Owning your own home

I'm no legal expert but if your salary is needed for mortgage then you'll be on the deeds. Therefore it would definitely be owned by both and not just her.

If her dad wants to protect the deposit, you can get a simple legal agreement drawn up whereby in the event of a sale, the deposit is returned to her (plus interest if she wants), then the remaining amount can be split.

That's what my dad-in-law did when he lent my wife and me some funds for our first flat. he's an ex-lawyer btw.

If she's renting a room to you then she needs to be able to cover the mortgage herself, without your help - and then you arrange a rent agreement separately.
If she can't do that then you're on the mortgage and it's entirely fair that you end up owning some % of it as a consequence.

I'd assume that she starts off with a % of the house ~= to the deposit. That sounds fairer to me than simply repaying the deposit. Or you agree which way to slice it, in the event of a house price crash and the deposit being worth less.

Then what's remaining of the house (i.e. the mortgaged bit) ends up split in line with what you're paying monthly.

All in writing of course. But hers and rent sounds unfair.

I had a similar position previously. Less extreme salary gap and greater deposit. But we wouldn't have been able to buy the flat we were thinking of without both of us. (if only we had bought it!)

My better half is an excellent negotiator and put forward a strong case as to what her share should be. In the end we didn't buy at that time, but I remember thinking I might feel a bit hard done by.

Basically there are always two sides and I think it really comes down to the detail.

I'm not sure how helpful this is but...

senario 1
Property = £550k (strong property)
Deposit = £80k
Your salary = £80k
Her salary = £40k
Monthy costs = £2.5k

Here she'd be fine covering her half you're just enabling her securing the mortgage. It would be fair imo for you to have some skin in the game but you could look at it as you potentially gaining capital on a great investment whist enjoying a likely reduction in living costs.

senario 2
Property = £320k (less strong)
Deposit = £50k
Your salary = £45k
Her salary = £25k
Monthy costs = £2k

Here she may struggle to pay half the monthly costs. As well as needing you to purchase she may need you to subsidise her contributions. You are doing more than just facilitating and your total capital gain is likely to be lower.

ready to buy a house in the next 12 months or so

Also consider your deposit situation may change to > £5K
But would her ~15% also go up?

Sounds like a disaster that is going to cause resentment(?). I appear to be late to comment but hopefully there are some new bits in here...

I understand the dads perspective but if you are going to be named on the mortgage then I don't agree with fobbing you off as a 'renter'. If you end up in negative equity and split up, is the dad happy to accept any loss too? Doubtful!

We have calculated the value of our place as a % value taking into account our significantly different deposits. This way, if we separate, we take a % which covers us for a rise or fall in value. This is written down and with the land registry, IIRC.

You'll want to look at Tenants in common where you can declare a % value. You may then also choose to have your solicitor provide a Deed of Trust which outlines what happens in certain events.

On a side note, you're in a relationship, I trust you'll probably end up with joint accounts and not argue over who earns more (nor care) so why should it matter with where you live.