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Small Cabin Forum / Cabin Construction / Foundation for a cabin in a flood plain?
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Julie2Oregon
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# Posted: 16 Jul 2016 16:25
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Hey all --
Well, things have been crazy-busy and have changed substantially. Yeah, again, lol, but this is due to some market-driven and other realities. Existing properties in southern Oregon are flying off the market, to the point where county appraisers are now scheduling appointments in OCTOBER and other offices are overwhelmed. It makes buying from a distance nearly impossible.

Lots of land for sale, though. So my current home is now in the hands of a Realtor, I'm preapproved for construction loans, and have decided to go modular. I'm negotiating on an acre in a great location now.

And this is the modular cabin I will be building. One bedroom, about 540 sq. ft.

I spoke with the county clerk and she emailed me the CCR document for the subdivision the land is in. Such as they are, lol. 2 pages -- no minimum square footage, no crazy restrictions. Buildings can't be left unfinished for more than 2 years and tarpaper has to be covered; no outdoor bathrooms. Keep the property clean and presentable. Yay!

Spoke with the Assistant Planning Director about the area and the particular parcel and she called up (and sent me) map overlays while we were talking. There's a creek on the property and it's in a flood zone. I figured it would be. Now, the area hasn't flooded in more than 50 years and FEMA has revised the zone so that only about a quarter of this parcel along the western boundary and the very bottom would still be in the flood zone. Basically, where the creek is. But the revisions haven't yet taken effect/been adopted.

She sent me both overlays so I know where to build. In the future, then, my cabin won't be in a flood plain. For now, though, I WILL be building in a designated flood plain. What that means, she said, is the county will require a surveyor to be involved in the building of the foundation. The foundation will have to be higher and the location and number of vents will be affected. But it's not as bad as it sounds. Basically, the goal in the event of a flood would be to have the water pass through the vents and not batter the foundation and home.

Makes sense. And for a cabin this size, probably not pricey. I like a higher foundation, anyway, to help keep out pests. We were going to do a concrete stemwall foundation, with some piers (embedded in the concrete pour) in the middle to provide even more support for the floor joists.

Will my foundation plan have to change? Will this be really pricey? Are there other designated flood plain building considerations? That's all the Planning Director could see as being different. Septic isn't an issue in this area. And, gah, well depths are AWESOME.
Modular_cabin.jpg
Modular_cabin.jpg
modular_cabin_inside.jpg
modular_cabin_inside.jpg


Bret
Member
# Posted: 16 Jul 2016 18:01
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Looking good. Higher foundation wall equals root cellar, storm cellar. Not a bad way to go.

Julie2Oregon
Member
# Posted: 16 Jul 2016 18:06
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Bret
Yeah, I was thinking that. An access door was part of the equation, anyway, so perhaps we can just make it a little bit bigger so I have easier access more regularly.

I actually like the fact that there's a creek there. Maybe I'm being naïve and the creek/flood plain adds more issues than it potentially contributes, I dunno. But I'm super-glad that good groundwater is easily accessible via well.

rockies
Member
# Posted: 16 Jul 2016 18:12
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Last year I remember watching a news report of a woman who had been saved from her half sunken house by a fire rescue crew that had cut through her roof in order to reach her. As she was being brought to the edge of the flooded field the news crews were there to document the rescue. She turned her eyes to heaven and said "Why God? Why did you do this to me?"

I remember thinking "God didn't do this to you. You built your house in a flood plain. It's called a "Flood Plain". It floods.

High price to pay to lose all your belongings, your home and investment.

Julie2Oregon
Member
# Posted: 16 Jul 2016 18:22
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Oh, forgot to mention that I'm going to have my original choice of builder add a mudroom where that side door is, lean-to style with another entry door, plus a pump house right after the cabin is built and everything is approved/signed off. The roof for it will be attached to the cabin just below the overhang but the lean-to itself won't be attached to the cabin so it's not part of the structure and, hence, part of the square footage, taxable, subject to codes.

And, next spring, I'll hire them to build either a small garage or a carport with breezeway.

They're good guys and do good work but don't regularly do larger habitable structures so I think it's best that I go modular for the cabin and then have them do the auxiliaries.

Julie2Oregon
Member
# Posted: 16 Jul 2016 18:29
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rockies
Did you even read my post or did you just chime in to crap on me again? FEMA has revised the flood plain map for the area and I'm going to build in the section that is NO LONGER designated as a flood plain by FEMA. But because the revisions haven't been adopted by the county yet, I will still have to build according to flood plain criteria.

Julie2Oregon
Member
# Posted: 16 Jul 2016 18:35
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Now I would really appreciate some ideas from others for foundations that would meet code in a designated flood plain. Being told that my cabin is going to be swept away isn't helpful. Or reality.

rockies
Member
# Posted: 16 Jul 2016 18:56
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I did read your post. Since you always go off like a nuclear missile every time I question one of your "plans" I read your posts very, very carefully.

The lady who got washed away was also in a "50 year Flood Plain". I guess she just happened to build in the 49th year. So FEMA is about to remove it from their "Flood Plain Map".

Good for FEMA. They sure did a great job with New Orleans. And God knows that Mother Nature reads the FEMA recommendations.

It was made a "Flood Plain" once because IT FLOODS! It will flood again. God, get over yourself Jules baby.

Julie2Oregon
Member
# Posted: 16 Jul 2016 19:10
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Typical.
Peace out.

Steve_S
Member
# Posted: 16 Jul 2016 19:23
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FOUNDATIONS FOR UNSTABLE SOILS & FLOOD PLAINS is a foundation system for just such an application. There are several different ways to do the foundation but it all really depends on the soils, depth to bedrock etc...

On the "designated flood plain" tag... I assume that if FEMA or the State declare it a flood plain, the insurance would be that much higher than if it wasn't. To be honest, never trust a shmuck sitting at his government office to decide if your safe or not... Regardless of the 'official' designation, assume the worst case potentials and build accordingly... Just consider how many "Storms of the Century" or "Once in a 100 years" events have been occurring recently... seems to be at least one per month and it feels like it's increasing in frequency too...

Julie2Oregon
Member
# Posted: 16 Jul 2016 19:36
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Steve_S
The West Coast has the opposite problem -- drought and wildfires -- so that's been my main consideration. I actually want to locate near water because of it. And the climate models show that persisting well into the future and getting worse. The exception is the coast, where there is tsunami threat, but I'd be hundreds of miles from the coast. The State of Oregon has incurred huge costs trying to get wildfire insurance coverage and the deductibles make it almost worthless.

So I guess it's six or one-half dozen -- either I'll pay high premiums due to a high wildfire risk or I locate near water and pay higher premiums due to a flood plain designation. At least the latter will cease once that overlay is removed.

Thank you for the link! I will read it and discuss it with the contractors! This is a volcanic area so we might still want to excavate down to bedrock and build up from there!

Steve_S
Member
# Posted: 16 Jul 2016 19:47
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I hear ya there Julie... So many little devil's to sort through eh... I'd prefer being closer to water as well...

I built on a ridge in the midst of a mostly Cedar, mixed bush and am quite heavily surrounded... No water access at my place.

I was reading about a company that is building homes on floating concrete foundations for flood plains and how they borrowed the idea from the Netherlands using a concrete hull (that acts like a boat)... Interesting idea I thought but it's maybe a tad overkill in general. Maybe if in Jersey or Florida as they will be swimming soon enough.

Julie2Oregon
Member
# Posted: 16 Jul 2016 20:10
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Yeah, the West is drying and the East is swimming. It's been wretched here in the Southwest. Aside from those weeks of non-stop rain we got in the Spring, we now can't get rain to save our lives where I live. I watch the radar, and HUGE thunderstorms coming down from Oklahoma literally hover just north of us until the rain disappears entirely. It's that hot. Scary stuff.

It would take years of way above average rain and snowpack to get the West back to normal soil conditions. It was a decent snow year but it got warm quickly and the snowpack started melting too soon, I read.

Again, I'm not so worried about flood; it's wildfire. Balancing the two, I'm looking at land that has some proximity to water and a good mix of open areas and trees. Trying to split the difference. Not doing so will make the property either mondo-expensive to insure or completely uninsurable.

Asher
Member
# Posted: 18 Jul 2016 22:01
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Are you sure you won't have any issue with you septic? I live between the Mississippi and Missouri rivers, I can reach either one of them on about 20 minutes from my house (I was waist deep in 85, 93, 95 and helped gut a lot of homes for rebuilding)... I spent a lot of my childhood around river cabins... these are all built more then 10' off the ground on stilts and survive repeated flooding, river currents, debris dams, ice flows, etc... Some of these places were at or over the roof's in 93 and still held up to the rivers forces.

My advice is to use piers, go higher then you will ever think you will need it to be... place a concrete pad below to park cars under the cabin. Don't cover the sides up, make sure the water can flow through and make sure there is no curb/edge around the pad, because if the water does come up, you can make quick clean up of the mud with a pressure washer. If you need a lift, a lot of guys down there find an old forklift truck, take the front mast off of it mount it to the side of the cabin and drive the mast pump with a electric motor = instant elevator...

The biggest issue (around here) now has to do with the septic's, if the cabins get sold the septic have to meet the new codes and those are very $$$$... The new design has a way of capping off the system in the event of a flood to keep waste from escaping...

Julie2Oregon
Member
# Posted: 21 Jul 2016 19:51
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Asher

Tests would have to be conducted, of course, but the water table in this area isn't as high as it is closer to the lake. When I was looking at existing cabins near the lake, my buyer broker recommended extreme caution, due diligence and contingencies because of reported, repeated septic failures there. We expanded our search.

This land is in a higher elevation, a few miles from the lake. There aren't rivers around it but there's a creek that meanders near one side of the property line and comes onto the property a bit near the southern boundary. If I bought the land, I would be building on the northern end of the property closer to the road, with the septic installed in the middle of the property where there aren't many trees. Incidentally, the northern end isn't all flood-plain designation.

I think we'd still be looking at a 24-inch frost line and I would like to build on bedrock for mega-stability. What sort of piers would you suggest that could work with bedrock and that height? This is a volcanic area so you don't have to dig super-deep to encounter rock.

Just
Member
# Posted: 21 Jul 2016 20:50
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Julie2Oregon
As the pic shows , we live in a flood plane , taken a few years ago . Our septic is just on the other side of the board fence , our county regulator told us to add 400 yards of sand to the area before installing the septic . it has never given any trouble even in this flood , I believe they call it a raised bed system .
now thats a flood plain
now thats a flood plain


Packerman
Member
# Posted: 22 Jul 2016 01:07
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Julie2, my daughter and son-in-law had to do this. They bought 2 acres with a small creek at the back and so they were in the 100 year flood plain. They ended up building a cabin but their concrete foundation was completely out of the dirt. One end they have a 2 stall garage, the other end is laundry/storage, etc. Looks weird but it works. They have those flood vents in the wall to let the water thru if it does flood. They could just open the garage doors, but I guess that's not good enough, LOL!

NorthRick
Member
# Posted: 22 Jul 2016 14:32
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Julie, google "outer banks houses" and click on the "images" option in google. The outer banks of North Carolina see some magnificent storms and any old house is built to withstand serious flooding.

A lot of the houses shown are pretty extravagant, but mixed in there will be some more modest ones. On some it is very obvious they are on pilings, others it is more hidden. As mentioned in other posts on this thread, parking under the house is common.

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