We are one of those poor sods with a rainforest in their loft this year (and end of last year). Roofer said we need new breathable membrane for £11K, that doesn't even include a new roof, just new membrane. He said this is the only solution and ventilation tiles etc won't work. We can't do that £££ at the moment so we are doing other smaller jobs that we hope will make a difference.
I put pipe noodles/insulation in every single cavity they could go in the loft and the very next day the loft was drying up 🎉. I bought a super accurate humidity/temperature meter and will start to gather data. I am also installing a sealed/insulated loft hatch, will seal gaps in ceiling (eg ceiling lights) and will get a ceiling extractor for the bathroom for good measure! I honestly think that this should do it. Will keep an eye on the conditions in the loft and will reevaluate at the end of this year.
Now the question! (Sorry, way longer than I intended) during my research PIV systems came up quite a lot. Positive Input Ventilation units take "fresh" air from the loft and into your house. With lots of people saying things like "I can breathe better now", "I wish I knew about this years ago" and "completely solved my condensation issues", "improves air quality indoors" and "ventilate house without opening windows" I think I want one!
I do worry though. lofts smells like... lofts, I am paranoid that the air it's not truly "clean" when the filter these units have are for dust only (G3). What happens with mould spores, animal waste (if you ever get intruders), loft insulation particles, etc etc!
Please share your experience about the freshness of the air and general usefulness of these things!!! :)