Hello,

I'm planning to build a panel door (a gate, 34.5" x 62") with
shiplapped boards inside a grooved frame. While I understand the
basic layout, I have a few questions on the details:

As regards wood movement, should the boards be tight up against each
other, so the whole panel moves together? Or should each board be
held back slightly from its neighbor, so that it can move
individually?

An obviously related question: my frame will have two z-braces, on
either side of the rectangular panel of shiplap boards. Do I want to
secure each board where it crosses one of the z-braces? Presumably if
I do I need to hold each board back slightly from its neighboards.

As to aesthetics, is it conventional to treat the exposed corners of
each shiplapped board, such as with a chamfer? Would leaving these
corners square look odd?

Lastly, I need to cut a mail slot through one of the gates. I'm
thinking of building a small frame grooved on the outside which would
float within the panel. Is this viable?

Thanks,
Wayne

P.S. I've always heard that wood shingles should be secured with only
two nails, for reasons of wood movement. But it seems like the width
of the shingle between the two nails is still trapped and could split
from expansion/contraction. Is it just that one nail is structurally
inadequate, and so two nails is a compromise? Or is it that it is OK
to trap a small width of wood (e.g. up to 6"), and that therefore when
nailing a very wide shingle, the nails should be set inward more than
usual to keep them less than 6" apart?