The Party Wall Act, in plain terms.

What the Act is

The Party Wall etc. Act 1996 applies in England and Wales. It governs building work on a wall or structure shared with a neighbour, new walls on the boundary, and excavation near a neighbour's building. It is separate from planning permission and from building regulations: you can hold both and still be in breach of the Act if you start without serving notice.

When it applies

Three kinds of work bring the Act into play, and each has its own notice period.

• Work to an existing party wall or structure. Cutting into the wall to bear a beam, which is what almost every loft conversion on a terraced or semi-detached house does; raising it, thickening it, underpinning it, or cutting off projections. Notice: at least two months before the planned start.
• A new wall at or astride the boundary. The flank wall of a rear extension built up to the line between two gardens. Notice: at least one month.
• Excavation near a neighbour's building. Within 3 metres of their building or structure, where your excavation will go deeper than their foundations; or within 6 metres, where it will cut a line drawn downwards at 45 degrees from the bottom of their foundations. The foundations of a rear extension usually fall into the first case. Notice: at least one month.

The notice

A notice is a letter, and there is no set form, but it must give the building owner's name and address, describe the work, say when it will start, and, for excavation, include drawings showing the depth and position of the new foundations. It remains valid for twelve months; if the work has not started by then, it must be served again. The government publishes example letters with its explanatory booklet, listed under sources below.

A notice can be served before planning permission is granted. Serving it early, with a conversation before the letter, is the single most useful thing a building owner can do.

What the neighbour can do

The adjoining owner has 14 days to respond. They can consent in writing, in which case the work can proceed, ideally with an agreed schedule of condition of their property. They can dissent. Or they can say nothing, and for work on a party wall or for excavation the Act treats silence after 14 days as dissent. In either case a dispute is deemed to have arisen and the Act's procedure for resolving it begins.

For a new wall on the boundary the position is different: if the neighbour does not agree in writing, the wall must be built wholly on the building owner's own land.

Surveyors and the award

Once there is a dispute, surveyors are appointed. The two owners can agree on one surveyor, called the agreed surveyor, or each can appoint their own; if two surveyors cannot agree, a third surveyor is selected to settle the point. The surveyors produce a party wall award: a document that sets out the work to be carried out, how and when it will be done, a record of the condition of the adjoining property before work starts, and the surveyors' right of access to inspect while it is under way. Either owner can appeal an award to the county court within 14 days of receiving it.

Usually the building owner pays all the costs of the award, including the adjoining owner's surveyor's fees, where the work is solely for the building owner's benefit.

What this means for your programme

The notice periods are the reason the Act belongs on the programme and not in the last week before the start. A loft conversion needs two months from the notice; an extension near the boundary needs one. If the neighbour dissents, the award takes its own time on top. When the studio draws an extension or a loft conversion, the drawings show exactly what touches the boundary, which sections of the Act apply is settled from the drawings, and the notice periods are built into the programme alongside planning and building control. The order of those approvals is described in planning permission versus building regulations.