New Code for Post & Pier ?

[Rob Tucker]

I built mine myself ten years or so ago, It cost me $80 psf.

[MarkP]

I have not built one (yet) but it seems to me that if you can get satisfactory results with insulated concrete forms or straight poured concrete then you can build a similar structure out of concrete blocks as long as the concrete blocks are filled solid with concrete and similar amounts of rebar are used in each case. The blocks are just another type of form. It all comes down to proper reinforcement with steel rebar. The concrete blocks allow you to build at a slow pace instead of setting up all the forms beforehand and pouring all at once. I have long contemplated a basically square reinforced CMU/concrete house with a wrap around lanai.

For a long time I was really intrigued by the idea of building with stone since we have so much of it around here. When you look at earthquake deaths around the world you see hundreds of deaths in developed countries like New Zealand vs thousands of deaths in relatively undeveloped countries like India, even for similar sized quakes. The difference is that in India and other undeveloped nations so many people build with stone rubble or compacted earth, which readily returns to a horizontal distribution across the surface when shaken, having negligible tensile strength. Ironically these areas have some tradition in building with stone and there are some ancient buildings that have stood through centuries of earthquakes, their very wobbliness being the key to their survival. They do incorporate judicious use of timber reinforcement. Usually these timber resources are a thing of the past and even then would only have been available to the wealthy but it all proves that it is possible to build earthquake resistant buildings out of masonry.

ETA I can't imagine using timber reinforcement effectively in Hawaii due to rot in the wet areas and termites everywhere. OK maybe halfway up the mountains where the climate is like Northern India where these structures originated. A piece of Ohia turns to mush here in Puna in a few years.

[BillyB]

Try Dry stacking CMU

USDA came up with dry stacking like 80 years ago. You will still need to grout the cells and use #4 or #5 rebar with something like a 2X2 grid . It is very simple.

https://www.youtube.com/watch?v=TAswNJyZjvM

[Rob Tucker]

You still have the thermal mass issue. Thermal mass is a positive attribute in colder climates... a negative in warm climates.

Insulated Concrete Forms (ICF) is the way to go for a concrete building in Hawaii.

[MarkP]

Sorry I don't recall the source but in my wanderings on the net I recall some folks from Australia concluding the same. Well, they said there was no advantage to the thermal mass. I don't recall that they said it was really a negative. Is high thermal mass a negative in the tropics? All thermal mass does is even out the highs and the lows so although it will stay warm longer into the evening which may be perceived as a negative it was slower to heat up earlier in the afternoon.

ETA: How is concrete block any different from poured concrete or from ICF for that matter if you put some insulation on the outside of the wall? ICFs are a neat idea and clearly have some advantages in terms of labor savings but I think you can build a wall with similar properties out of block or formed and poured concrete.

ETA: The hottest days in Eden Roc are close to uncomfortably warm. The coldest nights are COLD! Hit me with some of that thermal mass please.

[kalakoa]

How is concrete block any different from poured concrete or from ICF

Concrete (block or poured) is available on-island; I don't know about ICF.

[Rob Tucker]

Mark,

The thermal mass issue only affects lifestyle inasmuch as the house will hold heat and give off heat. That is an asset in Alaska... not so much in Hawaii.

The ICF system I used is six hour fire-rated at 2000#730; and has an R value of 30 and requires 26% concrete grout by volume to get a full strength concrete wall. Concrete is expensive. Block walls are not fireproof (they just seem like they might be).

[MarkP]

Interesting about block not being fireproof. I imagine that there are definitions involved. I can't imagine that block is not fireproof the way 2x4s and plywood are not fireproof. I imagine that the waffle/egg-crate shape of the structural concrete inside the finished ICF wall is more efficient than a solid wall. I imagine that this cost savings is offset by the cost of the ICFs or the concrete blocks for that matter.It still is not clear to me where the sweet spot lies.

How does the ICF achieve this fire rating? There is foam on the outside, is there not? What is the insulation material?

[Rob Tucker]

The sweet spot Mark, is in the eye of the beholder.

Here's the ting with concrete and fire:

Concrete has great compressive strength and lousy tensile strength. Rebar provides the tensile strength. The rebar is shaped (deformed) to increase the bond with the concrete. The rebar must be in bond with the concrete.

In a fire the block walls or poured in place concrete heat up. The rebar expands and contracts with heat at a different rate than the concrete does. The bond is lost and the wall will need to be demolished (if it is still standing).

The ICF I used was certified at 6 hours at 2000#730;. At the end of six hours the core of the wall had increased about 40 degrees in temperature. That wall survives a fire. Insulation has value.

[kalakoa]

The ICF I used

Is this wonderful non-wood construction material available on-island, or would I have to design a complete project and wait for it to be shipped in?