Party Wall Questions #7

Wednesday, 17th August 2011 | by: Peter Barry


The Government Explanatory Booklet lists certain jobs as being so minor they do not warrant the serving of a notice:

  • Drilling into a party wall to fix plugs and screws for ordinary wall units or shelving
  • Cutting into a party wall to add or replace recessed electric wiring and sockets
  • Replastering

Which of the following works would you put in the same category?

  • Drilling in to a party wall to inject a supplementary damp-proof course
  • Replacing existing flashings to a party parapet wall
  • Fixing a timber frame to a party wall to support a suspended ceiling

This is another question that was raised at a recent FPWS North London forum meeting which I helped to organise. I would welcome the views of other surveyors. If you are a surveyor involved in party wall matters and would like to attend future meetings please email me at and I’ll keep you updated.


There are many situations where a literal interpretation of the Act (particularly Section 2(2)(f)) would lead a Building Owner to conclude that notice should be served.

Take for example drilling a single hole in to a party wall to allow for the insertion of a rawlplug and picture hook. That would seem to be covered by Sections 2(2)(f) but there are not many Owners that would risk incurring surveyor’s bills of up to £2,000 to hang a picture.

In such cases the Building Owner must rely upon the legal principle de minimis non curat lex (or de minimis for short) meaning that the law takes no account of very trifling matters.

The authors of the Government Explanatory Booklet* clearly realised this problem and provided some examples of works (listed above) considered so minor that they would not require a Building Owner to serve notice. The Booklet also puts forward the following entirely sensible principle upon which decisions should be based:

[Works that] might have consequences for the structural strength and support functions of the party wall as a whole, or cause damage to the Adjoining Owner’s side of the wall.

Moving on to the 3 examples of works noted in the question:

Drilling in to a party wall to inject a supplementary damp-proof course

While drilling relatively small diameter holes in to a party wall will not compromise its structural integrity there is a significant risk of damage to the Adjoining Owner’s side of the wall. It was pointed out during the meeting that injecting half of a party wall does not make practical sense as the dampness will simply rise through the other half. It would therefore be necessary to inject the full thickness of the wall which increases the possibility of damage occurring.

When Section 2(2)(f) of the Act was updated from the corresponding section of The London Building Acts 1939 a specific reference to the insertion of a damp course was added – as the current method of drilling and injecting walls was already common place in 1996 I think we can assume that such works were included in that reference.  Notice should be served.

Replacing existing flashings to a party parapet wall

If the flashings were being replaced on a like for like basis it should be possible to rake out and utilise the existing chase. De minimis.

Cutting out a new chase effectively reduces the thickness of the wall and as a result its ability to withstand loads; although those should be minimal with a parapet. Section 2(2)(j) refers specifically to flashing – although 2(2)(j) covers a different scenario (inserting a flashing in to a Adjoining Owner’s flank wall to weather a gap) it does suggest that the authors of the Act considered the cutting in of a flashing significant enough to be notifiable. Notice should be served.

Fixing a timber frame to a party wall to support a suspended ceiling

Although this will again be a simple case of drilling the wall to allow fixings to be inserted it is more significant than the picture hook example provided above because the fixings will be larger and will be transferring some additional load to the wall.

In the majority of cases the loads are likely to be insignificant so the critical factor will be the depth of fixing compared to the thickness of the wall. It is unlikely that the fixing will have to be inserted any deeper than 100mm in to the wall so assuming that the wall is at least 1 brick thick (215mm) the risk of damage should be negligible. De minimis.

*Currently being updated with the assistance of the Faculty of Party Wall Surveyors

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