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RJH
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# Posted: 16 Sep 2021 06:10pm
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I’ve been searching through threads and haven’t seen a similar post. Been seeing a tons of good ideas and advice on other peoples projects, hoping to get steered down the right path
We have a purchased a cabin on a river last year in MN. The previous owner had it surveyed and he built it above flood plain at the time. FEMA has expanded their 100 year flood plain and our mortgage is making us cough up $1k a year for flood insurance. We are in the process of applying for LOMA. We hired a surveyor and we’re about 2 feet short of the ground elevation requirement that get us out of the flood zone. Most of it is under the screen porch which is decked with 5 1/2†boards. His advice was to skirt our screen porch and living space and backfill to get to the proper ground height. He’ll come out again and take the new elevation measurements to submit.
Our thought was to dig a trench a few inches below the concrete footings, add 1/4†wire mesh for critters and class 5. Run 4x4†Ground contact green treat horizontal from post to post, pound in some r-rod to help hold it in place. Frame 16 on center 2x4†with a 2x4 top plate attached to the joist. Skirt it with 3/4†Green treated for ground contact. Take basketball size rocks and packed with class 5 to help lock them in place. We’d keep the cheese wedge of rocks a few inches away from the plywood so there isn’t a ton of pressure pushing on the skirting wall.
- Has anyone come up with a better solution/materials?
- Since we would be burying half the plywood should we use a one way vapor barrier to increase lifespan of the plywood?
About half the area that will be skirted is under a screen porch the rest is under the insulated part of the cabin. We are not planning to insulate the skirting under the porch (decking above) but we do want to insulate the part under the cabin. We lost a ton of heat with just rocks underneath with cold drafts easily pushing through. Our shower “p†trap is under there and would freeze even with RV antifreeze in the trap after showers. We have electric heat which got up to $350 in January with plenty of days below 0. For the insulated portion we’re planning to frame it similar and use rigid styrofoam inside the 2x4 cavities and spray foam the cracks and seams.
- Do we need to add vents that we can open up in the summer?
- Keep it dirt floor or put plastic down?
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BRADISH
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# Posted: 16 Sep 2021 06:31pm
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Just for reference sake, how high is the bottom of the joist off of the average ground level?
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RJH
Member
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# Posted: 16 Sep 2021 07:28pm
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The front (around the porch) is roughly 3-4 ft. The insulated part is roughly 32†tapering to 2â€.
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RJH
Member
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# Posted: 16 Sep 2021 07:37pm
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Here's a visual of what we're thinking
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Fanman
Member
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# Posted: 16 Sep 2021 08:23pm
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As long as the floor is above the flood line isn't that all that matters? Like all the shore houses on stilts, they know it's gonna flood but it won't hurt the house.
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RJH
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# Posted: 16 Sep 2021 09:03pm
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That's been our argument too but the only way they will take away the flood insurance requirement is If we get the LOMA and they only way to get that is to to meet the ground elevation.
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frankpaige
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# Posted: 16 Sep 2021 10:40pm
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Everyone has to make their own decision. When I built ours, I said. If the fire, flood or tornado takes it. It is beyond me. Do many others say, no insurance?
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Brettny
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# Posted: 17 Sep 2021 07:21am
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Your going to turn your posts into a retaining wall and that's a very very bad idea. Think about how much weight could push against those posts. Then theres the fact that once this is done theres no guarentee you wont have to get flood insurance.
If you really want to do something I see two options.
1) pour new sono tubes and make them as tall as the horizontal beam, then backfill all the way under the porch and possibly the cabin.
2) raise the whole cabin
Btw is that a visual effect or is the front of your porch sagging?
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Nobadays
Member
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# Posted: 17 Sep 2021 08:51am
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Quoting: Brettny Your going to turn your posts into a retaining wall and that's a very very bad idea.
Brett is correct... you only have an insurance issue now. Pile rock and soil against those deck supports and it will eventually topple them. His suggestion of pouring new sono tunes is spot on. My guess is cost wise it might even be cheaper.
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RJH
Member
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# Posted: 17 Sep 2021 09:42am
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We thought of that, sono tubes under the deck would probably best and add dirt. But under the living part of the cabin we still want access to our plumbing under the bathroom and address the cold drafts that was freezing the shower's p trap under there. They built it more as a 3ish season cabin, we're trying to make it more efficient year round. The cabin is 18' wide and the ground is around 2:12 pitch. The crawl space under the bathroom would be less than a foot if we backfilled. We've thought of using landscape blocks with a lip and start the wall an inch from the plywood skirt, so there wouldn't be much fill and pressure on the plywood. Our worst case scenario is pony up for the annual FEMA insurance which is our lender's requirement
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Aklogcabin
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# Posted: 17 Sep 2021 10:03am
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I don't think you will have a problem with it getting pushed in. Folks have built homes with aww foundations for years.
If you wanted to pour a small footer under the wall to hold anchor bolts through the bottom plate could add that.
I would recommend a good waterproofing barrier such as bitathane on the outside of the plywood. You are correct when adding the fill in to watch for any large rocks that can fall on to it and damage it. A 6 mil. visqueen vapor barrier on the ground under your living space will be needed.
And to also put a water barrier just under the surface of the ground from the new wall out 4 foot or so. Sloping away from the cabin to divert rain water. So that it keeps the area near your cabin dry. Rain gutters would also help.
You have a nice looking cabin BTW.
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Brettny
Member
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# Posted: 17 Sep 2021 10:10am
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Quoting: RJH We've thought of using landscape blocks with a lip and start the wall an inch from the plywood skirt, so there wouldn't be much fill and pressure on the plywood. Our worst case scenario is pony up for the annual FEMA insurance which is our lender's requirement
Would this satisfy the insurance company? Would even raising the dirt about the cabin satisfy them?
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RJH
Member
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# Posted: 17 Sep 2021 10:45am
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Our surveyor that we hired that is filing the LOMA (Letter of Map Amendment) said we need to get our ground built up roughly 2' below the main cabin floor and crawl spaces that were lower were okay. Once our mortgage lender has been shown we're above the 100 year flood elevation, we won't be required to have FEMA flood insurance.
Thanks @aklogcabin, I'll have to research the bitathane and zisqueen. We don't want to be one of those folks. I think gutters would get ripped off over the porch with snow melts, nothing to anchor them into that's solid, metal overhangs the decking 3-4".
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snobdds
Member
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# Posted: 17 Sep 2021 11:53am
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I would put a retaining wall in.
One and done...
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spencerin
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# Posted: 18 Sep 2021 01:34am
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Would a wood retaining wall be easier and cheaper than a block one?
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Brettny
Member
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# Posted: 18 Sep 2021 08:02am
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It would be easier and cheaper to do wood...but then in 20yrs you get to do it again.
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spencerin
Member
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# Posted: 18 Sep 2021 11:07pm
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I dunno. Seen lots of landscaping retaining walls made with horizontal beams and rebar last a long time.
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gcrank1
Member
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# Posted: 19 Sep 2021 12:34am
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Railroad Ties should do it. Kinda nasty and heavy to handle; real bull work.
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