Investigating Damp: Flooding Under Floor – Case study 1


In this blog post I will be detailing an interesting case of dampness within a property and explain how it was resolved. Often with any dampness survey it is a process of elimination by where you go through and rule out each possible cause looking at the property holistically. As Prof. Malcolm Hollis stated “Surveying buildings is an art, verifying the cause of failure is a science”. I use this particular example because this shows some process of elimination. It is by no means the most complex of dampness cases but it does show the steps involved in investigating these issues.

The property being surveyed was a 2 bedroom semi-detached dwelling. The external walls were of a brick cavity construction. The building has a tiled pitched roof with uPVC rainwater goods. Windows are timber frames with double glazed units. The heating is a high efficiency gas central heating combination boiler which was recently installed at the time of the survey.

The neighbouring property had condensation issues in the past which had been verified by a data logging survey. The main contributing factors in that case were lifestyle and ventilation but with some advice and a replacement bathroom extractor fan we were able to rectify the issue.

There were some factors to indicate condensation could be a possibility here as well as the tenant owned a multi person fully fitted sauna. The sauna itself may not cause excess humidity but the presumption would be that the tenant would be using their shower more frequently on account of the usage of the sauna. I noted this as a point of interest and moved on.

There was a level access shower in the property and the extractor fan was in a working condition. A simple way to determine if the extract is working is by holding up a piece of toilet paper and if the extract pulls the paper on to its surface you will know that it is ventilating. There is specialist equipment available to determine exact flow rates but this was beyond the requirements for my initial survey.

There was no signs of mould growth in any of the rooms and the tenant stated that the heating was used frequently. The damp seemed to be mainly in the downstairs electric cupboard which ran underneath the stairs.

After satisfying myself that the risk of condensation was low I used a moisture meter to test the skirting and walls within the electric cupboard. The readings were high as shown in the below picture.

split pic damp meter48.jpg


When you use an electrical moisture meter in a plasterboard wall it will say the reading you get will be the wood moisture equivalent (WME). In the likes of plasterboard or masonry you can only use the readings found as an indicator to determine a pattern of potential dampness rather than a definitive finding as there are a number of things than can lead to a false reading. In this case it was clear that there were high moisture readings present in both the skirting and wall.

After acknowledging these high levels I decided to go to the neighbouring property to test their wall adjacent to the affected area to see whether the dampness was possibly originating next door or passing through. On testing the neighbouring property I found that their side was completely dry.

The next port of call was to remove the tenants laminate flooring and open up a section of the floor. When the flooring was removed it was found that their was a standing level of water of a couple of inches in depth so we knew we had some sort of leak on our hands. The pressure of the boiler was not reducing so we could rule that out as a source for the water.

The tenant needed to then be decanted to allow our contractor to remove the flooring and trace the leak. The floor was a solid concrete base with timber battens which held the ply sheeting, with insulation between each of the battens. The pipework ran between these layers. The horizontally placed battens segregated the water which prevented it from making its way through to the neighbouring property.


The leak was sourced to the kitchen drainage which had a long standing leak which had slowly over a period of time flooded the flooring. The source of the leak could then be fixed and the rest of the remedial works completed. New battens, insulation, flooring and skirting were fitted.


Hopefully this example shows how by process of elimination the root cause of dampness in buildings can be found. Patients and careful investigation is key in some of the more complex cases.

If you would like to learn more feel free to to view my PDF presentation on Dampness in buildings the link is here: Dampness in buildings. Unfortunately it does not show the notes on the slides which really flesh out the presentation but I may upload a video of the full presentation at a later date.



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