Surveyors! Do you fancy taking part in a national study on condensation?

The Property Care Association and Graham Colman of Remedial technical services have some interesting research in progress.

This is a study of the vapour pressure differentials inside randomly chosen homes around the UK, compared to external measurements. Condensation problems are common and seem to be growing. Those of us involved in condensation and mould control often use BS5250 ‘code of practice for control of condensation in buildings’, as a guide.

The document uses differentials between the inside and outside Vp to help assess the ‘’occupancy’ levels for purposes of defining whether a dwelling is ‘dry’ ‘moist’ or ‘wet’.  The data used to define these is outlined in BS5250.

In recent years, as the PCA have introduced many of us to data logging, we’ve come up with a wide variety of data sets and some of us, particularly Graham, have come to question the data behind the levels which are quoted. In particular, houses termed as moist or even wet, do not always seem to have a problem with condensation.  So at Graham and Steve Hodgson’s invitation, I and some other surveyors, scattered around the country, are data logging our own houses, with loggers outside too, so that we can provide more ‘real world’ data sets for analysis.

I’ve set two up today (see video). As you can see, setting up data loggers is fast and easy.

I live in a four bed semi, with my wife and daughter (two cats and a two fish tanks). The only mould growth I ever find is between tiles in the shower; nowhere else. The house is centrally heated and there are five extractor fans (two in the kitchen, the others are in baths and cloaks). This should be a dry occupancy – lets see what the data tells us over the next few months.

Once collected the data will be sent to the PCA for adding to the database.

If you would like to participate please set at least two loggers up. One internal and one external.  Set them for 1 hour intervals.  make sure the external one is sheltered from rain and direct sunlight. For further information talk to Steve at the PCA or Graham Colman at RTS.

Dry Rot.


  1. Dr Hindlefokker.

    Just to say that the data I have so far (including the monitoring of this house – 4 beds, 3 adults, 2 cats and their fleas if any left)indicates that the ‘dry’ to ‘wet occupanies’ can be grossly misleading and in many cases is likely to lead to the wrong information being given to alleviate a known problem.

    I have also compared external VP in Lanchshire, Dorset and Manchester – they are VERY similar with passage in time. Interesting.

    Kind regards


  2. George Dunnett says

    Thanks for the invitation

    Could I help you with your condensation research?

    I did a study on internal condensation in my house when my children were very young to assess ways of keeping the bedrooms warmer in winter (we had a combi at the time). This enquiry was prompted by GP Doctors alleging that my children had asmatha as they were both suffering from night time coughs. The coughs seem to coincide with condensation in winter but would disappear at other times. Another case of professionals making a default diagnosis.

    My results concluded that by moving the radiators further out from the wall under the windows (75mm), more heat was able to circulate within the room thus helping to keep air close to the windows drier. The curtains were able to pass behind the radiator which was also key.

    Kind regards


  3. Dry Rot says

    Hi George,

    Yes, thanks for the information. The thing is, that Doctors; like surveyors, visit lots of houses with streaming windows and I suppose that their anecdotal evidence is that streaming windows equals coughs and respiratory problems. Was there much in the way of mould growth?

    Graham Coloman has been using his thermal imaging camera to visualise the effects of air flow on walls and has found that even a relatively innocuous object like say, a laundry basket, can result in a cold section of wall. Still, the humidity still has a big part to play – lower the RH and you lower the dew point, so a combination of good airflow and slightly raised heating will often do the trick. Keeping the humidity in check with good extraction in the bathroom and kitchen is always beneficial though.

    More than 60% of my damp surveys are due to condensation at this time of year (I’ve done four condensation derived ones this week and we only came back on Thursday), so you are in good company.

    Have you any data loggers for monitoring humidity, air temperatures and dew point? If so, why not get them going and let us have a plot to add to Graham’s project? If not, the Lascar ones shown in my video are cheap and come with neat and easy to use software. I can supply a link to their site if you need it.


    Doctor Hindlefokker always appreciates your input. I bet my cats have more fleas than yours…

    Anyway, I should have some data for you soon, my loggers were set up on Boxing Day. I’ll let them run on for six weeks or so; is that enough for you?

    At the moment BS5250 is all we have so I am using the ‘occupancies’ to help clients understand the relationship between my findings and nationally ‘accepted’ standards. They have mould and streaming window fatigue and want easy to digest answers to there condensation problems, not reams of figures.

    Your study will really help us get a better benchmark, but clearly this is a complex topic and it may be that there isn’t a simple way of describing houses ‘occupancy style’.

    The BS5250 three levels of ‘occupancy’ dampness/dryness may be just too basic? Perhaps a six or seven levels of grading may be needed, with some sort of factor for heating; insulation and ventilation built in?

    • George Dunnett says

      I’ve got a couple of Lascar loggers now and am keen to test them out. It will be good practice

      Is 6 weeks okay starting mid-October 2011?


      • Dry Rot says

        You don’t need that long to practice – start now. All data is good data….

        Remember to make sure that the one outside is sheltered from direct sunlight.

        Did you get the LCD one’s?

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