Ouch!
We only had about seven below. [that's Fahrenheit.] The older cats are still refusing to go outside, well after sunrise; which is fine by me. The young cat went out for about ten minutes at a time twice yesterday and once so far this morning. He is currently in a patch of sun on the inside, note inside, of a window.
I don't know yet whether the lettuce, in windowboxes under row covers in an unheated greenhouse, has survived. IME it can take several days to tell for sure; sometimes very unhappy looking lettuce recovers, sometimes it doesn't. But also I haven't been out to look at it yet!
Róisín, very glad that you are cooler!