Condensation or damp

noseall · 27 May 2018

Ventilation on its own will not stop mould. Ventilation is not a sensible option in the Winter. Insulation is.
Sorry chaps but you are very naïve.

I am not.
Not very observant either....

EFLImpudence said:
As has been suggested above, some cavity insulation will bridge the gap causing a problem.

Solid 9" walls.
Say no more.

IWalkLikeHimaMartian · 27 May 2018

noseall said:
Ventilation on its own will not stop mould.

Ventilation must be combined with heating to avoid mould or other condensation related problems.

Empty houses, flats do suffer from condensation problems.
I think Elfi mentioned an empty car overnight, in the morning there may be condensation on the inside. This is similar to what happens in empty properties, only in a far faster process.
Air can enter (remember that external air [in temperate climes] can be anything around the 50% to 100%, usually at the higher end) then cools, What happens to the moisture that was in that air? Obviously if the dew point is reached that moisture is deposited on cooler surfaces.

Take a typical scenario for an empty property: a warm day, high external humidity, moisture laden air enters. Overnight the air and the building cools (the building, inside, may have been quite a bit cooler than the external air anyway!). Some of the moisture in the air condenses.

Additionally, in my previous incarnation I demonstrated how the building fabric and furnishings can absorb moisture over time. It can take many months, even years, for a building with a high moisture content in the fabric, to 'dry out'

A final point, mould needs a RH of between 65% to 100% to survive and grow. If the long-term RH is kept below 65% mould will not form or grow.
This diagram explains it:

(http://www.aboutdehumidifiers.co.uk/optimum-humidity.html

These references were included in my original paper, which is why woody's allegation of plagiarism was laughable, but heinous.

BTW, if a building suffers from a great variability in RH (due to large family, household habits of drying washing, etc) then some stability can be achieved through the use of construction materials with high hygroscopicity. Obviously, this is not a simple matter of replacing some materials with others. More a case of design of the building, in the construction phase.
The materials will absorb moisture during times of high RH of the air, and release that moisture during times of lower RH of the air.

“They looked at the water vapour permeability of a whole range of products and estimated the following absorption ratings:

• Plasterboard painted with emulsion - score 40
• Concrete, unfinished – score 90
• Brick, natural finish – score 110
• Softwood, unfinished – score 150
• Strawbale behind lime plaster – score 240
• Durisol board behind lime plaster – score 250

They reckoned that anything with a score of 50 or higher would work as a humidity buffer. They also pointed out that such walls work automatically, don’t break down and require no energy to operate.”

“What you don’t so often hear — in fact just about never — is what proportion of your home is made up of water. I am not talking about water in the pipes and in the hot water cylinder and various tanks: I am referring to water bound up in the fabric of the house. There’s a surprising amount.... very possibly around 10% of the mass of a house will be made up of bound-water. ....

... Masonry materials, even concrete, are hygroscopic to a surprising extent and can take on and release moisture according to conditions.....

.... The fact is that a detached house, which can weigh anything between 50 and 200 tonnes, depending on size and construction methods (and that’s excluding all the foundations), could be holding as much as 10 tonnes of bound water within the walls, floors and roofing, and a lot more within the fixtures and fittings as well....

.... All this bound-water doesn’t have to stay bound. When conditions dictate otherwise, it can either absorb more water or it can release water via evaporation. This does rather depend on the surfaces surrounding the materials: some are very water permeable, others are not. Exactly how much water transfers between the solids in the house and the air in and around it is unknown - it’s never been measured, as far as I know – but it’s likely to be fairly substantial. If it amounted to a change of just 1% of water by weight, we would be talking about 100 litres of water....

... Because the water vapour is floating around in the air, if you swap the internal air for some external air, then you will also be swapping the water vapour levels as well. You are basically sucking water vapour out of the house.

Diffusion is ignored in all this. The fact that there is over a thousand times more water bound up inside the building than there is floating around in its airspace just doesn’t come into the equation, despite the fact that everyone agrees that moisture levels within a building are constantly changing. “

http://www.housebuildersupdate.co.uk/2007/07/how-should-we-handle-humidity.html

References also included in my original paper, woody!

The Baker · 27 May 2018

One thing the original poster might want to do is use a USB Data Logger to measure the RH. This would enable him to show the Tenant the RH of the air in a particular room over a few day/week.

Tim

https://www.lascarelectronics.com/easylog-data-logger-el-usb-2/

motorbiking · 27 May 2018

One part of my house has a 4.5" brick bay window, i.e. single skin brick. We have a dehumidify on timer and the room has a radiator without thermostatic control (the only one left). We get mold on the dwarf wall under the bay. Some walls are just so poorly insulating that any moisture in the air will condense on the surface. Its on my to do list, but really the only option will be celotex and plaster board. When these house were built people didn't expect to heat their houses to 21 degrees and the heating was very much hot and cold.

anobium · 27 May 2018

Condensation, if that is what it is, only occurs at dew point.
Solution is one or a combination of 3 things, Ventilate , insulate, or increase heat.
Simples.

IWalkLikeHimaMartian · 27 May 2018

anobium said:
Condensation, if that is what it is, only occurs at dew point.
Solution is one or a combination of 3 things, Ventilate , insulate, or increase heat.
Simples.

As you nearly rightly said "a combination of things".
Ventilation (or heating) will not work on its own. The two must be combined. Cooler air comes in, is heated, thus reducing the RH, but increasing the capacity of the air to hold more moisture, which is then ventilated. The cycle continues ad infinitum.
Insulation alone does not reduce the RH, which is the real cause of condensation/mould.
Insulation merely reduces the amount of and the temperature difference of cool surfaces, especially the lesser hygroscopic surfaces. Thus reducing the risk of condensation forming.

Fir instance, today is a warm day, I have all the windows and french windows open. I would guess the temperature outside is about 22°C with a (guessing) RH of about 70 - 72%.
It is cooler inside because the house has stone walls, about 1 meter thick with lime plastered walls.
Thus the air cools down when it is in the house for a while, to 20°C, and the RH meter is showing 74%. I could not physically ventilate any more, and the RH is increasing. If the walls were not highly hygroscopic, there is the perfect conditions for mould to grow, except the thickness of the walls means that they are not so cold compared to the internal air.
If the surfaces were less hygroscopic, moisture could condense on the surfaces, this moisture would not be absorbed, and mould could grow.

It is not a worrying situation. This evening, when we close the windows, the latent heat will be released, the temperature inside will rise, some background ventilation will continue, the highly hygroscopic walls will release some moisture, the house in general will reduce in RH and moisture content.
The cycle continues ad infinitum.

EFLImpudence · 27 May 2018

noseall said:
Ventilation on its own will not stop mould. Ventilation is not a sensible option in the Winter.

FFS Noseall - Houses, homes HAVE TO HAVE ventilation.

Insulation is.

As said - it may help mask the situation.

Sorry chaps but you are very naïve.

Not sure that's the right word, but still,

I managed fifteen flats for ten years until I retired.

The flats frequently changed and could, with either -
tenant A - be a smart clean, little palace, or
tenant B - be a mould ridden smelly hovel.

Is the solution to tenant B insulation?

I would also point out that tenant A was usually foreign and tenant B wasn't.

Not very observant either....

Solid 9" walls.
Say no more.

Had we not moved on to a more general discussion where cavity insulation was mentioned and so my statement is true.

If not, and we are only discussing the OP, then there is no problem; it is such a small amount of mould that it will disappear with a wipe.
So, no need for insulation, then.

No more "yes it is, no it isn't". If you disagree, carry on disagreeing.

EFLImpudence · 27 May 2018

Oh, one last question for Noseall:

If you block off a chimney, do you have to install
A - ventilation or
B - insulation
and why?

noseall · 27 May 2018

EFLImpudence said:
No, you must ventilate - to remove the moisture.

No kidding. I'm a builder and I fit a multitude of vents in various locations frequently.

Ventilation will only partly do the job. The OP needs to insulate any walls that will struggle to rid themselves of moisture. The OP will also struggle to ventilate in the Winter that's why removing the cold spots (dew points) is a must.

noseall · 27 May 2018

EFLImpudence said:
Oh, one last question for Noseall:

If you block off a chimney, do you have to install
A - ventilation or
B - insulation
and why?

A chimney is kept healthy with a draught going up it to prevent stagnation of moist air. The air will move freely up a chimney. Please don't try and educate me about ventilation, I have forgotten more than you know.

However the OP situation is very different. The locations that are most vulnerable to black spot mould are those areas that are most difficult to ventilate - i.e. where the air is trapped and where remote ventilation is pointless. You can not and will not install vents in all areas that will succumb to mould that is why it makes sense to insulate these areas.

Trust me I have lived it, built it and successfully remedied it.

noseall · 27 May 2018

EFLImpudence said:
FFS Noseall - Houses, homes HAVE TO HAVE ventilation

Silly boy, when have I said otherwise? All I have said is that ventilation will NOT cure black spot mould in areas that have no air movement and that insulating these areas is the only sensible remedy.

gasbanni · 27 May 2018

IWalkLikeHimaMartian said:
As you nearly rightly said "a combination of things".
Ventilation (or heating) will not work on its own. The two must be combined. Cooler air comes in, is heated, thus reducing the RH, but increasing the capacity of the air to hold more moisture, which is then ventilated. The cycle continues ad infinitum.
Insulation alone does not reduce the RH, which is the real cause of condensation/mould.
Insulation merely reduces the amount of and the temperature difference of cool surfaces, especially the lesser hygroscopic surfaces. Thus reducing the risk of condensation forming.

Fir instance, today is a warm day, I have all the windows and french windows open. I would guess the temperature outside is about 22°C with a (guessing) RH of about 70 - 72%.
It is cooler inside because the house has stone walls, about 1 meter thick with lime plastered walls.
Thus the air cools down when it is in the house for a while, to 20°C, and the RH meter is showing 74%. I could not physically ventilate any more, and the RH is increasing. If the walls were not highly hygroscopic, there is the perfect conditions for mould to grow, except the thickness of the walls means that they are not so cold compared to the internal air.
If the surfaces were less hygroscopic, moisture could condense on the surfaces, this moisture would not be absorbed, and mould could grow.

It is not a worrying situation. This evening, when we close the windows, the latent heat will be released, the temperature inside will rise, some background ventilation will continue, the highly hygroscopic walls will release some moisture, the house in general will reduce in RH and moisture content.
The cycle continues ad infinitum.

You naughty naughty boy .......fancy using a user name like that !!!!! Walks with turkeys, Imamartion, himmagin and wannabe will be very very cross with you

gasbanni · 27 May 2018

More heat reqd to warm up the fabric of the property and extraction in the bathroom and kitchen ......but especially the bathroom.

If the walls warmer it won't condense on it, and if you have extraction that automatically comes on with humidistat in the bathroom it will help a lot especially with a timed overrun.

IWalkLikeHimaMartian · 27 May 2018

noseall said:
A chimney is kept healthy with a draught

The air entering the disused chimney at the bottom is warmer than the air within the chimney, therefore the RH of the air changes in the process.
Again from my paper, (with appropriate references as included in my original paper, woody!)

: http://ocw.usu.edu
A change of about 10°C doubles or halves the RH.
The warm entering at the bottom may be at about 20 - 25°C at about 45 -75% RH. It has the ability to absorb more moisture, especially from the fabric of the building ( the chimney) which may have a high moisture content.
The warm'ish air with a high RH is then ventilated out the top of the chimney, carrying with it any excess moisture that it has accumulated.
Warm air naturally rises.

IWalkLikeHimaMartian · 27 May 2018

gasbanni said:
If the walls warmer it won't condense on it,

The forum idiot is now suggesting that the external walls of a property are warmer than the internal air temperature.
No doubt he will soon be advocating "entombed wall heating", similar to underfloor heating.

Condensation or damp

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