These are not in violation if they were built/placed before zoning changed. My city recently updated zoning to allow for higher density, with the understanding that many of our most desirable historic neighborhoods could not be built under the more restrictive low-density codes from the mid 20th century.
Yes, I know people who did some major rework to their house, and ended up more or less having to move the house half a foot from the previous location (the foundation they were intending to keep was apparently in very poor condition and had to be redone, which triggered having to meet new setbacks).
Step 1 for this site, before anything else, is finding out if you
can legally build anything on it. That sort of skinny property is always a problem, and if planning and zoning says "No way, no how!" - no point wasting more time on it.
Why not just put in a new manufactured home? I feel like that wouldn’t be as great an investment. I feel like that would not appreciate as much value as a custom build. Also, I want to maximize the space of the specific lot.
A house isn't (shouldn't be...) an "investment." It's "a place to live." And as much as I've been informed repeatedly over the years that "manufactured homes go down in value," the county certainly doesn't seem to believe that's a thing, given our tax bill... my house is a manufactured, on a foundation, but still "legally a trailer," and that sure doesn't seem to mean anything with regards to value.
But look into single wides. A 70-80' long single wide may get you a lot of what you want, for rather less time and effort than building, and then you have a place to live while building an outbuilding out back for more space.
$400k and a shit ton of work just to save $100k? I don't care how ugly the other houses are, if they keep me and my shit warm and dry, buying one of those is a way better deal in my book.
There are two types of people in this sort of problem: Those, like you, who seem to view "Ugh, it's totally not worth the work to save a mere $100k," and those who, like the OP, view it more as "You mean I
get to build a house and save $100k in the deal? Sign me up!"
I've learned over the years that the two will never find common ground on things like this.
In the context of 40 years ago, you most likely would be able to build a nice house to live in. But in the context of modern era houses, I'm not sure you have the qualifications to even attempt it based on the above.
Ah, yes. Homes. So complex, you couldn't possibly do it yourself, you'd best hire the
experts to do all the fiddly little fjords and stuff! Despite it being the default throughout human history. Build a 40 year old home design that meets modern code. Problem solved.
I do a lot of home construction...
No particular offense aimed at you, but I find it amazing just how many people in an industry go out of their way to convince everyone else that their industry is so insanely complex that nobody else could
possibly manage to achieve that which they get paid very well for. Every "solar professional" out there seems to believe that solar is so hard, so complex, that their $4/W is a bargain (or $6/W for ground mount, because they don't want to). Meanwhile, I know more than a few people who've built their own for $1/W or $1.50/W, depending on the system style.
But I also know more than a few people who have built their own homes, often with some pretty esoteric features like massive thermal heat storage under the house. Yes, they're older homes, but "building your own home" is far from impossible.
Unless, in this particular case, that lot width and modern setbacks prohibit it.