Bill wrote:
Larry Jaques wrote:

What is the purpose of the furring strips, Bill? Electronic ballasts
don't get hot, the ceiling is flat, and the fixtures are flat. Butt
'em and forget 'em.

Temperature of attached garage varies between about 25F and 110F, and
humidity varies too. I know most expansion/contraction occurs between
the annular rings, but some also occurs along the grain too. Shouldn't
one leave space for it? Assume 6' to 8' std onebyfour lumber. This
looks like something I should be able to look up in a table (maybe
someone has a link handy).

Bill

no. the drywall won't be moving. even if they did, what do you expect to
occur? they fixtures will give a little because the screws holding them to
the ceiling won't fill the holes completely.