@dotdotdotdash you need to speak to an independent mortgage broker.
Some lenders have a “rent a room” product - see Bath Building Society” where the lodger income is considered in lending.
However, I still don’t see that you’re going to raise £375K, even with that. But I don’t know how many rooms you have to rent out, or market rate in your area.
You need to look at this from other angles too:
- can you change the £200K equity that you need to buy out? For example, would you be owed anything from other assets - particularity a Pension Sharing Order - that you could trade for more house equity to you, reducing the mortgage you need?
I’m curious about the £50K. You say that you need to extend as well as subdivide. £50K isn’t a lot... a new kitchen and bathroom for Flat 2 could take up £10K of that, and that’s separate to remodelling, building, new boiler, splitting the electrics and water... Have you had quotes to arrive at that £50K?
Have you any way of raising that £50K in future?
Think about your final aim here... it isn’t to stay in your house. It’s to have a flat with mortgage paid off by sale of the second flat. So - you’re going to end up in a flat.
If you just a different flat now, with your equity + mortgage, you’ll save a lot of the interest on the huge mortgage you’re talking about taking on - if you can get it. You’ll save £50K (or whatever the conversion cost is). You’ll save the council tax increases for having lodgers. Possibly save the tax on income from lodgers (if about about £7Kpa) You’ll save the conveyancing costs of selling Flat 2.
Have you fully researched the Capital Gains Tax implication of subdividing and then selling a portion of your home? Your new flat is not your Primary Residence. There are allowances, but so you know what these are? If you’re not covered and you’re hit with CGT, you might find that it wasn’t worth it all.
Not financial - you’ll save having your share with lodgers, the hassle of getting lodgers, the hassle of managing the remodelling and sale of Flat 2. Which you may not be bothered by, but it’s something to consider.
Have you really costed it all out, mortgage interest over the years included?