"gray barn board"
It's worth the effort. That is, to take five minutes to drive over to Handley Lumber Mill while visiting in Fenelon Falls. To ask the manager if I can get barn board, gray on both sides, enough to fill my trunk.
Back home in London, I use it for birdhouses and roofing material (3/8th inch slats), and it is by far some of the nicest pine I work with week to week.
And recently, after cutting the gray barn board into various parts for duplexes, I had one piece left over for a small birdhouse repair.
Link to The Workshop