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FEMA Flood Cert – Raised House
This is nuts, but here’s what happened: I did the initial flood certificate and survey on a house. Then I used the official Flood Insurance Rate Map with an Elevation of 11 and also noted the online Region 2 Coastal tentative elevation of 13. A plot plan was prepared setting the new finished floor at 16′ (well above either flood elevation).
The house gets raised actually to 16.5′ due to the way the block courses worked out. The insurance company says FEMA still wants to classify this as being in the flood elevation, so I look into it further and realize that the house was diagram 9, but since it’s been raised so high that the new difference between “top of bottom floor” (crawlspace) and “top of next higher floor” is in excess of 5 ft. Therefore it has to go to diagram 2 and is considered to have a “basement”. That is the reason for the insurance staying high even though it’s been raised.
The flood insurance people are telling the client to just fill in the inside of the basement to the point where the height differential is such that it’s back to a crawlspace. I mentioned that if they do that, the flood vents that are within 1′ of adjacent grade will be covered from the inside. Has anyone seen something like this before? I was not expecting this to be an issue, and I have done many of these certs and a lot of them on houses that were raised without having this problem. Can the inside of the foundation be filled? Perhaps rip rap would be better?
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10 Replies
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Fill the “basement” as much as possible. Then cut a hole in the finished floor and pour the void full of concrete, thus creating a slab on grade circumstance.
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Have you done this? Are the flood vents still effective if the basement is filled? It says they have to be within 1′ of adjacent grade, which they are. I have done many of these but have never had this specific problem.
I should mention this is all being done on the old form since that is what was available at the time. I may just revise the old form again, as I am not sure the new one has been adopted in practice yet.
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This might work if the fill in the basement was not higher than the bottom edge of the flood vent. If the fill on the inside is higher then the vents decrease in value to zero if the fill is higher than the top of the vent. You then have a situation where the crawlspace elevation is higher than the adjacent grade. You don’t really have a crawlspace, you have a lower, unoccupied room. That would be more like a house on stilts or stem walls.
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Dan Patterson, post: 355165, member: 1179 wrote: Have you done this? Are the flood vents still effective if the basement is filled? It says they have to be within 1′ of adjacent grade, which they are. I have done many of these but have never had this specific problem.
I should mention this is all being done on the old form since that is what was available at the time. I may just revise the old form again, as I am not sure the new one has been adopted in practice yet.
I believe that if you fill the crawspace, it becomes a “Stem wall” (check diagram 1B description) no vents required?
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Yea, that’s the issue. The elevation inside the wall is about 9.1-9.2′, but outside it ranges from 9.6-9.8′. The finished floor is 16.5′. I repeatedly expressed my concern about rendering the vents useless if we fill the inside to 12′, which would have to be done in order to get it back to a crawlspace.
I think they just have to pay the insurance as is. I don’t want to see them spend more money and create more problems.
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David C. Newell RPLS LS CFM, post: 355170, member: 6347 wrote: I believe that if you fill the crawspace, it becomes a “Stem wall” (check diagram 1B description) no vents required?
That says slab on stem wall though. There is no slab. On top of the foundation is just joists and the floor, so would it really still fit that scenario?
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Dan Patterson, post: 355174, member: 1179 wrote: That says slab on stem wall though. There is no slab. On top of the foundation is just joists and the floor, so would it really still fit that scenario?
I’m not certain.
Here’s the link to technical bulletin:https://www.fema.gov/media-library-data/20130726-1502-20490-9949/fema_tb_1__1_.pdf
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David C. Newell RPLS LS CFM, post: 355177, member: 6347 wrote: I’m not certain.
Here’s the link to technical bulletin:https://www.fema.gov/media-library-data/20130726-1502-20490-9949/fema_tb_1__1_.pdf
Thanks, this is helpful. I will try to digest what’s in here fully and see how the potential filling re-characterizes the structure.
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“As explained on page 14 (Height of Openings Above Grade), the bottom of each opening is
to be located no higher than 1 foot above the higher of the final interior or exterior grades
under the opening. Therefore, placement of the openings in the foundation wall requires
knowledge of the expected finished exterior grade and the final interior grade of the crawl –
space.”This is helpful to me. The house is already on top of the foundation, so compacting the fill and pouring a slab at this point probably won’t be an optimal solution. I think they may have to pop out the vents and move them up and then replace the moved vents with a block. The opening will be within 1.0′ of the inside grade.
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Holy Cow, post: 355161, member: 50 wrote: Fill the “basement” as much as possible. Then cut a hole in the finished floor and pour the void full of concrete, thus creating a slab on grade circumstance.
This would work too, according to what I am reading. It would be a raised slab stem wall situation. I think just filling with dirt and raising the flood vents is probably cheaper though. Thanks for the help.
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