Planning guest WC in new construction - How big should it be? (DIN?)

A basement is financially not feasible. We are building in Hamburg. Combined with the expensive plot, that only leaves enough for the small semi-detached house. The "only" is relative because we are very happy to be able to fulfill the dream of owning a house in Hamburg at all. We don't have any extravagant ideas regarding space requirements; everything is more than what we had in our rental apartments before. We would prefer a bigger house, of course, but it is what it is.

Our very small plot size and the situation with access to the rear development, distances to the neighbors that prevent higher buildings, and, in our opinion, very strict guidelines from our caseworker at the building authority (under §34 Building Code) dictate certain things for the floor plan. Here, it means being very pragmatic, not having too wild ideas, and making the best out of the living/dining area/kitchen, bedroom, and children's room.

I'll see if we get a draft in the next few days that can be put up for discussion.

A general contractor is almost found. We will probably decide on one of two offers next week.
We are planning the semi-detached house together with our neighbors. However, they are planning a shower bathroom on the ground floor and therefore need more space anyway. We will forgo the shower and would be satisfied with the smallest guest WC in the world.
The plans are not professionally drawn yet, and I actually wanted to spare us all my amateur Roomsketcher draft here. Just for orientation, here is the draft for the hallway corner + guest WC. Dimensions are only available for money with Roomsketcher. [...]
Fundamentally: The conditions on the plot are complicated. The house will be small (105-110m²). My main concern here remains to find out if a bathroom must have a minimum width.

The semi-detached house will have a footprint of 8.50 x 7.70m. 2 full floors, 1 attic. In my search for inspiration in the forum, I did not find anything. It seems that barely anyone plans under 140m². I’ll think again about whether to discuss the first professionally drawn drafts in the forum.
The info about the non-existent DIN standard for room width is good, thank you very much.
A few notes:
- On the upper floor, at that spot, a kind of is planned with the same dimensions as the guest WC. [...]
- The gained space with a narrower guest WC could be 100% invested in the living/dining area (and every centimeter really counts there)
- There are hardly any other savings options

I strongly advise you to tell much more about your construction project. First, you need far more help than such a single piece of information like that an 85 cm wide guest WC has comfortably sufficed for me for decades even in long sessions. And secondly, your centimeter budget strategy is at best a shot in the dark, but never a path to success, I can guarantee you that from four decades of planning experience. The smallest possible tiny rooms won’t get you anywhere with your almost tiny semi-detached half; from my point of view, you simply cannot accommodate an exclusive guest WC as a single-function room here, I see your guests having to put up with the company of a washer-dryer tower; and even the “use” of the WC tiny room counterpart on the other floor as a broom closet does not heal such a waste of space. By the way, you will be helped much better if instead of a snippet from Roomsketcher you show a whole floor (start especially difficult planning always with the upper floor*!) – gladly even as a “pen scribble on paper,” that is better than the “most professionally drawn” nonsense (which you should expect from drafting minions). And that brings us directly to the next urgent advice: don’t waste money on “saving” a proper architect without quotation marks, because you will sorely need one in this special situation even if the plot is perfectly level. From the joint planning you will smartly also go to the same general contractor for the entire semi-detached house, at least at the shell construction stage (after that, you can then choose different craftsmen than the neighbors). Actually, even the little you have told so far smells like a case for the involvement of , who unfortunately is no longer active here. But I at least summon and into the discussion, both of whom have experience with small semi-detached houses/detached houses; and also (albeit with a comparably spacious house) as well as (with a two-unit semi-detached house).
*) google (including the quotation marks) "Das Obergeschoss hat Vorrang"

*) google (including the quotation marks) "The upper floor has priority"

The domain of the building plot is for sale, unfortunately the content is lost with it. :-/

@Topic: I completely agree with 11ant: An extra toilet is hardly possible, an extra broom closet even less so. Walls also take up space, so these need to be minimized as well.
Guest toilet in the utility room and broom closet (only ~18 mm thick walls!) in the bedroom are helpful in this regard.

best regards

Thank you .

Since we have an old building, I can contribute very little. We have a tiny guest WC on the ground floor with a sink (18cm deep and 36cm wide, a friend said it’s similar to the dentist’s :cool:), an outward-opening door with a width of 60cm. It is 86cm wide and about 101/127cm deep (with and without the pre-wall element). The WC is standard size, the sink super small, there is a small window at the top and in the wall niche above the WC is a hanging cabinet for cleaning supplies and towels, as well as a small radiator there. It’s definitely fine. It’s certainly better than always having to go upstairs. It is often used by guests because it is the closest WC from the garden and also occasionally by us. In the 1921 building plans, it is called "Abort," which probably describes the size well. So, I can only say, be brave with the small WC. You only go there to use the toilet. Nobody stays there. For that, I would always want to sacrifice as little space as possible. A little wider than ours would certainly be better. But small is definitely sufficient.

I would also recommend posting the floor plan here (even if drawn with a pen). And of course, I would keep the guest WC. Because it can be cleverly accommodated in just a few square meters (e.g., under the stairs). And with the building authority, I wouldn't rely on just one clerk but actively check yourself whether they might be lying to you. Because without a development plan, there is usually an easier way to build if the neighbors have already given a lot of free space.

The domain is for sale, unfortunately the content is lost as a result. :-/

Oops, the search engines missed a name change. The "Baulotse Hoffmann" is now called "Bauen jetzt".

Since we have an old building, I can contribute very little.

I have already mentioned you with consideration: a hundred years ago there were also reasons for building houses on a modest scale.

And at the building authority I would not rely on the one caseworker but actively check yourself whether she might be lying to you. Because without a development plan, normally there is often a simpler way of building, especially if the neighbors have already given a lot of free space.

I would not phrase it that way, but I basically agree with you: "factual building windows" are – especially by caseworkers – often interpreted overly cautiously and narrowly. Here, too, the advice to the OP can only be to lay out the facts generously on the house’s table (of course without a link). But I already recommended going to the architect without quotation marks; they detect such things already in performance phase 1.