# Does anyone have any experience with building stilt houses?



## pokerdonkey (Oct 6, 2007)

...or know of any good books or websites that outline the process? 

From what I gather, the construction is pretty conventional once the stilts are sunk and the top deck is installed?


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## concretemasonry (Oct 10, 2006)

thery blow away in very high winds (tornadoes, hurricanes. etc.) because of connection problems.

If you are in a seismic area, you better thave it engineered.

They are not as forgiving as traditional construction.


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## troubleseeker (Sep 25, 2006)

concretemasonry said:


> thery blow away in very high winds (tornadoes, hurricanes. etc.) because of connection problems
> .


That is exactly why they blow away.."connection problems". If they are built correctly they will not blow away any more than the structure of a slab house will blow away under the same weather conditions.

Right, once the stilts are in place and the deck is framed, there is no difference in building, except for everything being more difficult because it is higher in the air and more labor intensive to handle materials.


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## pokerdonkey (Oct 6, 2007)

Yeah, this whole "labor intensive materials" thing is getting to be a heacache. I'm building on an island, so there's a huge effort just to get the materials out there, and then there will be another pain in the backside in manipulating the materials up onto the construction deck. 

Also, does anyone know if rebar enforced concrete filled PVC pipes would be appropriate for the stilts?
Given the salt water influence, whatever I can make out of non-rotting material will be better.


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## concretemasonry (Oct 10, 2006)

Are you building in a hurricane/strom surge area?

I inspected several hundred damaged/destroyed homes in Mississippi and Louisiana after Katrina.

On/near the coast, the wood snapped at about 6' above ground.

Steel usually rusted and bent above 6'.

Concrete piles usually tilted, wracking the house so it was totalled.

The only thing that really was hurricane proof was deep (6') spread footings with rectangular concrete or reinforced block piers that had the long dimension perpendicular to the coast. - Blow-out walls between the piers for extra seasonal space on ground level.

If you are concerned with hurricanes, have a professional do the design, then build it yourself.


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## pokerdonkey (Oct 6, 2007)

Yup, hurricane zone, however it's on an interior barrier island, so the surge impact wouldn't be as as dramatic as it is on bare beach coastline. 

Also, Katrina was a real beast- not typical of any given storm. Unless you're on the upper gulf basin or lower peninsular Florida where you can expect a monster storm (Cat 4/5) every 30 years or so, storms like Katrina tend to be 100/200 year storms everywhere else. As long as my place is reasonably set up for a Cat 2/3 surge, I'm willing to risk it for anything beyond that since its statistically unlikely in my lifetime.


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## concretemasonry (Oct 10, 2006)

The return surge is worse than the inflow because of the difference in debris.

Katrina was a 100/200 year storm based on a very short storm history. Now it is probably a 30-75 year storm, which is about the economic life of typical American homes. Just becuase a storm is 30 years does not mean it will not come for 50 more years - it could be next week.

Land values went up significantly after Katrinia because of the junk housing being washed away and not rebuilt - people put lots together ($800,000 plus, each) for investment.


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## pokerdonkey (Oct 6, 2007)

concretemasonry said:


> Land values went up significantly after Katrinia because of the junk housing being washed away and not rebuilt - people put lots together ($800,000 plus, each) for investment.


It depends on where.
I own two lots in Shoreline Park that quadrupled in one year after Katrina.
All the mobiles were washed away and a protective covenant was in place that wouldn't allow any more to be built. The only reason they were as cheap as they were was because the place was filled with terribly crappy houses. Now, it's all being rebuilt with nice spec homes.

Funny, how that works...

Anyway, as far as the likelihood of storms, it's one of those positive versus negative expectation questions. 
Building every home to withstand a cat 5 storm would have a negative financial expectation over time, as the costs associated with the increased structural durability for all homes would outweigh the costs associated with rebuilding any given area, given the frequency ratio of huge storms. It's actuarial stuff, but overall, I'm quite comfortable building to a cat 2/3 standard. If a 4 or a 5 hits, oh well. It's the chance I took, but the odds are definitely in my favor.


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## philS (Jul 10, 2007)

Pokerdonkey -- FWIW, I built cabin on stilts in middle of hurricane zone, top of 600 ft hill for view. (Stilts also get you up into the breeze and away from creepy-crawlies.) No flood or surge issue of course but the wind exposure is as bad as possible (also a seismic zone). Engineered (pro) for 130 MPH wind and overbuilt (me). It's only 16' x 32' and one story on top of the stilts, but his calculations showed that to get it to stay put even in 130 MPH wind required 15 footings (1 cu yd each). The 15 (8 ft high) columns are heavily reinforced concrete with 1/4" steel saddles with hooks into the rebar. The wooden girders were then through-bolted through the saddles. After that, construction was standard wood frame (P-T) except that every possible connection was strapped and/or reinforced with framing anchors. (It's amazing how much wood-frame design has to change though when you need to worry more about uplift forces than live and dead weight.) 

No real test yet. My main worry is that the many hundreds of 2" "tech" screws attaching zinc roofing to roof sheathing and framing are starting to rust (after only 6 years). Yes, if a cat 5 hits it may all go, at least down to the girders, but like you I wasn't willing to design or build for that. I just finished a 30x30' garage/shop that's poured concrete and 8" back-filled concrete block. I'll try to be in the garage when the cat 5 hits and in the cabin for the mag 7 earthquake! 

On the stilt construction, you might be able to sonotube the columns but I found it easier to build forms from dimensional lumber, then recycle the form wood into floor joists and porch decking. Steel requires constant maintenance in marine environments. Concrete is the way to go but I suggest you plan on 2" protection for the rebar. We were (just barely) able to get transit-mix and a line-pumper to the site but the footings and columns "could" have been done by hand (gas-powered mixer and some kind of forklift). 

Good luck

Phil


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## ratherbefishin' (Jun 16, 2007)

pokerdonkey, here's some info that might be helpful: http://www.fema.gov/pdf/rebuild/mat/fema499/hgcc_fact14.pdf

Even on an interior island, you're probably still in a V zone and given the access problems, adequate piers or pilings will be very costly. Why not build a dock and a houseboat, instead? Then, when a storm comes, you can move the boat to a safe place and not lose anything except maybe some decking on the dock.

As an aside from here at ground zero, eastern eyewall, Katrina......I had the opportunity to speak extensively last year with the oceanographer who headed the team writing the new Flood Insurance Rate Maps for this area. At that time, Katrina was officially listed "conservatively" as a 500yr storm, and core samples dating back 1500 yrs showed nothing like it in that period of time. That's not to say it can't happen again next year, but I feel fairly comfortable with my odds. I'm not gonna sell out just yet....:no:


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## troubleseeker (Sep 25, 2006)

concretemasonry said:


> Are you building in a hurricane/strom surge area?
> 
> I inspected several hundred damaged/destroyed homes in Mississippi and Louisiana after Katrina.
> 
> ...


I have lived in south Lousiana my entire life, and have not seen structures that were built on approriattly sized stilts "snapped off" unless rammed by a drifting barge or such. Many of the old pre stringent coastal building code weekend fishing camps were often built with woefully undersized 6 x 6's or sometimes even 4 x 4's for supports, and as you observed, they were no match for a wall of debris pushed by 130mph plus winds pushing a 15 to 30 foot storm surge.

Rienforced block piers fared pretty well if done correctly , with multiple, full height lengths of rebar and filled with concrete, but the often seen scenario of the masons just filling then blocks with morter as the build it were mostly buckled in half, the morter obviously not nearly as strong as concrete.

No insult intended, but whether the blocks of the pier are perpendicular or parallel to the coastline is of no consequence . In a true "beach" setting where you have water on one side of the building and nothing but dry land beyond, the surge will obviously come from the coastal side, but in a typical coastal marsh setting, you usually have water and marsh on all sides, so the direction of the surge is purely a function of the direction the storm is travelling.

The engineered blow out walls are the key to the structures' survival. When the wall fails, and allows the surge to "flow through" the supporting columns, the building has a chance. A wall that is not engineeered properly and does not give way will result in the destruction of the building . Most people have no comprehension of the thousands of tons of force posed by a moving wall of solid water.


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## pokerdonkey (Oct 6, 2007)

Great, great advice one and all!
Thank you so much!

Right now, we are reconsidering the stilt house option.
We're examining some non-traditional construction options, such as eco-lodges










Think of a big deck platform with an extremely spacious "tent" type structure on top! :thumbsup:

Even if we do decide to go with a stilt house, I'm pretty confident in the overall concept. Here in my part of FL, the last major storm we had pretty much leveled all coastal homes _save_ for those few which were built on stilts. Ironically enough, it's been nearly 40+ years since we've had a direct impact and during that time, the general theme of oceanfront construction is definitely towards 6000+ SF poured foundation McMansions rather than smartly designed hurricane resistant structures. When the next one comes, all of those people will be reminded why it's wise to build right for the storms, when their homes are reduced to rubble and washed out to sea.


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## ratherbefishin' (Jun 16, 2007)

Hmmmm....I kinda like that! I noticed in your other thread you mentioned "cabin" and thought this was a weekender. Is this going to be your primary residence?
One word of advice I'd have, with the insurance companies being who and what they are these days (expletives deleted...lol!), is build in excess of wind codes and don't let your investment exceed the total value of your flood insurance.


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