“A cruck frame is one where the structure of the building depends on two or more ‘A-frames’ which go from the top of the building down to the ground. These frames are usually constructed of curved timbers (the cruck blades) using the natural shape of a tree and in many cases the tree is sliced long-ways down the middle so that whatever the shape of the curve the two sides are symmetrical. The two beams are joined together at the top by a ‘collar’ or tie-beam.
Cruck barns probably evolved in Anglo Saxon times and the earliest archaeological evidence comes from 4th century excavations in Buckinghamshire, but this building technique really came into its own in medieval times. Large halls were built in towns and villages and a large cruck barn also became a sign of an individual farm’s prosperity. The barns could be easily divided into sections or bays and threshing would have been done indoors.
The inverted ‘v’ shape has the advantage that the roof load is carried directly to the ground so that the wall frames can be made using a lighter construction and the walls also use the cruck frames for support. In medieval times the timber would have been felled using a two man saw and axe and then squared up with an adze. The procedure for construction would usually involve assembly on the ground and subsequent erection to a standing position. Once this is done the heaviest part of the operation is complete.
There are various types of cruck frames. Most seem to start at ground level whilst others start just below the wall plate level (raised cruck frames). In some constructions of wider buildings the frame starts at ground level but finishes at the collar which is a piece that joins the two cruck blades and this collar then supports the main roof timbers.”
Read the full article at the source: Woodlands
From the Cruck House website that shows each step of construction: “In Tudor times all straight oak timber was reserved for building ships. This left only curved or crucked oak, as shown opposite, for the building of properties such as houses and barns. This led to the development of the cruck house.”
Image source: The Cruck Barn
Image source: Timber Structures.net (upper cruck frame and full cruck frame)
Image source: Woodlands
5 thoughts on “Cruck Frames”
I know I’m raising an ancient thread from the dead, but if anyone is still out there, I’m interested in building a full cruck frame, but the trees I have access are the big Douglas Firs of the Pacific Northwest (US). These trees only grow straight but they can be very wide (50″ on my property) and I am able to cut curves out of straight beams, but not at the lengths shown here. My ideal design is the magnificent Seagull House in Devon (http://naturalhomes.org/timeline/seagullhouse.htm) or the Shipton Conservatory in France (Cercles?) (https://louismawgreenoak.com/timber-framing/case-studies/shipton-conservatory/). Anyone know architects who are designing these kind of structures in the US?
The key point about base-cruck frame building is that the weight of the roof is carried directly down to the ground so that any sort of wall can be used and even changed without touching the basic structure. So waddle and daub, mud & stud, brick, stone and even earth bags can all be used.
Not sure, but it’s possible the word “crucked” has the same origin (or is the same word, just in an older form) as our word “crooked”.
Just a random thought. Love the houses! :-)
You’re probably right. Good idea.
Variations include hewing or milling the timbers flat, or leaving the wood in the round. Yesterday’s blog post showed roundwood crucks in Ben Law’s house. Roundwood is stronger and saves lots of work. And as noted above, you can cut the crucks in half lengthwise to create a matching pair.
Curved versus straight crucks? Both are possible. My first choice would be curved, because they’re more graceful and provide more headroom underneath. Look for leaning trees in the forest that are naturally curved. Sometimes a tree will fall against another tree and cause it to bow. The challenge is finding enough curved trees of similar size and shape.
Note other details:
– The collar can serve as the loft beam.
– Side walls (earthbags, timber frame, etc.) can extend above the loft as shown in yesterday’s video. With additional purlins on the crucks, you could build a ceiling and insulate the attic.
– The timber frame helps stabilize earthbag walls. No buttresses would be needed with this design.
– Ben Law’s house gives a good sense of scale, more so than simple drawings. Compare the modest size timbers to his fairly large house. Not sure what type of hardwood he used. One site says chestnut.
And for new readers, all these various building techniques we’re discussing can be used with earthbags.