=============

Well, this took some time. We had some discussion about double board roofs some time ago, and as I recall Jack Mullens posted a link to a diagram of the construction used by the Milwaukee Road. Rather than search for that, I thought I'd use the time to see if I could find an applicable MCB/ARA standard, or Recommended Practice. The ARA adopted standard lumber sections to be used in carbuilding in 1914, revised in 1920. The sections are illustrated in the 1922 CBC. I could not find illustrations from earlier, so can't say what was revised. As of 1920, the standard for "roofing and lining" was 1x4 or 1x6 boards, dressed 13/16" thick with tongue and groove edges, either 3-1/4" or 5-1/4" face. These did not have V grooves. This is what we are seeing on the left side of the roof in the photo.

The double board roof material was harder to track down, as it was apparently never made to any standard. However, illustrations appear in both the 1879 and 1895 Car Builder's Dictionary, both available on-line. Here is a link to the 1895 CBD:

https://books.google.com/books?id=0UJttWHSwNYC&pg=PP9#v=onepage&q&f=false

Unfortunately, There doesn't seem to be any way to link directly to the page. The illustration in question is Fig. 2379 on the bottom of page 205 of the file.

Briefly, the boards are square edge (no T&G) with a half round groove about 1" in from each edge. On the top layer these are intended to catch most (some) of the water sluicing across the roof, and channel it to the eave.  The boards are laid up with a half board overlap, so what water seeps through the joint in the top layer ends up in the middle of the board below. As it spreads sideways, it comes to the half round grooves in the layer below, which channel it out to the eave, or so the theory goes.

Did it work? If it worked well, there never would have been a need to try to develop sheet metal coverings for freightcar roofs. But it did work well enough to be in common usage for three or four decades.

Dennis Storzek