Google Earth (finally) just added 3D imagery of Washington, DC. As a resident, I've long suspected some of the heights in the database were a bit off, but I didn't have sources to demonstrate it. I'm posting below some heights as measured in the Google Earth imagery, focusing on taller buildings without official heights in the database and buildings with a large discrepancy between database height and height in Google Earth. If the mods trust the existing source more, feel free to disregard any of these as "unofficial," but I think these numbers are pretty accurate.
Lydian 400 K
Building:
https://skyscraperpage.com/cities/?buildingID=113952
Height (spire):
46.0 m (Measured from northeast corner)
Height (roof):
45.1 m
700 Eleventh Street
Building:
https://skyscraperpage.com/cities/?buildingID=48365
Height (roof):
48.5 m (Measured from east side entrance)
Renaissance Washington DC Hotel
Building:
https://skyscraperpage.com/cities/?buildingID=76176
Height (roof):
47.6 m (Measured from west side entrance)
1090 Vermont Building
Building:
https://skyscraperpage.com/cities/?buildingID=10336
Height:
44.8 m (Measured from east side entrance)
1111 Pennsylvania
Building:
https://skyscraperpage.com/cities/?buildingID=48323
Height (roof):
48.2 m (Measured from southwest corner, does not include mechanical equipment)
Avalon at Foxhall
Building:
https://skyscraperpage.com/cities/?buildingID=113952
Height (roof):
45.4 m (Measured from southwest entrance)