I am currently in the building permit / planning permission process and just found out through a call to the building authority that my property is located in the HQ100 EXTREME risk zone, so I have to take flood protection measures. This requirement has apparently been in effect since 2018 in Baden-Württemberg.
To explain: HQ100 EXTREME means there is a levee protecting my site next to the Danube River, but this levee could break (which seems very unlikely...). Because of this, I need to implement additional flood protection, whatever that may specifically involve. The exact wording states:
“At locations in risk areas outside designated flood zones, where no local land-use plan exists, construction projects may only be built or significantly extended using building methods adapted to the specific flood risk, according to generally accepted technical standards, provided this type of construction is technically feasible given the nature and function of the structure.”
I am building a solid structure without a basement, and my finished floor level is 61cm (24 inches) below this theoretical extreme flood level. I do not want to raise the ground level further. Although this would be technically possible, it would be expensive and would not look good.
I spoke by phone with the responsible official about whether I could build a wall around my property as a possible solution. She said she wasn’t sure if walls that high would be permitted there and reminded me to consider the entrance driveway. She recommended building 81cm (32 inches) higher for safety, but 61cm (24 inches) might be acceptable. However, I got the impression she wasn’t very knowledgeable. Maybe installing barriers or flood gates on the doors could work – I have seen sliding flood barriers online. Overall, this is really frustrating as none of the more than 100 houses nearby (all built before 2018) have anything like this, there has never been an extreme flood, and I think potential damage would probably be less than the cost of these measures. I also have insurance that costs an additional 100€ per year for flood coverage. To be safe, I will probably install my heat pump about 0.5m (20 inches) higher.
Does anyone have experience with this or a good idea on how to solve this as cost-effectively as possible?
To explain: HQ100 EXTREME means there is a levee protecting my site next to the Danube River, but this levee could break (which seems very unlikely...). Because of this, I need to implement additional flood protection, whatever that may specifically involve. The exact wording states:
“At locations in risk areas outside designated flood zones, where no local land-use plan exists, construction projects may only be built or significantly extended using building methods adapted to the specific flood risk, according to generally accepted technical standards, provided this type of construction is technically feasible given the nature and function of the structure.”
I am building a solid structure without a basement, and my finished floor level is 61cm (24 inches) below this theoretical extreme flood level. I do not want to raise the ground level further. Although this would be technically possible, it would be expensive and would not look good.
I spoke by phone with the responsible official about whether I could build a wall around my property as a possible solution. She said she wasn’t sure if walls that high would be permitted there and reminded me to consider the entrance driveway. She recommended building 81cm (32 inches) higher for safety, but 61cm (24 inches) might be acceptable. However, I got the impression she wasn’t very knowledgeable. Maybe installing barriers or flood gates on the doors could work – I have seen sliding flood barriers online. Overall, this is really frustrating as none of the more than 100 houses nearby (all built before 2018) have anything like this, there has never been an extreme flood, and I think potential damage would probably be less than the cost of these measures. I also have insurance that costs an additional 100€ per year for flood coverage. To be safe, I will probably install my heat pump about 0.5m (20 inches) higher.
Does anyone have experience with this or a good idea on how to solve this as cost-effectively as possible?
Ötzi Ötztaler20 Jun 2020 15:24
Baumaxxx schrieb:
That’s a good tip. I’m especially interested in those cosmetic things like dam seals—are they effective or not? When I buy stuff like that, I don’t want the insurance to be the only fallback in case the worst happens. Don’t overlook water ingress through the sewer system. A backwater valve in the utility room might not be sufficient in some cases.
Try contacting the local emergency services (e.g., THW) about the seals.
However, I strongly doubt that these measures provide more than a false sense of security. It’s better to save your money and fully accept the risk instead.
H
hampshire20 Jun 2020 16:50Baumaxxx schrieb:
Who has experience with this or a good idea on how to solve it as cost-effectively as possible??? Mechanically raising the house will be the most cost-effective solution that can be approved, if the budget is "only" €10,000.
Even on a small 500 m² (5,400 sq ft) plot, you already have at least 100 m (330 ft) of distance requiring a waterproof solution. So, including the access route, you would need to stay below €100 per linear meter, which is quite challenging.
Take a look at how the Dutch partially solve this: they have a concrete basin under the house, which in turn rests on a pontoon guided by steel piles. When flooding occurs, the house is lifted along the piles. When there is no flooding, it sits like a normal house. Of course, you won’t get this solution for €10,000 – but it is certainly elegant, and you can easily plan for 1 m or more of elevation.
That would be my solution to combine aesthetics and function – I consider it cost-effective, but I also recognize the increased upfront investment.
hampshire schrieb:
Look at how the Dutch sometimes solve this: They have a concrete basin under the house, which in turn sits on a pontoon guided by steel columns. When there is a flood, the house rises guided by the columns. When there is no flood, it sits like a normal house. It’s clear that you won’t get this solution for 10k, but it is definitely elegant, and you can easily plan for 1 meter or more.
That would be my solution to combine aesthetics and function – I consider it cost-effective, although it does require higher upfront capital. WOW, of course it’s five times cheaper to repair the damage. If the dam really breaks, the maximum would be 60cm (24 inches). Let’s assume it’s not the highest water level and emergency services are working against it, then it might be 10–20cm (4–8 inches), and that actually hasn’t happened in the last 70 years.
Anyway, I just need something I can present. What exactly is a matter of design preference, and I would like to hear from people with experience.
H
hampshire20 Jun 2020 17:33Baumaxxx schrieb:
WOW, of course it’s five times cheaper to repair the damageI see money as a tool, not an end in itself. I value quality of life more. Money comes and goes – but time is irretrievably lost. When I think about the quality of life of a family I know who had to leave their house twice for extended periods due to flooding in the Donau / Vilshofen area, pure cost calculations take a back seat.Of course, it is completely valid and understandable to see it differently. People who know their options can usually make better decisions.
If there is ever 10-20cm (4-8 inches) of water in front of the house, and even if it reaches 60cm (24 inches), that does not necessarily mean that the water will get inside the house. As I said, I have insurance and I am building a solid concrete house, so why should I invest 100,000 € in a concrete basin, especially since I neither have that money nor will I get it. On top of that, the construction delays... that could ruin my entire dream. The bank has also approved the financing for this specific house with these costs, who knows...
H
hampshire20 Jun 2020 17:44Baumaxxx schrieb:
why should I invest 100,000 € in a concrete pool nowYou’re not supposed to. The solution was declined, and that’s fine. Don’t worry about it any further. The only problem would have been if later you thought, “If only I had known back then.” That’s what the post was meant to be – an option to consider, not a “my suggestion is the only right one.”