Notifiable works will fall in to one of three categories.
These works fall under Section 2(2) of the Party Wall Act and quoting directly from the Act a building owner shall have the following rights -
(a) to underpin, thicken or raise a party structure, a party fence wall, or an external wall which belongs to the building owner and is built against a party structure or party fence wall;
(b) to make good, repair, or demolish and rebuild, a party structure or party fence wall in a case where such work is necessary on account of defect or want of repair of the structure or wall;
(c) to demolish a partition which separates buildings belonging to different owners but does not conform with statutory requirements and to build instead a party wall which does so conform;
(d) in the case of buildings connected by arches or structures over public ways or over passages belonging to other persons, to demolish the whole or part of such buildings, arches or structures which do not conform with statutory requirements and to rebuild them so that they do so conform;
(e) to demolish a party structure which is of insufficient strength or height for the purposes of any intended building of the building owner and to rebuild it of sufficient strength or height for the said purposes (including rebuilding to a lesser height or thickness where the rebuilt structure is of sufficient strength and height for the purposes of any adjoining owner);
(f) to cut into a party structure for any purpose (which may be or include the purpose of inserting a damp proof course);
(g) to cut away from a party wall, party fence wall, external wall or boundary wall any footing or any projecting chimney breast, jamb or flue, or other projection on or over the land of the building owner in order to erect, raise or underpin any such wall or for any other purpose;
(h) to cut away or demolish parts of any wall or building of an adjoining owner overhanging the land of the building owner or overhanging a party wall, to the extent that it is necessary to cut away or demolish the parts to enable a vertical wall to be erected or raised against the wall or building of the adjoining owner;
(j) to cut into the wall of an adjoining owner's building in order to insert a flashing or other weather-proofing of a wall erected against that wall;
(k) to execute any other necessary works incidental to the connection of a party structure with the premises adjoining it;
(l) to raise a party fence wall, or to raise such a wall for use as a party wall, and to demolish a party fence wall and rebuild it as a party fence wall or as a party wall;
(m) subject to the provisions of section 11(7), to reduce, or to demolish and rebuild, a party wall or party fence wall to -
(i) a height of not less than two metres where the wall is not used by an adjoining owner to any greater extent than a boundary wall; or
(ii) a height currently enclosed upon by the building of an adjoining owner;
(n) to expose a party wall or party structure hitherto enclosed subject to providing adequate weathering.
This type of work is covered by section 6 of the Party Wall Act and can be divided in to two parts. Again quoting from the Act itself:
Section 6(1) applies where -
(a) a building owner proposes to excavate, or excavate for and erect a building or structure, within a distance of three metres measured horizontally from any part of a building or structure of an adjoining owner; and
(b) any part of the proposed excavation, building or structure will within those three metres extend to a lower level than the level of the bottom of the foundations of the building or structure of the adjoining owner.
Section 6(2) applies where -
(a) a building owner proposes to excavate, or excavate for and erect a building or structure, within a distance of six metres measured horizontally from any part of a building or structure of an adjoining owner; and
(b) any part of the proposed excavation, building or structure will within those six metres meet a plane drawn downwards in the direction of the excavation, building or structure of the building owner at an angle of forty-five degrees to the horizontal from the line formed by the intersection of the plane of the level of the bottom of the foundations of the building or structure of the adjoining owner with the plane of the external face of the external wall of the building or structure of the adjoining owner.
The construction of new wall at the line of junction is covered under Section 1 of the Party Wall Act and states.
This section shall have effect where lands of different owners adjoin and -
(a) are not built on at the line of junction; or
(b) are built on at the line of junction only to the extent of a boundary wall (not being a party fence wall or the external wall of a building),
The new wall may be built up to the boundary line but wholly on the land of the Building Owner or astride the boundary line i.e. with part of it on each owners side. If the Adjoining Owner refuses consent then the wall must be built wholly on the Building Owner's side.