist to allow more head room?