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You nailed it. This is the key point to keep track of. I have been monitoring this since years in certain areas in hour house (in the ground and in the attic) using sensors and related logic in Node-RED (earlier with EventGhost). I'm measuring the temperature & relative humidity, calculating the delta (difference from actual temperature to dew point). If delta goes negative there is a problem. Luckily we have never had any condensation so far, I have also verified this regularly with an instrument checking the relative humidity in the wooden construction. It might be surprising but highest risk is during warm summer days, at least here in the Nordics. Reason is because warm air can carry more water and when the air is cooled down (entering the ground or attic), the dew point is reached earlier

Many times you hear people are scared due to high relative humidity but is is not necessary dangerous with high relative humidity alone, it is condensation that is. So monitoring the relative humidity is not enough, you have to calculate the dew point (and delta) to know if you are close to condensation or not

This is my javascript code I use in a function node in Node-RED to calculate the delta:

// See: http://arduinotronics.blogspot.co.uk/2013/12/temp-humidity-w-dew-point-calcualtions.html
// delta max = 0.6544 wrt dewPoint()
// 6.9 x faster than dewPoint()
// reference: http://en.wikipedia.org/wiki/Dew_point
function dewPointFast(celsius, humidity) {
    var a = 17.271;
    var b = 237.7;
    var temp = Math.log(humidity * 0.01) + ((a * celsius) / (b + celsius));
    var Td = (b * temp) / (a - temp);
    return (celsius - Td).toPrecision(4);
}
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