When I get into a house I take a RH%, mostly for conversation and figure how sick I will be in a few hours. I did a home inspection where the house was rh 72%, had mold on walls, and mushrooms growing out of the carpet. Since the air was moist, the spores had to be thick. I felt like I chain smoked a pack of cigs when I was done.
$20.00, works fine. I do outside, home interior and basement/crawlspace. Outside provides a baseline, interior and crawl readings can alert you to moisture intrusion you can’t see.
Knowing the average wood moisture contents for homes in your area from season to season would be a start. Plus using the chart of wood moisture content when exposed to high (70-80%+) continuous air RH’s would allow one to make an educated recommendation that if conditions continue or aren’t changed longterm rot/fungal growth may begin.
Oh, just some extra information. On the house that had a 70% RH, everything came up ‘alarm’ levels with my moisture meter. Having the RH helped me explain how I could not differentiate between the past like damage stains and an present water damage.
You have a good point there Brian, but I find that if I do it on every home I start to get a feel for humidty levels. The readings I get are not something I’d typically use in a report but a high one inside makes me pull out the moisture meter and poke around.
Outside humidity levels here seem to average between 25% and 40% but wood levels measured in log home exteriors are typically barely measureable with the surveymaster which has about 10% as the bottom of its range. Even with the conversion chart, wood moisture levels don’t appear to mirror average realtive humidity.