Unmarried couple, kids and plans for life together. House bought as tenants in common 80/20 in Partner A's favour due to savings that pre-dated the relationship. Largely equal relationship in terms of working, childcare, housework, household admin etc. Both pay into a joint account in proportion to income which covers majority of household outgoings. Any other big expenditures usually split relatively equally - Partner A sometimes paying more due to slightly higher income/more savings, although both fairly financially comfortable with personal and joint savings.
Thinking about some big-ticket maintenance/improvements on the house ~£20K ish for things like windows replacement, bathroom upgrade etc. Should the costs be split equally or 80-20 as per ownership of house?
On the one hand, both partners will equally enjoy and benefit from the improvements. Idea is that both will live there long term and be together for life. Partner B has a smaller share of the house, but 'gets the benefit' of living in a more expensive house than they could otherwise afford to.
On the other hand, nothing is guaranteed and if they split and the house is sold, Partner B will only get back their 20% share. So splitting the cost of improvements equally means they are paying more than their fair share.
So how to split costs?
YABU - 50-50
YANBU - 80-20