Our development plan requires permeable paving for the driveway and parking spaces. In principle, there's nothing wrong with that, but the problem is that the soil underneath is very clayey and hardly suitable for allowing water to simply drain away. Even days after the last rain, a layer of mud several centimeters thick sticks to boots, and the infrastructure work was probably delayed because every hole filled up during this wonderful summer. During heavy rain, a stream often runs through the neighbors’ gardens in the first construction phase as well.
I just reviewed the soil survey again; it states loess-bearing fluvial clay with a kf value of 9.5*10^-8 m/s (approximately ~10^-7). According to Wikipedia, soil with a permeability of 10^-6 or less is considered impermeable.
Now the question is how to deal with this situation. I see the following problems here:
- Originally, I planned to use the same paving for the path from the driveway to the front door, but now I worry that this could direct water underneath the foundation.
- An additional problem is that the road is located almost at the highest point of the property, and with a connected substructure, the water will likely follow the path of least resistance.
- Where should the water that seeps through the paving go? Probably less of an issue with light rain, but heavy rain could cause significant ponding.
- How to handle frost? The subsoil itself is classified as F3 and is already somewhat problematic, and having trapped water on top sounds like a recipe for problems. Our property is at 666 meters (The Number of the Beast... 😉 ), so we can expect significant frost.
- The neighbors to the east and northeast are at higher elevations, and depending on their construction, heavy rain could flow toward our front door. That’s exactly why permeable paving in front of the house was appealing.
Of course, I have already considered possible solutions:
- For the path to the house and the terrace, maybe avoid permeable paving so that rainwater flows away from the house on the surface and is directed by a slight slope into the lawn?
- Some sort of water barrier within the substructure using deep edge restraints between the driveway and the path so that each substructure is reasonably separated? The paths need much less sub-base than the driveway anyway.
- Or simply use permeable paving all the way up to the house but excavate extra deep under the driveway so that all water drains and infiltrates there? The driveway will be about 30cm (12 inches) higher than the ground floor level, so that would indeed mean excavating quite deep and probably extra cost.
- Or is diverting all this water unnecessary, and would a standard 30cm (12 inches) base layer plus 30cm (12 inches) frost protection under permeable paving be sufficient?
- Does it make a difference whether porous stones are used or if infiltration happens through the joints? I’m not really a fan of wide joints because they always seem to become completely covered with moss.
I just reviewed the soil survey again; it states loess-bearing fluvial clay with a kf value of 9.5*10^-8 m/s (approximately ~10^-7). According to Wikipedia, soil with a permeability of 10^-6 or less is considered impermeable.
Now the question is how to deal with this situation. I see the following problems here:
- Originally, I planned to use the same paving for the path from the driveway to the front door, but now I worry that this could direct water underneath the foundation.
- An additional problem is that the road is located almost at the highest point of the property, and with a connected substructure, the water will likely follow the path of least resistance.
- Where should the water that seeps through the paving go? Probably less of an issue with light rain, but heavy rain could cause significant ponding.
- How to handle frost? The subsoil itself is classified as F3 and is already somewhat problematic, and having trapped water on top sounds like a recipe for problems. Our property is at 666 meters (The Number of the Beast... 😉 ), so we can expect significant frost.
- The neighbors to the east and northeast are at higher elevations, and depending on their construction, heavy rain could flow toward our front door. That’s exactly why permeable paving in front of the house was appealing.
Of course, I have already considered possible solutions:
- For the path to the house and the terrace, maybe avoid permeable paving so that rainwater flows away from the house on the surface and is directed by a slight slope into the lawn?
- Some sort of water barrier within the substructure using deep edge restraints between the driveway and the path so that each substructure is reasonably separated? The paths need much less sub-base than the driveway anyway.
- Or simply use permeable paving all the way up to the house but excavate extra deep under the driveway so that all water drains and infiltrates there? The driveway will be about 30cm (12 inches) higher than the ground floor level, so that would indeed mean excavating quite deep and probably extra cost.
- Or is diverting all this water unnecessary, and would a standard 30cm (12 inches) base layer plus 30cm (12 inches) frost protection under permeable paving be sufficient?
- Does it make a difference whether porous stones are used or if infiltration happens through the joints? I’m not really a fan of wide joints because they always seem to become completely covered with moss.
WilderSueden schrieb:
Combined cistern for garden irrigation and retention with emergency overflow to the stormwater drainage system. The full modern package 😉 What price range would you estimate for something like this, if you don’t mind me asking? Just a rough idea?
X
xMisterDx28 Jun 2023 17:55Well, let’s think about it. A DN100 pipe usually drains the water from about half a roof, so maybe 50-70m² (540-750 sq ft).
Your gutter is supposed to carry away the water pushed to your front door by heavy rain combined with wind. We’re talking about 2 to 3m² (22-32 sq ft), since the paved area in front of your door won’t be much larger. And it should have a slope, I hope. That should be manageable with DN50.
Even heavy rain doesn’t suddenly dump 50 liters per square meter (1.6 gallons per square foot) as if someone poured a bucket of water out. If you get 120 liters (31.7 gallons) in an hour, that’s 2 liters (0.5 gallons) per minute; with 3m² (32 sq ft) that’s 6 liters (1.6 gallons) per minute that the drain must handle.
The real problem will more likely be that your drainage system can’t take all that water in, and it will start to back up in the pipes after a few minutes. Then it will overflow. This also happens with downspouts and can’t really be avoided.
With 100m² (1,076 sq ft) of roof area and 50 liters per square meter per hour (1.6 gallons per square foot per hour), a 10m² (108 sq ft) rainwater cistern fills up in 2 hours if it was completely empty before. The emergency overflow will also be full because the public stormwater system is usually not designed for heavy rain events.
Your gutter is supposed to carry away the water pushed to your front door by heavy rain combined with wind. We’re talking about 2 to 3m² (22-32 sq ft), since the paved area in front of your door won’t be much larger. And it should have a slope, I hope. That should be manageable with DN50.
Even heavy rain doesn’t suddenly dump 50 liters per square meter (1.6 gallons per square foot) as if someone poured a bucket of water out. If you get 120 liters (31.7 gallons) in an hour, that’s 2 liters (0.5 gallons) per minute; with 3m² (32 sq ft) that’s 6 liters (1.6 gallons) per minute that the drain must handle.
The real problem will more likely be that your drainage system can’t take all that water in, and it will start to back up in the pipes after a few minutes. Then it will overflow. This also happens with downspouts and can’t really be avoided.
With 100m² (1,076 sq ft) of roof area and 50 liters per square meter per hour (1.6 gallons per square foot per hour), a 10m² (108 sq ft) rainwater cistern fills up in 2 hours if it was completely empty before. The emergency overflow will also be full because the public stormwater system is usually not designed for heavy rain events.
W
WilderSueden28 Jun 2023 21:32kati1337 schrieb:
What is the approximate cost for something like this, if I may ask? Just roughly? It was included in the building specification, so I don’t have an individual price we paid. However, the price list from Mall can be found on Google; the Reto (cistern with retention and use) is about 3,500 (around 8 cubic meters). Plus, of course, earthworks, pump, and connection of the whole system.
xMisterDx schrieb:
Your channel drain is supposed to divert the water that heavy rain combined with wind pushes up against your front door. We’re talking about 2 or 3 square meters (around 20-30 square feet), as your pavement in front of the door won’t be much bigger. And hopefully, it’s sloped.
That should be handled by a DN50 (approx. 2-inch) pipe. The problem isn’t the pavement. The problem is probably the neighboring properties because they are slightly higher and slope towards mine. Also, the eastern side of the property is a bit elevated. While water can flow around the house, the question is whether that will be enough when it comes with force.
W
WilderSueden28 Jun 2023 21:38Jonas90 schrieb:
But even with a DN75 pipe, you would need to significantly shorten the paving stone in height. You’d have to check how many centimeters remain; otherwise, the stone could obviously break much more easily.Above a DN75 pipe, only 2.5cm (1 inch) remain at the narrow end, and further along the pipe it’s 4cm (1.6 inches). The paving bricks are 7.1cm (2.8 inches) thick. However, I think I’m slowly getting my girlfriend to agree on placing the gutter flush directly in front of the wall. We want to lay everything out again tomorrow evening 😉X
xMisterDx28 Jun 2023 21:45Oh wow. I have a similar issue.
Not the neighbors, but the street is partially at or above the finished floor level.
You need to act much earlier because a small channel won’t be able to handle a sudden surge.
A channel, okay. But shallow and with a DN50 (2 inch) drain?
As a solution for the rear neighbor, who is about 50cm (20 inches) higher, I planned a terraced garden.
I want to have drainage above the step—still figuring out how. And towards the street, in front of the hedge, which should anyway have a 50cm (20 inch) setback from the property line, I’m planning a small ditch with a “sump pit.”
Something like that.
Then, if necessary, I’ll pump the water back onto the street through a hose running through the hedge. Not exactly legal, but who’s going to check when everything is flooding.
Regarding costs... in early 2022 I paid about 4,000 net for a 7m³ (about 2,470 gallons) concrete cistern including installation. Without the connection, which is still pending... but try finding a civil engineer.
Mine is probably bankrupt... on Google it’s been “temporarily closed” for weeks now…
Not the neighbors, but the street is partially at or above the finished floor level.
You need to act much earlier because a small channel won’t be able to handle a sudden surge.
A channel, okay. But shallow and with a DN50 (2 inch) drain?
As a solution for the rear neighbor, who is about 50cm (20 inches) higher, I planned a terraced garden.
I want to have drainage above the step—still figuring out how. And towards the street, in front of the hedge, which should anyway have a 50cm (20 inch) setback from the property line, I’m planning a small ditch with a “sump pit.”
Something like that.
Then, if necessary, I’ll pump the water back onto the street through a hose running through the hedge. Not exactly legal, but who’s going to check when everything is flooding.
Regarding costs... in early 2022 I paid about 4,000 net for a 7m³ (about 2,470 gallons) concrete cistern including installation. Without the connection, which is still pending... but try finding a civil engineer.
Mine is probably bankrupt... on Google it’s been “temporarily closed” for weeks now…
W
WilderSueden25 Jul 2023 08:39A quick update here. We've solved it like this now.
Not flush, but with a full row. This provides more space to work and saves a few cut pieces. When we pave the pathways in autumn, we will connect to this. For now, there is only the small entrance area so that people can wipe their dirty shoes. During the paving work, the rest of the ground will be raised a bit as well, allowing for step-free access into the house (just in time, as the stroller phase is slowly coming to an end...).
Pro tip: install the grates in the channel before paving, otherwise the channel will compress and the grate will only go back in with force 😉
Also, we learned an important lesson during this time. A roofed area doesn’t necessarily provide protection in bad weather. Two weeks ago, we had a thunderstorm with rain hitting the patio door at head height. So even with a covered area, don’t try to save on the slope or drainage.
Not flush, but with a full row. This provides more space to work and saves a few cut pieces. When we pave the pathways in autumn, we will connect to this. For now, there is only the small entrance area so that people can wipe their dirty shoes. During the paving work, the rest of the ground will be raised a bit as well, allowing for step-free access into the house (just in time, as the stroller phase is slowly coming to an end...).
Pro tip: install the grates in the channel before paving, otherwise the channel will compress and the grate will only go back in with force 😉
Also, we learned an important lesson during this time. A roofed area doesn’t necessarily provide protection in bad weather. Two weeks ago, we had a thunderstorm with rain hitting the patio door at head height. So even with a covered area, don’t try to save on the slope or drainage.
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