An experienced damp investigation surveyor will carry out an internal inspection of the property, and also an external inspection. On the external inspection survey they should be looking for possible problems relating to the internal problems and any other obvious defects. One of the most common problems is high external ground levels where the damp proof course has been bridged, or potential for rainwater to splash over the damp proof course.

The below diagram shows what bridging of the damp proof course looks like, caused by high ground levels.

By simply lowering external high ground levels, this will allow wall base evaporation, to help control rising dampness.

External ground levels ideally need to be lowered 150mm below the damp proof course – or the internal flooring. Mass ground excavation isn’t necessary, simply cutting out a channel and using terram to supress any weed growth and pebbles is a simple procedure.

Complete Preservation carry this type of work out normally using the typical drawing below.


Before any cutting into the ground is carried out it is imperative to use cable avoidance detection equipment.

We use the below Rigid SeekTech SR-20, along with our rigid drain cameras. Our drain cameras also have a sonde, so we can be very precise when cutting or breaking up the ground.

We use specialist Hilti dust extraction systems connected to professional Hilti cutting equipment to minimise dust.

Below are some pictures of cutting and breaking out the concrete.

photo 1photo 3

Geo-membrane is placed above the earth to stop weed growth and golden gravel is poured on top

photo 4

The picture below shows the level of what the ground level used to be before we lowered it, the sub floor vent was blocked which we cleared out.



This is very effective in helping evaporation of rising dampness at the wall base.

Often people can presume that because the ground level is slightly high reducing this will fix the issue; however if hygroscopic salts are present in the plaster finish lowering the ground levels will not remove the hygroscopic salts. Gravimetric analysis can confirm if moisture and/or hygroscopic salts are present; this is a service we also offer.

A damp wall takes time to dry out, as a general guide the drying rate is given as 1 month for every 25mm of wall thickness (BRE,”Drying out of buildings”) A 230mm thick wall will take approximately 9 months to dry. However, the drying processes depend on many conditions, ventilation and the type of masonry, so drying may take considerably longer than anticipated.

When ground levels are lowered it is also highly likely that a small amount of lime pointing will also be necessary at the base of the wall.

Ground levels should be lowered by a competent person or you should take advice from a structural engineer in order to ensure the structural integrity of the building isn’t compromised.

If you would like a survey, and price to lower external ground levels if they are high, please contact us on or on 01225 769215. We can also carry out the plaster sampling internally following the methodology in BRE DIGEST 245 to confirm if hygroscopic salts are present and the plaster will need replacing.

Please see the video of Ross Charters explaining how to lower ground levels, and also some tips for you.

Posted by Complete Preservation


  1. I’ve had a survey carried out on a Grade II listed building. The survey states that the ground level around the outside of the house needs to be reduced to help reduce damp. As the building was built in 1850 and has no DPC I can’t see how this will help!!


    1. Hi Kevin,

      This is a sensible approach to allow evaporation at the base of the wall, also check for any other external defects especially when its raining. You may also wish to have a drain survey, if you continue to have dampness problems a survey should be carried out to BRE Digest 245.


  2. This is what I think I need to have carried out to stop this rising damp issue I have. Do you do damp surveys in Devizes? I will need the whole house surveyed and a CCTV drain survey which I see you also do.


    1. Hi Dean, I cover Devizes for damp surveys. Please email your details and I will ring you to discuss.


  3. Chris Lansdown March 15, 2021 at 17:28

    Hi. Great article and something I think my house will benefit from. The problem I have is that the DPC appears to be only one brick above where the brick foundations start. The layer below the brick line with the dpc and the layer below that are stepped out (imagine how a pyramid looks). It’s a Victorian semi I think (not sure on the date) Can this still be effective in this instance? Appreciate it’s hard to describe (hence the bad diagram!). Could do with some advice please! Thanks

    | __ dpc


    1. Hi Chris, thanks for the kind comments. Lowering ground levels along with checking drains is a great help with damp issues. Unfortunately I cant really give advice without actually seeing your issue myself. sorry bud. Have a look on my Youtube for tips


      1. Chris Lansdown March 16, 2021 at 09:14

        Fully appreciate it’s hard to convey using the written word. I’ll take a look at the video. I’ve been watching most of them for the last day or 2. Great content. Nice to see a common sense approach to these things. So much BS out there.
        Appreciate you taking the time to respond.

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