# Hawaii pier and post



## JamesT. (Jul 21, 2015)

I'll be building a pier and post house on the Big Island, not far from Naalehu/South Point. The soil(?) is rocky (the dreaded blue rock), and I dread having to dig down 12 inches for my piers and corner footings. So I thought it would be easier to bring in enough fill and compact it to make a pad at least 12" high. I could then dig down in the compacted fill for my footings, which would then be resting on the original undisturbed surface. I didn't see anything in the code that would prohibit this (Hawaii uses the 2006 IBC & IRC), but that doesn't mean a lot. Has anyone done or heard of something similar?


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## cda (Jul 21, 2015)

welcome!!!


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## JamesT. (Jul 21, 2015)

Thanks (mahalo)


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## conarb (Jul 21, 2015)

This is a question for a structural engineer in conjunction with a soils engineer.  I had a similar situation where we couldn't drill through sandstone boulders, the solution was 4'x4' "square piers" as described by the engineer, the county plan checker called them "spread footings".  After we dug everything out the soils engineer had to approve each one, he got down in each hole and I had men there to clean everything by hand to his satisfaction, there could be no fines at all on the rock.


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## cda (Jul 21, 2015)

JamesT. said:
			
		

> Thanks (mahalo)


Working on your island groove


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## cda (Jul 21, 2015)

Do you know what other foundations are used on the island??

Any regulations on volcano or are you near one of the zones??


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## JamesT. (Jul 21, 2015)

conarb said:
			
		

> This is a question for a structural engineer in conjunction with a soils engineer.  I had a similar situation where we couldn't drill through sandstone boulders, the solution was 4'x4' "square piers" as described by the engineer, the county plan checker called them "spread footings".  After we dug everything out the soils engineer had to approve each one, he got down in each hole and I had men there to clean everything by hand to his satisfaction, there could be no fines at all on the rock.


In my case, it isn't solid rock. It's lava that may or may not have been ripped before. But if I dig in it/break it up, I'll probably wind up with bomb craters. At any rate, if the bottom of the poured pier is resting on undisturbed soil, that should be good enough for Hawaiian standards. In fact, many lots are sloped, so either the posts are long or there's several feet of compacted fill with piers on top of that. It hasn't been that long since people just slapped down tofu blocks (16x16x8 concrete) then put a pier block on it to hold a post that was braced to the beam. Then held a luau. Before that they found big rocks to put the posts on. I don't see much difference between digging down in undisturbed soil and digging down in compacted soil to undisturbed soil unless the compacted soil offers little lateral stability.


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## JamesT. (Jul 21, 2015)

cda...

A lot of slab foundations now. In fact, most of the moderately priced houses look a lot like 1980s cheap California tract homes. The only difference is the amount of roof overhang. That's because California designers designed Hawaiian homes.

My next door neighbor's house is on stilts. Actually narrow corner walls, about ten or twelve feet high. That's not all that uncommon. People park their cars under the house or even treat it as a room.


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## JamesT. (Jul 21, 2015)

cda...

Forgot about the volcanoes. All of the island has lava zones. ! and 2 are bad news. I'm in lave zone 6, which is good.


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## conarb (Jul 21, 2015)

James:

I doubt that you are going to get any sympathy with that argument here, if there is anything they hate it's a contractor telling them: "That's the way we've always done it."  My advice is talk to a soils engineer, but knowing nothing about code enforcement in Hawaii maybe your best rout is running it by your local building department just like you've run it by us here.  When I've been in Hawaii I've marveled and houses sitting up high on piers with lattice around the base, I understand it's for full airflow in a humid climate and I agree with that, but the bracing of those high piers bothered me, or course I come from earthquake country.


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## Robert Ellenberg (Jul 21, 2015)

Hawaii would be in a hurricane zone I presume.  On the Gulf Coast where I live the recommendation is for no bracing between the piers and the floor system so that it can "move" some in strong winds.  I assume the principal is similar to how bridges are built to move but I am not an engineer.


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## Dbronson (Jul 21, 2015)

JamesT:

The Big Island is in a very high seismic risk area.  You really should consult a structural engineer on this.  Buildings on stilts don't do well in an earthquake.

Regards,

DB


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## JamesT. (Jul 22, 2015)

conarb said:
			
		

> James:I doubt that you are going to get any sympathy with that argument here, if there is anything they hate it's a contractor telling them: "That's the way we've always done it."  My advice is talk to a soils engineer, but knowing nothing about code enforcement in Hawaii maybe your best rout is running it by your local building department just like you've run it by us here.  When I've been in Hawaii I've marveled and houses sitting up high on piers with lattice around the base, I understand it's for full airflow in a humid climate and I agree with that, but the bracing of those high piers bothered me, or course I come from earthquake country.


I was just giving a little history to point out that Hawaii has been slow to adopt newer methods. The saying in Hawaii (seen on bumper stickers) is "We don't give a damn how you do it on the mainland."

Hawaii is earthquake country also, and during the last sizable earthquake, a lot of the older pier and post houses slid off their tofu blocks. Changes came in the form of foundation shear panels bolted to corner foundations.

I'm trying to find out if the idea I had is common, at least in no freeze areas, and if it doesn't run afoul of code. I know that the perimeter footings of slab foundations are often at least partially supported by compacted fill.


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## JamesT. (Jul 22, 2015)

Robert...

Historically, most hurricanes have missed the islands, although some have come close. Iselle was a tropical storm, which apparently posed more threat to trees than buildings. If a category five made a direct hit on the big island, the mountains would be plastered with metal roofing.


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## ADAguy (Jul 22, 2015)

What you propose will create a slip plane between the two materials. Volcano shakes, you slide Bruddah.

Mahalo

Kimo


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## ICE (Jul 22, 2015)

ADAguy said:
			
		

> What you propose will create a slip plane between the two materials. Volcano shakes, you slide Bruddah.Mahalo
> 
> Kimo


I agree.  If there was an over-excavation of 3' and it was surrounded with a boundary of adjacent terra firma....well that sounds about right. Plopping a 12" layer on a hard substrate doesn't.  The 3' over-ex gets scarified and the 12" pancake doesn't.  What you need is a giant Vermeer trencher. I worked a job on a lava cap in Chico, Ca where they wore out two of them that dwarfed this one.


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## JamesT. (Jul 22, 2015)

ADAguy said:
			
		

> What you propose will create a slip plane between the two materials. Volcano shakes, you slide Bruddah.Mahalo
> 
> Kimo


Yes, I can see that. I know that can happen when certain soils become fluid during an earthquake. You have to wonder if having a lot ripped and then building doesn't create some of the same effect.


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## steveray (Jul 23, 2015)

Can you pin to or dowel into the rock to eliminate the slip plane.....I agree that engineering would be required it seems.


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## north star (Jul 23, 2015)

*= & = & =*



JamesT.,

Because Southpoint is located in a high Seismic area [* RE:* Seismic Area E ],

...a high wind area [ *RE:* Wind Category of 105 mph ], ...and depending

upon the location of your proposed build, ...maybe even a tidal V Zone,

and the conditions of the soils too, ...you most definitely need a structural

engineered design for the foundation........Also, the wind bracing on the

structure itself will require a design professional to provide a design

for wind & Seismic bracing as well.



*= & = & =*


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## zigmark (Aug 7, 2015)

There is no requirement for wind design until you reach 110 mph.  Seismic Zone E does induce the requirement for design by a licensed design professional unless you can demonstrate compliance with R301.2.2.1.

ZIG


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## north star (Aug 7, 2015)

*$ ~ $*



ZIG,

The Notes in Figure R301.2(4)B indicate that Wind Design would

be required in Hawaii, because all of Hawaii is a Special Wind Region.

Also, since there is no map of the Hawaiian islands to indicate the

Special Wind Regions, ...I'm thinking that all of Hawaii would require

structures to be designed by a registered design professional.

Is this incorrect ?...........I am looking in the `12 IRC.

Thanks !



*$ ~ $*


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