 Raising a Traditional Timber Frame
A traditional timber frame uses a bent system--in part, specifically to
facilitate raising the frame. The bent assembly represents a cross section of
the structure, including posts, tie beam, and rafters. The bents are trial
assembled in the shop, to ensure an exact fit. Then they are taken apart, coded,
and stacked to await shipment. At the time of the raising, the timbers are first assembled on the ground.
The bent that will go up last is assembled first, followed by the next in order
of placement, with the first bent to be raised on the top of the pile. The crane
lifts the first bent up and places it on the floor deck. It is braced to hold it
steady while the connecting girts are fitted into the bent. They too are braced.
The next bent is flown in by the crane and connected up with the girts. Once the
two bents are tied together by the connecting girts, we have a more stable
structure to work on.
After the bents are secured with connecting girts, the loft floor joists are
flown in and installed in the loft area. Finally, the ridge beam and roof
purlins are flown in and dropped into their housings on the rafters. The area
defined by two bents and these horizontal members (connecting girts, purlins,
and joists) is called a bay.
We find that it generally takes the Goshen crew approximately two days to
assemble and raise a 3- to 4-bent frame, such as standard frames Blackberry Cove
and Walnut Creek. A larger frame, with side sheds (such as Sugar Fork) may take
up to three days. The conditions of the site have a bearing, of course, since it
is a very different proposition to raise a frame on a steep slope which limits
crane access compared to raising a frame on level ground.
Raising a Common Rafter Frame Common rafter frames are constructed with horizontal plates running through the
structure. The rafters are set on the plates, usually on 2' to 4' centers. There
are no purlins in a common rafter frame.
This system, too, serves a purpose in
terms of the raising, especially of very large frames, since the bents might
become so large that they would be dangerously heavy. When raising a common
rafter frame, the bent posts are raised in sections and topped with the plates,
which tie them together. Then loft floor joists are seated. Finally, the rafters
are flown in and seated on the plates.
In general, common rafter frames are quickly and easily raised. However, a
large common rafter frame, such as Goshen's Gentry's Mill, can take a
considerable amount of time, because there are so many separate timbers to be
installed piece by piece with the crane. Consequently, we plan on 3 to 4 days to
raise this frame. |
