ᐅ New Construction with Basement | Waterproof Concrete plus Perimeter Drainage
Created on: 5 May 2021 10:55
H
Hotdogxxxx
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.
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.
I work in a construction company myself, but in multi-family residential buildings. Here, waterproof concrete components, such as underground garages, have become standard, yet the discussion is always the same.
The contractor can only include in the bid what is specified. Initially, they cannot know what is desired, and among the requirements, the method of execution is decisive. Also, the contractor cannot initially know according to which concept the work will be carried out (allowing and sealing cracks, avoiding cracks, etc.). So, there is not much they can say at first (technically speaking).
The problem is that companies offer "waterproof basements" or "basements made of waterproof concrete" despite the lack of clear specifications, because the terminology is not legally protected.
Long story short 😉
The contractor can only include in the bid what is specified. Initially, they cannot know what is desired, and among the requirements, the method of execution is decisive. Also, the contractor cannot initially know according to which concept the work will be carried out (allowing and sealing cracks, avoiding cracks, etc.). So, there is not much they can say at first (technically speaking).
The problem is that companies offer "waterproof basements" or "basements made of waterproof concrete" despite the lack of clear specifications, because the terminology is not legally protected.
Long story short 😉
@Jann St: What would be the safest possible clause to include in the offer text for this?
Of course, ideally you have a detailed plan/specification with all waterproof concrete components precisely described and specified, but apart from that, assuming you want to buy a prefabricated basement as a builder, how can you protect yourself?
Of course, ideally you have a detailed plan/specification with all waterproof concrete components precisely described and specified, but apart from that, assuming you want to buy a prefabricated basement as a builder, how can you protect yourself?
First, back to your geotechnical engineer –
Exterior groundwater pressure does not affect condensation inside. If you want to use the basement for higher-quality purposes, insulation should be considered. A waterproof (WU) structure keeps water out from the outside; when the building element cools down, moisture from the inside air can naturally condense. To me, this connection does not make sense.
Of course, airtightness is especially important – that should always be the case! Usually, a waterproof basement in construction is only sealed because the water pressure is low. If water seeps in slowly like that, you should especially consider the wall-to-ceiling connection. Windows or light wells both exist as waterproof against pressurized water – designed with sufficient height so that surface water does not enter above ground there…
A geotechnical engineer is not a waterproofing specialist… a good waterproof construction requires no additional support.
Certainly, the transition from ground floor to basement must be considered, but with proper planning this is feasible.
Exterior groundwater pressure does not affect condensation inside. If you want to use the basement for higher-quality purposes, insulation should be considered. A waterproof (WU) structure keeps water out from the outside; when the building element cools down, moisture from the inside air can naturally condense. To me, this connection does not make sense.
Of course, airtightness is especially important – that should always be the case! Usually, a waterproof basement in construction is only sealed because the water pressure is low. If water seeps in slowly like that, you should especially consider the wall-to-ceiling connection. Windows or light wells both exist as waterproof against pressurized water – designed with sufficient height so that surface water does not enter above ground there…
A geotechnical engineer is not a waterproofing specialist… a good waterproof construction requires no additional support.
Certainly, the transition from ground floor to basement must be considered, but with proper planning this is feasible.
If you decide to build a basement, the “seller” should at least ask what you plan to use the basement for and then inform you about the possible construction methods and the resulting conditions, so that the client can make an informed decision.
Questions to be asked include:
How will the basement be used? Will the walls and floors be covered?
What is the usage class?
What design principle applies?
What are the wall thicknesses and how are they constructed?
What joint sealing system is used?
How are any future cracks handled? Who is responsible for sealing them?
How is the basement connected to the aboveground masonry?
The specifications (e.g., in the bill of quantities) should definitely include references to the usage class (there are A and B) and design principle (a, b, or c). If the company cannot explain these two points, do not choose them.
There should also be information about the joint sealing method (sheet metal or sealing tape).
It is important to also address how to deal with (inevitably expected) cracks beyond the joint sealing.
I would also advise against basements built with element walls—semi-finished walls that are later filled with concrete. In case of cracks, this can lead to costly consequences.
I can’t answer your question quite that easily 😀
Questions to be asked include:
How will the basement be used? Will the walls and floors be covered?
What is the usage class?
What design principle applies?
What are the wall thicknesses and how are they constructed?
What joint sealing system is used?
How are any future cracks handled? Who is responsible for sealing them?
How is the basement connected to the aboveground masonry?
The specifications (e.g., in the bill of quantities) should definitely include references to the usage class (there are A and B) and design principle (a, b, or c). If the company cannot explain these two points, do not choose them.
There should also be information about the joint sealing method (sheet metal or sealing tape).
It is important to also address how to deal with (inevitably expected) cracks beyond the joint sealing.
I would also advise against basements built with element walls—semi-finished walls that are later filled with concrete. In case of cracks, this can lead to costly consequences.
I can’t answer your question quite that easily 😀
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