“My Dad told me about them!”: Dragon ties

12.10.2016
Blog Post
Image of dragon ties in a roof

Dragon tie with simple decorative detail (courtesy of castleringoakframe.co.uk)

When traditional roof construction was the norm, a dragon tie was often incorporated beneath the hip rafter, particularly where they were carrying purlins. The hip therefore had a much heavier load. 

The dragon tie could be constructed in a number of ways; from a simple diagonal strut made of timber or plywood fixed to the hip with a metal strap. Or, as shown in the photo, it could be a lap jointed angle tie notched into the hip with an exposed detail.

But what does a dragon tie do? 

It prevents the wall plate from spreading where the load transferred down the roof is at its greatest. A dragon tie is very effective as it creates a mechanical joint where everything pulls against one another to reinforce the corner.

You may recall the changes to Building Regulations Approved Document Part A (structure) in 2004 which introduced additional controls for re-roofing work where loads were increased by more than 15%.

This was as a direct result of problems in the 1990’s caused by re-covering slate roofs with newer concrete roof tiles. The extra weight caused the wall plate to be pushed out, usually together with the top three courses of masonry, as the roof started to spread with the additional weight.

Diagram of a dragon tieA long history

The dragon tie technology developed in the 16th Century (diagram courtesy of chestofbooks.com) alongside timber frame construction, stood the test of time long before this issue arose. It’s still seen today as a feature detail in green oak construction, particularly where the roof carcass is exposed internally. 

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Comments

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Submitted 6 months ago

When I started work as a trainee draughtsman in architecture at 16 in 1955 my employer a Mr McDermott sent me out weekly to make sketches of various types of construction. I remember one of them being to go to a particular site and find out what a Dragon tie does and sketch its details.

(No subject)

Submitted 6 months ago

I'm a 63 yr old joiner always have used dragon ties, you can feel the difference in a structure without one , many the times I have had to insert them into traditional 1920's terraced outrigger corners, may this method carry on forever , it has stood the test of time for centuries.

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Submitted 6 months ago

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