Tuesday, May 14, 2019

The Cabins on Magnolia Plantation in Louisiana

8 small brick cabins sit in 2 rows facing the Cane River in Natchitoches Parrish, Louisiana.
Built about 1845, each originally housed 2 enslaved families.
They were in use until the 1950's. Now they are part of the NPS  Magnolia Plantation. 

The red diamonds are the plates for tie rods added by the Park Service to stabilize the  walls.

When I was in Natchitoches, Louisiana, in April, presenting Practical Geometry workshops for PTN.org., we explored the geometry of the cabins.  I had not seen the cabins yet so we focused on the geometry of the end elevation.

Cabins were utilitarian, built using ordinary construction. Studying these simple structures helps us understand what geometries the local carpenters understood and used.

The brick walls, fireplaces, chimneys, and hearths were made with local clay  - probably by the enslaved people who lived in the cabins. The cabins had dirt floors. Wood was reserved for plates, rafters, sheathing, and doors; the hardware made by the plantation blacksmith.

I used HABS drawings for these cabins. Having not seen the cabins I thought the drawings might not be accurate. I was wrong. In the last 170+ years a lot of updating has happened, including floors, windows, replaced roofing.

The end walls are 2 squares wide. The size of the square was determined by the height of the cabin to the plate for the roof - see the arrows on the elevation.

The diagonals locate the ridge. The section makes this clear: the height of the square is the height of the brickwork.
The squares begin at  grade, not at the floor. The plate and the roof frame are above the square.

The diagonals of the squares becomes the radius for arcs; the point where they meet is the cabin's ridge.  Follow the  black  line and arc with arrows and the red line and arc with arrows.

The brick wings allow the roof to be set between the ends, not overlap. The bricks are turned, the ends flat, to make the wall weatherproof and neat. The end windows are not original.

The plan laid out the inside edge of the brick walls. This is common and intelligent; the  
line is there as a reference as the wall is built.
The cabin room is a 3/4/5 rectangle - see the left side.

The location of the hearth and fireplace is determined by the square - see the right side in the plan. This was not easy to check on site as the floors were added, but as  a hearth is an essential part of a fireplace, especially one used for cooking, this makes sense.


The window on the long wall is centered on the floor plan 3/4/5 rectangle. It is also called out by the geometry of the side elevation. 
I have drawn the square on the left with its sides all 3 units. On the right side is the 3/4/5 rectangle with its units. 
Below I have overlaid both. 
The black squares mark the location of the window and the beginning of the masonry for firebox and chimney. The red 3/4/5 rectangles mark the width of the window as well as crossing to lay out the location of the firebox and chimney. 

3/4/5 rectangles ensure a square, true, brick wall. This use of the 3/4/5 rectangle and square together is not a geometry I've seen before. The records show that the enslaved people at Magnolia came from the 'Gold Coast', now Ghana, along the Atlantic Ocean. Possibly they brought this geometry with them.

The use of the diagonal of the square to locate the ridge was also used, in a slightly different way, for a barn in upstate NY. See  https://www.jgrarchitect.com/2018/12/how-to-frame-barn-with-practical.html. This is the floor plan - a  root 2 rectangle - with the end elevation coming from its geometry.

Many people migrated north of Albany after the Revolution, included Huguenots who has come from France to  Pennsylvania and New York, in the 17th Century. Could this geometry be French in derivation?

The website for Magnolia Plantation is:  https://www.nps.gov/cari/learn/historyculture/magnolia-plantation-history.htm 

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