This will depend on the type of bee, the duration of the winter and the severity of same. Even your apiary topography can influence the minimum amount required. Favourable conditions to the worst scenario are poles apart. When I ran standard Nationals I tried to ensure a super of grub on top of the brood. It should not then matter how hard and long the winter would be.
Now, if you intend to feed, and to build up your colonies early in spring in these times of changeable seasons, the requirements can be more tailored to the beekeeper's choice.
I do not rely on my bees to yield an income (I am a hobbyist), so I tend to give them more than enough, save some for the weaker colonies and consequently not have to feed too much fondant in the new year. I can take the stores away, as honey, if I need to make space for brood in the spring. That means I can feed less sugar and can be confident that all the stores in the hive are proper honey. I would not do it that way if I needed to maximise profit from the bees.
All my colonies are on 14 x 12s. A brood full of stores late in the autumn should be more than adequate for most winters. You need to remember larger colonies in a warm hive may need less food than smaller ones in a draughty hive or location. Food = heat required to keep the cluster alive. Better insulation is good too - less heat loss equates to less energy needed to maintain the cluster at that optimal temperature.
Wasps in the roof? How? If they are above the crownboard and there is no top ventilation, your roof must have some poor fitting battens or the ventilation mesh is damaged/missing. I doubt any wasps would suvive for long in a very strong colony. I have fitted bee escapes on my Dartington roofs so that with no top ventilation, any bees trapped above the crownboards can escape rather than perish. Nationals are not quite so easy, unless one fits fancy gable ended roofs.
Regards, RAB
