Basement renovation in an old building: Do it yourself or hire someone?

Hello everyone,

I just registered here to gather experiences/opinions regarding the following described situation. Briefly about the framework conditions: We are renovating an old building (built around 1930), which is to be converted from a two-family house into a single-family house and upgraded to an efficiency house 70 or 55 standard. At the moment, we are working with the architects and the energy consultant to finalize the scope of the structural measures. For us, this means that until the building permit is obtained, we want to take care of the basement. Based on the hopefully incoming feedback here, we might be able to better assess whether we should do that.

About the basement: It consists of 3 basement rooms with a total of approx. 56 m², which in the past included a workshop (with heating system), a storage room, and a "sanitary area" (bathtub, shower, toilet). Two rooms have a light well, the third room's light well was bricked up because a conservatory was built above it. The last mentioned room (I will call it the wine cellar, as among other things we had to dispose of a lot of Weil there) was the "storage room". This room was characterized by the walls being constructed as follows: brick wall -> plaster -> Styrofoam -> wooden paneling (tongue and groove boards). So far, we have removed everything except the plaster, since the boards were extensively moldy. Since the plaster also shows efflorescence, it will be removed soon as well. On the floor of the wine cellar, chipboards are screwed down (there used to be PVC on them), under the chipboards a foil can still be seen. The chipboards are naturally also damp. What lies beneath the foil, I do not know yet.

In the other two rooms, the walls are tiled. Here, too, the joints are at least black on the exterior walls (getting blacker towards the floor). Here, too, we will remove everything down to the base walls in the next few weeks (we have to). Once we have reached that point and completely gutted the basement, the question arises for us how to proceed. The basement is to be used in the future for the following purposes:

[*]Housing the heating system
[*]Washing clothes
[*]Storage of tools/workshop
[*]Storage of food, beverages, housing the freezer

So far, we have had an expert and a company specialized in basement renovations on site. However, the expert opinions point in somewhat different directions:

The expert advised us to install a horizontal barrier just above the basement floor and another barrier around ground level, as water is drawn upwards by capillary forces. With some craftsmanship skills and good tools (both ), this could be done by ourselves. The costs would be manageable in this case, while hiring a professional company would cost at least a mid five-figure sum. His conclusion was, however, that despite all efforts, the rooms would never be 100% dry anyway.

The specialist from the renovation company, on the other hand (understandably from his point of view), said that one should definitely not do such work oneself since the solutions available on the market for installing a horizontal barrier last only 5-10 years. The specialist furthermore recommended injecting and grouting such a "barrier material" vertically into all affected walls. Additionally, moisture had almost penetrated up to the ground floor, the mold was highly dangerous, and cracks could also occur. Whether there was a certain degree of "scaremongering" involved, I cannot judge. We are currently awaiting the company's proposal regarding the measures to be taken. Both the independent expert and the specialist from the renovation company agreed that the rooms are partially more "wet" than "damp", but the specialist's conclusion was that the rooms could be dried enough to "build a children's room in there".

A third option, suggested by our architect, would be to proceed with the gutting down to the base walls as planned, make the light wells more air-permeable, and then monitor how the moisture develops in the rooms.

Given the described usage scenario, we certainly do not need 100% dry rooms. However, the fear that the moisture might spread up to the upper floors naturally exists. Installing a horizontal barrier sounds plausible to me; from the outside, we cannot access the walls anyway.

My questions to those who have read this far (thank you!) are therefore:

[*]Install the horizontal barrier ourselves, or
[*]Have the company do it, as they intend, or
[*]Gutt the basement first and wait, or
[*]Are there other ideas?

Best regards!

I would gut everything and clear it out down to the foundation wall, even remove the plaster. Then observe the moisture under different scenarios. Does the wall get damp when it rains, does the water come from below or from outside. What moisture values are present on which days. Is it constant or does it change.

In the meantime, the room can be used for laundry.

I don't understand your fear. If the moisture hasn't moved upwards in the last 90 years, then it won't do so in the next 90 years either. Or is there mold, plaster cracks, whatever in the ground floor?

If nothing else happens there, and the thing is only going to be used as a storage/laundry room, then one can live with it.

The gutting including chipping off the plaster will definitely be done. Then you will certainly get a better look at the foundations, so you can possibly see if there was ever a horizontal barrier. Additionally, you can then carry out the analyses you mentioned.

So far, we have not found any mold or cracks in the plaster etc. on the ground floor. In two spots on the ground floor, the floorboards are spotwise rotten or decayed. However, I suspect the cause is more likely from above, not from below (basement).

In the meantime, an offer has arrived which would unfortunately absolutely exceed our budget.

It's just a stupid task with follow-up problems. Report back in a year and tell me how the status is then.

Yeah, gut everything stripped down. There’s definitely no horizontal barrier installed. If you can’t get to the walls from the outside (why not?), you won’t get the basement dry either. The fact that everything is moldy is surely also due to the really catastrophically wrong interior finishing by the previous owner. Styrofoam traps moisture, so it has to mold. So knock everything off, put on new plaster, and then leave it like that. It will be a bit damp but will dry out with proper ventilation (only if it’s colder outside than in the basement). For the planned use, I would save myself the effort of any retrofit barriers that would only last a few years anyway. Structurally, the moisture is irrelevant. The house has stood for 90 years and will stand for another 90. During the construction phase, it’s definitely no mistake to observe the whole thing in the shell condition for a while; depending on the moisture, you can then decide on the right plaster.

First of all, thanks for your answers! You can't get to the "wine cellar" because one wall is also the wall to the neighbor's house (it is an end terraced house), two walls border the other cellar rooms, and a conservatory was subsequently built over one wall. You could get to each of the other two rooms at one wall each. According to the experts, however, excavating at these walls from the outside would be disproportionately expensive and complex.

Absolutely right, the completely wrong interior finishing of the rooms was the big mistake. However, I didn't want to apply new plaster during the construction phase at first, but just observe. Plaster can always be applied later when we actually need the rooms.

What I also think would be important is to check where the rainwater from the gutters is being drained. I wouldn't be surprised if it just seeps directly at the house, or if the gutters/downpipes are completely clogged.

Would the use of dehumidifiers help (a frequently heard, well-intentioned tip)? They would probably collect a lot of water, but basically, water would keep running in, and you'd basically have to run them all the time? That probably doesn't help, does it?