Post-tensioned Slabs, Termite Sand and Plywood

[Jared I]

I just recently relocated to Puna. Looking about at houses being build I have notice that people don't up post-tensioned slabs. Post-tensioned slabs are supposed to stronger, reduce cracks and are almost an industry standard. Why not here? Do any concrete cointractors around here to post-tensioned slabs? It also seems that slabs don't have rimmed or crossed foundations under the slabs. Are Hawaii codes that lax?

Termite sand. Has anyone used it? How much does it cost?

Plywood. A lot of houses I have seen around here arent subsurface with plywood. The houses just have the MDF (compressed particle board) exterior siding material. Is this some thing new? I have worked on a few custom homes and we always subsurface wall with plywood and then sided it. It provide additional strength to the framing. I have even seen a few houses that just have metal roof, no plywood underlayment. Maybe its a short cut? Any opinions on this?

Thanks

Jared

BTW: I will be building here soon.

[Rob Tucker]

Here's some opinions:

The codes here are very obsolete compared to mainland standards. Many building practices are allowed here which were disgarded long ago due to practical experience from earthquakes and hurricanes.

In many ways Hawaii is 20 years behind the times which has it's good points and bad points. So the basic answer to one of your questions is yes, the codes are very lax.

As for termite sand: It apparently works in the lab but the transport issue for large volumes of specialty material prevents it being distributed easily. The best way to avoid termites, in my opinion, is simple - stop building with wood. While that is hard to imagine for most people there are better, economical ways to build these days.

The plywood substrate under the siding is a shear wall practice not employed here yet. Currently people are complaining about having to shear their corners much less the whole building. Hold-downs are unheard of here. There are strucutral cement panels available for those who want them - fireproof and termite proof - they cost more. But you get what you pay for.

Edited by - Rob Tucker on 04/06/2006 14:17:59

[Seeb]

there is no need to tension a slab on grade and the math is a major headache

[Royall]

Jared, please don’t take what I post on this subject wrong. This is from a lot of observation on some very old homes I’ve worked on here.

The homes being built on the BI are so over built compared to what was built 75 to a hundred years ago or even 25 years ago. They were built on post and pier with no extra metal IE Simpson ties and brackets. They didn’t use plywood to “stiffen” the house or add any shear walls. They didn’t hinder air circulation by adding plywood underlayment below the roof. The amazing thing they have gone through countless earthquakes and a lot of windstorms (no hurricanes in recorded history here on the BI that I know of). The only thing that is doing them in is termites! If you look at the old homes you can tell by looking at the sagging lines of the house that the post are weakening because of loss of structural strength due to those little critters! Cathie and I are renting a new home while we build ours. The rental is a slab on grade and we are having mildew problems with our cloths due to poor ventilation. We keep the windows open all the time except when the wind is blowing the rain too hard. I feel when living in a tropical environment one should look and see what is doing well and not try to build things to the “mainland” specs. It isn’t necessary and can be very expensive in the long run.

Sorry to have gotten up on a soap box but new people just moving to the eastside are just making more problems for them selves using the Mainland building ideas here.

I guess what it boils down to is “if it aint broke, don’t fix it”!


Royall

What goes around comes around!

[Hotzcatz]

Aloha Jared,

Just because they do things on the mainland doesn't mean we want to do the same things here! Don't encourage them to make the codes more stringent, for heavens sake! If you want to build a mainland house go ahead, but don't try to make everyone else to do it.

If you want a mainland house, how about building one in Iowa? It will fit nicely there. Iowa probably even needs more houses. (Not that I know much about Iowa except you rarely meet a tourist from there.)

Most everywhere uses the Uniform Building Code, although some places such as rural midwest don't seem to have any code at all. Each particular area then adds additional codes for their area. We are using the 1991 UBC with amendments from Hawaii County. Oahu is using the '97 codes with their own amendments.

Perhaps the question should be "why here?" instead of "why not here." We don't need to heat our houses, we don't need to cool them. No need to worry about things freezing and breaking, either. We don't need all the tyvek, either. Ventilation is a good thing! We want the wind to blow through our house!

My house is built of boards twelve inches wide and one inch thick (actual, not nominal dimensions) with a batten inside and outside between each board and a "bellyband" on the inside, but not on the outside. These 12 by 1 boards are installed vertically and face nailed to the floor joists (with square cut nails). The floor joists are 2" x 4" at 24" o.c. and then a 1" thick T & G floor deck is nailed to those. The original footings were rocks, they have since been replaced with concrete footings. The posts are 4" x 4"s with cross bracing, no shear walls anywhere. The roof rafters are at 4' o.c. with perlins at 4' and metal roofing (the old heavy stuff) fastened to that. No drywall, no plywood.

In another five years, the house will be 100 years old. It was originally built by caneworkers for cane workers and a lot of the materials they used were recycled from other old houses. There is a lot to be said for a simple honest structure.

It isn't any more expensive to build a single wall house, actually. Even though single wall siding costs more, not having to install drywall makes up for it. Doing away with the plywood subflooring and using a T & G flooring directly on the floor joists can save money since you don't have to install some sort of finished flooring. The hard part about building a single wall house is finding a contractor willing to do it since it takes longer and most of their guys don't have any experience with anything other than double wall with drywall.

What Hawaii houses do have is large overhangs to keep the rain off the sides of the building as well as the sun off. A three foot eave is common and putting a lanai all the way around the house is even better. Many of them are built up on post and piers to let the house ventilate underneath, too.

Hey, have you heard about the folks up in Waimea that are rescuing old cane houses and relocating them? It is cheaper to relocate one of them to your property than to build new and you get a house with character.

A hui hou,
Cathy

[konadave]

Aloha Jared!

There is another consideration to using post tensioned slabs on grade in Hawaii. That is that lava, the soil and the environment in general are very corrosive. Have you seen a PT cable let loose after it has been tensioned? It can be quite exciting and dangerous.

It's not that you cannot build using this method. It is more of is it practical in such an environment? What will the benefits be from using this method? Since most of the construction on the BI does not involve post tensioning there may not be the supplies and equipment generally available either.

Just some more thoughts on this subject.

The Kona Forum
http://www.konaforum.com

"Only two things are infinite, the universe and human stupidity, and I'm not sure about the former". --Albert Einstein