The proposal, which is known as 'virtual unbundling', was first announced in March this year and will see UK ISPs using BT's infrastructure to offer their own superfast net connections.
Ofcom also said BT must offer other ISPs access to its underground ducts and telegraph poles to ensure they can "roll-out super-fast broadband to areas where BT does not plan to deploy its fibre network", and "to target specific areas earlier than BT's roll-out".
However, BT will be allowed to set the prices the ISPs are charged for access to enable a fair rate of return. The telecom giant has been given a deadline of mid-January 2011 to draft a document detailing the available capacity and quality of ducts and poles.
Ofcom said its "decisions" are designed to benefit all UK consumers and recognise that different areas require different solutions when it comes to rolling-out superfast broadband.
"The development of the UK's super-fast broadband future is well underway with the roll-out of services in large parts of the country," said Ofcom's Chief Executive, Ed Richards.
"Today Ofcom has finalised a clear regulatory framework to promote investment, competition and innovation to enable as many consumers as possible to benefit from these exciting new services."
See also: Ofcom to make it easier to switch ISPs