@chloegabrielle_ I too have my pigs outside over winter. I don't have a garage, there's no room for a shed in the garden and they can't live in the house as if they did my husband would spend a lot of time in hospital due to his severe asthma.
If you have a waterproof insulated shed could you move your hutch in there for the winter, it would help?
If like me you have no other option then your pigs can be snuggly and warm outside in a well prepared hutch.
Locate it in the most sheltered spot you can find. Have a well-built solid wood hutch – not one may from ply type boards which are much thinner. Insulate the hutch well. Give your pigs lots of bedding and plenty of hay to snuggle into.
If you can, on the coldest nights line the interior of their night area with thick cardboard and then give them corrugated cardboard boxes stuffed with hay to sleep in. Obviously cover over the front of the hutch with something warm (towels, blankets etc) under your waterproof layer on the coldest nights. Make sure you leave some gaps for ventilation though!
The most important thing is to keep your pigs dry. Change all damp/wet bedding regularly.
Keep close eye on them. Check they’re warm whenever you go out to them. On the coldest nights I will give my boys extra pellet rations, especially if they seem hungry – but only on the coldest nights otherwise they’ll fill up on them and won’t eat their hay!
Some people use snugglesafes that heat up in the microwave. I’d never heard of them before I joined the forum and I’ve not used them – but I’m sure someone will be along who has and can advise on how useful or otherwise they are.
My previous pair of boys had to make it through the worst winter we’ve had in our area for years a few years ago. The car thermometer was showing -10 some mornings and we had snow, which is practically unheard of for us in a low lying area close to a large river. We were worried about my boys that year. However, in spite of the extreme temps every time I checked up on my boys they were toasty warm. Their sleeping area resembled a tortoise hibernation box, but it did the job!
Next time we move house I'm going to ensure we have a shed/garage/outbuilding for my pigs - but until then with care and planning they can be kept outside over winter and be fine.