Loft Conversion Advice

Apodemus

I appreciate that the OP doesn't want to discuss the previous conversion but just in case anyone else refers to this thread I think it is worth mentioning that there is a big difference between plans having been passed by Building Control and there being a Completion Certificate in place!

kellym5, your solicitors should have requested a copy of the completion certificate when you bought the property and perhaps this is what you have?  Otherwise, in the absence of the completion Certificate being available on the Portal, then the only recourse is to ask the Building Control office to search their archived records.  

I would think that unless there is a completion certificate in place indicating that the original conversion was for a habitable space rather than storage, then the whole job will be considered as a new application and require all elements to meet current standards.

But we are all guessing - the only person who can give you a definitive answer is the Building Control Officer who is going to sign-off the plans for the new stairs and dormer.  Either give them a ring in advance, or submit your plans for just the two new elements and let them respond - you'll soon know if they require additional work.  

Presumably the dormer will also require Planning Permission?

Doozergirl

Most dormers are permitted development but that obviously needs checking before go ahead.