Wednesday, June 17, 2015

Geometry for the Cobb-Hepburn House, Part 1

When does geometry enter into the design and construction of a building?
Not at first.
Only when the basics are answered can layout and design begin, can geometry be considered.

The design of any building begins with need, ‘What?’ and ‘Why?’.
Next comes, ’How big?’, ‘Where?’
Then, ‘What material?’, ‘What will it look like?’  

Of course people often start with the vision, what they want the space to look like, materials they hope to feature. They may focus on a specific use for the space.
Sometimes they just begin with ‘Bigger than this!’ The planning then must cycle around to answer the other questions.
The Cobb-Hepburn House began with most of those questions already answered.

About 1780 the Charles Miles family needed a house on their land in Tinmouth, Vermont.

The house would look like houses they knew: a 2 story box with a gable roof and a center chimney, with a layout that was also familiar: a hall, a parlor on the front and a kitchen with service spaces behind. 

Here is their house after the modern siding was removed. The original house was probably not painted. It would have had small paned windows and a larger chimney.

The house would be framed of wood of which they had plenty. The foundation and chimney of stone – which also ‘grew’ right there. The frame would be 4 bents long and 2 bays wide.  
14 feet square +/- seemed good sizes for the Parlor and Hall. The space for the chimneys needed not be as large.

Here began the geometry.

Please read left to right. I have shown in the first 5 diagrams 2 points for each straight line. After that I have assumed the geometry is reasonably clear. I have also added a description even though I often find it easier just to read the drawings. 

1 -- The width of the house was laid out: 28’-6”: the length of the first bent.
 Just a line:  A -B

2 and 3 -- A square was drawn, using the line as an arc:  A -B - C - D
All the sides are equal.

E marks the intersection of the arcs.

4 -- Diagonals were added: F is the center.

5 -- The square divided in half both ways: the second bent. 

6 -- At E a vertical line was drawn: the third bent.

7 -- E is the center of the second square. The length of the sides of the square could have been stepped off to match the first square or laid out with geometry.

The fourth bent is the right side of the 2nd square.   

8 -- is the plan for the house, showing the locations of the posts - almost.

The as-built plan for the Cobb-Hepburn House, shown here, is not quite symmetrical. 

Here is the plan showing the posts and  beams for the 2nd floor with the 2 crossed squares in red.

I have seen the use of 'Crossed Squares' in many New England floor plans.Before I explored the geometry of this house I had not seen layouts use the intersections of the arcs as determining dimensions.

The framer used his intersections as the outside of the post location for the center bents. He seemed to set the center posts and beams back about 8" so that the chimney could more easily exit at the ridge of the roof. 

Here is an elevation of the bents from front to back for the house.
It fits within a square.

If the square is divided into its 4 smaller squares and the arcs of the length of the smaller square are drawn the intersection is the location of the top of the plate - see the green square on the upper left side and intersection.

Once the height of the house frame was set, the rafters could be laid out.
The second floor location was determined very simply: the top of the beam was located at mid point of the distance from the first floor to the plate  -  shown with a dotted green square on the lower right side 

In both cases the framer used his intersections as the outside, not center line, of his beams.

The elevations of the house used the same geometry. That's next.


Monday, June 8, 2015

The Cobb-Hepburn House frame , Tinmouth, VT

Here is the Cobb-Hepburn House coming down.

Glenn Tarbell recorded its dimensions as he and his crew dismantled the frame this past winter. I drew the framing diagrams. My measured drawings of the house before de-construction served as a reference.

The drawings tell a lot about how the house evolved.

Local records show that Charles Miles came to Tinmouth from western Massachusetts. He built this house about 1780. When he moved to Ohio about 1810, he sold the farm to Amos Brown. In 1821 Brown sold it to his son-in-law, Edward Cole. His daughter, Jane Cobb, inherited the farm and house when Cole died in 1852.
Hod Hepburn was the last owner who lived in the house. After he died the new owner asked Green Mountain Timber Frames to take down the house.

The house is 28'-6" wide by 39'-0" long, 2 bays (3 bents) wide and 3 bays (4 bents) long.
Its layout is derived from some of the earliest houses built in colonial New England

Center chimney floor plans were rarely built in seacoast New Hampshire and Massachusetts after 1760.  However, the first floor plan often appears in 2 story houses in New Hampshire and western Massachusetts up to 1770 and is a common plan for 2 story houses in Vermont through the 1840's.

The drawing is by William Lawrence Bottomley from his introduction  The Architectural Heritage of the Piscataqua, John Mead Howells, Architectural Book Publishing Company, Inc. 1937. His 10 page essay is one of the best introductions I know on early construction on the New England Seacoast from Salem, MA, to Portland, ME, .

Here is the probable floor plan for the Tinmouth House. I have labeled the rooms to match Bottomley's drawing.

The kitchen and the  pantry/dairy had been divided into smaller spaces by the time I measured the house in 2015. The other rooms still existed.
The first floor joists and sills were too rotted to be saved. The actual location of the original fireplaces is educated conjecture. A bake oven may have been beside the kitchen fireplace - we uncovered a mantle and cabinet door set in that wall.

The frame is massive, 10"x 10" posts rising to 10"x 14" and 10"x 16" gun stocks. The beams are 6"x 9", the plates 12" x 9". This is the 2nd floor SE corner seen from the 1st floor.
The roof rafters are of similar heft. The basic house frame was erected all at one time. Completing the interior frame took about 50 years.


The way the framer set back the longitudinal center bent -  about 12" from the center - allows the chimney (drawn in red) to rise through the roof at the ridge.


The frame for the north wall has missing and added studs as well as blocked windows, showing  how the house was changed through the years. The original 1st floor windows were directly below those on the second floor.

The west wall framing also shows window openings where we found no sash.
A door was added at some point and then closed off. A stud pocket remains in the beam above.

Empty joist pockets at the stair opening in the front hall indicate that the frame was reconfigured to allow space for the narrow, steep stair to the 2nd floor.

The second floor joists were made at the same time as the original frame.

The  Parlor, Hall, Bedroom and Kitchen joists are regularly spaced. The pantry/dairy joists aren't.
Quite a few of the joists have bark and wane; those above the parlor and the pantry/dairy are more logs than hewn.
The larger space between joists beside BII may indicate a stair.

Here is a possible explanation:

Charles Miles framed the house. He finished the Hall, Parlor and Kitchen; the Bedroom (which was usually reserved for the infirm or new mothers). Then he ran out of money, time, or energy. He finished the last joists with rougher wood. His family lived on the first floor.
Living in a partially finished house was not uncommon. Sections of a house were often used for storage and then added into the living space, just as we today add dormers to attics and insulation to  porches.

The attic framing was a different pattern: joists 2'-0" oc with intermediate 12" x 9" plates.
The joists all match: 3"x 6", cut by a sash saw at a mill.
The stair was relocated to where we found it.

As the frame was exposed we saw that bedrooms #1 and #2 were once one room, that bedroom #4 had neither lath nor plaster while the other rooms were finished.

Which owner installed the attic floor? The answer might depend on when sawn joists were readily available from a local mill.

The photograph shows the attic floor joist pattern. The window to the right had been blocked, but its outline was visible in the plaster wall. The window to the left was not original:the cut stud above and the lack of a stud on the left side were the signs of later construction.

Probably the Coles eliminated the fireplaces. Cast iron stoves were being manufactured in the 1820's.They were widely used by 1840.

 After stoves came central heat.We dismantled a modern cement block chimney serving a furnace and a modern wood stove.
Soot and char on beams implied that the framing around the chimney coincided with the installation of wood stoves.

For views of the house as dismantling began please see the previous post: