When are you planning to start the work? The changes to Part F are covered by transitional provisions which are:

i. Where building work has started before 1 October 2010, the work may continue
as if the amendments in the Amendment Regulations had not been made.

ii. Where a contract for work has been agreed and the all the building work would
fall within the types of work set out in Schedule 2A or Schedule 2B to the
Building Regulations, the work may be carried out as if the amendments in the
Amendment Regulations had not been made provided that the work begins
before 6 April 2011.

iii. Where a building notice, an initial notice, a plans certificate and amendment
notice or a public body’s notice has been given, or full plans submitted, before 1
October 2010, the work may be carried out as if the amendments in the
Amendment Regulations had not been made provided that the work begins
before 1 October 2011.

The current Part F is here http://www.planningportal.gov.uk/uploads/br/BR_PDF_ADF_2006.pdf

Addition of a habitable room to an existing dwelling is covered in 3.8 - 3.10.

You need to figure out which of those categories your extension comes under and then follow the document back to the relevant paragraphs to find out what the specified ventilation requirements are. Once you have done that you will then need to show how your design meets those requirements.