Why Are Houses in Hawaii Built Off the Ground?


Why Build Off the Ground in Hawaii_

You may have noticed as you travel across Hawai’i or other locations in a tropical climate that many of the homes are built off the ground on what is called a post and pier foundation.  What is the purpose of that design? Why not just build a slab on the ground?

Having a home built off the ground in Hawai’i serves many purposes.  Traditionally, homes in the tropics were built off the ground to ensure airflow, passively cooling the house in a warm environment.  It also helps with insect control, flooding and inhibiting mold growth.

Even though building a home on a post & pier foundation is a superior design for the tropics, concrete slabs are becoming more commonplace as Hawai’i adopts more and more mainland building codes.  


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GAIA’S GARDEN


CONCRETE SLABS VERSUS POST AND PIER FOUNDATIONS

Let’s compare concrete slabs versus post and pier foundations.

CONCRETE SLABPOST & PIER
More affordable*More difficult to build
Difficult to maintainEasily repairable
Needs level groundSuited for uneven lots
Can get hotAirflow keeps home cool
Flows into the landscapeSeparate from Landscape
Bad for the EnvironmentMinimal environmental impact

Let me be clear.  Concrete Slabs are considered more affordable than Post and Pier construction only because Hawai’i recently adopted new building codes that require costly foundational add ons to post and pier structures.

Before the changes, post and pier foundations were more affordable in Hawaii than concrete slabs foundations.  The price of concrete is very high in Hawai’i, but now even a post and pier foundation requires a large amount of it to pass code, eliminating its cost savings.

I for one look for the most ECO-nomical solution when I approach building.  What are the environmental costs as well as the financial costs?  

Concrete slabs have a much higher environmental cost.  Concrete is the world’s number one polluter. The manufacturing process destroys any local environment that it touches.  The material breaks down very slowly, leaving blight in the landscape for generations.

Back when post and piers were constructed before the recent code changes, there was very little concrete used in comparison to slab foundations.  A home built on post and pier can easily be removed and nature allowed to return to its natural state without longterm consequences.

I would recommend building your home with a post and pier foundation if you are building a small off grid ohana unit on your property that you aren’t looking to get permitted.  If you had the money and were going to get a permit, I’d still choose a post and pier foundation in Hawai’i due to the numerous other benefits it has over slab foundations.

POST & PIER FOUNDATIONS HAVE GREAT AIRFLOW

It can get pretty hot in Hawai’i, but one thing nature provides to counteract that heat and humidity are the cool tropical tradewinds.  It would be a shame not to take advantage of that.

Having a home elevated allows the winds to not only to pass through open windows or over the home, but also under the home.  The airflow passing under the home keeps the home cooler overall. It eliminates the need for A/C in most instances.

Another benefit of increased airflow in the home is it helps eliminate mold formation that is so common in humid environments. No need for dehumidfiers, smart design can help eliminate so many problems before they even start.

You have to do the math here, but a post and pier foundation built to code may be more pricey than a concrete slab in the short term.  Over the long term though, the savings from not having to use an A/C unit or dehumidifier in Hawai’i’s high electrical rate environment would make Post and Pier foundations more economical over the long term.

POST AND PIER FOUNDATIONS HANDLE FLOODING

Not many parts of Hawai’i are prone to flooding thanks to its mountainous nature, but that doesn’t mean where you build isn’t prone to flooding.  Having a post and pier foundation as opposed to a concrete slab can save your home from extensive damage.  

It happens, I have a few friends that have experienced flooding in Hawai’i.  We can have some big rainstorms at times. If their home was built on a slab, they could’ve saved themselves the trouble.

It’s better to ride out the flood a couple of feet off the ground as opposed to being on the ground level.  It is nice to have your home flow into the garden from a slab foundation, but I would not want to risk flooding.

Find out if you are in a flood prone region and if you are, consider a home that is on post and pier foundation.

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AN ELEVATED HOME HAS FEWER BUGS

Hawai’i is known to have lots of bugs.  Centipedes, fire ants, cockroaches they all seem to find their way into your house at some point.

A home elevated off the ground has less of an issue with these crawling creatures than their ground level counterparts.  It is harder for many of them to make it into an elevated home, giving you less interaction with them. Most of the insects prefer to nest in the ground.

An elevated home also has fewer mosquitos.  Not only do the mosquitos tend to congregate closer to the ground level, but they also do not like the increased airflow that a post and pier home delivers.

Some homes are mosquito magnets.  These little buggahs can totally ruin an afternoon outside on your lanai.  For this reason alone, I would choose an elevated post and pier home over a ground level slab home any day.

THE AFFORDABILITY OF POST AND PIER HOMES

As we mentioned before, a post and pier home is no longer more affordable than a concrete slab because of changes to the building code here in Hawai’i.  However, if you plan on building an off grid, unpermitted home, a post & pier home can be significantly cheaper to build than a concrete slab.

Most of us who build off-grid homes build small homes that do not require much engineering.  A simple post and pier foundation is more than adequate for these types of structures. There should be no need for the over engineering required in the building codes.

I have built a few homes of my own and have always found concrete difficult to work with.  I really enjoy the post and pier foundation and think any novice builder can construct one with relative ease and at low cost.  I know because my first home was post and pier and almost 20 years later, it is still standing.

OTHER BENEFITS TO BUILDING OFF THE GROUND IN HAWAII

In addition to the benefits to a post and pier foundation that I mentioned above, there are a couple more that you should consider.

Much of the land in Hawaii tends to be on uneven ground.  We’re on a volcano after all. Sometimes it just isn’t feasible to flatten a lot so that you can pour a slab.  Post & pier foundations work great on uneven lots.

A house that is built with a post and pier foundation has the added benefit of being able to access utilities much easier. If you ever have to fix a broken pipe, no problem, you can easily access most utilities.

With limited lot sizes that are common with many places in Hawaii, having room for storage under the house allows you to utilize more of your property for other things.  It also provides a safe dry place for your belongings without having to construct another building.

One of the main principles of permaculture is stacking functions, and by having your home raised off the ground, you are applying this permaculture principle to the design of your home.  It will also save you money from having to build other outbuildings on your land.

While I enjoy the feature of being able to walk right out of my home and into my garden from a concrete slab, there is also something to be said about having a view that is only offered from an elevated foundation.  

If designed right, an elevated foundation can provide an expansive view of the greater landscape.  With some house, the difference between having an ocean view and not having one may be just a couple of feet.  

I would much rather prefer to have an ocean view from my lanai than have the convenience of my home being ground level to my garden.

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THE DOWNSIDES TO POST AND PIER FOUNDATIONS

With all the benefits to post and pier foundations, there must be some downsides to them.  Of course there are.

If not constructed properly, a post and pier foundation can feel really shaking and unstable.  I have been in a few homes out here in Hawai’i that feel every sway and movement put onto the structure.  That does not leave you feeling too confident that you would be able to rough house with the kids or have more than 5 people over without toppling the place over.

This can be easily remedied by proper bracing and design.

These homes tend to be a bit noisier than their concrete slab counterparts as well.  Every creak and bend in the floorboards are heard in a post and pier foundation whereas a concrete slab is silent.

If you are in a colder part of the islands such as upcountry Maui or Hawai’i Island, it may be too cold for a post and pier structure.  Their ability to encourage good airflow is not necessarily a good thing in the colder microclimates.

Lastly, the price.  I am not a fan of the new building code changes to post and pier foundations.  In my opinion, they require post and pier foundations to be way over engineered.  There are places still standing from the 40’s built on post and pier foundations of old.  They have proved their worth. Why change things?

Because of this, post and pier foundations are more costly than slab foundations which in turn will lead more homes to be reliant on unnecessary electrical consumption to keep their homes cool and free from mold.

THE “ECO”NOMICS OF POST AND PIER FOUNDATIONS

Traditional homes in these tropical environments have been taking advantage of the features of post and pier foundations for generations.  They are by far the most eco-friendly option out there when comparing the two modern foundations in use today.

Homes on a post and pier foundation use up less concrete and consume less energy to cool.  The post and pier homes have less of an impact on the environment, they do not require massive excavation and do not remain in the landscape for an obscene amount of time like concrete does.

When designing your home in Hawai’i or any tropical climate, I would seriously consider choosing a post and pier foundation over a concrete slab.  The environment will thank you for it.

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Sean Jennings

Sean has been living simply Off-Grid in Hawai'i for over 18 years. He lives debt free on Hawai'i Island with his family and over 40 chickens. When he's not tinkering around the homestead, he's off exploring the shorelines for fish & surf.

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