Robert Brenchly's comment about having at least a 3" solid board at the
front of the screened area, in order to avoid bees becoming confused and
going under the screen, is a useful piece of information and perhaps
explains why the screened bottom board shown at beesource .com is shown
as 4".
Perhaps the 3/4" space above the screen is also important since a
previous screened bottom frame which I made with a 1/2" space caused the
bees to build brace comb down from the frames, although this frame was
simply inserted between the deep and the existing solid floor (top bee
space Smith hives).
On the top ventilation versus insulated top cover debate I would
probably favour ventilated tops but with the proviso that the
ventilation should be at the sides rather than in the middle to prevent
chimney drafts. It is common in the west of Scotland (a damp area) to
insert a matchstick under each corner of the top cover in winter prior
to replacing the roof.
The absorbent top covers still used by many beekeepers in the UK on WBC
hives (a type of twin walled bottom beespace hive) is usually placed
directly on top of the frames and probably works by "wicking" the
moisture right up through the top into the upper open ventilated space
within the outer box.
Water vapour as well as being colourless and much lighter than air is
also "thin" and would escape through textile material easily.You can
only see water when it recondenses into water droplets - as your breath
on a cold day. Just as well water vapour is lighter than air or we'd
have the clouds continually round our ankles.
Alan Riach
Bathgate,Edinburgh