5% VAT Rate Building Services

Hello all, I process the admin for my husbands small building business which is registered for VAT and CIS. He has a new project, where the client believes he meets the criteria for a reduced rate of VAT at 5%. (Converting a single household into 3 independent flats). In practice how does this work?

My husband will buy materials from the builders merchants and pay 20% VAT. In turn my husband will invoice the client for his services and materials. Will he not have to charge 20% VAT on the materials on his invoice to the client (and 5% on his services(time))?

Or should i look at the credits and debits like this?

Purchase building materials from supplier at 20%: DR
HMRC VAT Return Input tax at 20%: CR
Net liability -= zero


Sales invoice to client with 5% VAT: CR
HMRC VAT Return Output tax at 5% VAT: DR
Net liability -= zero

Any help will be most gratefully received.

Thanks,

Clare