Hi - it would be highly unlikely that your builder is not registered for VAT as they limit for supply of services is E35,000. These days it has become increasingly difficult for traders to evade taxes. If a trader works as a sub-contractor to another builder or holds a credit account with a builder supplier, then their name will cross an inspector's desk at some point. If your builder holds a bank account, the branch manager will request a set of accounts each year to be held on file.
With regard to your question on the rate charged on materials, I have never seen a builder charge at 21% (and I see a lot of invoices in my job) as the two thirds rule generally applies and Revenue have never disputed builders charging 13.5%.
All VAT invoices must show the traders and customer details and show the VAT registration number. I have never seen it stated anywhere that a VAT reg should be shown on any other headed paper. It is not necessary for a trader to provide a VAT invoice to an unregistered trader but most do. This has been confirmed to me by an inspector at a client's audit. She told him that as he mostly dealt with private customers there was no need to issue VAT invoices and that receipts would suffice. His receipts do show his VAT number but not a breakdown of the rate.
Hope this (probably long winded) reply helps. Although, to be honest, if I were in your position and didn't trust this builder on this issue I don't know why you would trust him on anything else.
