To want SD’s room to be multifunctional?

Also just talk to her! She’s 13, she can understand, the main reason kids want their own space is because they like the idea of some privacy and a safe space that is theirs. “Sally, the new house we are moving to is a bit smaller than this one. We’ve a nice room picked out for you when you come and stay with Dad, I’m going to put a desk in there to work from when you’re at Mum’s but I’ll make sure all my stuff is tidied away before you get here. I thought we could get you these drawers / chest / storage / shelves for your room, I promise they are private and I won’t go through any of your things when I’m in there. This basket is for your washing, if you could pop anything for dad and I to wash in there when you stay that would really help.”

I think you are being totally reasonable.
If they say 'no' then what is the alternative, working at a kitchen table is NOT reasonable. Particularly if you are the main earner, a man woukd NEVER put up with this.
Stand your ground or reduce child maintenance so you can stay in your current home.
Good luck op.

Your husband isn’t working due to his medical condition and you are the breadwinner.

Your son needs to have the biggest room, you need the box room for your dedicated office. That leaves the remaining bedroom for you.

If your husband wants his daughter over every second weekend then she can sleep on the couch. If he doesn’t like this then he can leave.

You need to consider the stress on your only child - having to watch his father not contribute to the house and being a witness to his illness.

Further, why would your step daughter get a bigger room than your son?? You’re downsizing because your husband can’t support himself, your child or his daughter. That doesn’t mean you should have an empty bedroom 12 days out of every 14 days. She doesn’t get a bedroom- she should sleep on the couch.

Sorry, what ? DSD is thirteen, she doesn’t get to dictate what she wants to the inconvenience of everyone else. OP and her DH are the adults, they make the decisions, and quite honestly, given OP’s update l would be reading DH the riot act. OP is subsidising his CMS for the benefit of DSD, so he doesn’t get a say in where she works from. Her four year old is there all the time - his room would be unusable for the time OP is working, while another room stands empty except for four days a month. It’s batshit. Step children should be welcomed into the home, but the extent to which MN thinks they should be prioritised over everything else is batshit.

Well, you're going to have to stop the £700 and stay in your current house.
I don't doubt she relies on it, but your husband's circumstances have changed. She'll have to get more work or downsize herself.
It seems ludicrous that the payments to her mean that you have to downsize.

£700 is a lot for child support. I'm not saying cut it to £100 but perhaps somewhere in the middle, especially if it means that you can stay where you are - this benefits all. Why is mum reliant on so much - does she work? It's not about putting her into poverty but she also has responsibility for providing for their child and unless you are talking about school fees, it doesn't cost £1400 a month to provide for a 12 year old. What about your own DC? You are the one working, but your child loses out while ex maintains the status quo. That doesn't seem right to me.

I don't understand the problem. You won't be working in there whilst SD is staying with you. She doesn't leave much stuff in her room and you have a laptop you don't need to store in the room when she's visiting.

So all this argument is about whether there's a desk in the room or not? Presumably she needs a desk for homework anyway.

I don't think I'd be giving her the choice tbh. But I would ensure the desk is clear for her visits. I wouldn't work at the dining room table either - it's higher than the desk and gives me backache.

To me it seems fairly simple. If you are the breadwinner and you feel you cannot work at the dining room table, cupboard under the stairs, or similar, then you put your foot down on that. Just: "no, not happening." Or, if that seems too abrupt then, "No, that's not possible."

Then you discuss, what are the alternatives?

And you pick from those, whether that's using SD's room as an office or withdrawing the 700 payment to his ex, or other alternatives you or he develop.

I don't think you should let yourself be bullied into working at the dining room table when the family relies on your job to put a roof over your heads. It will end badly: you will burn out or break up or a meeting will get messed up because people are making lunch loudly and your boss gets annoyed at your lack of professionalism. I just wouldn't take the risk.

For the posters that say DC should have their own room at each parent’s house, if any of you were stepchildren, did you always have your own room at both houses? Genuine question as I’m not sure if things have changed in the 100 years since I was a kid or if our family “did it wrong”.

My DF was the NRP and when i stayed with him I slept in his wife’s daughter’s bed (when she would be at her own DF’s house)

You can't possibly put your desk in your DS room and work from there, leaving another room empty for all but 4-6 days a month. You need space to work sensibly, without it being public. I'm sorry your DP can't work full time, but this is the consequence and they both have to suck it up while you support the family.

How much stuff do you have? If it’s just basics (laptop, keyboard, monitor etc) then put a desk in SD’s room and get a couple of decent storage boxes. Stick your laptop etc in them on Friday and pop in your room / above wardrobe or something. SD can use the desk for homework when she stays. I use our spare room as my office space, we frequently have family staying so this is what I do - sweep everything off desk into storage crate then pop it back out on a Monday morning. You could get a small neat storage unit to go next to the desk to lock away any paperwork?

This seems the best compromise to me. You get a working space, SD doesn’t feel like she’s sleeping in an office and has a desk for studying / use as a dressing table.

That's a very difficult situation then @SamphireSupper , SD is already struggling so more information might not help.

In that case, would DP go along with you appearing to have "given in" and setting the room up as SD's bedroom...but of course you're using the desk when she's not there? If your work stuff is never in her room when she gets there, and it's all aired and ready for her, she never needs to know any different?

A little while lie to take the heat out of the situation for everyone's benefit?

OP I’m in total agreement with you in terms of how the space it’s used.

could a slight compromise me a fold up desk or similar that can be taken out when she stays?

is it the desk or the fact you’re in her room?

Why ? DSD is there every other weekend so it makes sense that OP uses the room the rest of the time, rather than inconvenience her DS who is there all the time. I don’t get why a thirteen year old gets to dictate her terms, to the inconvenience of everyone else.

Either reduce cms or work from the sd room.

Id give your dp the choice.

There is no way id be working from my bedroom or a communal area whilst subsidising his ex after he dropped his hours.

It all sounds very difficult and id explain this to both sd and ex. You shouldnt have to be the doormat in this.

Your posts here show that you're good at thinking practically and logically, but don't have a huge insight into your DPs or SDs emotions.

How you've gone about framing this is all wrong. Does your SD have any understanding of yours and your DPs financial situation. About how you're making compromises left right and centre to accommodate his health and her current lifestyle? Teenagers are all about fairness. You could have pitched this post with an entirely different, more honest, and more sympathetic spin. But if you pitched the room situation to DP and SD like you've presented it here, there's no wonder they're not happy. You could have presented it as a problem and seen what SD thought was reasonable. This could have been her idea.

You sound perfectly reasonable to me, OP, but the problem is convincing your husband. (Imo, as a child, SD just has to go along with what the adults decide in these types of matters. Not a popular opinion these days, but there it is.)

If you can't afford more room at the moment, this is the best solution. SD won't actually be affected if she's never over on your workdays.

I’d make the desk match the room and make sure you fully clear it of all your stuff when ur daughter comes round pop a tv on it or make it like a dressing table or something for her so it’s like it’s also hers idk

£700 a month! Why so much?

What you are basically saying is she will have a desk in her room that you will also use when she's not there. I really don't see the issue. Don't most kids have a desk, space allowing?

She’s only with us on weekends, when I’m not working. I’d take my laptop out. She’d be welcome to use the desk for homework too

Exactly. This makes perfect sense. She is only there four days a month at most and those are the days when you are not working. So it makes absolutely no difference to her.

I don't understand the problem OP. Just tell your DH it's the only relatively quiet and private working area so it's happening.

Your update @SamphireSupper , is that something SD is aware of? Not in an unpleasant way, just in terms of her understanding the context?

I know teenagers are not always great on "the bigger picture", especially when it appears to disadvantage them (the part of their brain that helps them not be entirely self-centred is still developing), but I wonder if it might help?

Wow.
So not only are you financially supporting his ex, you also have your ‘D’P and SD making demands on the bedroom allocation.
Sod that for a game of cards. YOU get to decide.
If they don’t like it then you can afford the new 3 bed house with your little boy and your partner can provide a bedroom that’s only used 4 days a month .
Working in the kitchen?? Fuck that. Ergo working in your bedroom.
The cheek of some people and the expectation on women to just lay down while people walk all over them never ever fails to amaze me.

I voted YABU because I hadn’t read your update. If it’s literally a laptop you’ll need to take out, not a full office setup, I think YNBU.