Ten Tips to Avoid Buying a Damp Property

Ten simple but valuable checks for potential homebuyers

High external ground levels are a problem, but less so in cavity walled construction.


  1. Check external ground levels are not too high when compared to internal finished floor levels. If a physical damp proof course is installed then external finished floor levels should be a minimum of 150mm below internal finished floor Level. In older buildings, if no physical damp proof course is installed then this is not necessarily a problem, simply ensure that external finished floor levels are a minimum of 200mm below internal finished floor level.
  1. Make sure external masonry is not painted. Brickwork cannot dry out when it is coated with impermeable masonry paint. If it is painted then you should at least have the paint removed from the bottom three courses of brickwork. Similarly, you should generally avoid clear waterproofing products despite claims that they are ‘breathable.’ Cement render can cause similar problems and you should ensure that cementitious render is in sound condition and not bridging the damp proof course at lower level.


  1. Respect the buildings construction type. If it is an old building built with lime mortar then it should be repointed with lime mortar and not Portland cement. Understand that old buildings are meant to breathe if they are to dry out, and Portland cement prevents moisture evaporation and causes spalling of brickwork.
  1. Avoid buying any property that has an original rotten timber floor replaced with a retrofit concrete slab. Retrofit concrete slabs will often cause wall base damp by pushing moisture up the walls under hydrostatic pressure. Again, this is about understanding how the building was originally built.
  1. Measure the wall thickness at a door or window reveal, is it around 240mm or less including the plasterwork? If so then its likely to be solid walled and therefore more likely to suffer from penetrating damp or internal cold surface condensation issues. You may even discover some single skin brickwork, particularly on gable walls in very old buildings. Mortgage companies do not generally like to lend against these properties due to perceived structural and damp issues. Buying an old solid walled property does not mean you are buying a damp property but you should understand the implications.
  1. Find the incoming water main and see if it is Polyethylene pipe. An old building may still be on the lead water main and these are susceptible to leakage that may go undetected under the floor of the property for quite some time. Many of the worst damp problems we’ve encountered have been caused by leaking water mains.
Rising Damp? Technically no, since this was caused by a leaking lead water main buried in the subfloor
  1. If the property is cavity walled, is cavity wall insulation installed? CWI can occasionally cause penetrating damp, particularly the blown fibre variety. However, when correctly specified and installed we still believe it is a worthwhile addition to most suitable properties.
  1. Check your airbricks! Timber floating floors should as a general rule of thumb have airbricks installed every 2 linear metres to ventilate the subfloor and prevent timber decay. These are a critical technical feature so don’t ignore them!
  1. Has the property been treated with retrofit chemical injection? You will know the obvious telltale signs such as a row of plastic plugs installed into the brickwork at low level but what you may not know is that this is a two-part system that includes the application of internal waterproof renovating plaster. This renovating plaster dams in the damp and often gives the appearance of a dry wall at surface when in fact the underlying wall can be saturated. These management systems are almost never required despite the volume sold, and can prevent walls from drying out so don’t kid yourself that these treatments are a good thing. They are a management solution rather than a cure and as such are destined to fail.
  1. Know that condensation damp is the biggest cause of dampness within properties. To combat this, ensure that the property is well insulated, has a fully controllable central heating system installed and has a means of controlled mechanical extraction installed in the kitchen and bathroom areas.

4 responses to “Ten Tips to Avoid Buying a Damp Property”

  1. Em Stein avatar
    Em Stein

    Hi Joe,
    Thanks for the incredibly helpful posts you have here. We’re first time buyers and have “rising damp” highlighted by our surveyor, leading us to try to find out more. Walls and suspended timber floors had high readings. I notice you mention avoiding homes where the internal floor is not raised above the level of the external floor. Our prospective property is a mid-Victorian terrace with very little step up between external and internal floors, definitely less than 150mm. The external walls are rendered so I can’t see the level of any damp course. If this is exacerbating the damp is it something that can easily be fixed?

    1. Joe Malone avatar
      Joe Malone

      Hi Em,

      If you can’t see the DPC, then you should assume there isn’t one. This isn’t necessarily a problem, buildings can manage dampness perfectly well without a physical DPC, so long as external ground levels are a minimum of 200mm below internal finished floor level.Can the high ground levels be easily reduced, possibly as part of renewing the hardstanding? If there walls are rendered, then this too should stop 200mm short of the external finished floor and be finished with a bellcast bead (Drip detail).
      It’s important that you understand the ‘high readings’… were these taken in scan mode or pin mode? High scan readings should always be followed up in pin mode, and critically you need to understand if readings were greater that 20% relative? If they were then further testing for moisture at depth in the masonry is required.


      Joe Malone

  2. Caroline Kennedy avatar
    Caroline Kennedy

    Thanks for your very useful expertise. My husband and I are looking at a 1890s semi detached home that a structural survey a year ago highlighted damp in the lounge and in the chimney breast of the dining room (party wall). We have found out that the lounge has been treated twice, once in 2006 and once in 2015. It is under guarantee. Why would this need two treatments and now be a problem again?

    In addition, there is dry rot in the attic but we don’t know the extent and it has not been treated despite the vendor knowing about it for at least a year.

    We have a friend who is a structural engineer specialising in historical buildings (aren’t we lucky?!), but will he be able to see what’s happening in the house? We like the house so much!

    1. Joe Malone avatar
      Joe Malone

      Hi Caroline,

      You state that;

      “We have found out that the lounge has been treated twice, once in 2006 and once in 2015. It is under guarantee. Why would this need two treatments and now be a problem again?”

      Quite simply because it was likely misdiagnosed and never needed treatment for rising damp, or the treatment has caused induced rising damp. No one needs damp proofing treatments!

      You also state that there is; “dry rot in the attic but we don’t know the extent and it has not been treated despite the vendor knowing about it for at least a year.”

      Again, no one needs treatment for dry rot and there is a simple three stage approach to remediation.

      1. Remove the source of moisture
      2. Introduce rapid drying and improve ventilation to the affected area.
      3. Cut out and replace infected timber a meter past the last sign of infection.

      In short, you do not need any treatments, these issues simply need proper investigation.


      Joe Malone

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