I found this thread on Rightsnet
www.rightsnet.org.uk/Forums/viewthread/20204/ The gist of it seems to be that the reference in Schedule 5, paragraph 6 of the UC regs
www.legislation.gov.uk/uksi/2013/376/schedule/5 to "any owner-occupier who immediately before the commencement of an award of universal credit is entitled to an employment and support allowance" means New-Style ESA as a result of the general interpretation provisions at reg. 2, so if the claimant was receiving New-Style ESA rather than CB ESA in the month BEFORE they are migrated to UC, the time for which they were receiving New-Style ESA will count towards the 9-month period to qualify to claim service charges as an owner-occupier.
It also says that the CPAG handbook (not sure what that is) suggests that if the claimant is already receiving the service charges as part of their IR-ESA, that entitlement transfers to UC without needing to wait at all, regardless of how long they were receiving the service charges. This seems to be confirmed by Regulation 29 of the The Universal Credit (Transitional Provisions) Regulations 2014
www.legislation.gov.uk/uksi/2014/1230/regulation/29 It's a bit worrying that in paragraph 18(2)(c) of Schedule 6 of The Employment and Support Allowance Regulations 2008
www.legislation.gov.uk/uksi/2008/794/schedule/6/made it seems to say that any charges for repairs and improvements will be deducted from the eligible housing costs under ESA. As far as I can tell, this isn't true under UC and any charges which an owner-occupier is required to pay as a condition of occupying the property are eligible, but I need to be sure about that.