ᐅ New Construction with Basement | Waterproof Concrete plus Perimeter Drainage

Hello knowledgeable people,

We are planning to build a new house with a basement. According to the soil survey, the ground up to a depth of about 5 meters (16 feet) consists of impermeable glacial till. Below that is permeable sand. There is no problem with rising groundwater here. However, due to the soil, surface water can be directed towards the basement wall.

The expert says the basement could be constructed either with masonry and drainage boards on the walls or with waterproof concrete. For masonry, a perimeter drain with a sump pit should be considered. If waterproof concrete is used, the expert states that no drainage is necessary.

The construction company recommends a masonry basement with waterproofing against hydrostatic pressure and perimeter insulation boards. Additionally, a perimeter drain and a sump pit should be installed. Alternatively, they suggest using waterproof concrete with open water management. However, they generally still recommend a perimeter drain with a sump pit for waterproof concrete to avoid long-term problems.

These measures/recommendations would increase the cost of a masonry basement by about €17,000 and for waterproof concrete by €7,000 with open water management or €16,000 with perimeter drainage and sump pit.

Basically, we would lean towards using waterproof concrete, but the recommendation to still install drainage seems a bit like a double safety net to us. The construction company justifies this because of the hydrostatic pressure and the expected higher humidity in the basement due to capillary action.

Since we are building the house with a central ventilation system, connecting the basement rooms to it would be straightforward.

We now have to decide what to do and are a bit unsure. What is your opinion? Does anyone have experience with waterproof concrete and glacial till soil? Is moisture an issue here?

Thank you very much for your input.

Actually, all of this should be included in the soil report.

Waterproof concrete with drainage is basically redundant (if the soil report requires one or the other), but do you really want to save money there? In my opinion, anything that quickly and safely directs water away from the house is worthwhile.

First, I would ask why the additional cost? For us (with about 150 sqm (1,615 sq ft) of basement), the drainage costs around 2,700 euros.

And the decision whether to install a soakaway or not is certainly not only about basement drainage... where does the rainwater from the roof go according to the current plan?

Why the additional costs occur is a good question!
According to the cost estimate, draining the partial basement (about 50 m² (540 sq ft)) costs around €4,000, and the soakaway pit at approximately 6 meters (20 feet) deep adds another €8,000. Since the basement is in glacial loam, drainage without a soakaway pit doesn’t make much sense, right? The water can’t drain away otherwise.

Rainwater from the roof goes into the sewer system.

Hello,

I am professionally involved with waterproof concrete (WU) elements and wrote my thesis on this topic in civil engineering.

Installing drainage with it is quite unusual. I also do not consider it reasonable – why would I then spend extra money on the waterproof concrete element?

However, during planning and execution, it is important to ensure that you actually get a waterproof structure and not just a basement made of concrete labeled as “WU” on the delivery note. A waterproof basement is much more than just waterproof concrete.

Arrange for construction according to waterproof concrete guidelines – this means a proper waterproof design must be developed.
If you choose this option, involve experts and do not just blindly hire a supposedly specialized company.
I am also happy to take a look if you need further assistance there.

Best regards,
Jann

@Jann St

Now you're even taking away the cash cow from the contractor! Why didn't the contractor factor this in and include it in the offer from the start? After all, they know the building site.

By the way, I completely agree with you.