A couple of weeks ago I've posted here regarding humidity in our house as I noticed it went up to ~75% indoors. I've bought a dehumidifier, but noticed that the humidity went up again after dehumidifying a room to eg 60%. Then, I installed a temp/humidity sensor outdoor and also calculated the absolute humidity to be able to compare easily. And... then I noticed when it's moist, like now, the outdoor humidity would be close to 100%. Thus, it would almost be impossible to get it <60% indoors, unless you would heat it to 25c +
Right now, it's 99% humidity @ 11c outside, which comes to 9.9g / m3 absolute humidity:
In the bedrooms it's 16.4 @ 65% which is as expected. In the living room it's 21c @ 55% which is almost the same absolute humidity as outside:
Still, it's important to heat your rooms to ensure RH doesn't reach 100% as that may cause dampness/mould. I've installed temp sensors & panel heaters in all rooms and set the min temp to 16c.
Yeah, I've basically come to the conclusion that in many cases it's just not possible to keep humidity under 60% in NZ all the time. It's partly how homes are built, but it's also just that NZ is just a pretty bloody humid place, at least in a lot of regions. All you can do is upgrade your home as best you can (good insulation and double glazing can help, but won't fix it on its own), and heat and extract moisture as best as you can.
We've upgrade our insulation, got some double glazing, a good heat pump, oil heaters in some rooms, 2x desiccant dehumidifiers and temperature/humidity sensors. We're a bit stingy with our electricity usage, so generally only heat rooms we're using. We manage to keep humidity to around 55-65% most of the time without blowing out our power bill. Not really any problems with mould (which we did before we developed this strategy - even 70% is enough for mould to form). I'm not sure there's a lot more we can do, short of running heating/dehumidifiers 24/7 which would probably triple our power bill.
The real issue is our building regulations are an absolute joke. It should be mandatory to include ducting to each room and then at least include a balanced pressure ventilation system. That alone massively reduces errant humidity from sources like cooking / showering etc (no, an asthmatic range hood or pathetic fan wired to the light switch is NOT sufficient).
I live in a crappy 80s house with single glazing and poor insulation. I’ve got to run 3 dehumidifiers 24/7 at 60% here or else it’s mould city. In winter it’s massively helpful if I heat the place - have heat pumps in every room just about and as the house is pretty open plan I run them on a timer to maintain a minimum of 21 in the living areas during the day and 18ish when sleeping. In summer I cool as well which removes the humidity from the air.
But you’re right, NZ, and specifically Auckland is hella humid as it’s a thin piece of land in the oceans. I’ll be moving to central NI soon, bit further from the coast. The weather seems way more stable compared to living so close to the coast, and the slightly more sane property market doesn’t hurt either.