ᐅ Basement Exterior Walls Not Accessible – Is This a Problem?

Hello everyone,

My partner and I are considering buying a semi-detached house from the late 1960s. It is very well maintained, and two extensions were added in the 1970s. What is now on my mind is this: because of the extensions, it would not be possible to access the exterior walls of the basement if there is moisture. This raises the following questions:

1. Is it inevitable that a basement will eventually become damp or wet, or are there basements from the 1960s that stay dry indefinitely?

2. Since the basement could only be renovated from the inside, the main problem (damaged external waterproofing) could not be fixed, and the masonry would remain permanently damp. Would such continuous dampness cause the masonry to deteriorate completely within 10 to 20 years, potentially even threatening the structural integrity of the house?

3. What kind of costs should one expect if a company were hired to carry out waterproofing work (just asking out of curiosity)?

Thank you very much for any helpful answers!

Of course, there are basements that stay "permanently" dry. So what exactly is supposed to change suddenly that would make the basement damp?

It obviously depends on the groundwater situation. Or surface water, although if there are extensions built on top, the water will initially drain elsewhere.

Similarly, there are basements that are constantly damp. However, this usually does not lead to demolition.

I think you are worrying too much about a hypothetical problem...

Thanks first of all for the response, that would be great. Although I thought that the material from the 1960s would inevitably deteriorate at some point!?

And yes, I am concerned, as it involves a lot of money.

Therefore, I would appreciate further assessments.

Just find a qualified building surveyor from your area and have them inspect the property. During the walk-through, you can also directly discuss your concerns about the basement, and they can take a closer look at its location, materials, condition, and so on.

der_Schwede schrieb:
It is very well maintained,

If you are referring not only to the partner but also to the house in question, then I wouldn’t worry. "Very well maintained" is typically not the impression given by a rundown property in disguise.

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der_Schwede schrieb:
1. Does a basement inevitably become wet or damp over time, or are there basements from the 1960s that remain "always" dry?

Basements in new buildings made of waterproof concrete with additional XPS insulation might remain "always" dry. In the 1960s, waterproof concrete (WU concrete) did not yet exist, and basements were usually not insulated on the outside. The standard at that time was two horizontal barriers made of bitumen sheets above the basement floor slab and just above ground level. These barriers actually last indefinitely. Additionally, a vertical barrier made of bitumen, a thick bitumen coating, was usually applied. This has a service life depending on the substrate and weather conditions of about 40-60 years. Whether and how much moisture then penetrates through the wall strongly depends on the groundwater level and soil moisture caused by surface water.

If all walls are currently dry, not much will change in the built-up areas, simply because moisture input from above is low and apparently there is no pressing groundwater. The exterior walls might be slightly damp, but when using vapor-permeable, mold-resistant lime plaster, no flaking or problems are expected here.

In the non-built-up area, especially on the weather-exposed side, good drainage of rainwater should be ensured, and if walls become increasingly damp and plaster starts flaking, the exterior vertical barrier should be renewed (bitumen thick coating + insulation + drainage membrane).

der_Schwede schrieb:
Does such persistent dampness not lead within 10-20 years to the masonry crumbling completely and, in the worst case, to the house needing to be demolished?

If the basement walls are made of concrete, which was often the case in the 1960s, permanent moisture in the outer wall does not affect the structural stability of the material. However, persistent damp walls create a humid indoor climate, limiting the usability of the basement. In the case of strongly damp walls, it is therefore recommended to waterproof the non-built-up exterior areas from the outside. If this is not enough and moisture damage also occurs in the built-up areas, it can be addressed from the inside. Concrete is not harmed by this.

More important in this case is the presence of a continuous horizontal barrier—a strip of bitumen sheet—just below the basement ceiling. This prevents moisture from rising from the basement wall into the walls of the living spaces.

der_Schwede schrieb:


3. What costs could be expected if a company was hired for basement waterproofing (just asking out of interest)?

Costs for exterior basement waterproofing with the application of a vertical barrier usually range between 200-500 €/linear meter (around 60-150 USD/linear foot) of basement wall, depending on the substrate, location, and basement depth below ground. Without precise details, it is difficult to provide a more exact figure.

Do not be sold on having a horizontal barrier installed; this is generally already present in 1960s buildings. For concrete basements, due to lower capillary activity, it is less critical. Its cost is roughly 100-150 €/linear meter (around 30-45 USD/linear foot).

Interior waterproofing is somewhat cheaper than exterior but is still not inexpensive.

Conclusion: If the basement is still dry now, and you do not alter the soil around it, it will likely remain dry—just keep an eye on the weather-exposed side.