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.

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 whichgenerally 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.