Keeping Humidity down to prevent Mould

Benzino · 18-11-2021 1:08pm #1

Hey,

I know there are tons of posts about how to deal with mould, but I'm wondering how to keep Humidity down to <60% inside?

I don't know the current humidity, I've a meter coming tomorrow, but I have found mould under a window and potentially mould mites, so I know it's an issue.

I have a dehumidifier, should I be leaving the windows open when that is running, or should they be closed (along with doors) while the dehumidifier on, and then open the windows when it's off? I've read conflicting reports online about this.

Thanks!

steamsey · 19-11-2021 9:54am

If you leave the windows open, with the dehumidifier on, you will be attempting to dehumidify Earth. Definitely keep windows, doors closed if you want to dehumidify a room. Is it a good dehumidifier? You could be wasting your time if not. I've a ProBreeze 20L and it does a great job. You could open all windows in the morning for a few hours and get a good air flow going. Then close windows & doors and turn on dehumidifier later in the day.

The rooms with the mold must be underheated for the condensation to be occurring - try heating them more. If you have cold spots on walls they will be prime targets for condensation (as warmer air comes into the room) which can cause mold. Keep these areas clear of furniture if you can and wipe down any excess moisture daily. Ensure rooms have working vents, extractor fans in bathrooms and kitchen. Don't dry clothes indoors.

Not sure if this affects you, but if you have for example a fire or stove or just a well heated downstairs then the warm air will travel upstairs and just condense on colder walls in bedrooms. This is where heating those bedrooms comes in.

If none of that helps, might need insulation in these rooms to keep walls warm.

Lumen · 19-11-2021 10:49am

@steamsey wrote:

If you leave the windows open, with the dehumidifier on, you will be attempting to dehumidify Earth. Definitely keep windows, doors closed if you want to dehumidify a room.

I know this seems logical, but I have found via experimentation that demisting a bathroom after a shower works best with the humidifier on and the window open, at least until the mirrors have cleared.

Benzino · 19-11-2021 1:47pm

Thanks for the replies!

Yeah we find the dehumidifier good (it's an EcoAir one, cost about 200 euro I think at the time), it's great for clearing the bathroom after a shower (no vents, just a window). The room with the mould has no vents, so we just need to be better at opening the windows more and putting the heating on more. The mould appears on the inside of the front facing wall and unfortunately it's a rented property so not a lot we can do regarding better windows, insulation or vents (and owners plan to sell, so won't be investing in it).

I did your suggestion today, open windows for about 2-3 hours this morning and now the dehumidifier is going with the windows closed. The hygrometer has arrived so I will be keeping checks on the humidity in the room.

The plan tomorrow is to move all items out and into storage and try to tackle the problem with mould remover.

My main concern is the adjacent bedroom where we see no mould but have noticed a few mould mites (well at least we think they are mould mites). I'm not sure how far they can travel, or if it suggests there is mould hidden somewhere that room too, so will have to investigate nooks and crannies in that room. It's gonna be a fun weekend 😅

Stoner · 20-11-2021 11:40pm

also, i have some smart TRVs in my house, all the rooms have rads, I don't use all the rooms, but I heat them all if necessary, so spare bedroom would be set to say 15 degrees they have a boost button on them if they are in use. This is not very warm, but warm enough so that some of the moisture wont fall. Cold walls will still be an issue, but this does help, not heating rooms and heating others, as highlighted above is an issue. keeping doors closed at night can help to stop the warm air getting into the colder walls and condensing on the colder external walls.

obviously something like external insulation can really help. The only place i ever got mould was in the upstairs shower cubical, two of the walls were external, once I had the external installation installed I have no had any black mound on the grout appear.

I had 80mm of bead insulation blown into the walls before that, and it did not solve the issue, but it did take a chill out of some unused rooms

So I address it all with external insulation

Smart TRVs

Heating system rebalance

Benzino · 21-11-2021 12:14am

We heat all the rooms, this particular room is pretty much unused, but is heated like the rest of the house. Unfortunately this house has no smart functionality regarding heating. Unlike other rooms, there is no vent in this particular room.

The sensor I got is pretty interesting (although I cannot confirm how accurate it is). My findings so far are:

Opening windows seem to have a short term effect, it can cause a drop in humidity by as much as 5% (so far) within an hour, but leaving it opened for long durations such as 2 hours and usually it will rise above 60%rh. This is when the dew point is apparently 46-48F in the city.
Heating has a marginal affect. The RH of the room doesn't really differ much after 2 hours of heating going. In fact sometimes it rises.
The dehumidifier has a huge impact, can reduce the RH by over 10% within 2 hours. As soon as it goes off though, it begins to rise, can go up 5% within an hour.

Unfortunately our Dehumidifier doesn't have the ability to turn itself on at specific times or at specific RH %, gonna see if I can use one of the smart plugs lying around to try and achieve the same thing.

Maybe we are not heating the house enough? Obviously with fuel prices so high at the moment, I don't want to be putting it on more than we need (and we are not cold in the house with our current settings), but like I mentioned above, 2 hours of continuous heating basically had no impact, in fact it sometimes increases the humidity.

LillySV · 21-11-2021 12:18am

leave the humidifier on for afew hourse every so many weeks , works a treat . Windows closed as guy advised already . When using it make sure you have curtains open to extract all the moisture around windows

Stoner · 21-11-2021 12:30am

https://www.boards.ie/discussion/comment/118199640#Comment_118199640

the sonoff 16th has a humidity sensor lead. would set you back about 20 euro

also you can use the humidity setting of one sonoff to switch a different sonoff , so say a cheaper 10 amp one, or get the sonoff inline plug for the humidifier you have.

Cheapest option, if placement suits is to have the 16 amp unit with the humidity sensor plugged into in , wired inline with the flex of the humidifier

you'd have full wifi control

Benzino · 21-11-2021 12:56am

https://www.boards.ie/discussion/comment/118199683#Comment_118199683

Oh interesting, I hadn't heard of these. Will look into getting one over the black Friday sales, cheers!

Argo foc yourself · 23-11-2021 12:54pm

Following this topic with interest. I have a problem in one bedroom. I am getting a lot of black mould and spots along the window reveal. Also along the windowsill against the window. The windowsill was actually wet this morning. Any suggestions? The windows were replaced about 5 years ago. The problem was there before this.

Would ripping down walls and replacing with insulated boards make any difference?

I am getting a moisture reading of 35% along the reveal.

Windows are opened for a few hours every morning.

It is north facing.

Walls were pumped externally.

Triple glazing windows installed about 5 years ago.

KaneToad · 23-11-2021 12:57pm

A cheap plug timer can ensure the dehumidifier comes on/off at key points during the day.

Emma2019 · 26-11-2021 9:15am

https://www.boards.ie/discussion/comment/118210633#Comment_118210633

Would you consider leaving one of them locked on open all the time for a week and see does it help? Box rooms are usually the worst as they have 2 external walls. I've been leaving the small window locked but open a crack and haven't had any mould so far.

10-10-20 · 26-11-2021 9:47am

https://www.boards.ie/discussion/comment/118210633#Comment_118210633

What age is the house? If you have triple-glazing and the units were installed correctly, then it sounds like a cold bridge at the window reveal.

Argo foc yourself · 30-11-2021 8:53pm

https://www.boards.ie/discussion/comment/118225176#Comment_118225176

built in 1997. installed by a reputable company. Issue was there beforehand. Also have it in another room. kitchen corner where two external walls meet.

Argo foc yourself · 30-11-2021 8:55pm

https://www.boards.ie/discussion/comment/118225004#Comment_118225004

it is not a box room. it is north facing. and the room is adjoining to the semi detatched next door.

10-10-20 · 30-11-2021 9:29pm

I'd guess it's the cold bridge at the reveal then. It's likely to be caused by what's called a "return brick" where the builder uses a brick rotated 90-degrees to close off the window cavity. This gives good support for the windows later on, but it creates a cold-bridge at the reveals. The problem appears to be worse at the bottom of the window as this is where the coldest moisture-laden air rolls off the window pane and creates a mould growth.

Even if the walls were pumped with bonded bead or exp-foam, this problem would remain as the cold-bridge can only be slightly improved but not overcome via the cavity insulation.

A remedy for that is to remove the reveals, seal up the return bricks as well as possible, check/seal the lintel and then apply a thin (~27mm) plasterboard to the reveals. It's a bit messy and is a difficult DIY job due to the use of adhesives and then plaster skimming, etc. It would be more feasible if you were considering installing insulated plasterboard on the North wall of the room. That's what I'm doing currently in my master bedroom - tearing out reveals and then overboarding with 50mm board (and 27mm in the reveals).

Keeping Humidity down to prevent Mould

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