groundwater / moist problems

Hi all,

I have a question about a moisture problem - not sure if this is the right place to put my question.

We have a house in The Netherlands - built in 1926 - masonry outer walls, about 22 cms thick. The ground is clay - and groundwater levels are during winter often high. We have a wooden floor and the floor lays on wooden beams which lay in the masonry walls under the floor. The distance between floor and ground is about 40 centimeters.

During the winter, we have condensation problems as the beams which lay in the walls, and carry the floor, are moist, especially where they lay in the wall under the floor. There are also a lot of yellow salts to be seen on the under floor wall surfaces.  I think these come from the mortar and / or ground water (we live close to the coast).

There are natural ventilation openings in the outer walls under the floor and we always keep them open so there is natural ventilation.

But there is one company / guy here, who is ecologist, who says one should stop the natural ventilation as this cools down the outer walls and moves the warmer crawl-space air out and during it's movement out it hits the colder walls and condensate. His opinion is to close all natural ventilation holes in the outer walls and insulte / cover the ground, so no groundwater can evaporate anymore. He adivces to use polyethylene screen, or aerated concrete.

Personally I doubt about his adivice and adviced materials. Personally I would prever sea-shells as ground covering to polyethylene screen or aerated concrete - as sea shells are natural. But this ecologist tells me sea shells are not water vapour proof which could be true.

I measured water content of 1 floor beam close to the under floor wall and I measured 33% moisture content on the surface. The wood is treated / painted and looks ok. 1 floor tile close to an inner wall has water stains and I remove the salts on the wall close to the floor tile, but these stains still feel moist.

I would like to preserve my old home and I don't like modern materials like concrete and plastics (although some parts of our home have - originally - concrete from 1926).

There are a lot of different opinions about how to treat moisture problems / high groundwater levels in crawling spaces. I'm wondering if there is anyone here who can give me some advice? It seems like a very difficult thing to tackle...  I'm aware my local conditions can be very different to that of most readers on this forum as I live in The Netherlands. During winter temperatures are about 0 - 10 degrees Centigrade (32 - 50 Fahrenheit), and winters are getting more and more moist.

You have an interesting situation there.
I found this statement; From Damp in Buildings
"Our listed and historic buildings are also damaged and destroyed by damp.
-We heat our buildings to a higher temperature than in previous times.
-Additionally, ventilation by ill-fitting doors, windows and open fires is reduced in the modern era.
-When the temperature is low and the relative humidity is high, evaporation of water is slow.
-When relative humidity approaches 100 per cent, condensation can occur on surfaces.
-This may lead to problems with mould, corrosion, decay, and other moisture-related deterioration.
-Condensation can be more common than rising damp, and is a particular threat to structural timber and doors and windows.
Yours may not be a listed building, but the information is still relevant.
THIS IS AN INTERESTING SITE
https://www.heritage-house.org/damp-and-condensation/all-about-the-pca/the-damp-con-collection/holland-damp-proofing-system-another-expensive-fraud.html

It discusses the issue of rising damp and wether it exists!!

I have come across a series of articles which suggest rising damp as such does not exist.
Any dampness is caused by other issues.
https://www.heritage-house.org/damp-and-condensation/all-about-the-pca/the-damp-con-collection/holland-damp-proofing-system-another-expensive-fraud.html
From that site
"It's inevitable that you will find dampness somewhere in an old house. Nothing lasts forever, but despite English weather, our old buildings stand the test of time better than any modern house.
The worst enemy of old houses is we humans - it's what we do to them, or fail to understand about them, that causes problems and makes you think you have to 'Damp Proof'.
Almost 100% of damp issues in buildings are caused by condensation, and lack of adequate ventilation.

If the only thing I can teach you on this website is to understand the difference between water as a gas, and water as a liquid, and how temperature drives this difference, then I've done my job.
So: Read through this introduction, and start to get your head around the building blocks of damp problems and their solutions.
None of it is rocket science - but as you explore the internet, you will find that vast amounts of complete rubbish and scientific nonsense has been written, and continues to be written - most of it in an attempt to sell either chemicals or widgets.
This website is dedicated to blowing that rubbish out of the water, and giving you a sound basis on which to learn about your home, how it works, where damp comes from, why it is there, and how to deal with it."

Just happened to see this and thought that I would add...

The ground, regardless of whether it's covered or not (if the surrounding ground is saturated, do you think that the relatively dry earth beneath the structure would not wick that moisture ?) contains a lot of moisture and often-times, that moisture travels in one direction - up.

Concrete is in no way a vapor barrier.

Darkness and moisture = mold.

Clear, 10 mil plastic = bits of recycled plastic that has been re-heated/re-formed into a sheet that also is not an effective vapor barrier and degrades over a period of time.

I read your distaste for plastic, but I would not hesitate to possibly jack the dwelling up give you some working room, install a true vapor barrier (Stego 15 mil) that has been tested for vapor transmission, possibly add a venting system similar to a radon mitigation system and then install a frost apron around the structure, using environmentally unfriendly 4x8 sheets of two inch thick foam insulation - to direct rain water away from the structure.

I personally feel that your air quality could have an effect upon your health.

And...

if you are using natural gas or propane cooking appliances, rip them out immediately and replace with electric.

I apologize in-advance for advocating the use of plastic.

On my dwelling in Maine, which has a shallow, frost-protected slab on grade, I installed a Stego vapor barrier (to keep the slab dry and retard vapor transmission into the structure), a frost apron and applied a water-proof coating on the sides of the concrete (a dry slab = a warm slab) and the entire slab was poured on top of 2 inches of foam board insulation and I affixed the same 2 inch foam to the vertical sides of the slab.

The above processes were gleaned from university and Department of Energy standards for this type of slab and as well, I installed a radon mitigation system to be building code compliant, but never actually installed a fan or activated the system.

"Rising damp" in walls may not be a real thing as opposed to condensation from moist air, but the ground does have moisture (more or less depending on climate and season) which will evaporate into underfloor spaces and make structures damp.

I once lived in an early 1900s house in upstate New York while renovating it for my mother. The basement had a thin concrete floor with some holes in it, and was always damp. I put a scrap of plastic in a hole before patching it, and that spot was no longer damp while the floor around it was still damp.

At the same period, I helped my father spread sheets of 6 mil black plastic on our bedroom wing crawl space dirt floor which had always been extremely damp, and following that the moisture level in the bedrooms was much lower.

Shells may not absorb or transmit water, but they have many spaces between them which will not hinder the movement of water vapor at all. Their only benefit would be to give a surface that would not get muddy when crawled over. If you want to control damp in and under your floor, you need to put a vapor barrier on the ground, along with mitigating any exterior sources of water like unguttered roof eaves or slopes that direct water toward the walls. The easiest and cheapest barrier would probably be plastic, but there may be other products that are effective in that location. Also, wood sitting directly on masonry close to the ground will absorb water from the masonry. You need an impervious barrier between all wood and masonry, like copper or aluminum. If you can jack each beam up a few millimeters at the bearing point, you could probably slip a flashing piece into the gap.

Hi,

first of all thanks a lot for your extensive responses!

I'm aware of the heritage house website and I sudied it extensively. I watched videos by the man who runs this company and they seem knowledgable.

The only thing I miss is his opinion about ground covering. If I interpretet his advices correctly, he is a proponent of adequate ventilation. This means one should ventiltate humid air out and drier air in. So if outside air is more humid than for instance air in the livingroom, one shoud take air from the living room inside the cellar, and then vent it out. If, for instane during winter time, the outside air is dryer than the inside air, one shoud turn this around. One should always use absolute humidity to compare mosture levels. This is how I interpret his advices - corret me if I'm wrong.

But I can't find any information on this website about groundwater and covering of the crawling space under the wooden floor. Buildings should be able to breath and this is something we select our desicions on. All materials we use can breath, let water vapour through. So as long as condensed air can vaporise again there is no problem. But in our situation floor bearing wood construction - and 1 small area on a floor tile - show darker moist spots. It could be salts which keep moist at certain areas, and I only measured moisture leven in wood at it's outer surface - not in the core of the wood.

By covering the ground it feels like a big change in how things work under the floor. Maybe you are right and this is a good thing. But I'm afraid to make wrong decisions so I tend to be careful. Some people advise sea shells as a ground cover - other tell this won't help and I should use lightweight concrete. But some people think light weight concrete (airated concrete) is still water permeable and one should use a special damp proof screen.

A local ecologist advices to close all natural ventilation holes in the outer walls under the floor as the wind cools the walls and warmer humid air in the crawling space condenses on these cooled down walls. He advices to close all holes during winter and use ground covering. But this seems to contradict the advice by heritage house - who advices to use adequate ventilation and not block ventilation holes...

Glenn Herbert wrote:John Bos,
I have merged your topic into this topic. I hope that helps.

Thanks!

Crawl space ventilation is a tricky topic. In summer, or when the air is warmer than the deep ground, moderate ventilation will let warm humid air enter the crawl space, cool, and condense water on the cool surfaces, actually increasing the amount of water. If the air can sweep through the space, it may not have time to cool and may warm the soil surface and help dry it.

If there is a good vapor barrier on the ground (but not on the underside of the floor), a sealed space may let excess vapor travel up and be carried away by room ventilation, where outside air is warmed, achieves lower relative humidity, and absorbs water vapor from moister materials. All this depends on the particular conditions which can vary for every house.

Given the complexity of your situation and the unique conditions in your area, it's advisable to consult professionals who specialize in older homes and moisture-related issues. Engaging a structural engineer, architect, or preservation specialist can provide valuable insights and tailored recommendations specific to your home's needs and local climate.

Maybe a drawing would help here, I say this because I don't really know the landscape and how the house is situated.  What if the entire building is in a knoll or a basin?

Also, what kind of roof is this?  Where does it shed water?  Soil type in grade (sand, all clay, bedrock?),

Watch the rain, see where it goes, all water has to flow somewhere and yes the ground will absorb some.  Many times you can eliminate this with laying some draining.  Since you want it all natural you can dig a trench and fill that with sea shells and then get some #2 stone, slop all of this away from the house.  Lots of things you can do but.. need more info.

It's important to consult with a local professional who can assess your situation more accurately. They will have a better understanding of the climate, building techniques, and regulations in your area, which will help in providing tailored recommendations for your specific moisture problem and historic home.

Preserving an older home while addressing moisture issues can be a delicate balance, and seeking expert advice will give you the best chance of finding an appropriate solution.