To develop a design for the reconstructed terras roofs, the Restoration Team first looked for surviving evidence found on the house itself.  After the investigation, evidence was found on both the framing of a surviving partition in the North Wing and on the exterior walls.  The most important evidence found on the exterior walls were reglets, or narrow grooves cut into the brickwork that were used to anchor the top of the roof's flashing.  The reglets clearly showed that the Madison-era roof had a very low pitch that could only have been possible if a terras roof had been used.  The framing for the surviving ca. 1812 partition in the North Wing was also important.  Evenly spaced mortises were found cut into the top plate that survived on top of the North Wing's surviving ca. 1812 partition.  These mortises recorded the original spacing and width of the lower level of joists.