At what point do you move a modular home in next to the place you’re living in? Having done a complete gut remodel of a place on a solid foundation, you’re biting off quite a chunk. Ours had a solid basement, and good siding. We did all the rest over...windows, insulation, wires, bathrooms, moved walls new plumbing, new hvac, and roof. Came out good on it, but was a lot of work. I’ve seen quotes from $100-250/sq foot for additions. I’m still waiting on a guy to get back with me on it all, but he already told me I’ll have $35/sq foot of addition just in lumber in ours...a basic living room on a slab. I guess I find having my house on fire a lot less funny than you do...even if it is little bits at a time. Best of luck to you. It will warm up one of these days.