Underpinning for renovation (not subsidence!) - yes or no?

House_Cat

We are planning a major remodel of our end terrace Victorian house, which would essentially transform the ground floor into one open plan space. This would involve knocking through what used to be the rear wall of the original ground floor, and installing an RSJ and two vertical posts to support the floor above.

We just received the RSJ calculations from a structural engineer, with the following comment:

"We have designed the frame with stiff moment connections at the top to avoid the need for large underpins. However if your builder finds the existing foundations are very poor and shallow, underpins may be required anyway (Builder to check that existing foundations are at least 500mm wide and 600mm deep. If not, allow for provisional 900x900x300thk GEN3 underpins, under both posts)"

This potential underpinning concerned me, as far as both resale and insurance is concerned. However, having spoken to my home insurance provider, I was reassured that it wouldn't affect my premiums, as long as underpinning is done for remodelling, rather than subsidence reasons. They said they deal with these situations a lot, as old houses were built to different standards.

But what about trying to sell the house in the future? Will we be shooting ourselves in the foot, and turning off the majority of prospective buyers, who will hear "underpinning" and run the other way? Or is there enough precedent for this kind of work for buyers to differentiate between remodelling- and subsidence-related underpinning?

I've also come across some posts warning against the dangers of "partial underpinning" (i.e. only one side of the building, which is what we'd be doing if it turns out our existing foundations are not sufficient), which has apparently been known to put stress on the building and lead to future problems. Again, I'm not sure if this is only an issue with underlying subsidence, or if it's a problem in and of itself.