Earthquake concerns and general structural stability
There are many ways to build a house and with the reintroduction or natural building, it amplifies the possibilities.
This project, was to build a “rubble trench” foundation -- which is a type of “floating foundation.”
This system was introduced by Frank Lloyd Wright for a few reasons. For one, it’s a proven technique used for centuries around the world, in some of the most seismic areas. When an earthquake strikes, it passes in waves, and a house situated on a floating foundation is able to slide, move and flex with the earth’s movements. In conventional construction, you’re setting a foundation in the ground with large amounts of re-bar and concrete to permanently pin /anchor the structure into the ground. If the earthquake passes with too much force for the foundation, it creates tension and breaks.
Please also understand, all well-built structures use some type of grade beam to hold the building together at the base. This can be done with stabilized earth containers, blocks, rocks etc. .
For the Casitas, we are using is a hybrid foundation. The casitas will be floating on a drainage ditch (rubble trench) of piedren or other drainage rock, 18” deep with 4 “ perforated PVC to drain any water that may enter into the foundation. The conventional part of this hybrid is the grade beam. It is engineered for thickness and the caliber of re-bar to be used, but it’s safe to say a 10” continuous beam of concrete, with four rounds of re-bar will be cast to tie in the structure from the bottom.
Other attributes for going with rubble trench under your grade beam is that peidren is obviously less expensive than using concrete, which is also very energy intensive and a non-degradable material. As sustainable builders, we need to take into consideration the energy footprint or the embodied energy incorporated into the construction of a structure.
On a historical note, Mr. Wright also advocated these foundations in the northern parts of the US, where people have to calculate for frost heaving. In some areas in the north, you may have to dig down, say, 4 feet to get below the frost line, so people of modest-means couldn’t afford these deep conventional foundations because of the abundant use of concrete and re-bar. Mr. Wright also determinedthat ,with rubble trenches, only a percentage of the depth of the frost line had to be excavated, as the drainage rock in the foundation would allow the water to expand in the trench when freezing temperatures arrived – turning the water from a liquid to a solid.
Any question re mold or any dirt/material interaction that could be visible in this damp climate?.
There wouldn’t be any different mold elements then we are already accustomed to in Nica. The same advice applies -- the more air flow, light and ventilation… less mold.. We include large eaves and high stem walls specifically for this – in this case, see Fred’s house with it’s roof and overhang. His house was designed with this concept in mind and it’s beautiful. The design is from his house as it combines traditional tropical design , great air flow and lots of light.
Another benefit is that little to no processed chemicals are used. This type of housing is great for people who have allergies or sensitivities to chemicals, and for parents who don't want their kids crawling across floors that are emitting unhealthy elements.
Roof supports any type of roof – tile, etc
The roofing will be held by posts. Once the posts are up and the exterior in-fill wall systems are in, a bond beam will be placed. This is another continuous beam like the grade beam, and this will tighten the building up from the top and also set a place to anchor in the roof. You can place on any type of roof that you want from here. The bond beam can be done with wood or cement, and will be reinforced with re-bar.
The structures for the Casitas are actually more conventional than alternative. It’s virtually a post and beam structure, which is common in today’s traditional building world, but the in-fill wall systems will be with compactednatural materials.
Other question regarding septic, electric, foundation, etc?
The septic will be done conventionally or directly into the new septic system which runs right by the entrance to El Encanto Electric –Utility ducts will be set under the rubble trench, so wires and tubes can be pulled through when needed later in the process.
As for the foundation, we touched on this above as well. Please know that if preferred, you can request a completely traditional foundation with footers, stem wall, etc., and still maintain the walls. The difference is that you’ll be anchoring the houses, rather than having them float.