Under pavement vault conversion

[Madreamer]

Im considering extending my property into the underpavement vault area by knocking together 4 existing vaults and creating habitable space. Apparently this can be done, but I'm wondering if it would be worth the money and effort or is likely to start having damp issues in a few yrs? Looking for opinions from anyone who has had similar work done. The vaults are victorian and leak like a sieve at the mo.

The walls of the vaults are what holds the pavement up. If you knock them into one the pavement will fall down. It is also quite likely that any new construction will have to meet current building and planning laws. I don't know what they would be.

I know someone with a basement flat in pimlico who's done this. They were only able to create 2 small spaces, not one big one (leaving a thick wall between the 2 spaces). One is a large wardrobe and the other a study. They had major flooding issues during the building work and I think they then had damp issues, though think they have now finally sorted it (not sure though, it's been quite dry this year so hard to say).

TBH it seems like a lot of effort for not a huge amount of usable space...

@piglet, the walls will be replaced with structural beams. I've seen planning permission granted for these within my borough, so know it is doable.

@minipie, I'm actually worried about flooding and damp as happened with your friends. I also understand that the damp proofing insurance does not cover any work under ground level,so any additonal corrective work would cost me extra.

My vaults would add a lot of space if done as one, but pointless if they can't be connected.

A friend of mine is doing this with her flat in central London at the moment. It's costing about £120k and they will end up with a double bedroom, small office area, and shower room.

@lottie, have they completed the works? Have there been ongoing issues? Has it been worth the expense? I worry it will turn into an eternally leaking extension that costs lots to fix.

No, they're almost finished. I know it's been very stressful, but they do have very high standards and it's being finished to a high spec. They are very 'together' people working with a good architect and I can't believe they would have gone ahead if there was a risk of ongoing leaking. Have you spoken to an architect about it to see what they think?

Yes, I've spoken to an architect who has done planning permission for similar project before, but don't think he supervised the build of it. I've had a few builders look at it as well and general feedback is that it is doable. I would like confirmation from someone who has successfully done it on their house before before I proceed though.

I would be really keen to know if you went ahead with it? How did it go? Cost?