High humidity & white mites

NorthernLasd

Hi. 
After some advice as I'm feeling at a bit of a loss at the minute as what to do for the best. We live in North East England and have a North facing 3 bed semi with a conservatory to the rear. Had a full refurbishment downstairs over the summer to open up the sitting room, kitchen and conservatory area. I work from home currently so have set aside a corner of the room for desk area. Around 10yr ago we had real bad condensation issues,  mould etc, appearance of mould mites/psocids in rear bedroom, bathroom and conservatory. Following a full house survey we opted for a piv to be fitted with new bathroom and kitchen extractor fans and subfloor airbricks to allow underfloor ventilation. Humidity levels dropped significantly and no real issues til 2 yr ago when we spotted the mites again in the same places. Humidity around 65-70% in late summer then once heating kicked in and temp dropped then so did the humidity and mites disappeared. 2 yrs ago we had all new windows fitted upstairs as part of the works programme and although slight condensation last yr due to the piv not working as it should the mites made an appearance again and seemed even worse in the conservatory. We got several quotes and opted for a new piv to be fitted from envirovent along with a new bathroom fan and a cyclone fan in the kitchen. Conservatory was closed off for the winter as it usually was. We'd also had a log burner fitted in the sitting room. Once everything was up and running the humidity once again dropped, but to an even lower amount some days when We'd had the log burner on. Mites also disappeared.  Fast forward to now. Over the summer we had works done to downstairs and the builders had commented that the subfloor area seemed quite damp but it was after heavy rainfall. We are now back to the higher humidity readings of 65-70 throughout the house with the conservatory reading even higher. (Atmos unit on setting 3). We have also spotted the mites in the conservatory area in the same corner as previous years. I'm absolutely gutted as we have spent a fair bit trying to get the house the way we want it. I feel physically sick at the thoughts of them being around again. OH doesn't seem phased by them at all. Im now running a dehumidifer in the conservatory which is keeping the humidity in there at around 55% but as soon as its switched off it goes straight back up. The floor is suspended insulated floor with subfloor airvents too. Sorry for the long post but I'm asking the following questions for advice and reassurance- 
1. Will the dehumidifier cancel out the piv efforts?
2. Is it a case of keeping temp maintained downstairs and when outside temp and humidity drops then indoor one will as well and mites should disappear- again.
As the log burner seemed to have a better effect on lowering the humidity we will probably use that more this winter.
3. Is it likely we have a problem with the wet ground under the house as low level bricks appear wet and mossy but are nowhere near the dpc level.
Again sorry for the long winded post - many would have stopped reading by now. Any suggestions or advice would be greatly received.

RelievedSheff

Do you have any drainage runs beneath or adjacent to the conservatory that could be damaged? 

Is the wet beneath the floor localised or throughout the property? (We have high groundwater where we are so our sub floor void is often damp)

Keep_pedalling

The mites (or possibly some other insect such as booklice) are almost certainly harmless and are not the real problem which is damp and mould. Even if you can’t see the mould it will be there thriving on the damp conditions and providing a plentiful food source for the ‘mites’. Get rid of the damp and you get rid of the mould, get rid of the mould and you get rid of the insects.

jazzyja

Definitely get a few dehumidifier’s. Absolute game changer. 

I have a damp humid house. I’m end terrace in a hill and we get a ton of rain water so when it’s heavy downpour we feel it. I had mould issues in the back room often. Since investing in a dehumidifier I’ve had zero problems but I keep it on in that room majority of the evening when I come in from work and it fills right up with water it’s actually shocking how much it collects. I’m due to have my house repointed and an extra drain pipe fitted to carry away the water but for now this works a treat 

markin

The piv may now be less effective if the air is just going out the new window vents and fireplace.

A drain camera survey may be a good idea.

This thread also belongs over in the DIY/in-my-home forum.
 https://forums.moneysavingexpert.com/categories/in-my-home-includes-diy-moneysaving