Hello everyone,
I have an issue with the drainage of a light well and would appreciate your expert advice.
The situation:
The light well is approximately 50 cm (20 inches) deep and 1.50 m (5 feet) below ground level (bottom edge of the window). It is not preassembled but presumably built with bricks and plastered. (The house was built in 1968.)
Ground structure in the well: At the bottom there is a concrete slab that slopes away from the house.
Problem: After testing by pouring about 2 liters (2.1 quarts) of water into the drain, the water remains in the drain even after 24 hours. It hardly soaks away.
Measures taken so far:
I have already cleared the drainage hole of sludge and stones to a depth of about 30 cm (12 inches), but I cannot feel the end of the concrete slab.
The consequences:
The basement was damp around the skirting boards. After removing the boards, and as there has been no rain for a long time, the area is currently dry.
My questions to the forum:
Should I try to deepen the area at the end of the concrete slab (away from the house) horizontally to allow water to flow further back (toward the garden)?
Is there a risk that standing water for over 24 hours (despite a dry period) could be groundwater or a water layer?
What structure would you recommend for the drainage hole once flow is restored (gravel bed or similar)?
Thank you very much for your assessments!
I have an issue with the drainage of a light well and would appreciate your expert advice.
The situation:
The light well is approximately 50 cm (20 inches) deep and 1.50 m (5 feet) below ground level (bottom edge of the window). It is not preassembled but presumably built with bricks and plastered. (The house was built in 1968.)
Ground structure in the well: At the bottom there is a concrete slab that slopes away from the house.
Problem: After testing by pouring about 2 liters (2.1 quarts) of water into the drain, the water remains in the drain even after 24 hours. It hardly soaks away.
Measures taken so far:
I have already cleared the drainage hole of sludge and stones to a depth of about 30 cm (12 inches), but I cannot feel the end of the concrete slab.
The consequences:
The basement was damp around the skirting boards. After removing the boards, and as there has been no rain for a long time, the area is currently dry.
My questions to the forum:
Should I try to deepen the area at the end of the concrete slab (away from the house) horizontally to allow water to flow further back (toward the garden)?
Is there a risk that standing water for over 24 hours (despite a dry period) could be groundwater or a water layer?
What structure would you recommend for the drainage hole once flow is restored (gravel bed or similar)?
Thank you very much for your assessments!
Hello
If water is still standing in the drain after 24 hours, even though it has been dry for longer, I would no longer consider this normal slow infiltration. Especially with a construction year of 1968, it is quite possible that the original infiltration system has completely clogged over the years or was initially designed with tight dimensions.
Before you start digging horizontally toward the garden, I would first try to find out whether the concrete slab actually ends somewhere or if there might still be an old drain underneath. Digging deeper only on the side is not very useful if the surrounding soil is heavily clayey and water also remains standing there. Do you have an idea of what kind of soil you have? That would be important for the assessment.
I would at least keep groundwater in mind. The fact that water remains standing even during a longer dry period and that there was previously moisture at the baseboards unfortunately fits with this. This does not have to mean a big problem right away, but I wouldn’t ignore it either.
Once the drain is working again, I would fill the area below with coarse gravel 16/32 and place a geotextile fabric on top to prevent it from clogging again with fine particles. Finer mixtures tend to clog over time, especially with older light wells.
If water is still standing in the drain after 24 hours, even though it has been dry for longer, I would no longer consider this normal slow infiltration. Especially with a construction year of 1968, it is quite possible that the original infiltration system has completely clogged over the years or was initially designed with tight dimensions.
Before you start digging horizontally toward the garden, I would first try to find out whether the concrete slab actually ends somewhere or if there might still be an old drain underneath. Digging deeper only on the side is not very useful if the surrounding soil is heavily clayey and water also remains standing there. Do you have an idea of what kind of soil you have? That would be important for the assessment.
I would at least keep groundwater in mind. The fact that water remains standing even during a longer dry period and that there was previously moisture at the baseboards unfortunately fits with this. This does not have to mean a big problem right away, but I wouldn’t ignore it either.
Once the drain is working again, I would fill the area below with coarse gravel 16/32 and place a geotextile fabric on top to prevent it from clogging again with fine particles. Finer mixtures tend to clog over time, especially with older light wells.
Thank you for your assessment!
Currently, the gap is so tight that I can barely fit my hand in. At about 30 cm (12 inches) deep measured horizontally away from the house wall, the edge of the concrete slab is still not detectable.
Soil condition: My garden soil consists almost entirely of construction debris and gravel after the first 20 cm (8 inches) of topsoil. The house underwent a complete renovation five years ago, but the light wells don’t seem to have been addressed during that process.
Should I carefully enlarge the hole now in order to find the edge of the concrete slab at all?
Thank you very much for your help!
Currently, the gap is so tight that I can barely fit my hand in. At about 30 cm (12 inches) deep measured horizontally away from the house wall, the edge of the concrete slab is still not detectable.
Soil condition: My garden soil consists almost entirely of construction debris and gravel after the first 20 cm (8 inches) of topsoil. The house underwent a complete renovation five years ago, but the light wells don’t seem to have been addressed during that process.
Should I carefully enlarge the hole now in order to find the edge of the concrete slab at all?
Thank you very much for your help!
That would indeed be the logical next step. As long as you don't know whether the concrete slab ends somewhere or if there used to be a proper drain, you are essentially searching blindly. For houses from the 1960s, simple infiltration solutions were often installed in the light well, which have become clogged after decades.
I would carefully enlarge the hole and selectively expose the area toward the garden, but in a controlled manner—not just digging deeper. If there is only a solid concrete surface below, additional depth won’t help much, except that more water could accumulate there. What matters more is whether the slab slopes away or if there is an old drain connection somewhere. Have you checked to see if there might still be an old clay pipe or a drain line outside?
The ground construction with rubble and gravel generally suggests adequate infiltration. That’s why it doesn’t quite fit that hardly any water disappears even after 24 hours. For that reason, I would first clarify the actual construction before refilling anything.
Once the passage is clear again, I would install coarse gravel 16/32 at the bottom and place a geotextile fabric above to prevent the infiltration area from clogging again quickly. Avoid using fine material or chippings, as they will silt up over time! And if 2 liters of water remain standing for a long time, the current drainage is basically not working properly—you have to accept that reality.
I would carefully enlarge the hole and selectively expose the area toward the garden, but in a controlled manner—not just digging deeper. If there is only a solid concrete surface below, additional depth won’t help much, except that more water could accumulate there. What matters more is whether the slab slopes away or if there is an old drain connection somewhere. Have you checked to see if there might still be an old clay pipe or a drain line outside?
The ground construction with rubble and gravel generally suggests adequate infiltration. That’s why it doesn’t quite fit that hardly any water disappears even after 24 hours. For that reason, I would first clarify the actual construction before refilling anything.
Once the passage is clear again, I would install coarse gravel 16/32 at the bottom and place a geotextile fabric above to prevent the infiltration area from clogging again quickly. Avoid using fine material or chippings, as they will silt up over time! And if 2 liters of water remain standing for a long time, the current drainage is basically not working properly—you have to accept that reality.