One month deadline for counter notices, and the risk created by raising a party wall to half its thickness
posted 2nd September 2026
1. Purpose of this note
The right of an adjoining owner to serve a counter notice is subject to a strict one month deadline. Once that period expires the right is lost and cannot be recovered, whether by agreement of the surveyors, by an award, or otherwise. This is one of the few genuinely fatal deadlines in the Act and it is the one most easily missed, because adjoining owners routinely sit on a party structure notice for two or three weeks before instructing us.
The point has particular practical bite where a building owner proposes to raise the party wall to only half its thickness as part of a loft conversion or dormer. Handled without thought, this can permanently prejudice the adjoining owner's ability to carry out the same works in the future. Every fee earner taking an adjoining owner appointment must read and apply this note.
2. The statutory position
2.1 The right to counter notice
Section 4 of the Party Wall etc. Act 1996 allows an adjoining owner who has been served with a party structure notice under section 3 to serve a counter notice requiring the building owner to carry out works to the party structure that are additional to, or different from, those set out in the building owner's notice, where those works are reasonably required for the convenience of the adjoining owner. It also covers chimney copings, breasts, jambs, flues, piers, recesses and similar works.
2.2 The deadline
The counter notice must be served within one month beginning with the day on which the party structure notice was served on the adjoining owner.
Note that the clock runs from the date of service, not the date printed on the notice, and not the date we are instructed. Where the notice was posted or emailed, establish the actual date of service under section 15 before you calculate anything. If the notice was posted, do not assume same day service. Where there is any doubt, work to the earliest arguable date.
2.3 Form and content
▪ It must be in writing and must specify the works required.
▪ It must be accompanied by plans, sections and particulars where those are appropriate. A counter notice that simply asks for "a thicker wall" without specifying what, where and to what dimension is of little use and invites argument as to validity.
▪ It must be served on the building owner in accordance with section 15. Sending it to the building owner's surveyor is not service on the building owner.
▪ Keep proof of service on file in every case.
2.4 What happens next
Under section 5, if the building owner does not consent to the counter notice in writing within fourteen days of service, a dispute is deemed to have arisen and the matter falls to be resolved under section 10. The building owner is obliged to comply with a counter notice unless doing so would interfere with or cause unnecessary inconvenience to his own works, cause unnecessary inconvenience to any adjoining owner or occupier, or involve unnecessary expense or unnecessary delay.
2.5 Where section 4 does not apply
▪ There is no counter notice right in respect of a section 6 notice for excavation and adjacent construction. Requests for additional works there are dealt with through the section 10 process, not by counter notice.
▪ Line of junction notices under section 1 have their own separate one month deadline. Where a building owner serves notice under section 1(2) of an intention to build a wall wholly on his own land, the adjoining owner has one month to serve notice indicating a desire to build a party wall astride the line of junction. Miss it and the building owner may build wholly on his own land. Diarise this in exactly the same way.
3. Why this matters when the party wall is raised to half its thickness
On a typical terraced or semi detached loft conversion, the building owner needs to raise the party wall to form the flank of the new dormer or to carry the new roof structure. There are two ways of doing it.
(a) Raise the wall to its full thickness, so that the new masonry sits astride the boundary in the same position as the wall below. The raised section is then a party wall, and both owners have the benefit of it.
(b) Raise only half the thickness, wholly on the building owner's own side of the centre line. This is cheaper and quicker, and it is what most contractors and architects propose.
Option (b) is the problem. The raised masonry sits entirely on the building owner's land. It is not a party wall. The adjoining owner has no right to use it and no right to build off it.
3.1 The consequences for the adjoining owner
▪ When the adjoining owner comes to convert their own loft, they cannot simply build up. They must either construct their own separate half thickness wall alongside the building owner's, or enclose upon the building owner's wall and pay for the privilege as subsequent use of work carried out solely at the building owner's expense under section 11.
▪ Two independent half thickness leaves with a void between them create a poor junction. Fire separation and sound insulation between the two dwellings are both harder to achieve and may need additional construction to satisfy Building Regulations.
▪ A half thickness wall may not be adequate to carry the adjoining owner's future roof, purlin and dormer loads without additional steelwork or thickening, which eats into their headroom and their usable floor area.
▪ The adjoining owner's dormer cheek may have to be set in from the boundary, losing width and creating an asymmetric pair of dormers that can attract planning objection.
▪ The abutment between the two dormers becomes a long term weathering risk. Flashings, cavity trays and upstands have to be resolved retrospectively, on a wall the adjoining owner does not own and cannot alter.
The practical effect is an encumbrance.
The building owner's cheaper detail transfers cost, complexity and risk onto the adjoining owner's future scheme. The one opportunity to prevent that is the counter notice, and it lasts one month.
4. What the counter notice should require
Where we act for an adjoining owner who has, or may have, an interest in converting their own loft, the counter notice should ordinarily require the building owner to:
▪ raise the party wall to its full thickness, so that the raised section remains a party wall astride the boundary and is available to both owners;
▪ construct the raised section to a thickness and specification capable of accepting the adjoining owner's future roof and dormer loads, with the loading assumptions stated;
▪ provide for the future junction, including toothing or bonding provision, cavity trays, damp proof courses and fire stopping at the abutment;
▪ provide a weathering detail for the future abutment of the adjoining owner's dormer; and
▪ where appropriate, carry out associated works to chimney breasts, flues and copings while access and scaffold are available.
Attach a drawing. A counter notice supported by a marked up section through the party wall is far more likely to be complied with than one expressed in words alone.
4.1 Who pays
The additional or different works required by a counter notice are carried out for the benefit of the adjoining owner, and the cost of them falls on the adjoining owner. The apportionment is a matter to be determined in the award under section 11. Advise the client of this in writing before the counter notice is served, and obtain a costed view from the building owner's side wherever the timescale allows. Clients must understand that they are buying a benefit, not obtaining one free.
5. Practice requirements
The following apply to every adjoining owner appointment without exception.
1. Date stamp the party structure notice on the day it reaches us and record the date of service, not the date on the notice. Establish how it was served.
2. Diarise the one month expiry immediately, together with a working back reminder at fourteen days and a final reminder at seven days before expiry.
3. At first contact with the adjoining owner, ask directly whether they have any intention, now or in the future, of converting their loft, forming a dormer, extending, or otherwise building against the party wall. Record the answer on file. Do not wait for them to raise it.
4. Obtain and check the building owner's drawings for the thickness of the raised wall above the existing roof line. If the drawings do not show it, ask. Half thickness is often not annotated at all.
5. Where we are instructed late and the deadline is close, deal with it the same day. A short, specific counter notice served in time is worth far more than a comprehensive one served a day late.
6. If the month has already expired before we are instructed, tell the client in writing straight away, explain plainly what has been lost, and record the advice. Do not leave it to be discovered later.
7. Do not assume the section 10 process will fix it. The surveyors' jurisdiction is to determine the matters in dispute arising from the notice as served. We cannot compel a building owner to carry out additional works that the adjoining owner ought to have requisitioned by counter notice and did not.
6. When we act for the building owner
▪ Warn the client at the outset that a counter notice may be served and that they may be required to raise the wall to full thickness, at the adjoining owner's cost. Programme and scaffold implications should be flagged early rather than treated as a surprise.
▪ Where the client's scheme raises the wall to half thickness, raise the long term implications with them and with their architect. In many cases full thickness is the better outcome for both parties and avoids a dispute that costs more than the extra masonry.
▪ Make sure the notice and drawings state clearly what is proposed. A notice that is silent on the thickness of the raised wall is an invitation to a dispute later about what was actually authorised.
7. Risk to the firm
Failing to identify and serve a counter notice in time, on an appointment where the adjoining owner had an obvious interest in their own future loft conversion, is a straightforward claim against us. The loss is readily quantifiable, being the additional cost the client must later incur to achieve what the counter notice would have secured. There is no defence in saying that the client did not ask, because identifying the point is precisely what they instruct us for.
Any case where the deadline has been missed, or where you consider it may have been, must be reported to me on the day you become aware of it. Do not correspond with the client about it first.
Please raise any queries with me directly.
Carl O'Boyle BSc MRICS FCIOB MFPWS
Managing Director
Tayross Associates Limited
