Another bedroom one. Disagree with DH, AIBU?

I shared a bedroom with my sister until she left home. A child doesn’t need separate bedrooms unless they are different sexes.

This is a first world problem. I wouldn’t be wasting money on this.

If he wants to do a loft conversion he needs to fund it. Or find a way to divide the room . You shouldn’t have to lose a downstairs room or make your kids share. They are coming less because they are older and they are prioritising friends/events. If they had their own rooms it’s possible the may come more if their friends can come round but it’s not guaranteed. And when they turn 18 it will likely get less.

my dds saw their dad eow and a night in week. When they got to around 15 it got less as they had plans. My home was their base, exdh wasn’t. By the time eldest went to uni she would see her dad once every few months which is roughly what both of them see him as adults.

I would have absolutely hated sharing a room as a child - sex of sibling wouldn't have made any difference to that

Not having any private space to arrange and have as you want, having to negotiate the whole time about when it's quiet time to study and when you can have music on/talk on the phone, when it's lights out for bed, no ability to just close a door and have peace without someone walking in whenever they want.

i dont think a loft conversion always adds in a large house

I actually changed my vote YABU. I think you need to change something here to make it more like a home for them. And a loft conversion will add value to your house. But I don't think you're going to change your mind.

am not against DSC having their own room, but I don't want to spend all of my money on doing so, I was willing to do it but the cost is significantly more than we were expecting due to the work required unfortunately.

Well if this was true, you'd give one of them the sitting room. But you don't want to, because your kids need for 3 rooms to play with their toys in is more important than the dsc having privacy in their teenage years. You are finding excuses not to properly consider all the options.

You shouldn't have had the 4th child (or 3rd!) if you weren't willing to treat them all equally.

Windows can be moved. Get quotes for dividing their existing room into two, with a window for each.

If you ensure the windows remain centrally positioned in the wall for each bedroom, then the symmetry will mean future owners can knock the bedrooms through to create one again without awkwardly placed windows.

Skylight windows are are a good alternative too.

It'll probably be cheaper than a loft conversion so you protect your savings and your step children and husband are happier.

So you do have two reception rooms downstairs..... I agree with your DH, OP. The largest living room you could share which leaves your own bedroom upstairs to give to the 15yo.

This is the least invasive and cheapest option all round. If it doesn't work out, move on to Plan B!

I'd be more inclined to think of a garden based solution at that age. It sounds like a loft conversion would leave the house unbalanced with not enough downstairs space.

A loft conversion would add value to your house. You could look at increasing your mortgage to cover some of it to save eating all saving up and have the kitchen done at the same time.

I’d split their current room with IKEA Kallax units, cheap and will give plenty of storage. They don’t need the partition to be floor to ceiling, surely

I think you'd do it in a flash if it was for your DC and he was the step-father.

He's probably right that they'd come more if they had their own bedrooms. It could well be a factor in them being there less, as well as just getting older. Regardless of getting older, you'd still want your DC to have their own room I bet. You'd never think - oh they're almost 16 and seeing their friends more so they can share a room now. Course you'll say yours are boy/girl so can't share, but I still think you'd want this for your kids so should do the same for his as a family.

They both chose for him to have the fourth child

as a blended family my dad took away our room, so his younger/newer dd's could have a room each.
we had the sofa in the sitting room

I agree.

So often it’s hidden behind financial “ prudence”; it’s just meanness.

It’d be one thing if OP’s H had an every other weekend set up, but the DC spend 3/7ths of their nights at his house and share, whilst thejr younger half siblings have a room each plus a ‘playroom’.

What about the little ones moving into the bigger room to share?

absolutely

Staying at the house of the parent who has less space for them may die off during the early/mid teens, in favour of being in their main home where they have their own room with their things in, and can nip out to see local friends in the evenings. At least that happened with my DSC. Their dad still saw them regularly but they chose not to come and stay in our house as they had done for years previously, except occasionally at Christmas.
In OP's case, having their own bedrooms at their mum's will be a powerful incentive to stay at her place all the time, and they will soon be old enough to decide for themselves.
Children of blended families have a rough time. Step parents with children of their own are not always able to provide a home large enough for 4 or more children to have their own bedrooms, and, like OP, expect their own children to get the single rooms 'because they are there all the time'. But who would want to spend 3 nights sharing a bedroom with a sibling in a house with younger children taking their dad's attention, when they have their own space at home with their own things around them?

I mean, don’t expect them to be totally honest about why they as young adults might want some privacy as their bodies change and their sexuality develops 🙄

I really am gobsmacked at the way people are trying to excuse this second class treatment of these kids.

Why don’t you go the whole hog and have a kitchen cupboard that only the chosen children are allowed to eat from too.

I think the person who chose to have four children should pay for the extra room.

I’m with OP. I would not agree to spending my personal savings on this.

That doesn’t make much difference. The problem here is the OP thinking her children deserve something that his do not and her refusal to accept any of the options that would allow them all to be treated fairly.

Because at these ages, one may be studying for GCSE whilst the other wants to play Xbox. One may want to chat to a boy/girlfriend whilst the other is sat in the room reading. There isn't another good place to do those things as the rest of the house is communal space.
At 15 you need a bit of privacy and the gap between 13 and 15 is pretty big in my experience.
The house isn't small and I think it's unreasonable to not offer the DSC a space with some privacy given the number of days they are there. If you don't want to create a loft room then I'd convert that downstairs room and perhaps just put up with the lack of space for a few years until the oldest goes to uni?

Nah you just put air con in?

id suggest a garden room if it was an office that was needed. Not a bedroom.