DIYjake

Thanks for the input all. I've told the likely builder that I want to stick with the drawing for peice of mind more than anything, I don't fancy this biting me down the line by not going to drawing Sorry, the joists are 150x50. No idea why I put x100.

I have a dormer bungalow that was built in 1969. I've had structural drawings made up to extend the front and rear dormers out as far as possible. The current joists are 100x150 at 400 centers. The drawings specify for the joists to be 75x195 and raised 25mm and to be doubled up below the bathroom. The longest span is 4584mm. One of the carpenters/builders has said that doubling up the current joists will be substantial enough and has been in contact with building control who seem to agree but haven't yet visited I have a gut feeling that it should be done to drawing. Any thoughts?