The restoration carpenters are in the process of re-creating the terras roof that Jefferson designed over the wing of offices that extend from the east side of the house.  This flat roof, like any flat roof, presents drainage challenges.  The complex design was developed by Jefferson to facilitate channeling water off the roof.
The model at right shows the construction that exists beneath the flat deck boards of the terras roof. First, restoration carpenters hoisted 43 gutter joists in place that span the width of the wing and weigh about 300 pounds each. The joists rest on large timbers called plates that are set on top of the brick walls of the wing.

The restoration crew then began shingling the ridge and gutter joists of Jefferson’s unusual flat roof system. An original shingle from the East Wing, found on the site, exhibits a well-made piece of old growth pine 5- 3/4” wide x 17- 1/2” long  x  ¾” thick. On its top surface were two 3/8” grooves close to each side that acted as miniature gutters should any water get under the top-most shingle layer. Each shingle had been neatly hand-planed on the top and secured by two 2- ½” long cut nails. Jefferson himself described the roof:

 “A single  length of shingles reaches from the top of the upper joists to half way down of the gutter which is made in the lower joists, overlapping just enough to deliver the water safely into the gutter. These gutter joists, as well as those constituting the ridges of the rooflet have a descent of 6 I. from their middle point to each end, which overjets the wall so as to deliver its water clearly over it. A floor is laid over the whole to walk on, the water first falling on that & passing thro’ its cracks drops into the gutters. I have had upwards of 20 years experience of these roofs in this house [Monticello], also in one I built at another residence [Poplar Forest], and more than half our buildings at the University are flat and so covered. They have never leaked, cost less than a rafter roof, as needing no rafters and admit repair more easily than any other.” 

Jefferson’s last phrase was prophetic since he had to “admit repair” to the Poplar Forest wing roof ten years later in 1825. While they might not have leaked, the gutters apparently rotted. Because of this failure the restoration carpenters only put down one layer of shingles and then had a waterproof membrane put down (photo, left) to protect the shingles and gutters - an unseen concession to the inherent problem to which Jefferson alerted us. Still, one layer of shingles consisted of about 4500 pieces that had to be individually cut, shaped, and fitted.

	Drawing of the terras roof structure