Walls are shared.
Advice should be too.

No — owners can agree directly without one. But if a dispute arises (or is deemed to arise after 14 days of silence), the Act requires either an Agreed Surveyor or two surveyors, one for each owner. In practice, most projects involve at least one surveyor.

After 14 days of no response, a dispute is deemed to have arisen. The building owner can then appoint a surveyor on your behalf — meaning you lose the chance to choose your own. It is almost always in your interest to respond.

Generally, the building owner (the one carrying out the works) pays the reasonable fees of both surveyors. The Award itself sets out fees and apportionment.

You cannot block notifiable works under the Act, but you can dissent and have a surveyor protect your interests. The Award will set conditions — working hours, methods, protection — but it does not grant or refuse planning permission.

Typically 6–10 weeks from notice to Award for a straightforward domestic project. Complex schemes or uncooperative parties can extend this considerably.

The Award sets out how damage is to be made good. The Schedule of Condition (taken before works) is the reference point. Disputes about damage can be referred back to the surveyors.