Damp-proofing at an Adjoining Property

by The Party Wall Surveyor

Question

I’ve received a Party Wall notice concerning the insertion of a chemical damp proof course in the adjacent ground floor flat. I’m aware that the
property is in a poor condition (it’s been occupied by an old lady since the 1940’s). There is undoubtedly damp in the external walls but I was surprised that the owners are intending to damp proof the internal party wall.

Can you advise me whether there are any questions / concerns I should raise with the owners, or any undertakings I should request as a condition to signing the notice.  If there is damp on their side of the party wall is it possible that the damp will be ‘pushed through’ to my side of the party wall and possibly affect the plaster / internal decoration of my flat when they install the damp proof course?

My flat was modernised in 1999 and stripped back to bare brick (mine had also been occupied by an elderly tenant). I had a new damp proof course put in but only the external walls were done.

Answer

If the owners of the property next door believe the dampness to be rising from the ground (rising dampness) then party walls will require remedial works in the same way as external walls.

The insertion of a chemical damp proof course (DPC) alone should not have any detrimental effect on your side of the wall but injecting a DPC is normally carried out in conjunction with the application of some sort of waterproof rendering – and that could alter the path of any dampness that rises through the new chemical DPC.

Chemically injected DPCs are notoriously unreliable and their success or otherwise is very dependent upon the quality of the workmanship. There are many questionable damp proofing contractors in business today. If you do not appoint a surveyor you will have no input in to how the work is carried out and any possible knock on affects to your property.

In this situation I would advise you to appoint a surveyor who could then request full details of the proposals and suggest alternatives to anything which may put your property at risk. The party carrying out the works will be responsible for your surveyor’s reasonable fee.