Humidity Question...

Lizbetty

Good morning folks

I would be really grateful for some advice on humidity levels. We have a 1930's detached house with a square bay to one room. We noticed when we moved in a year ago that the bay had some pretty bad damp in the corners, the general consensus from builders and damp proof men seems to be that it's condensation as it's a cold wall. It does have holes as if cavity insulation is in there, but I figured it was a duff job when I used the thermal detector and discovered a few large cold spots in other walls.

We have knocked through and now the bay is in a large kitchen diner, which I am conscious may exacerbate the issue with condensation from cooking.

I have a dehumidifier on low next to the bay (mainly because it's cheaper to run!) and a cheap digital hygrometer which is showing between 55-60% humidity in the bay window area.

We have just had the entire room replastered and prior to putting the dehumidifier there, black spots of mould were showing again I'm keen to try and manage the problem and wondered whether this level of humidity is ok or whether there is anything more I can do to reduce it further if needs be?

Thanks in advance for your help, this sort of thing gives me sleepless nights!

Best wishes

Lucy

Lizbetty

We do have a cooker extractor hood which is externally vented too, unfortunately I chose a kettle to use on the induction hob which creates a lot of steam but I do switch the hood on when boiling the kettle to help reduce moisture.

Robwiz

The danger level for condensation and mould is generally stated as 70% but I haven't seen the original research papers. We leave our dehumidifier set at 55% and with the variations in temperature and external humidity it keeps the room RH around 60% most of the time and there's no sign of mould.

It's amazing though how quickly the room RH rises when you do any sort of cooking – even toasting a slice of bread makes a difference!

We also use a kettle on the induction hob. When boiling 250 ml (for one mug) I notice that the water boils for a while before the whistle starts, so I know to switch off by the sound of the water in the kettle.

Horizon81

55-60% isn't abmormal as far as I'm concerned. My house stabilises at the mid 50's. It rises when drying washing and cooking etc so I knock the dehumidifier on to get it back to normal levels.

DRP

Horizon81 wrote: »

55-60% isn't abmormal as far as I'm concerned. My house stabilises at the mid 50's. It rises when drying washing and cooking etc so I knock the dehumidifier on to get it back to normal levels.

Agree. Our house is 55-65%.

We also have a known problem area where there is damp underfloor and poor ventilation - the RH is about 70-80% there. Clearly high humidity cannot be the only factor as we do not get mould growing in that area (property is a 1901 terrace with solid stone walls, no insulation).

saveallmymoney

OP you need to work out the "Dew Point" - measure your humidity / temperature and then you can see if the "cold" wall is safely above the dew point.

http://www.dpcalc.org

diamond_dave

I live in a 1880 semi with exactly the same problem- and what I discovered was that whilst the main walls were 30" thick and built of stone the bays themselves are constructed of single brick. What happens is that any moisture/ condensation hits this cold surface and you get a wet surface. I have battened and insulated the bays, finishing with P/b and skimmed and the problem is solved. Ok, the square bays were a bit fiddly, but with a bit of effort, all good.The air bricks that are let in to ventilate the floors add to the problem by creating a cold spot on the wall.

bloss0m

I live in 1930's semi and we use a dehumidifier which isnt on all that much humidity level tend to be around 50-60% rises a little is steaming veg. We have fans in kitchen and also in bathroom

SG27

The humidity in my 1700s cottage is currently around 35 - 40% with the fire going. It's more like 60% in the summer, or higher when humidity is high outside.

Lizbetty

saveallmymoney wrote: »

OP you need to work out the "Dew Point" - measure your humidity / temperature and then you can see if the "cold" wall is safely above the dew point.

http://www.dpcalc.org

Thanks for all of your replies. I feel a lot calmer about it now! :beer:

The dew point calculator is fantastic! I managed to find an android app on my phone and so I can check whenever I need to, haha!

A neighbour did mention getting the bay insulated, they said we would lose space but to be honest, we weren't planning on putting anything at all in the bay as it would just create more of a problem with damp if we did as it is at the moment.

That might be something to look at in the next year. The plasterer had a look and said the bay might need repointing too as the previous owners had the entire house repointed - rather than grinding out the old pointing they just wiped a load of new mortar over the old stuff, the plasterer said. It's blown in places (which we thought was cavity wall tie issues!) and that that can't help with any damp.

I really appreciate your replies and feel like a can breathe out a bit now! (Obviously with the cooker hood on to catch the condensation, haha!) Thanks again. :T