This is the Old Baptist Church at Streetsboro, Ohio, built about 1820.
Here are the HABS drawings.
I wondered about its geometry. What framing traditions had the master builder brought with him to Ohio?
It looked linear, simple, obvious. Was it?
I explored the plan and elevation. While many forms of the Lines created by circles and squares worked pretty well, nothing quite fit.
I went back to the basics, the construction: What did the carpenter do? In what order?
He was asked to build a church about 'so big' - here about 36' x 50'. He laid out a rectangle using the 3/4/5 Triangle. The HABS drawings are blurry and tiny. The dimensions appear to be 38'-4.5" wide by 51' long, 3 units wide by 4 units long. (The length is about an inch too short.)
The triangles are ABC and ADC. They could also be ABD and BCD. The 2 layouts cross in the center.
The carpenter could check his diagonals, just as workers do today. When the diagonals were the same length the floor frame was square.
The bents for the frame were naturally the same width as the floor. It seemed possible that the framer used the floor of the church for his layout. I had seen this in an upstate NY barn. I wrote about it here: https://blog.greenmountaintimberframes.com/2014/12/04/geometry-in-historical-frames-a-guest-blog/
The elevation of the front of the church appears to be 2 squares wide. But the pediment did not come easily from that form - slightly too big.
However when I laid out the frame based on Lines laid on the inside edge of the sill and posts, everything fit and the peak of the bent, the location of the ridge of the church was the center of the rectangle. So simple, so easy!
How was it to the framer's advantage to lay out the frame from within the frame, not outside?
He needed at least 3 bents, probably 5 or more. He needed consistent marks for lengths and widths of all members and for each mortise and tenon. The Lines laid inside the frame would not be disturbed while the frame was laid out and marked. The timbers could be moved off the floor to cut the joints; another bent could be laid out. Or the bents could be stacked on each other.
Modern framers using timber and dimensional lumber stand within their work, measure, mark, and check from inside. Then they cut the lumber someplace else. Why not this earlier framer too?
After the bents and the roof trusses came the walls and the windows.
The spacing of the windows and their width comes from the rectangles that are within the original larger rectangle.
The green lines are 2 of those rectangles, the dashed lines with arrows on the left show the window frame locations. The green dashed line with an arrow on the right ( top left) is the width.
The geometry of the bents determined the shape of the facade, the height of the pediment. The front elements of the church - the pilasters and a grand door - were designed after the frame. The front windows were in place, therefore the pilasters needed to be equidistant on each side.
The door went in the middle, that's custom. Then there was the left over space in between. (See more about this below.)
The framers also had to provide support for the steeple. I have only photographs to show where the steeple sits. Was it directly over the front wall? a few feet back? I would assume a bent supported the front and back walls of the steeple. The diagrams do show how the width of the tower and the size of the clipped corners were determined: the plan is a square with its corners cut off.
Carpenter squares began to be manufactured in the States - not imported from Britain - around 1820. They had true 90* corners and consistent dimensions. 3/4/5 triangles and rectangles were easy to lay out accurately. An inexperienced carpenter could erect a simple frame without much worry. A master carpenter working with church members as a volunteer crew could expect his crew to build a reasonably accurate frame.
Part 2, the design of the exterior of the church is here: https://www.jgrarchitect.com/2018/04/the-baptist-church-of-steetsboro-ohio.html
7/27/22: I wrote this post in 2018. When I reviewed it recently, I saw how much needed to be revised, simplified; how much I'd learned about using geometry in construction during the last 4 years. Understanding Practical Geometry (the name Asher Benjamin and Peter Nicholson used) is an on-going exploration.
Jane, on the plans of the church built in 1820 the roof pitch is called out as 5:12. Have you seen the roof pitch called out on other plans? Or do they call out the roof slope, like 22.5°
I'm not sure what your question is.
These plans were drawn in the 1930's for the WPA and are now in the Library of Congress.
The roof pitch was determined in modern times. We who are not educated in Practical Geometry use a ratio (5/12) to tell the carpenter what the pitch is.
I have never seen the roof pitch called out as a number (22.5*)
The roof slope on this church when it was built was called out by the Lines - not by a number. See the diagram which shows the elevation laid out on the floor plan.
Lay out the squares for the wall on the floor, note that the ridge is in the center of the floor plan, add a Line (capitalized as the writers then did) from the wall to the ridge - Voila! a roof slope!
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