High humidity

[a twig]

Again allowing for potential variance in accuracy of meters, in a well maintained UK period property I’ve never seen below 55 even in the middle of a cold dry winter week with the wood burning stove roaring away in the living room.

Based on the meters we have I’m usually pretty happy between 65 and 75, if it goes much north of that I’ve usually forgotten to turn a kitchen / bathroom extractor on somewhere.

 

[DaveG]

Here’s a super useful chart to show the relationship between RH and room temperature. In winter especially you may need to make sure RH stays at 60% or below but it all depends on what temps you run at.
What I can tell you is older houses don’t like being as warm as modern houses. But just as crucially they don’t like being cold either! It’s going to be my first winter in a stone walled house but I’m going to attempt to keep at 19 - 20c. In our previous more modern home we’d often be at 21.5 over the winter months

 

[Stevers]

Constant low heat could be our friend in keeping surface temperatures above dew point. In the example above maintaining an overnight temperature of even 14C (as we do at minimal cost with smart heating in our basement (and all through the house), could make all the difference at higher RHs.

 

[Stonehouse]

Good afternoon all

Still battling mould…I can now confirm it is linked to humidity as suspected. 90% humidity this week outside and despite running dehumidifier, mould has appeared. It quite likes to settle where the skirting touches the external walls which makes sense as the external walls are cold.

Some areas of the dry mdf have got mould on this week and they didn’t have before.

Still debating whether to remove the mdf. Mixed opinions. I’ve been advised to sort the humidity out as that should prevent the mould and therefore I shouldn’t worry about the Mdf as it’s not the Mdf but the moisture in the room? The Mdf was pre-primed and has been painted. Although on reflection, it would have been ideal to paint the edges including the bottom. In areas, I can see mould growing at the very edge.

If we had timber, I’d assume that moisture could still appear where skirting touches the wall as the walls are cold?

If anyone has any advice, it would be greatly appreciated. Thank you

 

[Cubist]

Sadly I think we are going to be seeing high and perhaps increasing levels of humidity in the future, certainly if the last two years are anything to go by. Unfortunately I think this trend may also bring with it a corresponding increase in the incidence and extent of detrimental impacts on our properties from all sorts of nasties.

Still debating whether to remove the mdf. Mixed opinions. I’ve been advised to sort the humidity out as that should prevent the mould and therefore I shouldn’t worry about the Mdf as it’s not the Mdf but the moisture in the room? The Mdf was pre-primed and has been painted. Although on reflection, it would have been ideal to paint the edges including the bottom. In areas, I can see mould growing at the very edge.

In my experience I've found MDF to be a material that absorbs more water than one may expect and hold onto it longer than wood. As well as losing much of its physical integrity it can also be a safe harbour for some of the nastier moulds and fungi. These considerations, in addition to the health risks attending working with the stuff, have led me to avoid its use and to get rid of it if/when the opportunity arises.

If we had timber, I’d assume that moisture could still appear where skirting touches the wall as the walls are cold?

Yes, that's entirely feasible. However, a good installer of new skirting, or any other moulding for that matter, would often paint or otherwise treat the wall facing side before fitment.

 

[a twig]

Second vote for removing the MDF - the only times I’ve had successful MDF skirting installations (even when primed and painted) was when plastering was done down to a batten fixed at the skirting height and then the MDF attached to that, i.e. creating an air gap behind the skirting.

If it is directly attached to a lime plastered wall then in my experience mould will result. Generally I aim for pine skirting as a minimum as I have had far fewer issues with that even when fixed directly.

 

[a twig]

Also if the walls are that cold relative to the house, that’s often a sign of moisture ingress into the walls so I’d be investigating potential causes of that (rain water goods, leaks, ground levels etc)

 

[Cubist]

With respect Stonehouse I think you need to reconsider your priorities and the potential root causes of the damp issues.

You must remember that mould outbreaks can behave rather like an iceberg insofar that you will only see 10% or less of the true scale of its magnitude. By far and away the majority of it will be hidden from sight behind fittings such as skirting boards and other materials abutting the walls. Some moulds can be extremely dangerous to the health of small children and the aged and can kill. It is not wise to be complacent and assume it is only an aesthetic/cosmetic issue and you should investigate further to establish the true extent of its presence. I would strongly recommend that you remove at least some of the MDF skirting to investigate further before developing a plan of action after perhaps taking further advice.

You do not mention the nature of the the floors in the affected rooms. Are these solid or suspended wooden boards of some kind? If the latter there is a strong possibility that the floors joists and planks are also contaminated

You seem to be assuming that the source of the damp is associated with rain driven against external walls. I might argue that this may be an unsafe assumption regarding the root source. The poor weather over the last couple of years, and this last in particular, has contributed to a a general increase in the height of normal groundwater levels. Depending on the topography of the land on which your house stands and the drainage characteristics of the land itself, any increased level of groundwater may be finding its way into the foundations/footings/brickwork/floor slabs. Some recent contributors here have reported finding water in the voids beneath wooden suspended floors due to this very cause.

Has the wood-burner in which you found white mould been used recently? If so, its not mould, white deposits are frequently produced when these stoves are burning efficiently.

As to the cabinet on which you've found white mould on the underside. Does this usually stand near or against one of the affected walls? Does it stand over a rug or carpet and are these damp to the touch? What is the construction of the floor beneath?

I apologise if you feel my tone or language is a little insulting but I believe you may be underestimating the scale of the health risk to yourself and those around you.