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Author Topic: High humidity - From insulation or wet summer?  (Read 4796 times)
Jr. Member
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« on: August 11, 2019, 07:37:15 PM »

Hi all

We live in an old stone built house, which was renovated/insulated in 2005.

At the start of this year we had our internal upper floor ceilings (no loft) torn down, and 50mm celotex installed (gaps between rafters sealed with expanding foam) then reboarded and plastered.

We also had about 5 new velux windows added and most internal walls skimmed.

A month ago downstairs we had the horrible plastic karndean pulled up and limestone tiles laid (with UFH + 25mm XPS insulation below). The concrete floor has a DPM and was dry to touch.

Previously our humidity levels were about 60-65% (expected to be a big higher as old house, no DPC). We'e noticed since about April (roughly when the ceiling work was finished) that our humidity levels have been above 70-75% on many days.

I'm fully aware that adding insulation/increasing air tightness can increase humidity,  but seeing as this house is probably fairly leaky, I didn't expect much of a shift when we did this. We've also added more ventilation from the velux vents. We have 3 decent DMEV trickle extractors which are running on boost mode 24/7 at the moment as the higher humidity levels are setting them off.

As its summer, we often have the velux open (the velux are only even closed to 'ventilate' mode at worst, and often open all day).

As it's been quite wet here (North West UK) with the humidity levels outside often 80%+ I'm hoping this is just due to inside/outside temperatures being the same (or often lower inside due to the stone keeping it cool) and so the internal humidity being the same (or more) as outside

Do you think it could be the weather currently, or think we've created an issue with the work we've had done?
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« Reply #1 on: August 12, 2019, 10:58:04 AM »

If the outside humidity is 80% and the windows wide open to ventilate, then the air inside (if the same temperature) will increase to 80%. If you close the windows at night when the outside temeprature drops the humidity inside will remain high. To lower the internal humidity you will either need to ventialte with dryer air (wait for a warm dry period - could be a long wait) or actively dehumidfy inside (though not much point if the rate of air change is high due to open windows etc).

Concrete being dry to the touch does not give that clear an indication if it will contribute to the internal humidiy or not, it can take a long time to properly dry out unless forced (I assume your UFH is not on presently!).
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