Low cost, simple to build catenary roofs use minimal materials

Low cost, simple to build catenary roofs use minimal materials


Excerpt from the “Journal of the National Institute of Building Sciences,” February 2016:
“The Swiss civil engineer and contractor Heinz Isler (1926-2009) is regarded as one of the pioneers of shell structures. He gained renown for his experimental, physical methods of form-finding and the resulting expressive shell structures produced in thin-walled concrete, and first triggered his lifelong fascination and professional work with such structures by draping a saturated bed sheet in freezing weather to form a catenary shell before inverting it. He proved that, what gravity forms when inverted, is resistant to the forces of gravity.

As a civil engineer, Theodore “Ted” Thoeny, PE, principal at San Juan Bautista, California-based Thoni Thermal Homes, has been interested in fabric structures for the past 55 years, and has experimented with different fabrics, from burlap and fiber glass to geo-fabrics. “Using fabrics to form roofs is very simple and efficient, especially when gravity is allowed to form the shapes,” he says. “Such lightweight roofs may answer the need in areas that lack more traditional resources (such as third-world countries), plus address both life-safety and energy concerns in modern settings.”

In this article, the Journal of the National Institute of Building Sciences (JNIBS) talks with Thoeny to gain an understanding of catenary roofs. When considering alternative construction techniques and methods, such as those used in catenary roof structures, this discussion may provide additional insight.”

Journal of the National Institute of Building Sciences (full text requires free registration)
Ted Theony, PE
Thoni Thermal Homes
San Juan Bautista, CA


Comments

The Case for Catenary Roofs — 8 Comments

  1. More from the author Theodore Thoeny:
    WE USE A STRONG, LIGHT WEIGHT FABRIC, ATTACH
    THE FABRIC TO THE TOP OF NEW OR EXISTING WALLS
    AND DRAPE THE FABRIC ON THE INSIDE OF THE WALLS
    INTO A SMOOTH DRAPE, NO WRINKLES AND THEN ATTACH
    THE FABRIC TO THE TOP OF THE WALLS AND INFLATE THE
    DRAPED FABRIC INTO DOMES AND THEN SPRAY THE
    INFLATED FABRIC WITH A LIQUID HARDENER TO CREATE
    A THIN SHELL ROOF.

    THE OTHER WAY TO CREATE A FABRIC ROOF IS TO DRAPE
    THE FABRIC IN SPACE FROM AN INVERTED PATTERN FROM THE
    TOP OF THE WALLS AND STIFFEN THE FABRIC WITH A POLYMER.
    WHEN THE POLYMER HAS CURED. FLIP THE ROOF OVER AND
    PLACE THE ROOF ON THE WALLS. A TRUE CATENARY.
    MY FIRST ROOF WAS DONE THIS WAY USING BURLAP OR
    HEMP FABRIC FOR A ROOF FOR A SEWAGE TREATMENT PLANT
    ON THE BEACH, EXTREMELY STRONG AND RESISTANT TO
    HIGH WINDS. HOPE THIS HELPS.
    REGARDS, TED THOENY
    P.S. YOUR COLLEAGUES FROM INDIA SHOULD HAVE ALL KINDS
    OF FABRICS TO WORK WITH.

  2. I didn’t register for the article, but I’ve done thin shell, hypar and ferrocement roofs. I’ve wondered about this. There is a certain draw to this inverted formwork, but any size is impractical, flexural cracking when moving, plus more logistical difficulties in size limitations , flexural stress cracks moving, weakness at panel and wall attachment points, etc.
    I vote form it up and apply in place. You can save a some time forming with airform (really just a drop in the bucket, considering all the time in every step), but time spent custom forming is worth it architecturally with such a sculptable medium.

    • Good input, thanks. The author emailed me and said this building method is popular in India and Pakistan. That means there are experienced builders and likely construction books on this method in their languages at least. He also said Lloyd Turner of Flying Concrete (good website) builds this way with an inflatable form. A polymer can be used to stiffen the mesh. The author also suggested looking into the use of geopolymers to avoid Portland cement. And he thinks this is the building system of the future.

  3. The full article didn’t give that much more data. It gives a list of a few people who do make them for you if you don’t feel like DIYing it, and does give the useful tidbit that you can inflate the fabric and get the same geometry. I’m just picturing trying to invert the form for a 30′ roundhouse and it keeps coming out ‘dancing with cranes’.

    • This is for small roofs. Note the drawings. My main questions are how to turn a draped piece of mesh into a shell. Dip it first? Spray it with a mortar sprayer?

      We need a simple step-by-step building guide for these roofs. Let me know if you find something free online.

      • The article was pretty vague on that point, I think it’s ‘whatever stiffener works for your application’. Plastic resins and foams were mentioned for invertables, and concrete for the inflatables.

  4. From what i remember antonio gaudi did this technique to build his sagrada familia cathedral in barcelona in d 1800’s. He used hanging chains i believe.

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