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Comment by sourcesmith | Hacker News Reader

The mechanical ventilation with heat recovery deals with the humidity problem.

And introduces its own mold problem.

For properly commissioned systems?

More important is properly maintained. People tend to forget to change filters. Those are a prime breeding ground for mold, and your central ventilation distributes the spores throughout the house.

That's why people should change the filter and have a yearly inspection, just like for cars.

But the filter is on the ingoing side and not on the outgoing side, so no moisture from the inside can aggregate there. Only the humidity from the outside but we've never had problems with that.

> But the filter is on the ingoing side

Okay. I guess I have been wrong.

My HRV has filters for both inbound and outbound airflow. I do change my filters regularly, but even in the rainy Pacific NW I haven never seen any mold growth on either filter, and I have an RPi logging air quality data with a decent sensor, so I can see my PM2.5 and PM 10 are both near-zero.

What if I don't want to live in a plastic box?

What plastic box would that be?

All the closed cell plastic foam needed to meat passive house requirements.

A point. All the energy savings disappear the moment you open a window.

I think this has already been addressed by the sibling comment to my question. Insulation does not have to impermeable. Its purpose to prevent the loss of air carrying heat with it, not the transfer of moisture/humidity.

If it's permeable then water will condense inside it and it will develop mold and deteriorate. That is the fate of all of these passive houses.

Not necessarily. Mold grows in certain conditions: food availability, right temperature, water/moisture.

Ideally you would want your insulation outside of vapour barrier:

* https://www.buildingscience.com/documents/insights/bsi-001-t...

* https://www.youtube.com/watch?v=rkfAcWpOYAA&t=22m58s

* https://www.youtube.com/watch?v=hTwq-qUnr9I

Because we stood in front of the same decisions this year, I can only recommend to use wood not stone as building material. And wood fiber insulation. Building techniques in that area are pretty advanced. (At least I hope so, let's talk about it in twenty years again :D )

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