2 weeks of work, so you give them 4 weeks because you don't want to deal with possible 2nd extension- cost? - Can you ask or expect only having to pay for 2 weeks of overhead for 4 weeks of work - for the above reason. Would you be concerned that they agree and then address different legally?
John, without knowing your contract pricing conditions and other circumstances, it's typical that daywork rates is used for additional work and that rates includes overhead, if that so, then 2-weeks extension will be fine...