The perfect breathable damp and condensation free house

[tobydog]

We often talk on PPUK about the removal of outer cement renders and other similar barriers, and the application of lime based products and breathability, as a panacea for damp and condensation related issues. We know it makes sense, however, does anyone have the 'perfect ' house but still experience windows soaked in water on certain days? I was just wondering because several people say they are going to go to some considerable expense to make the changes to their houses but does it actually make the huge difference they were expecting?

 

[Flyfisher]

That's an interesting topic for discussion. Based on little more than my own limited experience, I'll stick my neck out and say that I tend to think of damp and condensation as two different things. Both are unwanted moisture, of course, but I think of damp as a chronic condition and condensation as an acute condition.

In a previous house (1950s) with single-glazed windows, we had no damp problems but would often have condensation on the bedroom windows in the morning unless we kept the small window slightly open overnight. Similarly, showering without opening the bathroom window would always result in condensation except during the summer, but the simple answer was to open the window. I'd say that any house with minimal ventilation will be susceptible to condensation - all the humid air generated by modern living (showers, cooking, boiling kettles etc) will eventually find a cool spot somewhere in the house and cool air can carry less moisture so condensation is inevitable. Adequate ventilation will cure such things - opening windows is a low-tech approach or a whole-house heat-exchanging air-conditioning system is a higher-tech and (arguably) more energy-efficient method.

Classic damp however is, I'd suggest, more of a structural problem arising out of a fault with the house or an inappropriate mixture of modern and tradition building materials and methods.

Condensation, I think, is more of a lifestyle issue rather than a problem with the breathability of the house per se.

 

[MdB]

With a warm house and cold windows, you will get condensation on the windows. Within reason, this is independent of the construction of the rest of the house. If you make the house warmer through making improvements, then with the same windows, the condensation will get worse due the higher moisture content of the warmer air. The solution is better performing windows that allow less heat to escape and hence cool the air touching it less.

In our house, we have significantly improved the insulation in the front of the house and improved the warmth due to this. Our back room however now suffers from mould where it didn't in the past. This is no big surprise when you take into account the warm moist air from the front of the house hitting back room which has three external solid uninsulated walls and an uninsulated flat roof.

 

[CliffordPope]

Uninsulated 1880 traditional 3-storey stone house. Heated by woodburning range in the kitchen, providing cooking, hot water, and limited radiator heating on ground floor only.

Before
Old stucco bulging away from the walls, the fallen sections being patched up with cement render.
Condensation contained by use of dehumidifiers on landings.
Water penetration behind voids in the stucco.

After
All stucco/render hacked off.
Front and rear elevations sandblasted and repointed with lime mortar.
West-facing gable wall re-rendered in lime mortar and uncoloured tyrolean finish, owing to high wind/rain exposure
Opposite gable wall double-rendered in lime mortar on stainless steel mesh because of poor quality of stonework and substantial leeching from old chimneys. Tyrolean finish, lime mortar.

The water penetration eliminated.
Some reduction in condensation, but dehumidifier still necessary.


I take the point that improving and double glazing the windows would eliminate a cold spot, but won't this merely transfer the condensation to the walls? Two foot uninsulated solid walls in a partially heated house are bound to be colder than the interior air, but the condensation will be unseen and damaging. Isn't it better to focus the condensation on deliberate cold spots, ie the windows, where it is harmless?

Also, I see the point about ventilation. But for most of the day the outside air will be warmer than the walls. In my observation ventilation in those conditions merely lets in more air of greater humidity to cause further condensation.

 

[Zebra]

Very interested thread. Will watch with interest, as am due next year to go to considerable expense to install breathable external wall insulation to 17th/18th century solid wall/timber frame cottage.

 

[Penners]

I'll stick my neck out and say that I tend to think of damp and condensation as two different things. Both are unwanted moisture, of course, but I think of damp as a chronic condition and condensation as an acute condition.

Classic damp however is, I'd suggest, more of a structural problem arising out of a fault with the house or an inappropriate mixture of modern and tradition building materials and methods.

Condensation, I think, is more of a lifestyle issue rather than a problem with the breathability of the house per se.

Perfectly expressed.

Damp and condensation are different things, usually with different causes, although damp can contribute to condensation, and vice versa. To avoid condensation, you need to do several things:

1. Eliminate moisture-laden warm air within the house (no chance!)

2. Avoid having the inevitable moisture-laden warm air touch any cold surfaces (not completely impossible, but extremely difficult).

3. Ventilate well, so that the moisture-laden warm air is expelled from the house (moderately practicable at a cost).

Points 2 and 3 are achievable to a certain extent, but unless you're living in a high-tech, 21st-century, purpose-designed, closed-environment house, you're extremely unlikely to to be able to eliminate all condensation from your home.

 

[tobydog]

I suppose the issue in question was - does the stripping of cement and the likes, and it's replacement with lime based products, really make a big difference. From the responses it would appear it doesn't and it's ventilation that's more important. I think we accept that even with traditional coatings, the level of moisture we now produce internally can never be removed quick enough through lime render surfaces.

Recently I have been observing how condensation forms in my house relative to the weather outside and moisture generating activities inside. I've come to the conclusion that if we stopped breathing, stopped washing, stopped making endless cups of tea (with kit kats!!) and stopped doing the laundry, we would still have condensation on the all the windows if the weather outside was damp. This seems to be the overriding factor and it's particularly obvious on the mornings when everything outside is soaking wet but it hasn't actually rained. If it's a dry night we only have condensation in the bedroom. This suggests that it's as much to do with moisture ingress and much as moisture production. This is the point touched on by CliffordPope about letting moisture into the house via ventilation.

Although I'm no scientist, my understanding of moisture is that is moves around depending on pressure differentials within the house. Moist air is at a higher pressure than dry air and therefore dry air will be displaced by moist air. This is the principle by which a dehumidifier is supposed to remove moisture from an entire house while being placed in one spot. This same principle also works when moist higher pressure air in a house wants to find its way outside where it could be drier. The problem is that it also works the other way round, hence moist air wanting to enter a dry house.

 

[CliffordPope]

Exactly.
The fallacy in all considerations of condensation is that the moisture is generated internally. That is only true in very limited situations - bathroom, and kitchen sometimes.
When I moved into my house the attic was completely uninsulated, bare slates exposed, internal slate mortaring mostly fallen out. Perfect ventilation - large gaps under the eaves, holes in rotting soffit boards. The wind whistled through.
The end walls dripped with condensation.

The reasoning seems to me to be thus:

Thick walls are very slow to warm up and cool down. They are therefore effectively at a constant temperature somewhere between low night time and higher day time. Therefore during the day incoming air from outside will be WARMER than the walls. Therefore any moisture held in the air will condense on the walls. This will be true at any time of the year.

The answer is to stop up all ventilation, extract the residue with a dehumidifier, and then be very careful about letting in more air from doors etc. Hustle your guests in and out quickly.

 

[tobydog]

I posted this link on another thread recently. I have now read it, understood most of it, and it's opened my eyes completely on what could be the right and wrong products to work with and the appropriate / inappropriate methods of construction for new and old. It's 34 pages long but worth every page.

http://www.greensteps.co.uk/tmp/assets/1163178050906.pdf

By the way, I am now using the dehumidifier and, although it works well most of the time when it's on, I am beginning to look more like King Kanute every day trying to hold back the moist outside air!!

 

[Penners]

I suppose the issue in question was - does the stripping of cement and the likes, and it's replacement with lime based products, really make a big difference. From the responses it would appear it doesn't and it's ventilation that's more important.

I agree... and disagree. The problem is that it's impossible to write all-embracing rules for period properties. Every one is different. Thus it's likely that no two damp problems will be identical, nor will their solutions.

As has been frequently observed on this forum, all you can do is list the most likely causes of your damp problem, then work your way systematically through the most likely solutions. At every stage, allow the current attempted solution time to work, then if necessary move on to the next one.

It may be that in your case both those solutions will be necessary. Or it may not. But it will take you quite some time to discover the answer.

 

[Penners]

The fallacy in all considerations of condensation is that the moisture is generated internally.

I disagree that this is a fallacy. It may be in some cases and not in others. It all depends on the particular circumstances. Of course the ambient air often carries a large amount of moisture, but where that does or does not condense out can vary widely.

 

[JoceAndChris]

There is no condensation in this house. If it forms, (which only happens once in a blue moon) I open the front door immediately. The other ventilation includes 5 unblocked chimneys, suspended floorboards (bare) over earth with clear air vents, and huge gaps between the boards, a draughty glass porch and draughty sash windows. On top of that it's a windy, dry place, and I'm careful not to produce moisture if I can help it. Yes, I'm getting a bit cold now but I'd sooner protect my beautiful floors, sashes, plasters and beams than seal it all up and be warm and damp.

I totally agree with Mr P that the rules, conditions, and effects would differ depending on a thousand things.

If DWB were here she would say that her marathon efforts for the perfect damp free house worked - she picked off all the cement render, all the cement walls, all the cement floors. Underneath she described as "pouring water" - read back through her posts. She pulled out the rotten wood and stone and replaced, and then stuck it all back with lime. The last we heard from her she was 14 years into the project and still not living fully in the house, but the chronic damp problems appeared to be gone.

We plan to spend a lot on restoring limework but I have to say that it's as much for aesthetic appeal as the health of the building- cement render looks awful in my opinion. The proper lime render on the outside, scored to look like ashlar, and limewashed to look like stone, will utterly transform the place. Pity it will cost 25k and never be justified in resale value but there you go.

 

[Penners]

There is no condensation in this house. If it forms, (which only happens once in a blue moon) I open the front door immediately. The other ventilation includes 5 unblocked chimneys, suspended floorboards (bare) over earth with clear air vents, and huge gaps between the boards, a draughty glass porch and draughty sash windows. On top of that it's a windy, dry place, and I'm careful not to produce moisture if I can help it. Yes, I'm getting a bit cold now but I'd sooner protect my beautiful floors, sashes, plasters and beams than seal it all up and be warm and damp.

Quite so, Joce. I understand that there's no condensation in wind tunnels, either. :wink:

We plan to spend a lot on restoring limework but I have to say that it's as much for aesthetic appeal as the health of the building- cement render looks awful in my opinion. The proper lime render on the outside, scored to look like ashlar, and limewashed to look like stone, will utterly transform the place. Pity it will cost 25k and never be justified in resale value but there you go.

I can only say that, to the outside observer, your house looks a million miles from awful. However, if you wish to gild the lily, far be it from me to dissuade you!

 

[JoceAndChris]

Quite so, Joce. I understand that there's no condensation in wind tunnels, either. :wink:

:lol: :lol: :lol: Spot on.

And thanks for the nice comment. The render'slooking a lot worse than when you came though. Hopefully the wind will just blow it off, very soon.

 

[tobydog]

Joce - where does one start?!!! I have to say that you could live in a plastic bag but still not get any condensation with all those holes. I now know where the 4,000 litres of oil went!!! I think that goes back to Penner's point that you can let any amount of fresh air in at a cost. I suppose that is the issue - where is the tipping point between ventilation and draughts? If the ventilation is too small in order to avoid draughts - you probably get condensation. When my house was built it wouldn't have had glass in the windows and it's got an inglenook the size of a bed. I think I'll keep the cement, seal the place up with Duck Tape and install electrical / mechanical fresh air system. It's got to be way cheaper than lifting floor and replacing walls / render :wink: .

 

[Andrew Bodenham]

What this thread has shown is that the relationship between the variables (temperature and humidity) is a complex one, and one which is hard to understand intuitively. But there are certain fundamentals whhich need to be grasped. At a given temperature a given volume of air will hold a certain amount of water in vapour form. If you increase the temperature of the air it can hold more water. If you decrease the temperature it can hold less water. Condensation occurs when air is cooled to a temperature (the Dew Point) at which it can no longer hold all the moisture within it, and it either forms as droplets on a surface or in the air mass (i.e. fog) This is what you see happening near the spout of a boiling kettle, or when warm air meets your cold specs when you enter a warm building on a chilly day.

If you can keep all the surfaces in your house above dew point temperature then condensation will not occur. Conversely, if air comes into contact with surfaces below dew point temp then condensation will form in that surface.

The role of ventilation is to prevent the build-up of stale air with high humidity. Ideally you replace this with cold air from outside, which you then warm up, so reducing its relative humidity. As has beenpointed out, sometimes you can let in high humidity warm air (e.g. with the arrival of a warm front in the autumn) when the interior of your house is at a lower-than-outside temperature. Then condensation will be widespread. Think on this before opening the cellar door to 'dry it out' on a warm day. The best drying weather is when its icy cold - it was noticable in the cold snap last Dec/Jan that our internal woodwork was shrinking due to the very low humidity.

Like I said, its more complex than meets the eye.

 

[MdB]

Our old walls were incredibly damp when we moved in. One section had modern plaster so soft (due to moisture) that you could easily draw on it with your fingernail. A screwdriver could be pushed in to a depth of a couple of centimetres. Another section caused mould to grow on the back of photograph frames which standing on shelves in front of it.

Being damp, these walls also conducted heat very well making them cold. This of course caused condensation to form on them helping to keep them damp.

These walls have now had a large amount of render and tanking (at least 3 layers) removed from them - the walls stank when the bottom layer was initially removed. The moisture now has long since evaporated off, drying the wall out completely - indeed I had to throw a lot of water onto the outside to damp it down when repointing. Now dry, the walls are thermally much improved and don't suffer from condensation at all.

In our case at least, removing the render was very much the right thing to do. We also have a very nice stone wall to look at which is a bonus.

 

[Flyfisher]

I suppose that is the issue - where is the tipping point between ventilation and draughts? If the ventilation is too small in order to avoid draughts - you probably get condensation.

There's little doubt about the conflicting demands of ventilation and energy efficiency. Like many things, it's a trade-off and I'm sure we'd all choose a slightly different one. Personally, I like to have doors and windows wide open and to treat the garden as a seamless extention to the house - which is easy in the warmer months of course but the habit tends to persist into the autumn months until things really do get too cold.

I agree with the previous points about condensation sometimes being caused by external warm air finding some cold internal walls if doors and windows are left wide open (indeed, I've experienced this myself) but I do think it's only a short-term thing and very unlikely to contribute to any significant problems because the ventilation itself will quickly solve the problem as the warm air heats up the inside of the house and dries out any condensed moisture.

Again, it's an acute episode, not a chronic problem. Indeed, my feeling is that old, breathable houses will tend to absorb a certain amount of water during the winter months and then dry out during the warmer summer months, which is why it's generally beneficial to open up the house to the fresh air (humid or not) whenever possible.

 

[MdB]

It is also worth pointing out that the water content of air roughly doubles every 10 degrees increase in temperature. i.e. if it is raining outside with 90% humidity and 10°C temperature then this same air when brought into the house and heated to 20°C will have a humidity level of roughly 45%. This is how cold air from outside which is circulated through your heated house will help remove the moisture.

 

[Penners]

The fund of useful knowledge on this forum never fails to amaze me.