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What is the best relative humidity for building, and what are the problems that can arise when it is too low or too high?

-Matt

I like to build in 45% to 50% and I will turn the dehumidifier down to 35% overnight when I do bracing the next day .

Best relative humidity: Around 40% - 50% seems to work fine.

Problems with too low humidity: danger of wood shrinkage and cracking.

45% /-

If you will be cross-grain gluing (like gluing the X-brace or tone bars across the grain of a top), I want to be 40% humidity or less (John's suggestion of 35% is about perfect in my mind). I definitly want these glue joints made on the lower end of the scale so there is less pressure wanting to cause the top to split if the guitar is put in low humidity conditions.

Some other glue operations aren't quite as critical........but ideally even they would be made around 45%. That's my thoughts anyhow.

If I had to rely on a best humidity, I probably would not build guitars. I build my guitars at 16 to 28 % rel Humidity year round. My guitars will probably not be leaving the area, so it real doesn't matter what best is!