Most economical (cheap) way to build a house

Summary

I suggest building houses using a 1000 years old Chinese method for building bridges (see the “rainbow bridge” page at pbs.org).

Structure (joists, beams, arch) and assembly process

Original embodiment of rainbow bridge structure

Here are a few pics to quickly illustrate the rainbow bridge structure (original embodiment):

• lateral view;
• perspective view;
• recreation in town of Jinze;
• ancient drawing.

Proposed modifications

The following modifications improve the rainbow structure and simplify its assembly:

• the "joists" (boards forming the arch) should each support two beams instead of just one (as in the original embodiment);
• the joists should feature four circular holes (two on upper edge and two on lower edge) to accommodate/interlock the supported/supporting beams.

The proposed modifications are easily observable in these joist drawings:

• modified joists;
• modified joists assembled;
• modified joists assembled.

The above modifications further increase the strength/weight ratio (permitting lighter arches, more appropriate/convenient for a house) and, most importantly, make it easier to assemble the structure (by making the joists interlocking).

Assembly process

The assembly process is surprisingly quick and easy, it includes four steps:

• Step 1: start by laying two joists on the ground (parallel to each other) and connect them by setting in position the two beams on one side of this "section";
• Step 2: lift the "section" as shown in the drawing, by pulling up the outermost beam (which is supporting the green joists depicted);
• Step 3: with the section lifted at a sufficient angle, insert the pair of adjacent joists through the beams on the right of the section, until the holes on the left side of the inserted joists (highlighted with pink) are aligned with the holes on the right side of the section;
• Step 4: with the holes of the section aligned to the holes of the inserted joists (which form a new section), simply rotate the two sections to interlock them around the beams;
• Step 5: with the two sections interlocked we now simply repeat from step 1 to attach the next section. Set in position two new beams on the right side of the last section (new beams depicted in blue) then lift the structure by pulling up the outermost beam (green arrow). Then insert new joists and continue to completion.

"Cover" joists

With the arch complete one problem is apparent: the end of the joists stick out, impeding the application of roofing panels on the structure. The problem is solved by applying a second layer of "cover" joists (depicted in yellow) on top of the basic joists:

• The ends of the basic joists stick out (area highlighted in green), so a second set of "cover" joists needs to be applied on top of the basic joists to diminish the protrusion;
• The cover joists (colored light orange) are simple rectangles, need no holes, sit neatly on top of the basic joists, and can be conveniently connected to adjacent cover joists. The "sticking out" area (highlighted in green) is now significantly reduced. Trimming it results in a neat, convenient profile for applying roofing panels.

Joists and arch geometry

Determining the exact shape/dimensions of the joists requires either understanding the geometry or using a spreadsheet. Alternatively one could buy a ready-made kit and skip the manufacturing of joists altogether (hopefully this will become possible in the future).

The shape of the arch is determined by the shape of the joists, which in turn is determined by shape of the trapezoid inscribed in it (the one with vertices/corners in the center of the holes that seat the beams).

For simplicity is best to consider identical (and symmetrical) joists, and build an arch with a 180 degrees span:

• Joists with trapezoid inscribed within;
• Arch geometry results from joists geometry. Notice the trapezoid (inscribed in the joists), the rhombus (area of intersection of two adjacent joists) and the various angles at which the sides of the trapezoid are viewed from the center of the arch.

So, first decide the size of the structure (by setting the radius R of the circle) and the number of joists forming the arch (number labeled N). Then use this spreadsheet to determine the dimensions of the corresponding trapezoid: length (L) of the trapezoid's lower base, trapezoid height (h) and the projection (X) of a lateral side on the lower base (revisit this drawing for clarity).

In summary: decide R and N, then use spreasheet to get L, h and X, which determine the trapezoid shape and allows the manufacturing of the necessary joists.

Note, the spreadsheet allows one to also set the Aup/Alat angle ratio (to manipulate some joists proportions) but this is unecessary in most cases, and the ratio is set to 1 by default.

Creating a mold ("cookie cutter") for quick/precise joist manufacturing

To create the mold (basically a "cookie cutter") draw the trapezoid on a board, insert 4 screws through the board (at the vertices of the trapezoid), then extract the screws and insert them from the opposite side leaving just 2-3 millimeters out. This mold can be now used to quickly and precisely mark the 4 beam-hole centers on the joists (set it on top of a virgin board and gently tap the screw heads to leave hole marks). If 8mm rebars are used as beams, the holes must be 8mm in diameter (or perhaps 9mm). After boring the holes they must be cut open as previously shown, to allow easy interlocking around the beams.

I will attempt to post a short video showing the assembly of a small scale model, and the end result from various angles. It might take a while though...

Overview and supporting case for the proposed method

The free-market is quite good at finding cost-effective solutions to just about any problem/need you might have. But on one condition: that you have money! The free-market will put no effort/resources into finding solutions to the problems that people with no money typically face. There’s great opportunity here! But only for corporations that don’t mind not making any money... ;)

Let’s look at housing. Poor people (“poor” in financial sense) need homes. Both rich and poor require a home that is practical. But there is one main difference between the two groups: the poor worry less about how the home reflects on their social status. In other words pride does not make things unnecessarily complicated for them. The free-market neglects persons that: 1) are modest; 2) have no money; and 3) need a practical home. I believe the proposed method is a great fit for such persons.

A wide rainbow bridge erected over land can be used as supporting structure for a house.
The aesthetics might be poor (picture a half-cylinder laid horizontally) but the method has solid advantages:
- simple structure (only one type of board);
- easy to build (it's self-aligning with interlocking boards);
- easy to fix (boards are easily replaceable);
- optimal strength/weight ratio (arch property).

These advantages combine to actually make it feasible for someone with no carpentry experience to quickly build a strong, practical dwelling using few and cheap materials. The process is really simple and can be understood by either watching a short video or playing with a small scale model. Any mistake can be corrected by simply going back a few steps (the boards are interlocking so can be simply tied instead of being nailed). One single person can erect a large structure(probably as wide as 7-8 meters, with no limit on length) with no help from anyone at any point. No scaffolding is needed as the process entails weaving the boards from ground level and gradually lifting the structure. The boards are relatively short relative to the size of the structure. Short boards are cheaper and could conceivably be recovered from what building sites discard.

The structure is self-aligning: if boards are made identical (using a mold for better quality & productivity)then "weaving" them together and simply letting the structure settle on its weight will produce a nicely aligned structure. This unique feature circumvents the risk of inexperience resulting in a crooked structure (likely outcome with a traditional house building method). This in turn is the key in providing people with the confidence to build alone, without an expensive team of experienced carpenters.

Other less significant advantages: replacing old (even broken) boards is extremely easy; no pillars needed so entire floor space is open; personalized furniture can be easily attached to (or suspended from) the structure; arched shape without side walls means increased stability in high wind (due to downward push); curved (and light) ceiling greatly increases chance of survival in earthquake collapse; roof sloping all the way to ground makes gutters superfluous.

I built a rainbow structure with a 4 meters arch span in Romania, using fir tree boards. I had no prior carpentry experience yet I worked alone. Assembly can be done real quick. Structure is 8 meters long: 5 m garage in front + 3 m room at back. Next I will try use bamboo trusses (fir unavailable or expensive in the Philippines, while bamboo is not straight). Making trusses might be challenging, but if it works I will attempt a 6 meters span structure.

The boards (or trusses) have 4 contact points which require exact positioning. A self-made "mold" should allow a person with no carpentry experience to economically make identical boards/trusses. An industrial process for large-scale manufacturing of boards/trusses would make all this a breeze (the free-market could really make an impact here).

The PBS.org documentary that triggered my interest in this about 10 years ago might still be available on youtube.com (click here). My approach strays some from the original method. All modifications are in the public domain as I filed provisional applications in the US (without pursuing a patent).


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