Passive house with big humidity reading in floor void.

[tubularowl]

Hi, I’ve recently moved into a passive bungalow. 2800sqft in size. The house was built in 1985 and is in good condition. The passive airflow in the house is good with a steady 50% humidity level.
The house has an accessible void underneath around 4 ft high and any part of the underside of the house is accessible pipes, electrics, everything. I was taking a look under one of the bathrooms and found standing water in the void. I also found some in 2 other places. I’ve fixed and pumped the water away and it’s not returned. The void does have a musty smell thought so I’ve also checked and cleared a few buried air vents. So I’m reasonably happy no further water will come in.
Yesterday I put a wireless temperature and humidity gauge down there. This morning it returned a reading of 13 degrees C and a humidity reading of 95%. Obviously that’s really bad so what do I do next. Walls all look dry floor feels damp.
My 1st thoughts are an industrial dehumidifier but I really need to get that wet air out of there.

[ahfix]

Obviously that’s really bad so what do I do next. Walls all look dry floor feels damp.

I am in no way an expert but if there has been standing water it will take sometime for the area to dry out. Perhaps check again in a few weeks? It might take longer given we are now into damp weather.

[wes56]

By air vents do you mean air bricks? They should be 150mm above the outside ground surface, and provide continuous air flow through all suspended floors.
If the bungalow has all suspended floors then they should all have air bricks.
When you are under the bathroom look up at the bathroom floor and pipes. Look for water damage or leaks. Also check your WC for soil pipe area leaks.

Posting some photos of the outside air bricks and under the floor should be useful.
Is the bungalow on a hillside?