Exterior walls of the basement not accessible - Is this problematic?

Hello everyone,

my partner and I are considering buying a semi-detached house from the late 60s. It is very well maintained, and in the 70s, two extensions were made. What is now on my mind: Due to the extensions, one could not access the exterior walls in case of moisture in the basement! Now my questions are as follows:

1. Won't the basement inevitably become leaky/moist at some point, or are there basements from the 60s that remain "permanently" dry?

2. Since the basement could then only be renovated from the inside, the actual problem (defective external moisture barrier) could not be solved and the masonry would remain permanently moist. Wouldn't such permanent moisture lead, within 10-20 years, to the masonry completely crumbling and, in the worst case, to the house having to be demolished?

3. What costs should be expected if a company were to carry out the drying (just asking out of interest)?

Many thanks for helpful answers!

Of course there are cellars that stay "forever" dry. So what is suddenly supposed to change that the cellar becomes damp?

Of course, it depends on the groundwater situation. Or surface water, although if there are extensions on top, it first flows away elsewhere.

Likewise, there are cellars that are permanently damp. However, this usually does not lead to a demolition.

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

Thanks first of all for the reply, that would be great. Although I thought that the material from the 60s inevitably fatigues at some point!?

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

Therefore, I would appreciate further assessments.

Just grab a good building surveyor from your area and have him inspect the building. During the walkthrough with him, you can also directly address your concerns about the basement and he can then take a closer look at the basement (location, material, condition, etc.).

She is very well maintained,

If you mean not only the partner but also the house in question, then I wouldn't worry. Very well maintained is typically not the impression that a disguised wreck would leave.

1. Doesn't the basement inevitably become leaky/damp at some point, or are there basements from the 60s that stay "eternally" dry?

Basements of new buildings made of waterproof concrete with additional XPS insulation may remain "eternally" dry. In the 60s, there was no waterproof concrete yet, and the basements were usually not insulated from the outside. The state of the art were two horizontal barriers made of bitumen felt above the basement floor slab and above the ground level. These actually last forever. Additionally, a vertical barrier made of bitumen, a bitumen thick coating, was usually applied. This has a lifespan, depending on the substrate and weathering, of 40-60 years. Whether and how much moisture penetrates through the wall afterwards strongly depends on the groundwater and soil moisture caused by surface water. If currently all walls are dry, there will not be much change in the built-over areas, simply because the moisture input from above is low and apparently no penetrating groundwater is present. The exterior walls may be somewhat damp, but when using diffusion-open, mold-inhibiting lime plasters, no flaking or problems are to be expected here.

In the non-built-over area, especially on the weather-exposed side, good drainage of rainwater should be ensured, and if walls become increasingly damp and plaster flakes off, the vertical barrier should be renewed from the outside (bitumen thick coating + insulation + studded membrane).

Does such persistent moisture not lead within 10-20 years to the masonry crumbling completely and, in the worst case, the threat of demolition of the house?

If the basement walls are made of concrete, which was often the case in the 60s, permanent moisture penetration of the exterior wall does not impair the stability of the building material. However, with permanently damp walls, a humid indoor climate also occurs, which restricts the use of the basement. Therefore, in case of heavily damp walls, sealing the non-built-over area from the outside is recommended. If this is not sufficient and moisture damage also occurs in the built-over area, it can be remedied from the inside. Concrete is not harmed by this.

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

3. What costs would be expected if a company were to take over the waterproofing (just asking out of interest)?

Costs for external waterproofing with application of a vertical barrier here range depending on substrate, location, basement depth in the ground from 200-500 €/running meter of basement wall. Without exact details, it is difficult to specify more precisely.

Don’t let anyone sell you a horizontal barrier. It is usually present in buildings from the 60s, and with concrete basements, due to the lower capillary activity, it is also less critical. This costs somewhere around 100-150 €/running meter.

Internal sealing is somewhat cheaper than external, but also not a bargain.

Conclusion: If it is still dry now and you do not change anything about the soil, it will also stay dry; keep an eye on the weather-exposed side.