Ground floor flat extension - is this possible?

[Kai1981]

I'm about to buy a first floor flat. I've found out that the ground floor flat below have applied for a ground floor extension (done this week).

We've not exchanged contracts for my flat but I'm wondering if there's a way to add 1.5m by 3m to my property by building on top of this extension.

I know it'll depend on their skylights but the area I'm talking about adding is relatively small so hopefully it won't encroach.

It's a leasehold so I know I'd speak to the freeholder too. What would be the best way to even approach the ground floor flat (I'd be happy to pay towards their build costs to help to get them to agree) or do I have to wait until I've purchased?

Their build is due to start in July subject to planning permission

I believe they will have to revise their planning application, certainly the structural part if it is to support two floors. If I was the ground floor I wouldn't let you do this - I don't want someone walking above me on my extension!
And presumably the building will have to be done together, party wall (floor) agreement- I see a whole can of worms here.
Ask your lawyer if this is even possible. If they don't know, then of it's a deal breaker approach the flat owners.

Thanks.

I was thinking to offer to soundproof that part of the floor (it's barely the space of a king size bed) and as I say, contribute towards their costs (as well as paying mine) but I guess we'll have to see.

I already walk over the rest of their flat so don't see that much difference if I don't impact skylights.

The planning dept said I would just be able to submit my plans separately once I had agreement from the ground floor (as that would be a civil matter rather than anything for them to deal with).

I very much doubt their extension foundations and roof would support your extension. I really do not see this being a runner unless you do the planning and building jointly.

It will impact their extension massively. They will need to dig deeper for the foundations and reinforce the walls in order to enable a second storey. It's not as simple as it sounds.

It feels unlikely. As a leasehold flat you won’t “own” the space above the extension - the downstairs flat may have had the rights to the garden, and/or may have paid the freeholder for the right to build on it. If there is a loft you probably won’t own that either.

So you would need permission from both the freeholder (to make structural changes) and the downstairs leaseholder - who will probably say no, or might want to charge you for the plot - and then get planning permission.

None of this feels worthwhile for an extra 4.5sqm.

Thank you, agreed, sounds like more of a faff than it's worth!