Course News

Square Rule Framing

By 23 September 2019January 26th, 2021No Comments
Square rule framing

A response to Chalara ash dieback by Joe Thompson of Sussex Oak & Iron

Common Ash (Fraxinus excelsior), one of the most abundant of our native hardwoods and often known as an “aristocrat” of the tree world as it is the last to come (into leaf) and the first to leave, is currently suffering from a highly destructive disease.

The disease is caused by the fungus Hymenoscyphus fraxineus and it is impossible to look at the countryside now without seeing its effects. It is recognised by leaf loss and branch death that significantly reduces the crown of the tree and weakens it leaving it vulnerable to infection from other destructive fungi.

The fungus is particularly devastating on young trees in woodlands but all ages and habitats are susceptible. As a result Ash trees, particularly those which represent a health and safety issue, near to roads, footpaths etc. are being felled.

It is though vitally important to recognise and protect those trees that have an inherent genetic resistance to this disease, whose crowns are not significantly affected, as these will help to produce the new ash trees of the future. Further information is available from Forest Research or the Forestry Commission.

The timber from Ash trees has long been valued for its strength, flexibility and toughness; being used for the rims of Cart wheels, sports goods and tool handles. Many examples can be seen around the Museum Collection in the form of wagon and cart shafts, felloes on wooden wheels and numerous tool handles.

It has also been extensively used in contemporary furniture, valued for its grain pattern and ability to stain evenly. However it is very rarely found surviving as a structural timber due to its lack of durability when exposed to the weather for any extended period in poorly ventilated conditions.

Timber framed buildings prefabricated using the Square Rule can be easily designed so that the structural timber frame is fully enclosed behind a weathering envelope. This then significantly reduces the prospects for water ingress and subsequent decay.

The Square Rule is a system of prefabrication that utilises standardisation and interchangeability of parts to great effect. In essence all the required lengths, angles and tolerances can be marked and cut, either in a single or multiple workshops, before all the parts are assembled and reared up for the first and only time.

This is in contrast to the earlier scribing systems that were based on a unique fit and placement and required trial fitting.

The Square Rule workshop from 3–7 February 2020 is intended to inform, educate and inspire not only the course participants but anyone who wishes to use Ash timber for structural purposes.

It builds on previous Square Rule workshops that used Sweet Chestnut, Larch and Douglas Fir and demonstrated that a variety of timber species can be successfully used in large section structural frameworks.

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