Spacing on PT deck boards

Wet 1/8" spacing. Dry spacing 1/4".

You need to do it right away? Best bet would be to leave them out of a bit and let the humidity equalize in them. Otherwise, the spacing is going to be all over the place.

I was using framing nails as spacers. And you can fudge it a little as needed.

FWIW, narrower gaps will clog with evergreen needles. On wider gaps they'll fall thru, but
then be careful what deck furniture you can use.

EDIT: My boards were sopping wet when I got them. and the PT lumber I get here tends to warp a bunch. I installed immediately so they dried flat/straight in place.

Get exact width of the dry and the wet if they have shrunk 1/4, and you want 1/4" spacing, then you do a layout and snap lines for the leading edge for each board What ever wet they have they should dry to the same gap.

Geeze, he is building a shower for cryin' out loud. Why all the shrinkage calculations for such a small area? When we use public showers hunting out west, the slats have just big enough of a gap to where your toes don't fall through. Of course, out there the water just goes into the soil.

Just re-decked mine and jammed them up tight. 8 weeks later, there is a 1/4 inch gap everywhere. Lumber was from a lumber yard and not the big box store.

Thanks everyone for the advice! I didn’t want to end up with 1” gaps or no gaps at all, and this is all very useful.