i have worked in -4 before but i think the temp needs to at the same temp for 2-3 hrs before working to ensure its workable in the shade as well as the sun it can differ so much from house to house i have cleaned a few houses before then dropped on to the next house in the same street in the sun and its froze on the glass you can only go out and give it a go but when you have got everything ready to start work then go to your first house and it freezes on you feel a bit daft