Humidity in the House....Talk to me!

[dlockers]

Hi folks,

I am trying to wrap my head around humidity in the house (bedrooms, attic), the workshop, and my garden room. I feel I am misunderstanding some crucial bits around how it is calculated and what my sensors are showing me. For example, right now I am seeing an outside temperature of 8 degrees, with a humidity of 91%.

The house.bedrooms is pretty well sealed up - double glazed, insulated subfloor, modern doors. I do have trickle vents on the windows but these are closed (although they aren't fully sealed or insulated). We have started to notice condensation on the OUTSIDE of the windows, which is presumably a good thing.

Bedroom with 1 outside solid wall:
Current Temp: 17.8*
Current Humidity: 74.6%

Bedroom with tiled facade/single wood thickness wall:
Current Temp: 17.9*
Current Humidity: 74.1%

Bedroom with 25mm insulation on external walls:
Current Temp: 17.5*
Current Humidity: 74.6%

Bathroom with 25mm insulation and extractor (3 hours following showers etc):
Current Temp: 18.3*
Current Humidity: 76.7%

The house.attic is definitely draughty but no specific alterations to enable ventilation have been made. I have 50mm PIR down the hipped roof and 270mm insulation. I assume I get draught as a side effect of the eaves not being sealed - I can't see any visible ventilation holes. I have allowed 50mm between the PIR and the roof.
Current Temp: 11.7*
Current Humidity: 85.3%

<outlier as data from same time not available>
The workshop is very poorly insulated - single skin wood cladding, the roof is floating with gaps around all the eaves, there is a sizeable gap around the door.
(sensor has dropped off so using data from 1st Nov)
Temp: 6.6*
Humidity: 82%
[outside was 6* and 90% from what I can tell)
</outlier>

The Garden Room is totally sealed with an AC system.
Current Temp: 17.4*
Current Humidity: 80.9%
-- Interestingly I can't seem to get the humidity much lower, even with the Split-AC system on Dehumidify mode?

So what I can't work out - from a principled point of view is:
* Is the humidity number I am looking at "correct"? I have read something about relative humidity and water content at different temperatures.
* Is there a problem? It seems even I ventilate, because the outside humidity is so high, I can't really achieve anything?

Thanks!

 

[dlockers]

Is it always that high, or just temporarily due to the weather?
(high humidity happens even in my new build if it's high outside)

It is pretty much always this high. I often have doors open, windows open etc. I guess weather dependent to the extent that during summer it was lower:

I have very similar readings for temp/humidity in all of my rooms, similar situation with insulated external walls (75mm).

I also have a PIV in the loft, which brings humidity down marginally (a few % at best), and have read that the "average" humidity should be less. Not sure how that is meant to work as outside its 86% humidity at the moment and without a dehumidifier that is just not going to happen. Open the windows and again it will drop the internal humidity slightly due to the breeze, but still not below 75%.

Seems to be another of those numbers people get hung up on, providing you have enough air movement and surfaces insulated to prevent them dropping below the dew point then it should be fine. Even in the height of summer when it was 28 degrees in one of the rooms, humidity was still 61%.

Yeah doesn't seem like anything I do makes an ounce of difference. Bathroom windows open, closed, doors open throughout day. I guess I could heat the house really high every week or something? :S

I find dehumidifiers are less efficient in cold, heat the air up to 20-21 first. As mentioned above, then air has more water in it to remove.
For me, 18C and 70+% humidity is panic mode. It means there will be condensation around cold corners and windows overnight. Means mould in hidden spots.

Airing with 8C outside should help, that air will be drier than indoors. But heating the air up is the best humidity soak

I've put the dehumidifier on in here; we'll see how it goes. This room is generally at 20 odd anyway.

 

[dlockers]

I'm in a similar situation with the two lofts at each end of our property. Current Tapo readings are ~14ºC and 76% humidity. I was thinking about investing in a little dehumidifier with a 12L tank for both. Then just having Tapo control the on/off with a range %. But is it worth it for a loft? One of the two lofts has no windows and no ventilation. I have a nest thermostat in the main hallway and it is reporting 20ºC indoors and 64% humidity.

I've even considered this but I recently sold my Dehumidifer on marketplace, lol. Also, the house has been fine for over 100 years.

 

[dlockers]

The house is fine now?

It isn't a problem really as long as ventilation/humidity is controlled and you aren't getting mould. That's my understanding.

Its still very frustrating though, to be constantly dealing with 70%+ humidity levels when the optimum recommended is 40-60%. I get condensation on my windows in the morning under certain conditions. There are areas I have to keep an eye on for mould formation. I'd rather not have these problems but like you I don't know if its possible to stop it as its largely due to the construction of the house.

See my previous comment about chimneys and how they used to help drive ventilation and lower humidity. An open chimney (according to Google) can draw (depending on size) several hundred cubic feet per minute. 200 cfm would be 338 m3/hr. In a house with volume say 300m3 that is a whole air change every hour. There's no way we get anywhere near that in our modern homes with no open fire use and sealed up windows.

Yeah the house has been fine for 100 years and continues to be. I think we cross the dew point on the skirting board on the tiled false wall/detail at the front on the second story - but I'll be vapour barrier and insulating that next year. The rest of the house feels perfectly fine; the only issue is the Govee humidistat whinging at me.

I think you're correct RE: chimney. I've actually got mine plugged at the minute, as the draught is killer. I will unplug it when the weather starts picking up again Feb/March.

I may do the Garden Room experiment....we'll see.

 

[dlockers]

I set mine to a target value. It’s hard to beat Mother Nature, my aim is to take the humidity down a notch. Like I would aim for 55% (run it overnight) then turn it off in the day, it will rise slowly in the day and then do it again next night if rise high enough.

I don’t have it on all hours of the day, just a few weeks in the winter.

What's the "point" tho? Is going from 75 to 50 to 75 to 50 "achieving" anything?

Sorry for outrageous use of quote marks, but it seems like you're chasing numbers vs. actual outcome.

 

[dlockers]

I feel like this is a bit con from big-dehumidifier. I don't remember my parents fretting about this nonsense nor having a billion relatively-expensive sensors dotted around

 

[dlockers]

I aim for 50% in the machine but anything around 55% I’m happy to have it off.

I’ll leave it off until normally until it creeps back up to like 65%.

OK but why? It is still 65% shortly after anyway

 

[dlockers]

Well, in my house…for example, I will set it to run at night. It will stop sometime around 3am and I go to work, it will creep up slowly in the day but not rise to like 70%, it get to about like 60-62% or so the next day. It’s that amount of time frame.

So in my situation I don’t need to have it on 24/7.

OK but why are you running it/bothering anyway? Why is reducing it to 60 for a bit of the day for it to just rise back up a priority at all?

 

[dlockers]

Are there PIVs that are DIYable?

 

[dlockers]

I think that's what I may have had in mind (and assumed not really DIYable).

Are Dehumidifiers effective on top of things? I have a small space on top of a ~5ft wardrobe.

 

[dlockers]

Seems some are mindlessly chasing numbers reported on their thermostats than any actual benefit.

This is my current situation -

(the (S) sensors are the Hue motion detectors, miles off accuracy).

Looks like the house is "fine" at ~65% but the attic still high. I think I have a hole in the roof from the old F&E tank --- I might stick a dehumidifier up there. It'll all get fixed when we extend/get the loft converted.

 

[dlockers]

The attic isn't high because the temperature is way lower, it will be mirroring what's outside to a large extent. Like the shed is.

What do you mean it isn't high? It is 80 odd percent. Or are you saying because that's relative humidity because it's cold, it isn't an issue?

Are people chasing "absolute" humidity or relative humidity figures? I thought it was the latter?

Your garden room is high - perhaps the wood/plastering is still drying out internally. This should be a fairly well sealed room so shouldn't be this high when unoccupied and heated.

I've no idea why it is so high. It falls off a cliff when the heating comes on (80% down to ~70%). This is with AC/heating on, it must just be "me" being inside here.

 

[dlockers]

Quickie (and possibly theoretical) - If RH reaches 100%, does that mean that the air cannot hold any more moisture and will start dumping it out as water if it gets any higher?

You're asking if you can create a microclimate/rain cloud in your house? I am also interested in this

 

[dlockers]

Seems some are mindlessly chasing numbers reported on their thermostats than any actual benefit.

This is my current situation -

(the (S) sensors are the Hue motion detectors, miles off accuracy).

Looks like the house is "fine" at ~65% but the attic still high. I think I have a hole in the roof from the old F&E tank --- I might stick a dehumidifier up there. It'll all get fixed when we extend/get the loft converted.

^

So as per latest discussion; I don't actually have an issue then? I'm at the top end of recommended but within the tolerance of the sensors probably fine?

 

[dlockers]

Yeah you're lower than me. Solid wall older house will always be worse than new cavity wall house (assuming new house is ventilated).

Any mould spots in corners or behind furniture, especially on external walls?

Tiny bit on skirting board by the french doors - nothing anywhere else as far as I can tell.

 

[dlockers]

I'd maybe be checking calibration on some of these humidity measures ..... (earlier post somewhere) had done that on one I picked up for parents ... you put them in a sealed bag with a brine solution.

Only practical thing to do is check them against each other tbh