I inadvertently replied direct to Allen Dick rather than posting to Bee-L.
Thank you for pointing this out to me and I re-post the discussion below for
general information:
 
>> In respect of Garth Cambray's comment on the bees liking the extra space
>> in the lid so that mats may be a bad idea, perhaps this is the reason of
>> ensuring there is a margin of space so bees can move into the lid.  I
>> assume they sometimes use the lid to draw cooler air through the hive as
>> sometimes I lift the lid and find a mass of bees on top of the hive mat.
>
>I assume then, that the hive mats of which you speak are smaller than the
>inside of the top of the super?
>
>What then  are the dimensions of the supers you use and the mats?
>
I use standard size 10 frame supers either supplied by an apiarist supply
house or made in the workshop - outside measurement 510 cm. by 410 cm.  The
inner measurement would be 40 mm. smaller than the outside measurement.
The hive mats are cut from surplus vinyl flooring.  The original
instructions from my Beekeeping in Australia book by Fred Bailey
recommended leaving a 12.5 mm margin on all sides to allow moist air to
escape and prevent condensation dripping down onto the bees.  My hive mats
are cut to approximately the recommended size but I think as long as bees
can move up under the lid from the frames, the exact spacing is not
critical.
 
Betty McAdam
HOG BAY APIARY
Penneshaw, Kangaroo Island
j.h. & e. mcadam<[log in to unmask]
http://kigateway.eastend.com.au/hogbay/hogbay1.htm