I recently had an email that asked the following:
"Hi, I'm in surveyor training - could you please recommend a hygrometer to get? I was looking at Di-Log DL7108 but it's labelled as a "moisture meter" on their website rather than hygrometer. Thanks!"
This was my response:
Yes - you were right - the Di Log is just another damp meter that doesnt measure moisture.
"The best ones to get are the Vaisala HM series - not cheap mind you. I use the HM42, with the long probe. You can push the tip between floorboards, gaps between radiator pipes and sub floors and so on.
If you want to start with a cheaper one, York Survey supply do these: https://www.yorksurvey.co.uk/precision-thermo-hygrometer They do readout of Temp, RH , Dew Point, and Absolute - which is important so you can immediately see if there is too much moisture in the air.
Cheaper ones don't do the Absolute calculation.
When we do surveys, we do an excel table - each line is a location - so External (Must do ), front room, back room, kitchen, bathroom, bedrooms, loft space. Then in the columns I record Temp, RH, Absolute, Dew Point.
You can then colour code any readings (or room) that is too wet - for eg over a suspended floor, you might get 12 grams, and in the lounge 8 grams. That immediately tells me the sub floor is too wet and not ventilated. So then you go looking, and try to get the probe under the floor somewhere to confirm..
A high reading in the loft space for eg, tells you the loft is badly ventilated - don't rely on visual appearance - or with sticking a damp meter into timbers in the roof. It doesn't work - those timbers have been soaked in chemicals over the years and will always read very high as a result if using the standard RICS damp meter. Thermo hygrometer readings instantly show actual moisture levels, especially if you stick the probe underneath insulation. Readings are often scarily high in this situation. Putting the probe under sprayed foam insulation almost always gives very high readings.
I've looked at the cheaper thermo hygrometers and none of the others do the Absolute calculation, which is vital, otherwise you spend all day on a calculator doing conversions of the numbers.
I'd also get one of the thermal imaging add-ons for mobile phones - they're pretty good these days - so you can THEN compare wall temps - if for eg hygrometer says 12 grams, and dew point of 10 degrees, you can use the thermal imaging to find areas of wall below 10 degrees, and demonstrate active condensation. It happens a lot. Is good to demonstrate, and shows that what folk think are symptoms of rising damp are in fact not - its always condensation in one way or another, unless penetrating.."
It's important to use the right equipment - combining thermo hygrometer readings with thermal imaging is essential to properly diagnose moisture problems. Its also easy to do, and carefully recorded moisture readings as instructed are also a very solid fail-safe in surveying. If a client has any issues post-purchase, the readings are a great reference guide as to where attention is needed to the house and fabric. Moisture levels will always change over time, and with different lifestyles, but this gives a very good starting point.
