This tool as saved my career many times over, and countless properties from rot and misdiagnoses rising damp.
- Look up Hygrometer probe on eBay. The link may become out of date. The cheaper ones come from China are made for fridges and cost about £3.50 – compare to the image.
- There is nothing especially clever about hygrometers, they have a piece of plastic that curls-up with humidity and a thermocouple to measure temperature.
- I buy in bulk as I probably break one or two every week trying to probe through blocked sub-floor vents, or between the gaps in floor boards.
- I remove the plastic guard (gentle twist and pull), unknot it and attach to a thin extendable car arial.
- Ideally measure as far in as possible, at least 1M from the sub-floor, or the under stair cupboard and leave for 20 – 30 minute to acclimatise (so it should be the first job on site).
- Over 85%RH needs further investigation, normally a sign of penetrating damp or leak – but could be wet rot, or worse still Dry rot.
- Below 75%RH is normally incompatible with rising damp.
- There will be variation over time.
- As a home owner, be sure to have a hygrometer probe in your sub-floor and check it regularly, say weekly or monthly,
- if there is any risk of water leaking into the sub-floor, such as penetrating damp, waste water or mains water or
- you have an extension,
- decking, or
- otherwise blocked sub-floor vent.
- I plan to use these embedded long-term, deep behind insulation to ensure water doesn’t become trapped between a vapour barrier and wall, resulting in rotten joists.