If it's dark wood, it will certainly absorb a lot more light than a white ceiling would. As already mentioned, the height might also be a factor. If they are pretty high then the light has to travel from the flash to the ceiling, then bounce back, which means you have to pump a lot more juice out of it due to the inverse square law. This may drain batteries pretty fast, so would suggest using a higher ISO of maybe 2 stops above the native, so you get 4 times the juice from the batteries. For example, if you got 250 shots at full power on ISO 100. You can get 1000 shots at 1/4 power and ISO 400.
Also, if there are heavy wooden beams crossing the ceiling, they may act to contain the light somewhat, as happened to me in the past, although the ceiling was very low.