Reciprocal Roof Frame Building: How-To, Materials, and Supplies

October 1, 2008

Earlier this year, I was introduced to the concept of a so-called “reciprocal roof frame”. After hearing about the concept from a friend, we later browsed the internet in search of natural buildings featuring this mysterious design. When I finally saw examples of different reciprocal roofs, I was immediately enamored: here was a roof structure so totally simple, strong, and above all, beautiful.

A reciprocal roof is a self-supporting, round structure composed of interlocking beams that equally bear the weight of one another. Composed of as few as three beams, a reciprocal roof can incorporate practically any number of beams and span great distances while still maintaining its integrity. Best suited to round structures, this style of frame is incredibly strong, and “twists upon itself rather than spreading apart”, when pressure is applied from above. Notably, it is an appropriate frame for living roofs, because of its strength. The reciprocal roof is a glorious design for green buildings.

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In This Article

This article will examine this unique feat of architecture. By looking at the reciprocal roof, I hope to give you an understanding of reciprocal structures in general, and how this reciprocal frame is such a powerful, yet simple, design concept. We will first look at the basics of the reciprocal roof, then explain how they are built, and wrap up with some advantages & disadvantages.

Basics Of The Reciprocal Roof

The history of the reciprocal roof seems clouded due to a lack of comprehensive information. It is clear that it has been used in many aspects of architecture. In fact, the reciprocal roof is part of a large area of architecture which generally falls into the concept of “reciprocal frame”.

Basically, with a reciprocal frame, each pillar is supported and held upright by the weight of the other. Each rests on top of one another, forming a circle of support where they all work to hold up the structure as a whole. It is a natural building technique which essentially relies on the power of gravity to support the whole structure.

There are many types of reciprocal construction to consider, including a roof, a rafter, a dome, and more. But as you can see, in this article we are focused on the roof.

History aside, the reciprocal roof is also incredibly simple to build, and very appropriate for amateur green builders, and it is perfect for roundhouses and circular structures. It is perhaps most famously featured in the phenomenal low-impact woodland home of Simon Dale (see right), and Tony Wrench’s roundhouse in Wales, two well-known natural buildings in Europe.

How to build a reciprocal roof

There exists an overall dearth of how-to information on the construction of the reciprocal roof, although there is at least one comprehensive resource for aspiring reciprocal roofers.

Tony Wrench’s Building a Low-Impact Roundhouse features fairly complete instructions for building a frame, including plenty of photos and sketches to illustrate the process. Other than Earthbag Building by Kaki Hunter and Donald Kiffmeyer, which features a mere paragraph on reciprocal roofs, this is the only published resource. It is a good one and worth tracking down.

My experience building a reciprocal roof frame

Very recently, I had the pleasure of constructing my very own reciprocal roof for a small cob house that I am building (see above). It took two attempts (only because the poles of the first frame were a little lacking, in terms of diameter), but it was a very simple process, and one I would gladly repeat.

My own frame is composed of 28 total poles, hand-cut from nearby land, including fourteen primary black locust rafters, and another fourteen secondary rafters that are not tied into the main frame. Eventually, this roof will be covered with an impermeable membrane and become a living roof.

Ultimately, I hope others will learn about and experience the simplicity and beauty of the reciprocal roof frame. It is truly an ingenious design, and perfect for round natural buildings.

Advantages of a Reciprocal Roof

The main benefits of the reciprocal roof lie in the simplicity of its design. Basically all you need are poles which support each other. It results in a highly stable, strong, and durable structure. This simplicity is rare in modern architecture, and it is cool to see some of the basics still in use.

Another major advantage is that it is so unique. A structure with a reciprocal roof is sure to stand out. So much of architecture is about unique design choices, and this is certainly that. Even if you utilize a reciprocal roof in conjunction with a more sheltered roof, it is a great way to add your own design choices to your work.

Next, because it requires such basic resources, it is quite an environmentally conscious form of building structure. You can build it simply with wooden beams, and it can be done without machines for the most part.

Disadvantages of a Reciprocal Roof

Next up are the disadvantages. While the reciprocal roof is quite an interesting structure, it does have its share of drawbacks.

While simple in concept, it is not always so simple to build! It does still require quite precise measurements and placements in order to perfect. In order to get that exact “rounded” structure, you will need to be quite exact in your measurements and yourbuilding.

Also, although a reciprocal roof looks quite cool, it’s practicality is realistically quite limited. Not to mention the fact that it has a giant hole in the roof which would require further roofing to waterproof and insulate, it is simply not that practical to build and maintain. The fact is that there are much easier, and more economical ways to build a roof.

However, if you are interested in this unique building style, these hindrances are probably not your concern. Reciprocal roofs are a special type of construction, and it’s up to you whether you are interested.

Reciprocal Roof Resources

Here is an assembly of links that I have found useful in my pursuit of the reciprocal roof:

  • Simon Dale’s low impact woodland home has a gorgeous reciprocal roof with gnarly rafters and beautiful slab decking (construction information here)
  • Tony Wrench’s website has some photos and information about his living reciprocal roof
  • The LessPress Snail Cabin has a reciprocal roof made with dimensional lumber. Also, be sure to check out their Excel spreadsheet for calculating beam lengths and positions for both circular buildings and otherwise
  • For math nerds, visit The Pavilion for a very technical description of how reciprocal roofs function
  • Zone5 has a brief description with some images of a Tony Wrench-style reciprocal roof construction for a roundhouse here and here
  • Check out a scale reciprocal roof model and design using dimensional lumber at Casa de Baro
  • Cae Mabon in Snowdonia of North Wales features several buildings with reciprocal roofs. Images here.
  • Design Forward has a very brief snippet about the history of the reciprocal roof design

Conclusion

Thank you very much for reading our piece on the reciprocal roof. Our aim was to give you an outline on this interesting architecture technique and to let you decide whether this might be something you want to pursue yourself.

While definitely quite a specific area of architecture, it is quite an interesting one nonetheless. So whether you are reading this to gain some insight for your own projects, or are just interested in niche areas of architecture, we hope you have enjoyed this article!

(Image credit: Simon Dale, Daily Mail)


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I'm a 26-year-old currently living at Dancing Rabbit Ecovillage in northeast Missouri, an intentional community devoted to sustainable living and culture change. Things you might find me doing here (other than blogging) are building with natural materials, gardening, beekeeping, making cheese, candlemaking, and above all else, living simply.

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