Extract from Thomas Jefferson to Ferdinand Hassler
| Monticello. Dec. 3. 25 |
in the house in which I live, and it’s offices I have flat roofs of a different construction. they consist of rooflets 30. I. wide with gutturs between them. there are 2. strata of joists, the one about 9. I. higher than the other. arranged thus ... a single length of shingles reaches from the top of the upper joists to halfway down of the guttur which is made in the lower joists, overlapping just enough to deliver the water safely into the guttur. these guttur 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 over-jets the wall so as to deliver it’s water clearly over it. a floor is laid over the whole to walk on, the water first falling on that & passing thro’ it’s cracks drops into the gutturs. I have had upwards of 20 years experience of these roofs in this house, also in one I built at another residence, and more than half our buildings at the University are flat and so covered. they never have leaked, cost less than a rafter roof, as needing no rafters and admit repairs more easily than any other. I think it the best possible roof for an Observatory.