Mail CLG help@epbduk.info It goes through to a team who deal with these kind of queries. I'd expect an official OCEPC is not required in this case, as it's not going up for sale. But if it ever comes up for sale it wil need an RDSAP based EPC :-(

If you go back to the primary legislation - both the EU Directive and the UK Statutory Instruments you'll find that the purpose of EPC has been for the current owner to provide a potential purchaser / renter with energy performance information. Which makes me think self build will not be included.

Then again - they might want it done so they can gather stats on new builds!

RDSAP is No good for passive houses. I'd have thought the closest to a ISHS is a "commmunal biomass fuelled system". But would need to check the efficiencies first. I don't think RDSAP (or SAP) can handle "solar central heating" yet, and only factors in hot water production based on floor area not actual panel size. A good assessor should work with you and the accreditation scheme to get the balance right. You are allowed to put in stuff that's weird as long as you can justify it e.g. - Cob is not listed as a wall material. And what do you do if there are more than 2 wall construction types - 1800's, 1920 extension, 1970's extension and now a new 2009 extension? In these cases you make justifications on how you've entered the data and contact the accreditation scheme to explain what you're submitting.